An Update on Power Quality

Edited by Dylan Dah-Chuan Lu

 AN UPDATE ON
POWER QUALITY
Edited by Dylan Dah-Chuan Lu
An Update on Power Quality
http://dx.doi.org/10.5772/51135
Edited by Dylan Dah-Chuan Lu

Contributors
Sharad W. Mohod, Mohan Aware, Md. Raju Ahmed, Dylan Lu, Hadeed Ahmed Sher, Khaled E Addoweesh, Yasin
Khan, Ahad Mokhtarpour, Heidarali Shayanfar, Seiied Mohammad Taghi Bathaee, Mohamed Zellagui, Abdelaziz
Chaghi, Mitra Sarhangzadeh

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An Update on Power Quality

Edited by Dylan Dah-Chuan Lu
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 Meet the editor

Dylan Dah-Chuan Lu received his Ph.D. degree in

Electronic and Information Engineering from The Hong
Kong Polytechnic University, Hong Kong, in 2004.
In 2003, he joined PowereLab Ltd. as a Senior Engineer.
His major responsibilities include project development
and management, circuit design, and contribution of re-
search in the area of power electronics. In 2006, he joined
the School of Electrical and Information Engineering, The University of
Sydney, Australia, where he is currently a Senior Lecturer. He presently
serves as a Member of several Editorial Boards including International
Journal of Electronics and Australian Journal of Electrical and Electron-
ic Engineering. His current research interests include power electronics
circuits and control and engineering education. He has published over 80
technical articles in these areas. He has two patents on efficient power con-
version. He is a member of the IEAust and a senior member of the IEEE.
Contents

Preface XI

Section 1 Power Quality Issues and Standards

in the Electricity Networks 1

Chapter 1 Harmonics Generation, Propagation

and Purging Techniques in Non-Linear Loads 3
Hadeed Ahmed Sher, Khaled E. Addoweesh and Yasin Khan

Chapter 2 Power Quality and Grid Code Issues

in Wind Energy Conversion System 21
Sharad W. Mohod and Mohan V. Aware

Section 2 Power Quality Improvement in Transmission

and Distribution Systems 37

Chapter 3 Impact of Series FACTS Devices

(GCSC, TCSC and TCSR) on Distance Protection
Setting Zones in 400 kV Transmission Line 39
Mohamed Zellagui and Abdelaziz Chaghi

Chapter 4 A PSO Approach in Optimal FACTS Selection

with Harmonic Distortion Considerations 61
H.C. Leung and Dylan D.C. Lu

Chapter 5 Electromechanical Active Filter

as a Novel Custom Power Device (CP) 79
Ahad Mokhtarpour, Heidarali Shayanfar and Mitra Sarhangzadeh

Chapter 6 Reference Generation of Custom Power Devices (CPs) 95

Ahad Mokhtarpour, Heidarali Shayanfar
and Seiied Mohammad Taghi Bathaee

Section 3 Power Quality Improvement in End Users Stage 119

Chapter 7 Power Quality Improvement Using

Switch Mode Regulator 121
Raju Ahmed and Mohammad Jahangir Alam
Preface

There is an upward trend that human activities involve more electric power nowadays
and for years to come. And we will soon be facing shortage of electricity supply if we
rely solely on non-renewable power generation from fossil fuels such as coals.
Renewable energy generation has proven effective in meeting the demand. At the
same time it has brought about a few issues to existing electricity infrastructure such
as complex power flow due to distributed generations and unstable grid voltage
and/or frequency profiles due to local generation and intermittent nature of renewable
energy sources such as solar photovoltaic and wind power. Also the increasing
penetration of power electronics converters associated with the adoption of renewable
energies into the electricity networks has improved the functionality and flexibility in
terms of control but meanwhile due to their switching nature the harmonics issue has
to be dealt with. It is therefore important to investigate the causes of these power
quality issues and explore feasible and cost-effective solutions to assist with the
development of present and future electricity networks.

In the following chapters the reader will be introduced to power quality issues and
solutions at different sections of the electricity networks, namely, power generation,
transmission, distribution and end user stages. The book is divided into three sections:
Power Quality Issues and Standards in Electricity Networks; Power Quality
Improvements in Transmission and Distribution Systems; and Power Quality
Improvement in End Users Stage. A brief discussion of each chapter is as follows.

Chapter 1 provides an overview of the causes, impacts, standards and solutions to

voltage and current harmonics problems which are one of the key issues related to
power quality. Chapter 2 investigates the challenges of increasing wind generation to
the network. The chapter has identified and analyzed briefly several key issues
including voltage variations, flickers, switching operation of wind generation, current
harmonics and locations of wind turbine. Several solutions have been introduced such
as low-voltage ride through capability and international standards. Lastly, but not the
least, it describes the purposes of grid code to deal with power quality issues with
renewable energy generation.

Flexible Alternating Current Transmission System (FACTS) controllers have been used
in transmission and distribution systems to deal with power quality issues. Chapter 3
VIII Preface

identifies the limitations in the transmission systems, i.e., angular stability, voltage
magnitude, thermal limits, transient stability, and dynamic stability and presents a
comparative study of three different series FACTS for power quality compensation of
a single transmission line in Eastern Algerian transmissions networks. Chapter 4
applies particle swarm optimization technique to designing a shunt static var
compensator (SVC) for a radial distribution feeder. The objective function of SVC
placement is to reduce the power loss and keep bus voltages and total harmonic
distortion within prescribed limits with minimum cost.

Chapter 5 proposes an electromechanical active power filter which uses a synchronous

generator together with a unity power quality conditioner (UPQC). The idea originates
from the fact that embedded generation is becoming a viable option in distributed
generation and we should utilize this generator as a part of the power quality
compensation solution. An algorithm of reference generation has been proposed to
work with the two devices and simulation results are reported to verify the
effectiveness of the approach. Chapter 6 continues with the previous study but the
focus is on the speed to generate the references for UPQC. The general idea is that it
uses an adaptive approach to designing the window’s width for steady state and
transient state operations and to adjusting the reference points for reactive power
compensation. The proposed methods reduce the settling time to 1/12 of a cycle and
have been verified under voltage sag, swell and load change conditions through
MATLAB simulations.

In order to maintain the regulation of AC grid voltage, Chapter 7 investigates different

types of AC regulators which include, Solid-state tap changer and steeples control by
variac, Solid-tap changer using anti-parallel SCRs, voltage regulation using servo
system, phase controlled AC voltage regulator, ferro-resonant AC voltage regulator
and switch mode AC voltage regulator. A detailed design of a switch mode AC-AC
voltage regulator is presented. Simulation results are reported to show the
responsiveness and high power factor of the proposed method.

I hope this book will have been to you an enjoyable reading and a timely update of
recent research and development in the field of Power Quality.

Lastly, I would like to thank all the researchers for their excellent works and studies in
the different areas of Power Quality.

Dylan Dah-Chuan Lu
University of Sydney
Australia
 Section 1

Power Quality Issues and Standards

in the Electricity Networks
 Chapter 1

Harmonics Generation, Propagation

and Purging Techniques in Non-Linear Loads

Hadeed Ahmed Sher, Khaled E. Addoweesh and Yasin Khan

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53422

1. Introduction
Industrial revolution has transformed the whole life with advanced technological
improvements. The major contribution in the industrial revolution is due to the availability
of electrical power that is distributed through electrical utilities around the world. The
concept of power quality in this context is emerging as a “Basic Right” of user for safety as
well as for uninterrupted working of their equipment. The electricity users whether
domestic or industrial, need power, free from glitches, distortions, flicker, noise and
outages. The utility desires that the users use good quality equipment so that they do not
produce power quality threats for the system. The use of power electronic based devices in
this industrial world has saved bounties in term of fuel and power savings, but on the other
hand has created problems due to the generation of harmonics. Both commercial and
domestic users use the devices with power electronics based switching that draw harmonic
current. This current is a dominant factor in producing the harmonically polluted voltages.
The “Basic Right” of the user is to have a clean power supply, whereas the demand of utility
is to have good quality instrument/equipment. This makes power quality a point of
common interest for both the users as well as the utility. Harmonics being a hot topic within
power quality domain has been an area of discussion since decades and several design
standards have been devised and published by various international organizations and
institutions for maintaining a harmonically free power supply. In a wider scenario, the
harmonically free environment means that the harmonics generated by the devices and its
presence in the system is confined in the allowable limits so that they do not cause
any damage to the power system components including the transformers, insulators,
switch-gears etc. The deregulation of power systems is forcing the utilities to purge the
harmonics at the very end of their generation before it comes to the main streamline and
becomes a possible cause of system un-stability. The possible three stage scheme for
harmonics control is

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4 An Update on Power Quality

 Identification of harmonics sources

 Measurement of harmonics level
 Possible purging techniques

To follow the above scheme the power utilities have R&D sections that are involved in
continuous research to keep the harmonics levels within the allowed limits. Power
frequency harmonics problems that have been a constant area of research are:

 Power factor correction in harmonically polluted environment

 Failure of insulation co-ordination system
 Waveform distortion
 De-rating of transformer, cables, switch-gears and power factor correction capacitors

The above mentioned research challenges are coped with the help of regulatory bodies that
are focused much on designing and implementing the standards for harmonics control.
Engineering consortiums like IEEE, IET, and IEC have designed standards that describe the
allowable limits for harmonics. The estimation, measurement, analysis and purging
techniques of harmonics are an important stress area that needs a firm grip of power quality
engineers. Nowadays, apart from the traditional methods like Y-∆ connection for 3rd
harmonic suppression, modern methods based on artificial intelligence techniques aids the
utility engineers to suppress and purge the harmonics in a better fashion. The modern
approaches include:

 Fuzzy logic based active harmonics filters

 Wavelet techniques for analysis of waveforms
 Sophisticated PWM techniques for switching of power electronics switches

The focus of this chapter is to explain all the possible sources of harmonics generation,
identification of harmonics, their measurement level as well as their purging/suppression
techniques. This chapter will be helpful to all electrical engineers in general and the utility
engineers in particular.

2. What are harmonics?

In electrical power engineering the term harmonics refers to a sinusoidal waveform that is a
multiple of the frequency of system. Therefore, the frequency which is three times the
fundamental is known as third harmonics; five times the fundamental is fifth harmonic; and
so on. The harmonics of a system can be defined generally using the eq. 1

fh  hfac (1)

Where fh is the hth harmonic and fac is the fundamental frequency of system.

Harmonics follow an inverse law in the sense that greater the harmonic level of a particular
harmonic frequency, the lower is its amplitude as shown in Fig.1. Therefore, usually in
power line harmonics higher order harmonics are not given much importance. The vital and
 Harmonics Generation, Propagation and Purging Techniques in Non-Linear Loads 5

the most troublesome harmonics are thus 3rd, 5th, 7th, 9th, 11th and 13th. The general expression
of harmonics waveforms is given in eq. 2

Vn  Vrn sin  n t  (2)

Where, Vrn is the rms voltage of any particular frequency (harmonic or power line).

The harmonics that are odd multiples of fundamental frequency are known as Odd
harmonics and those that are even multiples of fundamental frequency are termed as Even
harmonics. The frequencies that are in between the odd and even harmonics are called inter-
harmonics.

Although, the ideal demand for any power utility is to have sinusoidal currents and
voltages in AC system, this is not for all time promising, the currents and voltages with
complex waveforms do occur in practice. Thus any complex waveform generated by such
devices is a mixture of fundamental and the harmonics. Therefore, the voltage across a
harmonically polluted system can be expressed numerically in eq. 3,

V Vfpsin  t  1   V2psin  2 t  2   V3psin  3 t  3   Vnpsin  n t  n  (3)

Where,

Vfp = Peak value of the fundamental frequency

Vnp= Peak value of the nth harmonic component
φ = Angle of the respected frequency

Figure 1. Fundamental and harmonics frequency waveforms

Similarly, the expression for current through a given circuit in a harmonically polluted
system is given by the expression given in eq. 4

I I fpsin( t  1 )  I 2psin(2 t  2 )  I 3psin(3 t  3 )   I npsin  n t  n  (4)

Harmonic components are also termed as positive, negative and zero sequence. In this case
the harmonics that changes with the fundamental are called positive and those that have
phasor direction opposite with the fundamental are called negative sequence components.
The zero components do not take any affect from the fundamental and is considered neutral
in its behavior. Phasor direction is pretty much important in case of motors. Positive
sequence component tends to drive the motor in proper direction. Whereas the negative
6 An Update on Power Quality

sequence component decreases the useful torque. The 7th, 13th, 19th etc. are positive sequence
components. The negative sequence components are 5th, 11th, 17th and so on. The zero
component harmonics are 3rd, 9th, 15th etc. As the amplitude of harmonics decreases with the
increase in harmonic order therefore, in power systems the utilities are more concerned
about the harmonics up to 11th order only.

3. Harmonics generation
In most of the cases the harmonics in voltage is a direct product of current harmonics.
Therefore, the current harmonics is the actual cause of harmonics generation. Power line
harmonics are generated when a load draws a non-linear current from a sinusoidal voltage.
Nowadays all computers use Switch Mode Power Supplies (SMPS) that convert utility AC
voltage to regulate low voltage DC for internal electronics. These power supplies have
higher efficiency as compared to linear power supplies and have some other advantages too.
But being based on switching principle, these non-linear power supplies draw current in
high amplitude short pulses. These pulses are rich in harmonics and produce voltage drop
across system impedance. Thus, it creates many small voltage sources in series with the
main AC source as shown in Fig.2. Here in Fig.2 I3 refers to the third harmonic component
of the current drawn by the non-linear load, I5 is the fifth harmonic component of the load
current and so on. R shows the distributed resistance of the line and the voltage sources are
shown to elaborate the factor explained above. Therefore, these short current pulses create
significant distortion in the electrical current and voltage wave shape. This distortion in
shape is referred as a harmonic distortion and its measurement is carried out in term of
Total Harmonic Distortion (THD). This distortion travels back into the power source and
can affect other equipment connected to the same source. Any SMPS equipment installed
anywhere in the system have an inherent property to generate continuous distortion of the
power source that puts an extra load on the utility system and the components installed in
it. Harmonics are also produced by electric drives and DC-DC converters installed in
industrial setups. Uninterrupted Power Supply (UPS) and Compact Fluorescent Lamp (CFL)
are also a prominent source of harmonics in a system. Usually high odd harmonics results
from a power electronics converter. In summary, the harmonics are produced in an electrical
network by [2, 16, 26, 42]

 Rectifiers
 Use of iron core in power transformers
 Welding equipment
 Variable speed drives
 Periodic switching of voltage and currents
 AC generators by non-sinusoidal air gap, flux distribution or tooth ripple
 Switching devices like SMPS, UPS and CFL

It is worth mentioning here that voltage harmonics can emerge directly due to an AC
generator, due to a non-sinusoidal air gap, flux distribution, or to tooth ripple, which is
caused by the effect of the slots, which house the windings. In large supply systems, the
greatest care is taken to ensure a sinusoidal output from the generator, but even in this case
 Harmonics Generation, Propagation and Purging Techniques in Non-Linear Loads 7

any non-linearity in the circuit will give rise to harmonics in the current waveform.
Harmonics can also be generated due to the iron cores in the transformers. Such transformer
cores have a non-linear B-H curve [37].

Figure 2. Voltage distortion due to non-linear current

4. Problems associated with harmonics

Harmonically polluted system has many threats for its stability. It not only hampers the
power quality (PQ) but when a current is rich in harmonics, is drawn by some device, it
overloads the system. For example third harmonic current has a property that unlike other
harmonic component it adds up into the neutral wire of the system. This results in false
tripping of circuit breaker. It also affects the insulation of the neutral cable. Overloading of
the cables due to harmonically polluted current increases the losses associated with the
wires. It should also be kept in mind that only the power from fundamental component is
the useful power, rest all are losses. These additional losses make the power factor poor that
results in more power losses. The overall summarized effects of harmonics in the power
system include the following [9, 18, 39]

 Harmonic frequencies can cause resonant condition when combined with power factor
correction capacitors
 Increased losses in system elements including transformers and generating plants
 Ageing of insulation
 Interruption in communication system
 False tripping of circuit breakers
 Large currents in neutral wires

The distribution transformers have a ∆-Y connection. In case of a highly third harmonic
current the current that is trapped in the neutral conductor creates heat that increases the
heat inside the transformer. This may lead to the reduced life and de-rating of transformer.
The different types of harmonic have their own impact on power system. For instance let us
8 An Update on Power Quality

consider the 3rd harmonic. Contrary to the balanced three phase system where the sum of all
the three phases is zero in a neutral system, the third harmonic of all the three phases is
identical. So it adds up in the neutral wire. The same is applicable on triple-n harmonics
(odd multiples of 3 times the fundamental like 9th, 15th etc.). These harmonic currents are the
main cause of false tripping and failure of earth fault protection relay. They also produce
heat in the neutral wire thus a system needs a thicker neutral wire if it has third harmonic
pollution in it. If a motor is supplied a voltage waveform with third harmonic content in it,
it will only develop additional losses, as the useful power comes only from the fundamental
component.

5. Harmonics monitoring standards

The identification of harmonics as a problem in AC power networks, has forced the utilities
and regulatory authorities to devise the standards for harmonics monitoring and evaluation.
The standards for harmonic control thus address both the consumers and the utility.
Therefore, if the customer is not abiding by the regulations and is creating voltage distortion
at the point of common coupling the utility can penalize him/her. Various renowned
engineering institutes like IEEE, IEC and IET have devised laws to limit the injection of
harmonic content in the grid. These standards are mostly helpful to achieve a user friendly
healthy power quality system. IEEE standards are widely cited for their capability to
address all the regions in the world. There are more than 1000 IEEE standards on electrical
engineering fields. IEEE standards on power quality, however, are our main inspiration
here. IEEE standard on harmonic control in electrical power system was published in 1992
and it covers all aspects related to harmonics [7]. It defines the maximum harmonics
distortion up to 5 % on voltage levels ≤ 69kV. However, as the voltage levels are increased
the allowable limits for harmonics in this standard are decreased to 1.5 % on all voltages ≥
161 kV. It is also worth mentioning that individual voltage distortion starts from 3 % and
ends at 1.0 % for voltage levels of ≤ 69kV and ≥ 161 kV respectively. Besides the standards
that are designed keeping in view the global requirements, regional authorities devise their
own standards according to their load profile and climatic conditions. Most of the standards
are made according to the regional requirements of the country whereas few are based on
the global needs and requirements. In Saudi Arabia there exists a regulatory body that
defines the permissible limits and standard operational procedures for electricity
transmission, distribution and generation. This body is known as electricity and co-
generation regulatory authority [38]. Apart from devising standards they also follow some
standards defined by UAE power distribution companies. One such standard defined by
Saudi Electric Company (SEC) in 2007 and is known as “Saudi Grid Code”. Harmonics limit
set by the Saudi authorities is almost the same as IEEE standard but with a bit flexible limit
of 3% THD for all networks operating within the range of 22kV-400kV [35, 38]. Table 1
compares the IEEE standard, the Abu Dhabi distribution company and the SEC standard for
the harmonics limit in the electric network. It is interesting to mention that IEEE standard
for controlling harmonics is silent for the conditions where a system is polluted with inter-
harmonics (non-integer frequencies of fundamental frequency). For such conditions power
 Harmonics Generation, Propagation and Purging Techniques in Non-Linear Loads 9

utilities use IEC standard number 61000-2-2 .The IEC also defines the categories for different
electronic devices in standard number 61000-3-2. These devices are then subjected to
different allowable limits of THD. For example, class A has all three phase balanced
equipment, non-portable tools, audio equipment, dimmers for only incandescent lamp. The
limit for class A is varied according to the harmonic order. So for devices of class A the
maximum allowable harmonic current is 1.08 A for 2nd, 2.3A for 3rd, 0.43A for 4th, 1.14A for
5th harmonics. The beauty of this IEC standard is that it also caters for power factor. For
example all devices of class C (lighting equipment other than the incandescent lamp
dimmer) have 3rd harmonic current limit as a function of circuit power factor.

SEC Standard Abu Dhabi Distribution IEEE Limits

Company
Harmonics THD limit is 5% for THD limit is 5% for 400 V 5% for all voltage
400 V system, and 4% system, and 4% and 3% for 6.6- levels below
and 3% for 6.6- 20kV and 22kV-400kV 69kV and 3% for all
20kV and 22kV- respectively voltages above 161
400kV respectively kV
Table 1. Comparison of Harmonic Standards [7, 35, 38]

The modern systems based on artificial intelligent techniques like Fuzzy logic, ANFIS and
CI based computations are reducing the difficulty of data mining that helps in redesigning
the standards for power quality harmonics [24, 25]. In developed countries like Australia,
Canada, USA the power distribution companies are already partially shifted to smart grid
and they are using sophisticated sensors and measuring instruments.
In terms of smart grid environment these sensors will help in mitigating the problems by
predicting them in advance. Smart grid, by taking intelligent measurements and by the aid
of sophisticated algorithms will be able to predict the PQ problems like harmonics, fault
current in advance. It is pertinent to mention that the power quality monitoring using the
on-going 3G technologies has been implemented by Chinese researchers. They used module
of GPRS that is capable of analyzing the real time data and its algorithm makes it intelligent
enough to get the desired PQ information [22].

6. Harmonics measurement
The real challenge in a harmonically polluted environment is to understand and designate
the best point for measuring the harmonics. Nowadays the revolution in electronics has
messed up the AC system so much that almost every user in a utility is a contributor to the
harmonics current. Furthermore, the load profile in any domestic area varies from hour to
hour within a day. So in order to cope with the energy demand and to improve the power
factor, utilities need to switch on and off the power factor correction capacitors. This
periodic and non-uniform switching also creates harmonics in the system. The load
information in an area although, provide some basic information about the order of
harmonic present in a system. Such information is very useful as it gives a bird eye view of
10 An Update on Power Quality

harmonic content. But for the exact identification of the harmonics it is necessary to
synthesize the distorted waveform using the power quality analyzer or using some digital
oscilloscope for Fast Fourier Transform (FFT). For example Fig.3 shows a general synthesis
of the current drawn by a controlled rectifier. Once identified, the level and type of
harmonics (3rd, 5th etc.) the steps to mitigation can be devised. It should be kept in mind that
proper measurement is the key for the proper designing of harmonic filters. But the
harmonics level may differ at different points of measurement in a system. Therefore,
utilities need to be very precise in identifying the correct point for harmonic measurement in
a system. Among the standards, it is IEEE standard 519-1992 that outlines the operational
procedures for carrying out the harmonic measurements. This standard however does not
state any restriction regarding the integration duration of the measurement equipment with
the system. It however, restricts the utility to maintain a log for monthly records of
maximum demand [5]. Various devices are used in support with each other to carry out the
harmonic measurements in a system. These include the following

 Power Quality Analyser

 Instrument transformers based transducers (CT and PT)

Figure 3. Typical line current of a controlled converter [26]

Various renowned companies are designing and producing excellent PQ analyzers. These
include FLUKE, AEMC, HIOKI, DRANETZ and ELSPEC. These companies design single
phase and three phase PQ analyzers that are capable of measuring all the dominant
harmonic frequencies. The equipment that is used for harmonic measurement is also bound
to some limitations for proper harmonic measurement. This limitation is technical in nature
as for accurate measurement of all harmonic currents below the 65th harmonic, the sampling
frequency should be at least twice the desired input bandwidth or 8k samples per second in
this case, to cover 50Hz and 60Hz systems [5]. Mostly, the PQ analyzers are supplied along
with the CT based probes but depending on the voltage and current ratings a designer can
choose the CT and PT with wide operating frequency range and low distortion. The distance
of equipment with the transducer is also very important in measuring harmonics. If the
distance is long then noise can affect the measurement therefore properly shielded cables
like coaxial cable or fiber optic cables are highly recommended by the experts [5]. In short,
 Harmonics Generation, Propagation and Purging Techniques in Non-Linear Loads 11

the measurement of harmonics should be made on Point of Common Coupling (PCC) or at

the point where non-linear load is attached. This includes industrial sites in special as they
are the core contributors in injecting harmonic currents in the system.

7. Harmonics purging techniques

Techniques have been designed and tested to tackle this power quality issue since the
problem is identified by the researchers. There are several techniques in the literature that
addresses the mitigation of harmonics. All these techniques can be classified under the
umbrella of following

i. Passive harmonic filter

ii. Active harmonic filter
iii. Hybrid harmonic filter
iv. Switching techniques

7.1. Passive harmonic filters

Passive filter techniques are among the oldest and perhaps the most widely used techniques
for filtering the power line harmonics. Besides the harmonics reduction passive filters can be
used for the optimization of apparent power in a power network. They are made of passive
elements like resistors, capacitors and inductors. Use of such filters needs large capacitors
and inductors thus making the overall filter heavier in weight and expensive in cost. These
filters are fixed and once installed they become part of the network and they need to be
redesigned to get different filtering frequencies. They are considered best for three phase
four wire network [18]. They are mostly the low pass filter that is tuned to desired
frequencies. Giacoletto and Park presented an analysis on reducing the line current
harmonics due to personal computer power supplies [10]. Their work suggested that the use
of such filters is good for harmonics reduction but this will increase the reactive component
of line current. Various kind of passive filter techniques are given below [18, 19].

i. Series passive filters

ii. Shunt passive filters
iii. Low pass filters or line LC trap filters
iv. Phase shifting transformers

7.1.1. Series passive filters

Series passive filters are kinds of passive filters that have a parallel LC filter in series with
the supply and the load. Series passive filter shown in Fig.4 are considered good for single
phase applications and specially to mitigate the third harmonics. However, they can be
tuned to other frequencies also. They do not produce resonance and offer high impedance to
the frequencies they are tuned to. These filters must be designed such that they can carry
full load current. These filters are maintenance free and can be designed to significantly high
12 An Update on Power Quality

power values up to MVARs [4]. Comparing to the solutions that employ rotating parts like
synchronous condensers they need lesser maintenance.

Figure 4. Passive Series Filter [18]

7.1.2. Shunt passive filters

These type of filters are also based on passive elements and offer good results for filtering
out odd harmonics especially the 3rd, 5th and 7th. Some researchers have named them as
single tuned filters, second order damped filters and C type damped filters [3]. As all these
filters come in shunt with the line they fall under the cover of shunt passive filters, as shown
in Fig.5. Increasing the order of harmonics makes the filter more efficient in working but it
reduces the ease in designing. They provide low impedance to the frequencies they are
tuned for. Since they are connected in shunt therefore they are designed to carry only
harmonic current [18]. Their nature of being in shunt makes them a load itself to the supply
side and can carry 30-50% load current if they are feeding a set of electric drives [13].
Economic aspects reveal that shunt filters are always economical than the series filters due
to the fact that they need to be designed only on the harmonic currents. Therefore they need
comparatively smaller size of L and C, thereby reducing the cost. Furthermore, they are not
designed with respect to the rated voltage, thus makes the components lesser costly than the
series filters [33]. However, these types of filters can create resonant conditions in the circuit.

Figure 5. Different order type shunt filters [3]

7.1.3. Low pass filter

Low pass filters are widely used for mitigation of all type of harmonic frequencies above the
threshold frequency. They can be used only on nonlinear loads. They do not pose any
 Harmonics Generation, Propagation and Purging Techniques in Non-Linear Loads 13

threats to the system by creating resonant conditions. They improve power factor but they
must be designed such that they are capable of carrying full load current. Some researchers
have referred them as line LC trap filters [19]. These filters block the unwanted harmonics
and allow a certain range of frequencies to pass. However, very fine designing is required as
far as the cut off frequency is concerned.

7.1.4. Phase shifting transformers

The nasty harmonics in power system are mostly odd harmonics. One way to block them is
to use phase shifting transformers. It takes harmonics of same kind from several sources in a
network and shifts them alternately to 180° degrees and then combine them thus resulting in
cancelation. We have classified them under passive filters as transformer resembles an
inductive network. The use of phase shifting transformers has produced considerable
success in suppressing harmonics in multilevel hybrid converters [34]. S. H. H. Sadeghi et.al.
designed an algorithm that based on the harmonic profile incorporates the phase shift of
transformers in large industrial setups like steel industry [36].

7.2. Active harmonic filters

In an Active Power Filter (APF) we use power electronics to introduce current components
to remove harmonic distortions produced by the non-linear load. Figure 6 shows the basic
concept of an active filter [27]. They detect the harmonic components in the line and then
produce and inject an inverting signal of the detected wave in the system [27]. The two
driving forces in research of APF are the control algorithm for current and load current
analysis method [23]. Active harmonic filters are mostly used for low-voltage networks due
to the limitation posed by the required rating on power converter [21].

Figure 6. Conceptual demonstration of Active filter [27]

They are used even in aircraft power system for harmonic elimination [6]. Same like passive
filters they are classified with respect to the connection method and are given below [40].

i. Series active filters

ii. Shunt active filters

Since, it uses power electronic based components therefore in literature a lot of work has
been done on the control of active filters.
14 An Update on Power Quality

7.2.1. Series active filter

The series filter is connected in series with the ac distribution network as show in Fig.7 [33].
It serves to offset harmonic distortions caused by the load as well as that present in the AC
system. These types of active filters are connected in series with load using a matching
transformer. They inject voltage as a component and can be regarded as a controlled voltage
source [33]. The drawback is that they only cater for voltage harmonics and in case of short
circuit at load the matching transformer has to bear it [31].

7.2.2. Shunt active filter

The parallel filter is connected in parallel with the AC distribution network. Parallel filters
are also known as shunt filters and offset the harmonic distortions caused by the non-linear
load. They work on the same principal of active filters but they are connected in parallel as
stated that is they act as a current source in parallel with load [21]. They use high
computational capabilities to detect the harmonics in line.

Figure 7. Series active filters [33]

Mostly microprocessor or micro-controller based sensors are used to estimate harmonic

contents and to decide the control logic. Power semiconductor devices are used especially
the IGBT. Some researchers claim that before the advent of IGBTs active filters were seldom
use due to overshoot in budget [11]. However, despite of their usefulness shunt active filters
have many drawbacks. Practically they need a large rated PWM inverter with quick
response against system parameters changes. If the system has passive filters attached
somewhere, as in case of hybrid filters then the injected currents may circulate in them [28].

7.3. Hybrid harmonic filters

These types of filters combine the passive and active filters. They contain the advantages of
active filters and lack the disadvantages of passive and active filters. They use low cost high
power passive filters to reduce the cost of power converters in active filters that is why they
are now very much popular in industry. Hybrid filters are immune to the system
impedance, thus harmonic compensation is done in an efficient manner and they do not
 Harmonics Generation, Propagation and Purging Techniques in Non-Linear Loads 15

produce the resonance with system impedance [29]. The control techniques used for these
types of filters are based on instantaneous control, on p-q theory and id-iq. K.N.M.Hasan
et.al. presented a comparative study among the p-q and id-iq techniques and concluded that
in case of voltage distortions the id-iq method provides slightly better results [12]. They are
usually combined in the following ways [21]

i. Passive series active series hybrid filters

ii. Passive series active shunt hybrid filters
iii. Passive shunt active series hybrid filters
iv. Passive shunt active shunt hybrid filters

7.3.1. Passive series active series hybrid filters

These type of hybrid filters have both kind of filters connected in series with the load as
shown in Fig.8 and are considered good for diode rectifiers feeding a capacitive load [32]

7.3.2. Passive series active shunt hybrid filters

This breed of hybrid filter has passive part in series with load and active filter in parallel.
AdilM. Al-Zamil et al. proposed such type of filters in their paper and used the high power
capability. of passive filter by placing them in series with the load. They used an active filter
with space vector pulse with modulation (SVPWM) and implemented it on micro-controller.
They used only line current sensors to compute all the parameters required for reference
current generation. Their proposed system worked satisfactorily up to the 33rd harmonic and
the results shown are based on a system with line reactance of 0.13 pu. In their system the
bandwidth required for active filter is relatively less due to the passive filter that takes care
of the rising and falling edges of load current. They proposed that while designing hybrid
system the line filter L and capacitance C of active filter needs a compromise in selection
depending on the acceptable level of switching frequency ripple current and minimum
acceptable ripple voltage [1].

7.3.3. Passive shunt active shunt hybrid filters

These types of filters have both the passive and active filters connected in shunt with the
load as shown in Fig.9 [21]. In a comparative study J.Turunen et al. claimed that they require
smallest transformation ratio of coupling transformer as a result they need a fairly high
power rating for a small load and in case of high power loads the problem of dc link control
results in poor current filtering [43].

7.3.4. Passive shunt active series hybrid filters

As its name implies it is a kind of hybrid filter that has an active filter in series and a passive
filter in shunt as shown in Fig.10. J. Turunen et al. in a comparative study stated that this
breed of hybrid filter utilizes very small transformation ratio therefore for same rating of
load their power rating required is large compared to the load [43].
16 An Update on Power Quality

Series passive filter

th th
5 7 High pass
ZL
L
o
a
d

Cr Lr Three phase diode full

bridge rectifier

Q3 Q5

Cd

Q6 Q2

Series active power filter

Figure 8. Passive series active series hybrid filters [32]

Mains Impedance
Vs iL
Nonlinear
is load
ih
Zs Passive
T1 T3
filter

Vdc
L Vo
C

T2 T4

Active filter

Figure 9. Passive shunt active shunt hybrid filters [21]

Figure 10. Active series passive shunt hybrid filters [29]

7.4. Switching techniques

Besides using the method of installing filters, power electronics is so versatile that up to
some extent harmonics can be eliminated using switching techniques. These techniques may
vary from the increasing the pulse number to advance algorithm based Pulse Width
 Harmonics Generation, Propagation and Purging Techniques in Non-Linear Loads 17

Modulation (PWM). The most widely used sine triangle PWM was proposed in 1964. Later
in 1982 Space Vector PWM (SVPWM) was proposed [20]. PWM is a magical technique of
switching that gives unique results by varying the associated parameters like modulation
index, switching frequency and the modulation ratio. The frequency modulation ratio ‘m’ if
taken as odd automatically removes even harmonics [17, 26]. Here the increase in switching
frequency reduces the current harmonics but this makes the switching losses too much.
Furthermore, we cannot keep on increasing switching frequency because this imposes the
EMC problems [15]. D.G.Holmes et al. presented an analysis for carrier based PWM and
claimed that it is possible to use some analytical solutions to pin point the harmonic
cancelation using different modulation techniques. Sideband harmonics can be eliminated if
the designer uses natural or asymmetric regular sampled PWM [14]. The output can be
improved by playing with the modulation index. One specialized type of PWM is called
Selective Harmonic Elimination (SHE) PWM or the programmed harmonic elimination
scheme. This technique is based on Fourier analysis of phase to ground voltage. It is
basically a combination of square wave switching and the PWM. Here proper switching
angles selection makes the target harmonic component zero [26, 30]. In SHE technique a
minimum of 0.5 modulation index is possible [41]. But even the best SHE left the system
with some unfiltered harmonics. J. Pontt et al. presented a technique of treating the
unfiltered harmonics due to the SHE PWM. They stated that if we use SHE PWM for
elimination of 11th and 13th harmonics for 12 pulse configuration then the harmonics of order
23th, 25th, 35th and 37th are one that play vital role in defining the voltage distortions. They
proposed the use of three level active front end converters. They suggested a modulation
index of 0.8-0.98 to mitigate the harmonics of order 23rd, 25th and 35th, 37th [30]. With some
modifications researchers have shown that SHE PWM can be used at very low switching
frequency of 350 Hz. Javier Napoles et al. presented this technique and give it a new name
of Selective Harmonic Mitigation (SHM) PWM. They used seven switching states and
results makes the selective harmonics equal to zero [8]. This is excellent since in SHE PWM
the selective harmonic need not to be zero. It is sufficient in conventional PWM to bring it
under the allowable limit. Siriroj Sirisukprasert et al. presented an optimal harmonic
reduction technique by varying the nature of output stepped waveforms and varied the
modulation indexes. They tested their proposed technique on multilevel inverters that are
better than the two level conventional inverters. They excluded the very narrow and very
wide pulses from the switching waveform. Unlike SHE PWM as discussed above they
ensured the minimum turn on and turn off by switching their power switches only once a
cycle. Contrary to traditional SHE PWM, in this case the modulation index can vary till 0.1.
The output is a stepped waveform for different stages they classify the production of
modulation index as high, low and medium and the real point of interest is that for all these
three classes of modulation indexes the switching is once per cycle per switch [41]. Some
researchers used trapezoidal PWM method for harmonic control. This kind of PWM is based
on unipolar PWM switching. Here a trapezoidal waveform is compared with a triangular
waveform and the resulting PWM is supplied to the power switches. Like other harmonic
elimination techniques in PWM based techniques researchers have proposed the use of AI
based techniques including FL and ANN.
18 An Update on Power Quality

8. Conclusion
This chapter summarizes one of the major power quality problems that is the reason of
many power system disturbances in an electrical network. The possible sources of
harmonics are discussed along with their effects on distribution system components
including the transformers, switch gears and the protection system. The regulatory
standards for the limitation of harmonics and their measurement techniques are also
presented here. The purging techniques of harmonics are also presented and various kind of
harmonic filters are briefly presented. To strengthen the knowledge base, this chapter has
also discussed the control of harmonics using PWM techniques. By this chapter we have
attempted to gather the technical information in this field. A thorough understanding of
harmonics will provide the utility engineers a framework that is often required in the
solution of research work related to harmonics.

Author details
Hadeed Ahmed Sher* and Khaled E Addoweesh
Department of Electrical Engineering, King Saud University, Riyadh, Saudi Arabia
Yasin Khan
Department of Electrical Engineering, King Saud University, Riyadh, Saudi Arabia
Saudi Aramco Chair in Electrical Power, Department of Electrical Engineering, King Saud
University, Riyadh

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* Corresponding Author
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20 An Update on Power Quality

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 Chapter 2

Power Quality and Grid Code Issues in Wind

Energy Conversion System

Sharad W. Mohod and Mohan V. Aware

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/54704

1. Introduction
The aim of the electric power system is to produce and deliver to the consumer’s electric
energy of defined parameters, where the main quantities describing the electric energy are
the voltage and frequency. During normal operation of system the frequency varies as a
result of the variation of the real power generated and consumed. At the same time, because
of voltage drops in the transmission lines and transformers it is impossible to keep the
voltage at the nominal level in all the nodes of the power system. It is also impossible to
keep an ideal sinusoidal shape of the voltage or current waveform due to the nonlinearities
in many devices use for electric energy generation, transmission and at end users. That is
why the electric power system require to keep the quantities near the nominal value[1]-[5].

Recently, the deregulated electricity market has also opened the door for customers own
distributed generation due to economical and technical benefit. The liberalization of the grid
leads to new management structures, in which the trading of energy is important. The need
to integrate the renewable energy like wind energy into power system is to minimize the
environmental impact on conventional plant of generation. The conventional plant uses
fossil fuels such as coal & petroleum products to run the steam turbines and generate the
thermal power. The fossil fuel consumption has an adverse effect on the environment and it
is necessary to minimize the polluting and exhausting fuel. The penetration of renewable
energy especially wind has been increasing fast during the past few years and it is expected
to rise more in near future. Many countries around the world are likely to experience similar
penetration level. During the last decade of the twentieth century, worldwide wind energy
capacity is doubled approximately every three years.

Today’s trends are to connect all size of generating units like wind farm,solar farm,biogas
generation and conventional source like coal,hydro,nuclear power plant in to the grid
system shown in Fig.1.0

© 2013 The
© Author(s).
Mohod Licensee
and Aware, InTech.
licensee This chapter
InTech. This is is
andistributed
open accessunder the terms
chapter of the under
distributed Creative
theCommons
terms of
the CreativeLicense
Attribution Commons Attribution License (http://creativecommons.org/licenses/by/3.0),
http://creativecommons.org/licenses/by/3.0), which
which permits unrestricted use,permits
distribution,
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
and reproduction in any medium, provided the original work is properly cited.
22 An Update on Power Quality

Figure 1. Grid integration of interconnected system

 Power Quality and Grid Code Issues in Wind Energy Conversion System 23

The critical power quality issues related to integration of wind farms have been identified
by team of Riso National Laboratory and Danish Utility Research Institute, Denmark and
Electronic Research and Development Centre, India in Nov.1998 .The power quality in
relation to a wind turbine describe the electrical performance of wind energy generating
system. It reflects the generation of grid interference and the influence of a wind turbine on
power and voltage quality of grid. The issue of power quality is of great importance to the
wind turbines. There has been an extensive growth and quick development in the
exploitation of wind energy in recent years [6]-[7]. The individual units can be of large
capacity up to 5 MW, feeding into distribution network, particularly with customers
connected in close proximity. However with rapidly varying voltage fluctuations due to the
nature of wind, it is difficult to improve the power quality with simple compensator.
Advance reactive power compensators with fast control and power electronic have emerged
to supersede the conventional reactive compensator [8]-[9].

It has been suggested that today’s industrial development are related with generalized use
of computers, adjustable speed drives and other microelectronic loads. It also becomes an
increasing concern with power quality to the end customer. The presence of harmonic and
reactive power in the grid is harmful, because it will cause additional power losses and
malfunction of grid component. The massive penetration of electronically controlled devices
and equipments in low voltage distribution network is responsible for further worsening of
power-quality problem [10]-[13].

The problems are related to the load equipment and devices used in electric energy
generation. Now a days the transmission and distribution system become more sensitive to
power quality variation than those used in the past. Many new devices contain
microprocessor based controls and electronics power elements that are sensitive to many
types of disturbances. The wind turbine generating systems are the highly variable sources
of energy and wind turbine are belonging to the source of such problem.

The wind power in the electric grid system affects the voltage quality. To assess this effect,
the knowledge of about the electrical characteristic of wind turbine is needed. The electrical
characteristics of wind turbine are manufacturer’s specification and not site specification.
This means that by having the actual parameter values for a specific wind turbine the
expected impact of the wind turbine on voltage quality is important. The need for consistent
and replicable documentation of the power quality characteristics of wind turbines, the
International Electro-technical Commission (IEC) started work to facilitate for power quality
in 1996. As a result, IEC 61400-21 was developed and today most wind turbines
manufacturers provide power quality characteristic data accordingly. Wind turbines and
their power quality will be certified on the basis of measurements according to national or
international guidelines. These certifications are an important basis for utilities to evaluate
the grid connection of wind turbines and wind farms.

The power quality is defined as set of parameters defining the properties of the power
supply as delivered to user in normal operating condition in terms of continuity of supply
and characteristics of voltage, frequency.
24 An Update on Power Quality

Today the measurement and assessment of the power quality characteristics of the grid-
connected wind turbines is defined by IEC Standard 61400-21 (wind turbine system)
prepared by IEC- Technical Committee 88.
The need of power quality in wind integration system and its issues are highlighted in
further section.

2. Need of power quality studies

The power quality studies are of importance to wind turbine as a individual units can be
large up to 5 MW, feeding into distribution circuit with high source impedance and with
customer connected in close proximity.
With the advancement in fast switching power devices there is a trend for power supply
size reduction. The current harmonics due to switching converters makes supply current
distorted. The increase of electronic controllers in drives, furnaces, household equipments
and SMPS are increasing the harmonic content and reactive power in electric supply. The
distribution transformers apart from reactive loads draw reactive current from the supply to
meet the magnetizing current. The ever-increasing demand for power is not fulfilled by
increase in generation and particularly in distribution for various reasons such as
environmental issues, increasing cost of natural fuel, opposition to nuclear power plants,
etc. This puts excessive burden on the electric supply resulting in poor power quality. The
term power quality here refers to the variation in supply voltage, current and frequency.
The excessive load demand tries to retard the turbines at generation plant. This results in
reduction in voltage and more severely reduction in the supply frequency. The authorities
are working for power quality improvement by using reactive compensators and active
filters on supply side and penalizing consumers for polluting the power grid.
The increasing problems and advances in power electronic technology, has forced to change
the traditional power system concepts. Use of fast reactive power compensators can
improve the power system stability and hence, the maximum power transfers through the
electric system.
The reactive power in its simpler form, for a single phase sinusoidal voltages and current
can be defines as the product of a phase current (reactive component) and the supply
voltage. There is a simple right angle triangle relation between active power, reactive power
and apparent power. But, this definition of the reactive power is not sufficient for non-linear
loads where fundamental current and fundamental voltage may not have any phase
difference. However, for such loads, power factor is still less than unity. The power factor
definition is modified to accommodate for non-linear loads.
The overall power factor has two parts, the displacement power factor and distortion power
factor. The displacement power factor defined as cosine of phase shift between fundamental
supply current and voltage.

Distortion power factor “DF” or harmonic factor is defined as the ratio of the RMS harmonic
content to the RMS value of fundamental component expressed as percentage of the
fundamental.
 Power Quality and Grid Code Issues in Wind Energy Conversion System 25

sum of squares of amplitudes of all harmonics

DF  *100% (1)
square of amplitude of fundamental


2
 Ih
h2
DF( for current) = (2)
I1

2.1. Issue of voltage variation

If a large proportion of the grid load is supplied by wind turbines, the output variations due
to wind speed changes can cause voltage variation, flicker effects in normal operation. The
voltage variation can occur in specific situation, as a result of load changes, and power
produce from turbine. These can expected in particular in the case of generator connected to
the grid at fixed speed. The large turbine can achieve significantly better output smoothing
using variable speed operation, particularly in the short time range. The speed regulation
range is also contributory factor to the degree of smoothing with the large speed variation
capable of suppressing output variations.

2.2. Issue of voltage dips

It is a sudden reduction in the voltage to a value between 1% & 90 % of the nominal value
after a short period of time, conventionally 1ms to 1 min. This problem is considered in the
power quality and wind turbine generating system operation and computed according to
the rule given in IEC 61400-3-7 standard, “Assessment of emission limit for fluctuating
load”. The start up of wind turbine causes a sudden reduction of voltage. The relative %
voltage change due to switching operation of wind turbine is calculated as

Sn
d 100 Ku (  k ) (3)
Sk*

Where d - Relative voltage change,

ku (  k ) - Voltage change factor,

Sn - Rated apparent power of wind turbine and Sk* short circuit apparent power of grid.
The voltage dips of 3% in most of the cases are acceptable. When evaluating flicker and
power variation within 95% of maximum variation band corresponding to a standard
deviation are evaluated.

2.3. Switching operation of wind turbine on the grid

Switching operations of wind turbine generating system can cause voltage fluctuations and
thus voltage sag, voltage swell that may cause significant voltage variation. The acceptances
of switching operation depend not only on grid voltage but also on how often this may
26 An Update on Power Quality

occur. The maximum number of above specified switching operation within 10-minute
period and 2-hr period are defined in IEC 61400-3-7 Standard.
Voltage sag is a phenomenon in which grid voltage amplitude goes below and then returns
to the normal level after a very short time period. Generally, the characteristic quantity of
voltage sag is described by the amplitude and the duration of the sags. The IEEE power
quality standards define the voltage sag when the amplitude of voltage is 0.1–0.9 p.u. value
and its duration is between 10 ms and 1 min. A voltage sag is normally caused by short-
circuit faults in the power network or by the starting up of Induction Generator/Motors.
The bad weather conditions, such as thunderstorm, single-phase earthed faults are the causes
of voltage sags. In addition, large electric loads such as large electrical motors or arc furnaces
can also cause voltage sags during the startup phase with serious current distortion.
The adverse consequences are the reduction in the energy transfer of electric motors. The
disconnection of sensitive equipments and thus the industrial process may bring to a
standstill.

2.4. Harmonics
The harmonics distortion caused by non-linear load such as electric arc furnaces, variable
speed drives, large concentrations of arc discharge lamps, saturation of magnetization of
transformer and a distorted line current. The current generated by such load interact with
power system impedance and gives rise to harmonics. The effect of harmonics in the power
system can lead to degradation of power quality at the consumer’s terminal, increase of
power losses, and malfunction in communication system. The degree of variation is assessed
at the point of common connection, where consumer and supplier area of responsibility
meet. The harmonics voltage and current should be limited to acceptable level at the point
of wind turbine connection in the system. This fact has lead to more stringent requirements
regarding power quality, such as Standard IEC 61000-3-2 or IEEE-519. Conventionally,
passive LC resonant filters have been used to solve power quality problems. However, these
filters have the demerits of fixed compensation, large size, and the resonance itself. To
overcome these drawbacks, active filters appear as the dynamic solution.
The IEC 61000-3-6 gives a guideline and harmonic current limits. According to standard IEC
61400-21 guideline, harmonic measurements are not required for fixed speed wind turbines
where the induction generator is directly connected to grid. Harmonic measurements are
required only for variable speed turbines equipped with electronic power converters. In
general the power converters of wind turbines are pulse-width modulated inverters, which
have carrier frequencies in the range of 2-3 kHz and produce mainly inter harmonic
currents.
The harmonic measurement at the wind turbine is problem due to the influence of the
already existing harmonic voltage in the grid. The wave shape of the grid voltage is not
sinusoidal. There are always harmonics voltages in the grid such as integer harmonic of 5th
and 7th order which affect the measurements.
 Power Quality and Grid Code Issues in Wind Energy Conversion System 27

Today’s variable speed turbines are equipped with self commutated PWM inverter system.
This type of inverter system has advantage that both the active and reactive power can be
controlled, but it also produced a harmonic current. Therefore filters are necessary to reduce
the harmonics.

The harmonic distortion is assessed for variable speed turbine with a electronic power
converter at the point of common connection. The total harmonic voltage distortion of
voltage is given as in (4).

40 Vh2
VTHD   100 (4)
h2 V1

Vh- hth harmonic voltage and V1 –fundamental frequency 50 Hz. The THD limit for various
level of system voltages are given in the table 1.0

System Voltage (kV) Total Harmonic Distortion (%)

400 2.0
220 2.5
132 3.0
Table 1. Voltage Harmonics Limit

THD of current ITHD is give as in (5)

40 I h2
ITHD   100 (5)
h2 I1

Where Ih - hth harmonic current and I1 –fundamental frequency (50) Hz. The acceptable level
of THD in the current is given in table 2.

Voltage level 66 kV 132kV

ITHD 5.0 2.5
Table 2. Current Harmonic Limit

Various standards are also recommended for individual consumer and utility system for
helping to design the system to improve the power quality. The characteristics of the load
and level of power system significantly decides the effects of harmonics. IEEE standards are
adapted in most of the countries. The recommended practice helps designer to limit current
and voltage distortion to acceptable limits at point of common coupling (PCC) between
supply and the consumer.

1. IEEE standard 519 issued in 1981, recommends voltage distortion less than 5% on
power lines below 69 kV. Lower voltage harmonic levels are recommended on higher
supply voltage lines.
28 An Update on Power Quality

2. IEEE standard 519 was revised in 1992, and impose 5% voltage distortion limit. The
standards also give guidelines on notch depth and telephone interface considerations.
3. ANSI/IEEE Standard C57.12.00 and C57.12.01 limits the current distortion to 5% at full
load in supply transformer.

In order to keep power quality under limit to a standards it is necessary to include some of
the compensator. Modern solutions for active power factor correction can be found in the
forms of active rectification (active wave shaping) or active filtering.

2.5. Flickers
Flicker is the one of the important power quality aspects in wind turbine generating system.
Flicker has widely been considered as a serious drawback and may limit for the maximum
amount of wind power generation that can be connected to the grid. Flicker is induced by
voltage fluctuations, which are caused by load flow changes in the grid. The flicker emission
produced by grid-connected variable-speed wind turbines with full-scale back-to-back
converters during continuous operation and mainly caused by fluctuations in the output
power due to wind speed variations, the wind shear, and the tower shadow effects. The
wind shear and the tower shadow effects are normally referred to as the 3p oscillations. As a
consequence, an output power drop will appear three times per revolution for a three-
bladed wind turbine. There are many factors that affect flicker emission of grid connected
wind turbines during continuous operation, such as wind characteristics and grid
conditions. Variable-speed wind turbines have shown better performance related to flicker
emission in comparison with fixed-speed wind turbines.

The flicker study becomes necessary and important as the wind power penetration level
increases quickly. The main reason for the flicker in fixed speed turbines is to wake of the
tower. Each time a rotor blade passes the tower, the power output of the turbine is reduced.
This effect cause periodical power fluctuations with a frequency of about ~1 Hz. The power
fluctuation due to the wind speed fluctuation has lower frequencies and thus is less critical
for flicker. In general, the flicker of fixed speed turbines reaches its maximum at high wind
speed. Owing to smoothing effect, large wind turbine produced lower flicker than small
wind turbines, in relation to their size.

Several solutions have been proposed to mitigate the flicker caused by grid-connected wind
turbines. The mostly adopted technique is the reactive power compensation. It can be
realized by the grid-side converter of variable-speed wind turbines or the Static
synchronous compensator connected at the point of common coupling (PCC). Also, some
papers focus on the use of active power curtailment to mitigate the flicker [5].

The flicker level depends on the amplitude, shape and repetition frequency of the fluctuated
voltage waveform. Evaluating the flicker level is based on the flicker meter described in IEC
61000-4-15. Two indices are typically used as a scale for flicker emission, short-term flicker
index, Pst and long-term flicker index, Plt. Plt is estimated by certain process of the Pst values.
 Power Quality and Grid Code Issues in Wind Energy Conversion System 29

It is assumed that wind turbines under study is running at normal operation; hence, the
long-term flicker index (Plt), which is based on a 120-min time interval, is equal to Pst and,
therefore, Pst is only considered in this work. The normalized response of the flicker meter
described in Figure 2.0.

10

Voltage
fluctuation
%
1

0.1

1 2 10 100

Hz

Figure 2. Influence of frequency on the perceptibility of sinusoidal voltage change

A quite small voltage fluctuation at certain frequency (8.8 Hz) can be irritable. The flicker
level (Pst ≤ 1) is a threshold level for connecting wind turbines to low voltage. The
measurements are made for maximum number of specified switching operation of wind
turbine with 10-minutes period and 2-hour period are specified, as given in (6)

S
Plt C(  K ) n (6)
SK

Where plt - Long term flicker. C(  K ) - Flicker coefficient calculated from Rayleigh
distribution of the wind speed. The Limiting Value for flicker coefficient is about  0.4, for
average time of 2 hours.

2.6. Reactive power

Traditional wind turbines are equipped with induction generators. Induction generator is
preferred because they are inexpensive, rugged and requires little maintenance.
Unfortunately induction generators require reactive power from the grid to operate. The
interactions between wind turbine and power system network are important aspect of wind
generation system. When wind turbine is equipped with an induction generator and fixed
capacitor are used for reactive compensation then the risk of self excitation may occur
30 An Update on Power Quality

during off grid operation. Thus the sensitive equipments may be subjected to over/under
voltage, over/under frequency operation and other disadvantage of safety aspect. According
to IEC Standard, reactive power of wind turbine is to be specified as 10 min average value as
a function of 10-min. output power for 10%, 20% … 100% of rated power. The effective
control of reactive power can improve the power quality and stabilize the grid. Although
reactive power is unable to provide actual working benefit, it is often used to adjust voltage,
so it is a useful tool for maintaining desired voltage level. Every transmission system always
has a reactive component, which can be expressed as power factor. Thus the some method is
needed to manage the reactive power by injecting or absorbing VAr as necessary in order to
maintain optimum voltage level and enable real power flow. Until recently, this has been
especially difficult to effectively accomplish at a wind farms due to the variable nature of
wind. The suggested control technique in the thesis is capable of controlling reactive power
to zero value at point of common connection (PCC).The mode of operation is referred as
unity power factor.

2.7. Location of wind turbine

The way of connecting wind turbine into the electric power system highly influences the
impact of the wind turbine generating system on the power quality. As a rule, the impact on
power quality at the consumer’s terminal for the wind turbine generating system (WTGS)
located close to the load is higher than WTGS connected away, that is connected to H.V. or
EHV system.

Wind turbine generator systems (WTGS) are often located in the regions that have favorable
wind conditions and where their location is not burdensome. These regions are low
urbanized, which means that the distribution network in these regions is usually weak
developed. Such situation is typical for all countries developing a wind power industry.

The point of common coupling (PCC) of the WTGS and the power network parameter and
structure of grid is of essential significance in the operation of WTGS and its influence on
the system. WTGS can be connected to MV transmission line and to HV networks.

The WTGS connected to the existing MV transmission line, which feeds the existing
customers is presented in Figure 3.

The distance between WTGS and PCC is usually small up to a few kilometers. Such
connections are cheap as compare to other types of connection but greatly affected on
consumers load (power quality).

If the location of WTGS is connected to an MV bus in feeding an HV/MV substation through

a separate transmission line (position 1), the connection has some advantages related to low
influence of WTGS on customers load. Such connection are expensive than presented above.

The location of WTGS connected to HV bus through a separate transmission line, when a
relatively large rated WTGS has to be connected in the power network, where the MV
network is weak. This type of connection are most expensive than other presented.
 Power Quality and Grid Code Issues in Wind Energy Conversion System 31

MV 1
HV PCC

Loads

LV LV

Loads WTGS Loads

Figure 3. WTGS coupled to MV transmission-line.

2.8. Low voltage ride through capability

The impact of the wind generation on the power system will no longer be negligible if high
penetration levels are going to be reached. The extent to which wind power can be
integrated into the power system without affecting the overall stable operation depends on
the technology available to mitigate the possible negative impacts such as loss of generation
for frequency support, voltage flicker, voltage and power variation due to the variable speed

Line-to-
Line 100
Voltage Lower
90
% value
of voltage
75 band

60

45

30

15

0 150 700 1500 3000

msec
Fault Ocuured

Figure 4. Low voltage ride through (LVRT) capability

32 An Update on Power Quality

of the wind and the risk of instability due to lower degree of controllability. Many countries
in Europe and other parts of the world are developing or modifying interconnection rules
and processes for wind power through a grid code. The grid codes have identified many
potential adverse impacts of large scale integration of wind resources. The risk of voltage
collapse for lack of reactive power support is one of the critical issues when it comes to
contingencies in the power system. The low voltage ride through (LVRT) capability, which
is one of the most demanding requirement that have been included in the grid codes and
shown in Fig. 4.

It defines the operational boundary of a wind turbine connected to the network in terms of
frequency, voltage tolerance, power factor, fault ride through is regarded as the main
challenges to the wind turbine manufactures. The wind turbine should remain stable and
connected during the fault while voltage at the PCC drop to 15% of the nominal value i.e.
drops of 85% for the part of 150 msec. Only when the grid voltage fall below the curve, the
turbine is allowed to disconnected from the grid.

Significant barriers to interconnection are being perceived already with the requirements
of the new grid codes and there it is a need for a better understanding of the factors
affecting the behavior of the wind farm under severe contingencies such as voltage sags.
Wind farms using squirrel cage induction generators directly connected to the network
will suffer from the new demands, since they have no direct electrical control of torque or
speed, and would usually disconnect from the power system when the voltage drops
more than 10–20% below the rated value. In general, fulfillment of LVRT by reactive
compensation will require fast control strategies for reactive power in wind
turbines/farms with cage induction generators. The LVRT requirement, although details
are differing from country to country, basically demands that the wind farm remains
connected to the grid for voltage dips as low as 5%.

2.9. IEC recommendation

For consistent and replicable documentation of power quality characteristic of wind turbine,
the international Electro-technical Commission IEC-61400-21 was developed and today,
most of the large wind turbine manufactures provide power quality characteristic data
accordingly.IEC 61400-21 describe the procedures for determine the power quality
characteristics of wind turbines. It is a guideline for power quality measurements of wind
turbine. The methodology of IEC standard consists of three analyses. The first one is the
flickers analyses. IEC 61400-21 specified a method that uses current and voltage time series
measured at the wind turbine terminals to simulate the voltage fluctuation on a fictitious
grid with no source of voltage fluctuations other that wind turbine switching operation. The
second one is regarding the switching operation. The voltage and current transients are
measured during the switching operation of wind turbine. The last one is the harmonic
analysis which is carried out by FFT algorithms. Recently harmonic and inter harmonic are
treated in the IEC 61000-4-7 and IEC 61000-3-6. The method for summing harmonics and
 Power Quality and Grid Code Issues in Wind Energy Conversion System 33

inter harmonic in the IEC 61000-3-6 are applicable to wind turbines. The inter harmonics
that are not a multiple of 50 Hz, since the switching frequency of the inverter is not constant
but varies, the harmonic will also vary. Consequently, the grid codes has been define to
specify the requirements that the wind turbines must meet in order to be connected to the
grid, including the capabilities of contributing to frequency and voltage control by adjusting
the active and reactive power supplied to the transmission system.

3. Grid code for wind farms

The Electricity Grid Code is a regulation made by the Central Commission and it to be
follow by various persons and participants in the system to plan, develop, maintain, and
operate the power system grid in the most secure, reliable, economic and efficient manner,
while facilitating healthy competition in the generation and supply of electricity.

The first grid code was focused on the distribution level, after the blackout in the United
State in August 2003. The United State wind energy industry took a stand in developing
its own grid code for contributing to a stable grid operation. The rules for realization of
grid operation of wind generating system at the distribution network is defined as - per
IEC-61400-21.The grid quality characteristics and limits are given for references that the
customer and the utility grid may expect. According to Energy-Economic Law, the
operator of transmission grid is responsible for the organization and operation of
interconnected system. The grid code also covers some of the technical standards for
connection to the grid.

To ensure the safe operation, integrity and reliability of the grid is utmost important. It is
mentioned that reactive power compensation should ideally be provided locally by
generating reactive power as close to the reactive power consumption as possible. The
regional entity except generating stations, expected to provide local VAr
compensation/generation such that they do not draw VArs from the grid, particularly under
low-voltage condition. Indian grid code commission mentions that the charge for VArh shall
be at the rate of 25 paise/kVArh w.e.f.1.4.2010, for VAr interchanges.

The wind farms must be able to run at rated voltage at a specified voltage range. The
voltage range depends on the level of the voltage on the transmission system, which varies
from country to country.

The wind farms shall have a closed loop voltage regulation system. The voltage regulation
system shall act to regulate the voltage at the point by continuous modulation of the reactive
power output within its reactive power range, and without violating the voltage step
emissions.

Voltage fluctuations at a point of common coupling with a fluctuating load directly

connected to the transmission system shall not exceed 3% at any time. The flicker
contributions Pst and Plt are defined in IEC 61000-3-7 (Electromagnetic compatibility).
34 An Update on Power Quality

The wind turbine generator (WTG) shall be equipped with voltage and frequency relays for
disconnection of the wind farm at abnormal voltages and frequencies. The relays shall be set
according to agreements with the regional grid company and the system operator. Following
are the technical requirements to be fulfilled to integrate the wind generation system.

Voltage Rise (u) -The voltage rise at the point of common coupling can be approximated as a
function of maximum apparent power Smax of the turbine, the grid impedances R and X at the
point of common coupling and the phase angle  . The Limiting voltage rise value is < 2%

Voltage dips (d) - The voltage dips is due to start up of wind turbine and it causes a sudden
reduction of voltage. The acceptable voltage dips limiting value is  3 %.

Flicker-The measurements are made for maximum number of specified switching operation
of wind turbine with 10-minutes period and 2-hour period are specified. The Limiting Value
for flicker coefficient is about  0.4, for average time of 2 hours

Harmonics  The THD limit for 132 KV is  3%.

Grid frequency- The grid frequency in India is specified in the range of 47.5-51.5 Hz, for
wind farm connection. The wind farm shall able to withstand change in frequency up to
0.5Hz/sec. Thus the requirements in the Grid Code can be fulfill the technical limits of the
network.

4. Conclusion
The chapter provides the challenges regarding the integration of wind energy in to the
power systems. Today the worldwide trend of wind power penetration is increased. The
integration of high penetration level of wind power into existing power system has
significant impact on the power system operation.
The wind turbines connected to weak grids have an important influence on power system.
The weak grid is characterized by large voltage and frequency variations, which affects
wind turbines regarding their power performance, safety and allied electrical components.
The strength of the distribution system is important from the point of power quality. The
needs for consistent qualification of power quality characteristics of wind turbines, the
International Electro-Technical Commission to facilitate for power quality parameters for
various issues are presented. The latest grid code requirements are to ensure that wind
farms do not adversely affect the power system operation with respect to security of supply,
reliability and for power quality.

Author details
Sharad W. Mohod
Ram Meghe Institute of Technology & Research,Badnera-Amravart, India

Mohan V. Aware
Visvesvaraya National Institute of Technology, Nagpur, India
 Power Quality and Grid Code Issues in Wind Energy Conversion System 35

5. References
[1] H. Holitinen, R.Hirvonen, “Power system requirement for wind power.”, Wind Power
in Power System, T. Ackermann, Ed. New-York, pp 143-157, Wiley, 2005
[2] R.C. Bansal, Ahmed F. Zobaa, R.K. Saket, “Some issue related to power generation
using wind energy conversion system: An overview” Int. Journal of Emerging Electric
Power System, Vol. 3, No.2, pp 1-14, 2005.
[3] J.Charles Smith, Michael R. Milligan, Edgar A. DeMeo, “Utility wind integration and
operating impact state of the art., IEEE Trans on Energy Conversion Vol.22, No.3, pp 900-
907, August 2007.
[4] Z.Sadd-Saoud, N. Jenkins, “Models for predicting flicker induced by large wind
turbines” IEEE Trans on Energy Conversion, Vol.14, No.3, pp.743-751, Sept.1999.
[5] Weihao Hu, Zhe Chen, Yue Wang and Zhan Wang “Flicker Mitigation by Active Power
Control of Variable-Speed Wind Turbines With Full-Scale Back-to-Back Power
Converters”, IEEE Trans on Energy Conversion, Vol. 24, No. 3, pp.640-648, Sept. 2009
[6] F.Zhou, G.Joos, C.Abhey. ”Voltage stability in weak connection wind farm.” IEEE PES
Gen. Meeting, Vol. 2, pp.1483-1488, 2005
[7] S.W.Mohod, M.V.Aware, “Power quality issues & its mitigation technique in wind
generation, ”Proc. of IEEE Int. Conf. on Harmonics and Quality of Power (ICHQP), pp. 1-6,
Sept. 2008
[8] S.Z. Djokic, J.V. Milanovic, “Power quality and compatibility levels: A general
approach.”, IEEE Trans on Power Delivery, Vol.22, No.3, pp.1857-1862, July. 2007
[9] Helder J. Azevedo, Jose M. Ferreiraa, Antonio P. Martins, Adriano S. Carvalho, “An
active power filter with direct current control for power quality conditioning.” Electric
Power Component and System, Vol.26, pp.587-601, 2008.
[10] Z.Chen, E. Spooner, “Grid power quality with variable speed wind turbines”, IEEE
Trans on Energy Conversion, Vol.16, No.2, pp.148-156, June 2001.
[11] Dusan Graovac, Vladimir A. Katic, Alfred Rufer, “Power quality problems
compensation with universal power quality conditioning system.” IEEE Trans on Power
Delivery, Vol.22, No.2, pp.968-975, April 2007.
[12] Juan Manuel Carrasco, Leopoldo Garcia Franquelo, Jan. Bialasiewicz, “Power electronic
system for the grid integration of renewable energy sources: A survey.” IEEE Trans on
Industry Electronics, Vol.53, No.4, pp.1002-1010, Aug. 2006.
[13] “A report on Indian Wind Grid Code” – Committee draft, Version 1.0, pp 5-42 July 2009.
[14] J.F.Conroy, R. Watson, “Low-voltage ride though of full converter wind turbine with
permanent magnet generator”, Proc. IET Renew. Power Generation. Vol.2, No.2, pp.113-
122, 2008.
[15] Bousseau, P.: “Solution for the grid integration of wind farms – A survey”, Proc. of
European Wind Energy Conf., pp.12-16, Nov. 2004.
[16] S.W.Mohod, M.V.Aware, “A STATCOM-Control Scheme for Grid Connected Wind
Energy System for Power Quality Improvement”, IEEE System Journal, A special issue
on sustainable development, Vol.4, Issue-3, pp-346-352, Sept-2010.
36 An Update on Power Quality

[17] S.W.Mohod, S.M.Hatwar, M.V.Aware. “Wind Energy Generation Interfaced System

with Power Quality and Grid Support” Journal of Advanced Materials Research,
Volumes 403 - 408, Tech Publication Swizerland, pp.2079-2086, Nov.2011.
 Section 2

Power Quality Improvement in Transmission

and Distribution Systems
 Chapter 3

Impact of Series FACTS Devices (GCSC, TCSC

and TCSR) on Distance Protection Setting
Zones in 400 kV Transmission Line

Mohamed Zellagui and Abdelaziz Chaghi

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/54257

1. Introduction
The electricity supply industry is undergoing a profound transformation worldwide.
Market forces, scarcer natural resources, and an ever-increasing demand for electricity are
some of the drivers responsible for such unprecedented change. Against this background of
rapid evolution, the expansion programs of many utilities are being thwarted by a variety of
well-founded, environment, land-use, and regulatory pressures that prevent the licensing
and building of new transmission lines and electricity generating plants.

The ability of the transmission system to transmit power becomes impaired by one or more
of the following steady state and dynamic limitations:

- Angular stability,
- Voltage magnitude,
- Thermal limits,
- Transient stability,
- Dynamic stability.

These limits define the maximum electrical power to be transmitted without causing
damage to transmission lines and electrical equipment. In principle, limitations on power
transfer can always be relieved by the addition of new transmission lines and generation
facilities.

Alternatively, Flexible Alternating Current Transmission System (FACTS) controllers can

enable the same objectives to be met with no major alterations to power system layout.
FACTS are alternating current transmission systems incorporating power electronic-based
and other static controllers to enhance controllability and increase power transfer capability.

© 2013 The
© Author(s).
Zellagui Licensee
and Chaghi, InTech.InTech.
licensee This chapter
This isisan
distributed under
open access the terms
chapter of the Creative
distributed Commons
under the terms of
the CreativeLicense
Attribution Commons Attribution License (http://creativecommons.org/licenses/by/3.0),
http://creativecommons.org/licenses/by/3.0), which
which permits unrestricted use,permits
distribution,
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
and reproduction in any medium, provided the original work is properly cited.
40 An Update on Power Quality

The FACTS concept is based on the substantial incorporation of power electronic devices
and methods into the high-voltage side of the network, to make it electronically controllable.
FACTS controllers aim at increasing the control of power flows in the high-voltage side of
the network during both steady state and transient conditions. Owing to many economical
and technical benefits it promised, FACTS received the support of electrical equipment
manufacturers, utilities, and research organizations around the world. This interest has led
to significant technological developments of FACTS controllers (Sen, K.K.; Sen, M.L., 2009),
(Zhang, X.P. et al., 2006). Several kinds of FACTS controllers have been commissioned in
various parts of the world.

Popular are: load tap changers, phase-angle regulators, static VAR compensators, thyristors
controlled series compensators, interphase power controllers, static compensators, and
unified power flow controllers.

The main objectives of FACTS controllers are the following (Mathur, R.M.; Basati, R.S., 2002):
- Regulation of power flows in prescribed transmission routes,
- Secure loading of transmission lines nearer to their thermal limits,
- Prevention of cascading outages by contributing to emergency control,
- Damping of oscillations that can threaten security or limit the usable line capacity.
The most Utility engineers and consultants use relay models to select the relay types suited
for a particular application, and to analyze the performance of relays that appear to either
operate incorrectly or fail to operate on the occurrence of a fault. Instead of using actual
prototypes, manufacturers use relay model designing to expedite and economize the
process of developing new relays. Electric power utilities use computer-based relay models
to confirm how the relay would perform during systems disturbances and normal operating
conditions and to make the necessary corrective adjustment on the relay settings. The
software models could be used for training young and inexperienced engineers and
technicians. Researchers use relay model to investigate and improve protection design and
algorithms. However, simulating numerical relays to choose appropriate settings for the
steady state operation of over current relays and distance relays is presently the most
familiar use of relay models (McLaren et al., 2001).

1.1. Problem statement

In the presence of series compensators the system FACTS devices i.e. GTO Controlled Series
Capacitor (GCSC), Thyristor Controlled Series Capacitor (TCSC) and Thyristor Controlled
Series Reactor (TCSR) connected in high voltage (HV) transmission line protected by distance
relay, the total impedance and the measured impedance at the relaying point depend on the
injected reactance by compensators. So there is a reel impact on the relay settings zones.

1.2. Objectives
This chapter presents a comparative study of the performance of MHO (admittance)
distance relays for transmission line 400 kV in Eastern Algerian transmission networks
 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 41

compensated by three different series FACTS i.e. GCSC, TCSC and TCSR connected at
midpoint of a single electrical transmission line. The facts are used for controlling
transmission voltage in the range of ±40kV as well as reactive power injected between -50
MVar/+15 MVar on the power system. This chapter studies the effects of GCSC, TCSC and
TCSR insertion on the total impedance of a transmission line protected by MHO
(admittance) distance relay.
The modified setting zone protection in capacitive and inductive boost mode for three
forward zones (Z1, Z2 and Z3) and reverse zone (Z4) have been investigated in order to
prevent circuit breaker nuisance tripping to improve the performances of distance relay
protection. The simulation results are performed in MATLAB software.

2. Apparent reactance injected by series FACTS devices

In general, FACTS compensator can be divided into three categories (Acha, E. al., 2004):
Series compensator, Shunt compensator, and combined series-series compensator. In this
chapter, we study the series FACTS devices.

2.1. GCSC
The compensator GCSC mounted on figure 1.a is the first that appears in the family of series
compensators. It consists of a capacitance (C) connected in series with the transmission line
and controlled by a valve-type GTO thyristors mounted in anti-parallel and controlled by an
angle of extinction (γ) varied between 0° and 180°. If the GTOs are kept turned-on all the
time, the capacitor C is bypassed and it does not realize any compensation effect. On the
other hand, if the positive-GTO (GTO1) and the negative-GTO (GTO2) turn off once per
cycle, at a given angle γ counted from the zero-crossing of the line current, the main
capacitor C charges and discharges with alternate polarity (Zhang, X.P. et al., 2006), (De
Jesus F. D. et al., 2007).

Figure 1. Transmission line in presence of GCSC

Hence, a voltage VC appears in series with the transmission line, which has a controllable
fundamental component that is orthogonal (lagging) to the line current.
42 An Update on Power Quality

The compensator GCSC injects in the transmission line a variable capacitive reactance
(XGCSC). From figure 1.b the expression of XGCSC is directly related to the controlled GTO
angle (γ) which is varied between 0° and 180° as expressed by following equation (De
Souza, L. F. W. et al., 2008), (Ray, S. et al., 2008) :

 2 1 
( ) XC max 1    sin(2 )
XGCSC (1)
   

Where,

XC max  1 (2)
C.

2.2. TCSC
The compensator TCSC mounted on Figure 2.a is a type of series FACTS compensators. It
consists of a capacitance (C) connected in parallel with an inductance (L) controlled by a
valve mounted in anti-parallel conventional thyristors (T1 and T2) and controlled by an angle
of extinction (α) varied between 90° and 180°.

Figure 2. Transmission line in presence of TCSC

From figure 2.b, the compensator TCSC injected in the transmission line a variable
capacitive reactance (XTCSC). The expression of XTCSC is directly related to the controlled
thyristors, angle (α) which is varied between 90° and 180° and expressed by following
equation (Acha, E. al., 2004), (Sen, K.K.; Sen, M.L., 2009):

XC .X L ( )
XTCSC ( )  XC / / X L ( )  (3)
XC  X L ( )

  
(4)
X L ( )  X L max  
   2  sin(2 ) 
Where,

X L max  L. (5)

 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 43

And,

XC  1 (6)
j.C.

From the equations (4), (5) and (6), the equation (3) becomes:

  
XC .X L.max  
   2  sin(2 ) 
XTCSC ( )  (7)
  
XC  X L.max  
   2  sin(2 ) 

2.3. TCSR
The compensator TCSR is an inductive reactance compensator at which its inductive
reactance is continually adjusted through the firing delay angle (α) of the thyristors as
shown in figure 3.a. It consists of a series reactor shunted by a thyristors controlled reactor
(TCR).

If the firing delay angle is 180°, the TCSR operates as an uncontrolled reactor (L1). When the
angle decreases below 180°, the inductive reactance of TCSR decreases and at 90° it is given
by the parallel connection of the reactors (L1//L2).

Figure 3. Transmission line in presence of TCSR.

From figure 3.b, the compensator TCSR injected in the transmission line a variable
capacitive reactance (XTCSR). The expression of XTCSR is directly related to the controlled
thyristors angle (α) expressed by the following equation (Acha, E. al., 2004), (Zhang, X.P. et
al., 2006):

  
X L 2 .X L1 max  
X .X ( )    2  sin(2 ) 
XTCSR ( )  X L 2 / / X L1( )  L 2 L1  (8)
X L 2  X L1 ( )   
X L 2  X L1 max  
   2  sin(2 ) 
44 An Update on Power Quality

Where,

X L1 max  L1. (9)

And,

X L 2  j.L2 . (10)

3. Power system protection

Fault current is the expression given to the current that flow in the circuit when load is
shorted i.e. flow in a path other than the load. This current is usually very high and may
exceed ten times the rated current of a piece of plant. Faults on power system are
inevitable due to external or internal causes, lightning may struck the overhead lines
causes insulation damage. Internal overvoltage due to switching or other power system
phenomenon may also cause an over voltage which leads to deterioration of the insulation
and faults. Power networks are usually protected by means of two main components,
relays that sense the abnormal current or voltage and a circuit breaker that put a piece of
plant out of tension.

Power system protection is the art and science of the application of devices that monitor the
power line currents and voltages (relays) and generate signals to deenergize faulted sections
of the power network by circuit breakers. Goal is to minimize damage to equipment that
would be caused by system faults, if residues, and maintain the delivery of electrical energy
to the consumers (Horowitz, S.H.; Phadke A.G. 2008), (Blackburn, J.L.; Domin, T.J. 2006).

Many types of protective relays are used to protect power system equipments. They are
classified according to their operating principles; over current relay senses the extra (more
than set) current considered dangerous to a given equipment, differential relays compare in
and out currents of a protected equipment, while impedance relays measure the impedance
of the protected piece of plant.

3.1. Principal characteristics of protection system

For system protection to be effective, the following characteristics must be met (Blackburn
J.L.; Domin. T.J., 2006), (Zellagui. M, Chaghi. A., 2012):

 Reliability: assurance that the protection will perform correctly in presence of faults on
electrical transmission and distribution line,
 Selectivity: maximum continuity of service with minimum system disconnection,
 Speed of operation: minimum fault duration and consequent equipment damage and
system instability,
 Simplicity: minimum protective equipment and associated circuitry to achieve the
protection objectives,
 Economics: maximum protection at minimal total cost.
 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 45

3.2. Principles of relay application

The power system is divided into protection zones defined by the equipment and the available
circuit breakers. Six categories of protection zones are possible in each power system:
 Generators and generator-transformer units,
 Transformers,
 Bus bars,
 Lines (transmission and distribution),
 Utilization equipment (motors, static loads, or other),
 Capacitor or reactor banks (when separately protected).

3.3. Protection zones

Most of these zones are illustrated in figure 4. Although the fundamentals of protection are
quite similar, each of these six categories has protective relays, specifically designed for
primary protection, that are based on the characteristics of the equipment being protected.
The protect ion of each zone normally include s relays that can provide backup for the relays
protecting the adjacent equipment (Zellagui.M; Chaghi.A. 2012.a ). The protection in each
zone should overlap that in the adjacent zone; otherwise, a primary protection void would
occur between the protection zones. This overlap is accomplished by the location of the CTs
the key sources of power system information for the relays.

Figure 4. Protection zone on power system

46 An Update on Power Quality

4. Setting zones for MHO distance relays

4.1. Principal
Distance protection is so called because it is based on an electrical measure of distance along
a transmission line to a fault. The distance along the transmission line is directly
proportional to the series electrical impedance of the transmission line.

Impedance is defined as the ratio of voltage to current. Therefore, distance protection

measures distance to a fault by means of a measured voltage to measured current ratio
computation (Zigler, G., 2008), (Zellagui, M.; Chaghi, A., 2012.b). The philosophy of setting
relay at Sonelgaz Group is three forward zones and one reverse zone to protect EHV
transmission line between busbar A and B with total impedance ZAB as shown in figure 5.

Figure 5. Principal operation of distance relay

4.2. Setting zones

4.2.1. First zone
In practice it is normal to adjust the first zone relays (Z1) at A to protect only up to 80% of
the protective line AB. This is a high speed unit and is used for the primary protection of the
protected line. Its operation is instantaneous (Dechphung, S.; Saengsuwan, T., 2008).

This unit is not set to protect the entire line to avoid undesired tripping due to over reach.
Over reach may occur due to transients during the fault condition.

4.2.2. Second zone

It is set to cover about 20% of the second line (BC). The main object of the second zone unit
is to provide protection to the end zone of the first section which is beyond the reach of the
first unit. The setting of the second unit is so adjusted that it operates the relay even for
arcing faults at the end of the line. To achieve this, the unit must take care beyond the end of
the line. In other words its setting must take care of under reach caused by arc resistance
(Dechphung, S; Saengsuwan, T., 2008), (Zellagui, M.; Chaghi, A., 2012.b).
 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 47

Under reach is also caused by intermediate current sources, errors in CT, and VT and
measurement performed by the relay. To take into account the under reaching tendency
caused by these factors, the normal practice is to set the second zone reach up to 20% of the
shortest adjoining line section. The protective zone of the second unit is known as the
second zone of protection. The second zone unit operates after a certain time delay. Its
operating time is 0,3 sec.

4.2.3. Third zone

It is provided for back-up protection of the adjoining line. Its reach should extend beyond
the end of the adjoining line under the maximum under reach, which may be caused by
arcs, intermediate current sources and errors in CT, VT and measuring unit (Zellagui. M.;
Chaghi. A., 2012.b). The protective zone of the third stage is known as the third zone of
protection.

The characteristic curve on MHO (admittance) relay for setting zones is shown in figure 6.

Figure 6. Characteristic curve X (R) for setting zones for distance protection.

Figure 7 represents the tripping time T1, T2 and T3 correspond to these three zones of
operation for circuit breaker installed at busbar A and MHO distance relay (RA).

The fourth setting zones for protected transmission line (forward and reverse) without
series FACTS are given by (Zellagui, M.; Chaghi, A. 2012.c), (Gérin-Lajoie, L. 2009):

Z1 R1  jX1 80%ZAB 0,8.( RAB  jX AB ) (11)

48 An Update on Power Quality

Z2 R2  jX2 RAB  jX AB  0,2.( RBC  jXBC ) (12)

Z3 R3  jX3 RAB  jX AB  0,4.( RBC  jXBC ) (13)

Z4 
R4  jX4 
60%ZAB 
0,6.( RAB  jX AB ) (14)

The total impedance of transmission line AB measured by MHO distance relay is:

KVT (15)
Z AB  KZ .ZL , KZ 
KCT

Where, ZAB is real total impedance of line AB, and KVT and KCT is ratio of voltage to
current respectively.
The presence of series FACTS systems in a reactor (XFACTS) has a direct influence on the total
impedance of the protected line (ZAB), especially on the reactance XAB and no influence on
the resistance RAB.

Figure 7. Selectivity of distance relay

4.3. Measured impedance by relay in presence fault

Distance relaying belongs to the principle of ratio comparison. The ratio is between voltage
and current, which in turn produces impedance. The impedance is proportional to the
distance in transmission lines, hence the distance relaying designation for the principle.

This principle is primarily used for protection of high voltage transmission lines. In this case
the over current principle cannot easily cope with the change in the direction of the current
flow, which is common in the transmission but no so common in radial distribution lines.
Computing the impedance in the three-phase system is a bit involved in each type of the
fault produces a different impedance expression. Because of these differences the settings of
the distance relay are needed to be selected to distinguish between the ground and phase
faults.
 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 49

In addition fault resistance may create problem for distance measurement because of the
fault resistance may be difficult for predict. It is particularly challenging for distance relays
to measure correct fault impedance when the current in feed from the other end of the line
create an unknown voltage drop on the fault resistance (Kazemi, A. et al., 2009), (Kulkami,
P.A. et al., 2010).

This may contribute to erroneous computation of the impedance, called apparent

impedance ‘seen’ by the relay located at the end of the line and using the current and
voltage measurement just from the end. Once the impedance is computed, it is compared to
the settings that define the operating characteristics of the relay. Based on the comparison, a
decision is made if a fault has occurred, if so in what zone.

The principle behind the standard distance protection function is based on measured
apparent impedance (Zseen) at the transmission line terminals. The apparent impedance is
computed from fundamental power frequency components of measured instantaneous
voltage and current signals (Liu, Q.; Wang, Z., 2008), (Khederzadeh, M.; Sidhu, T. S., 2006),
(Jamali, S.; Shateri, H. 2011), the apparent impedance is given by:

V 
Zseen   seen .K (16)
 I seen  Z

5. Case study and simulation results

The power system studied in this paper is the 400 kV, 50 Hz eastern Algerian electrical
transmission networks at group SONELGAZ (Algerian Company of Electricity and Gas)
which is shows in figure 8 (Sonelgaz Group/GRTE, 2011). The MHO distance relay is located
in the bus bar at Ramdane Djamel substation in Skikda to protect transmission line between
busbar A and busbar B at Oued El Athmania substation in Mila, the bus bar C at Salah Bay
substation in Sétif.

The figure below represents a 400 kV transmission line in the presence of a series FACTS
type GCSC, TCSC and TCSR installed in the midpoint of the transmission line protected by
a MHO distance relay between busbar A and B.

5.1. Characteristic curve of installed series FACTS devices

Figure 9 shows the characteristic curves of the different compensators used GCSC, TCSC
and TCSR installed on transmission line in this case study.

5.2. Impact on the impedance of a protected transmission line.

The impact of the angle variation γ and injected reactance XGCSC by compensator GCSC on
reactance and resistance of the total impedance for transmission line (XAB and RAB) and on
the parameters of measured impedance by MHO distance relay (XRelay and RRelay) in the
inductive and capacitive mode is summarized in table 1.
50 An Update on Power Quality

Figure 8. Electrical networks 400 kV study in Algeria

 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 51

Figure 9. Characteristic curve for series FACTS devices installed

52 An Update on Power Quality

Mode Inductive Capacitive

γ (°) 0 20 40 80 100 120 140 180

XGCSC (Ω) 32,000 18,3415 7,7466 0,0718 -0,0718 -1,8454 -7,7466 -32,000
XAB (Ω) 143,44 129,78 119,19 111,51 111,37 109,59 103,69 79,440
RAB (Ω) 11,526 11,526 11,526 11,526 11,526 11,526 11,526 11,526
XRelay (Ω) 7,1720 6,4891 5,9593 5,5756 5,5684 5,4797 5,1847 3,9720
RRelay (Ω) 0,5763 0,5763 0,5763 0,5763 0,5763 0,5763 0,5763 0,5763

Table 1. Variation of reactance and resistance as a function of γ and XGCSC

The impact of the angle variation α and XTCSC injected reactance by compensator TCSC on
reactance and resistance of the total impedance for transmission line (XAB and RAB) and on
the parameters of measured impedance by MHO distance relay (XRelay and RRelay) in the
inductive and capacitive mode is summarized in table 2.

Mode Inductive Capacitive

α (°) 90 91 92 100 140 180

XTCSC (Ω) 3,159.10 6 3,385.10 6 6,7825.10 6 -4828,0 -440.684 -106.670
XAB (Ω) 3,158 10 6 3,384.10 6 6,7826.10 6 -48177,0 -329,24 4,7697
RAB (Ω) 11,526 11,526 11,526 11,526 11,526 11,526
XRelay (Ω) 1,579.10 5 1,692.10 5 3,3913.10 5 -2408,9 -16.4622 0.2385
RRelay (Ω) 0,5763 0,5763 0,5763 0,5763 0,5763 0,5763

Table 2. Variation of reactance and resistance on function α and XTCSC

The impact of the angle variation α and injected reactance XTCSR by compensator TCSR on
reactance and resistance of the total impedance for transmission line (XAB and RAB) and on
the parameters of measured impedance by MHO distance relay (XRelay and RRelay)in the
inductive and capacitive mode is summarized in table 3.

Mode Inductive

α (°) 90 100 110 120 130 140 160 180

XTCSR (Ω) 32,000 32,021 32,170 32,563 33,308 34,506 38,645 45,714
XAB (Ω) 143,44 143,46 143,61 144,00 144,75 145,95 150,09 157,15
RAB (Ω) 11,526 11,526 11,526 11,526 11,526 11,526 11,526 11,526
XRelay (Ω) 7,1720 7,1731 7,1805 7.2002 7,2374 7,2973 7,5043 7,8577
RRelay (Ω) 0,5763 0,5763 0,5763 0,5763 0,5763 0,5763 0,5763 0,5763

Table 3. Variation of reactance and resistance on function α and XTCSR

 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 53

5.3. Impact on setting zones

5.3.1. Impact of GCSC Insertion
Figures 10 and 11 show the impact of the variation extinction angle γ and reactance XGCSC on
the value of setting zones reactance and setting zones resistance respectively in presence of
GCSC on transmission line.

Figure 10. Impact of insertion GCSC on reactance of setting zones

54 An Update on Power Quality

Figure 11. Impact of insertion GCSC on resistance of setting zones

5.3.2. Impact of TCSC Insertion

Figures 12 and 13 is show the impact of the variation extinction angle of α and reactance
XTCSC on the value of setting zones reactance and setting zones resistance respectively in
presence of a TCSC on transmission line.
 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 55

Figure 12. Impact of insertion TCSC on reactance of setting zones

56 An Update on Power Quality

Figure 13. Impact of insertion TCSC on resistance of setting zones

5.3.3. Impact of TCSR Insertion

Figures 14 and 15 is show the impact of the variation extinction angle α and reactance XTCSR
on the value of setting zones reactance and setting zones resistance respectively in presence
of TCSC on transmission line.
 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 57

Figure 14. Impact of insertion TCSR on reactance of setting zones

58 An Update on Power Quality

Figure 15. Impact of insertion TCSR on resistance of setting zones

6. Conclusions
The results are presented in relation to a typical 400 kV transmission system employing
GCSC, TCSC and TCSR series FACTS devices. The effects of the extinction angle γ for
controlled GTO installed on GCSC as well as extinction angle α for controlled thyristors on
TCSC and TCSR are investigated. These devices are connected at the midpoint of a
transmission line protected by distance relay. However as demonstrated these angles
injected variable reactance (XGCSC, XTCSC or XTCSR) in the protected line which lead to direct
impact on the total impedance of the protected line and setting zones.
 Impact of Series FACTS Devices (GCSC, TCSC and TCSR)
on Distance Protection Setting Zones in 400 kV Transmission Line 59

Therefore settings zones of the total system protection must be adjusted in order to avoid
unwanted circuit breaker tripping in the presence of series FACTS compensator.

Author details
Mohamed Zellagui and Abdelaziz Chaghi
LSP-IE Research Laboratory, Department of Electrical Engineering, Faculty of Technology,
University of Batna, Algeria

7. References
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Modelling and Simulation in Power Networks, John Wiley & Sons Ltd Publication, ISBN:
978-0470852712, London, England.
Blackburn, J.L.; Domin, T.J. (2006). Protective Relaying: Principles and Applications, 3rd Edition,
Published by CRC Press, ISBN: 978-1574447163, USA.
De Jesus F. D.; De Souza L. F. W.; Wantanabe E.; Alves J. E. R. (2007). SSR and Power
Oscillation Damping using Gate-Controlled Series Capacitors (GCSC), IEEE Transaction
on Power Delivery, Vol. 22, N°3, (Mars 2007), pp. 1806-1812.
De Souza, L. F. W.; Wantanabe, E. H.; Alves, J. E. R. (2008). Thyristor and Gate-Controlled
Series Capacitors: A Comparison of Component Ratings, IEEE Transaction on Power
Delivery, Vol. 23, No.2, (May 2008), pp. 899-906.
Dechphung, S.; Saengsuwan, T. (2008). Adaptive Characteristic of MHO Distance Relay for
Compensation of the Phase to Phase Fault Resistance, IEEE International Conference on
Sustainable Energy Technologies (ICSET’ 2008), Singapore, Thailand, 24-27 November
2008.
Gérin-Lajoie, L. (2009), A MHO Distance Relay Device in EMTP Works, Electric Power
Systems Research, 79(3), March 2009, pp. 484-49.
Horowitz, S.H.; Phadke A.G. (2008). Power System Relaying, 3rd Edition, Published by John
Wiley & Sons Ltd, ISBN: 978-0470057124, England, UK.
Jamali, S.; Shateri, H. (2011). Impedance based Fault Location Method for Single Phase to
Earth Faults in Transmission Systems, 10th IET International Conference on Developments
in Power System Protection (DPSP), United Kingdom, 29 March - 1 April, 2010.
Kazemi, A.; Jamali, S.; Shateri, H. (2009). Measured Impedance by Distance Relay with
Positive Sequence Voltage Memory in Presence of TCSC, IEEE/PES Power Systems
Conference and Exposition (PSCE’ 09), Seattle, USA, 15-18 March 2009.
Khederzadeh, M.; Sidhu, T. S. (2006). Impact of TCSC on the Protection of Transmission
Lines, IEEE Transactions on Power Delivery, Vol. 21, No. 1, (January 2006), pp. 80-87.
Kulkami, P. A.; Holmukhe, R. M.; Deshpande, K. D.; Chaudhari, P. S. (2010). Impact of
TCSC on Protection of Transmission Line, International Conference on Energy Optimization
and Control (ICEOC’ 10), Maharashtra, India, 28-30 December 2010.
60 An Update on Power Quality

Liu, Q.; Wang, Z. (2008). Research on the Influence of TCSC to EHV Transmission Line
Protection, International Conference on Deregulation and Restructuring and Power
Technology (DRPT’ 08), Nanjing, China, 6-9 April 2008.
Mathur, R.M.; Basati, R.S., (2002). Thyristor-Based FACTS Controllers for Electrical Transmission
Systems, Published by Wiley and IEEE Press Series in Power Engineering, ISBN: 978-
0471206439, New Jersey, USA.
McLaren, P. G.; Mustaphi, K.; Benmouyal, G.; Chano, S.; Girgis, A.; Henville, C.; Kezunovic,
M.; Kojovic, L.; Marttila, R.; Meisinger, M.; Michel, G.; Sachdev, M. S.; Skendzic, V.;
Sidhu, T. S.; Tziouvaras, D., (2001). Software Models for Relays, IEEE Transactions on
Power Delivery, Vol. 16, No. 12, (April 2001), pp. 238-45.
Ray, S.; Venayagamoorthy, G. K.; Watanabe, E. H. (2008). A Computational Approach to
Optimal Damping Controller Design for a GCSC, IEEE Transaction on Power Delivery,
Vol. 23, No.3, (July 2008), pp. 1673-1681.
Sen, K.K.; Sen, M.L., (2009). Introduction to FACTS Controllers: Theory, Modeling and
Applications", Published by John Wiley & Sons, Inc., and IEEE Press, ISBN: 978-
0470478752, New Jersey, USA.
Sonelgaz Group/GRTE, (2011). Topologies of Electrical Networks High Voltage 400 kV, Technical
rapport published by Algerian Company of Electrical Transmission Network, 30
December 2011, Sétif, Algeria.
Zellagui, M.; Chaghi, A. (2012.a). Distance Protection for Electrical Transmission Line:
Equipments, Settings Zones and Tele-Protection, published by LAP Lambert Academic
Publishing, ISSN: 978-3-659-15790-5, Saarbrücken - Germany.
Zellagui, M.; Chaghi, A. (2012.b). Measured Impedance by MHO Distance Protection for
Phase to Earth Fault in Presence GCSC, ACTA Technica Corviniensis : Bulletin of
Engineering, Tome 5, Fascicule 3, (July-September 2012), pp. 81-86.
Zellagui, M.; Chaghi, A. (2012.c). A Comparative Study of FSC and GCSC Impact on MHO
Distance Relay Setting in 400 kV Algeria Transmission Line, Journal ACTA
Electrotehnica, Vol. 53, No. 2, (July 2012), pp. 134-143.
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Control, Springer Publishers, ISBN: 978-3642067860, Heidelberg, Germany.
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 Chapter 4

A PSO Approach in Optimal FACTS Selection

with Harmonic Distortion Considerations

H.C. Leung and Dylan D.C. Lu

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/54555

1. Introduction
Static Var Compensator (SVC) has been commonly used to provide reactive power
compensation in distribution systems [1]. The SVC placement problem is a well-researched
topic. Earlier approaches differ in problem formulation and the solution methods. In some
approaches, the objective function is considered as an unconstrained maximization of
savings due to energy loss reduction and peak power loss reduction against the SVC cost.
Others formulated the problem with some variations of the above objective function. Some
have also formulated the problem as constrained optimization and included voltage
constraints into consideration.

In today’s power system, there is trend to use nonlinear loads such as energy-efficient
fluorescent lamps and solid-state devices. The SVCs sizing and allocation [2-4] should be
properly considered, if else they can amplify harmonic currents and voltages due to possible
resonance at one or several harmonic frequencies and switching actions of the power
electronics converters connected. This condition could lead to potentially dangerous
magnitudes of harmonic signals, additional stress on equipment insulation, increased SVC
failure and interference with communication system.

SVC values are often assumed as continuous variables whose costs are considered as
proportional to SVC size in past researches. Moreover, the cost of SVC is not linearly
proportional to the size (MVAr). Hence, if the continuous variable approach is used to
choose integral SVC size, the method may not result in an optimum solution and may even
lead to undesirable harmonic resonance conditions.

Current harmonics are inevitable during the operation of thyristor controlled rectifiers, thus
it is essential to have filters in a SVC system to eliminate the harmonics. The filter banks can
not only absorb the risk harmonics, but also produce the capacitive reactive power. The SVC

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62 An Update on Power Quality

uses close loop control system to regulate busbar voltage, reactive power exchange, power
factor and three phase voltage balance.
This chapter describes a method based on Particle Swarm Optimisation (PSO) [5] to solve
the optimal SVC allocation successfully. Particle Swarm Optimisation (PSO) method is a
powerful optimization technique analogous to the natural genetic process in biology.
Theoretically, this technique is a stochastic approach and it converges to the global optimum
solution, provided that certain conditions are satisfied. This chapter considers a distribution
system with 9 possible locations for SVCs and 27 different sizes of SVCs. A critical
discussion using the example with result is discussed in this chapter.

2. Problem formulation
2.1. Operation principal of SVC
The Static Var Compensator (SVC) are composed of the capacitor banks/filter banks and air-
core reactors connected in parallel. The air-core reactors are series connected to thyristors.
The current of air-core reactors can be controlled by adjusting the fire angle of thyristors.
The SVC can be considered as a dynamic reactive power source. It can supply capacitive
reactive power to the grid or consume the spare inductive reactive power from the grid.
Normally, the system can receive the reactive power from a capacitor bank, and the spare
part can be consumed by an air-core shunt reactor. As mentioned, the current in the air-core
reactor is controlled by a thyristor valve. The valve controls the fundamental current by
changing the fire angle, ensuring the voltage can be limited to an acceptable range at the
injected node(for power system var compensation), or the sum of reactive power at the
injected node is zero which means the power factor is equal to 1 (for load var
compensation).

2.2. Assumptions
The optimal SVC placement problem [6] has many variables including the SVC size, SVC
cost, locations and voltage constraints on the system. There are switchable SVCs and fixed-
type SVCs in practice. However, considering all variables in a nonlinear fashion will make
the placement problem very complicated. In order to simplify the analysis, the assumptions
are as follows: 1) balanced conditions, 2) negligible line capacitance, 3) time-invariant loads
and 4) harmonic generation is solely from the substation voltage supply.

2.3. Radial distribution system

Figure 1 clearly illustrates an m-bus radial distribution system where a general bus i
contains a load and a shunt SVC. The harmonic currents introduced by the nonlinear loads
are injected at each bus

At the power frequency, the bus voltages are found by solving the following mismatch
equations:
 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 63

0 1 2 i m-1 m

y m  1 ,m
1
y 01 y 12
1 1

...... ......

y ci P ni ,Q ni
P ,Q 1 1 P ,Q2 2 P li
, Q li P m 1
,Q
m 1 P m
,Q
m

Figure 1. One-line diagram of the radial distribution feeder.

 
2 m
1 1 1 1 1 1 1
P i V i G ii   V i V jY ij cos  ij   j   i i 
1,2,3 m (1)
j 1
j i

 
2 m
 V 1i Bii   V 1i V 1jY 1ij sin  1ij   1j   1i
Qi  i  1,2,3 m (2)
j 1
ji

where

P
i P li  P ni (3)

Q
i Qli  Qni (4)

 1
 y ij if i  j

1
Y ij  1
Y ij  1ij   (5)
1 1 1
 y i 1,i  y i 1,i  y ci if i  j

ii G ii  j B ii
Y (6)

2.4. Real power losses

At fundamental frequency, the real power losses in the transmission line between buses i
and i+1 is:

 
2
1 1 1 1

P loss i ,i 1 Ri ,i 1 V i 1  V i Y i ,i 1 (7)

So, the total real losses is:

N  m1 
n
P loss     P loss i ,i 1  (8)
 i 0
n 1 

2.5. Objective function and constraints

The objective function of SVC placement is to reduce the power loss and keep bus voltages
and total harmonic distortion (HDF) within prescribed limits with minimum cost. The
constraints are voltage limits and maximum harmonic distortion factor, with the harmonics
64 An Update on Power Quality

taken into account. Following the above notation, the total annual cost function due to SVC
placement and power loss is written as :

Minimize

m
f  Kl K p Ploss   Qcj Kcj (9)
j 1

where j = 1,2,….m represents the SVC sizes

Qcj  j * Ks (10)

The objective function (1) is minimized subject to

V min  V i  V max i  1,2,3m (11)

and

HDF i  HDF max i  1,2,3 m (12)

According to IEEE Standard 519 [7] utility distribution buses should provide a voltage
harmonic distortion level of less than 5% provided customers on the distribution feeder
limit their load harmonic current injections to a prescribed level.

3. Proposed algorithm
3.1. Harmonic power flow [8]
At the higher frequencies, the entire power system is modelled as the combination of
harmonic current sources and passive elements. Since the admittance of system components
will vary with the harmonic order, the admittance matrix is modified for each harmonic
order studied. If the skin effect is ignored, the resulting n-th harmonic frequency load
admittance, shunt SVC admittance and feeder admittance are respectively given by:

n Pli Qli

Y li 2
j 2
(13)
Vi1 n Vi1

n 1
Y ci  nY ci (14)

n 1
Y i ,i 1  (15)
Ri ,i 1  jnX i ,i 1

The linear loads are composed of a resistance in parallel with a reactance [9]. The nonlinear
loads are treated as harmonic current sources, so the injection harmonic current source
introduced by the nonlinear load at bus i is derived as follows:
 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 65

*
1
 P  jQ 
Ii   ni 1 ni  (16)
 Vi 

1
I i  C  n I i
n
(17)

In this study, C(n) is obtained by field test and Fourier analysis for all the customers along
the distribution feeder. The harmonic voltages are found by solving the load flow equation
(18), which is derived from the node equations.

n n n
Y V I (18)

At any bus i, the r.m.s. value of voltage is defined by

N 2
Vi   Vni (19)
n1

where N is an upper limit of the harmonic orders being considered and is required to be
within an acceptable range. After solving the load flow for different harmonic orders, the
harmonic distortion factor (HDF) [8] that is used to describe harmonic pollution is
calculated as follows:

N 2
 Vni
i %
n 2

HDF 1
 100% (20)
Vi

It is also required to be lower than the accepted maximum value.

3.2. Selection of optimal SVC location

The general case of optimal SVC locations can be selected for starting iteration. PSO
calculates the optimal SVC sizes according to the optimal SVC locations. After the first time
iteration, the solution of SVC locations and sizes will be recorded as old solution and add
more locations to consideration. PSO is used to calculate a new solution. If the new solution
is better than the old solution, the old solution will be replaced by the new solution. If else,
the old solution is the best solution. Therefore, this project will continue to consider more
locations until no more optimal solution, which is better than the previous solution. In this
chapter, the selection of optimal SVC location is based on the following criteria: voltage, real
power loss, load reactive power and harmonic distortion factor with equal weighting.

3.3. Solution algorithm

PSO is a search algorithm based on the mechanism of natural selection and genetics. It
consists of a population of bit strings transformed by three genetic operations: 1) Selection
66 An Update on Power Quality

or reproduction, 2) Crossover, and 3) mutation. Each string is called chromosome and

represents a possible solution. The algorithm starts from an initial population generated
randomly. Using the genetic operations considering the fitness of a solution, which
corresponds, to the objective function for the problem generates a new generation. The
string’s fitness is usually the reciprocal of the string’s objective function in minimization
problem. The fitness of solutions is improved through iterations of generations. For each
chromosome population in the given generation, a Newton-Raphson load flow calculation is
performed. When the algorithm converges, a group of solutions with better fitness is
generated, and the optimal solution is obtained. The scheme of genetic operations, the
structure of genetic string, its encode/decode technique and the fitness function are
designed. The implementation of PSO components and the neighborhood searching are
explained as follows.

4. Implementation of PSO
This section provides a brief introductory concept of PSO. If Xi = (xi1, xi2 ,…, xid) and Vi =(vi1, vi2
,…, vid) are the position vector and the velocity vector respectively in d dimensions search
space, then according to a fitness function, where Pi=(pi1, pi2,…, pid) is the pbest vector and
Pg=(pg1, pg2,…, pgd) is the gbest vector, i.e. the fittest particle of Pi, updating new positions
and velocities for the next generation can be determined.

For each particle

Initialize particle
END

Do
For each particle
Calculate fitness value
If the fitness value is better than the best fitness
value (pbest), set current value as the new pbest
End

Choose the particle with the best fitness value of all

the particles as the gbest
For each particle
Calculate particle velocity from equation (21)
Update particle position from equation (22)
End

Perform mutation operation with pm

While maximum iteration is reached or minimum error

condition is satisfied

Figure 2. The pseudo code of the PSO method

 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 67

  
Vid  t   Vid  t  1  C1 * rand1* Pid  Xid  t  1  C2 * rand2 * Pgd  Xid  t  1  (21)

Xid  t
 Xid  t  1  Vid t  (22)

where Vid is the particle velocity, Xid is the current particle (solution). Pid and Pgd are defined
as above. rand1 and rand2 are random numbers which is uniformly distributed between
[0,1]. C1, C2 are constant values which is usually set to C1 = C2 = 2.0. These constants
represent the weighting of the stochastic acceleration which pulls each particle towards the
pbest and gbest position. ω is the inertia weight and it can be expressed as follows:

itermax  iter

ω  i   f *  itermax
ωf (23)

where i and f are the initial and final values of the inertia weight respectively. iter and
itermax are the current iterations number and maximum allowed iterations number
respectively.
The velocities of particles on each dimension are limited to a maximum velocity Vmax. If the
sum of accelerations causes the velocity on that dimension to exceed the user-specified Vmax,
the velocity on that dimension is limited to Vmax.
In this chapter, the parameters used for PSO are as follows:
 Number of particles in the swarm, N = 30 (the typical range is 20 – 40)
 Inertia weight, wi = 0.9, wf = 0.4
 Acceleration factor, C1 and C2 = 2.0
 Maximum allowed generation, itermax = 100
 The maximum velocity of particles, Vmax =10% of search space
There are two stopping criteria in this chapter. Firstly, i(t is the number of iterations since
the last change of the best solution is greater than a preset number. The PSO is terminated
while maximum iteration is reached.
For the PSO, the constriction and inertia weight factors are introduced and (21) is improved
as follows.

V    
id  t  k  Vid  t  1  1 * rand1 * Pid  Xid  t  1   2 * rand 2 * Pgd  Xid  t  1  (24)

2
k (25)
2   1   2    1   2   4  1   2 
2

where k is a constriction factor from the stability analysis which can ensure the convergence
(i.e. avoid premature convergence) where ߮ଵ ൅ ߮ଶ > 4 and kmax < 1 and  is dynamically set
as follows:
68 An Update on Power Quality

max  min
ω  ω max  t (26)
tTotal

where t and tTotal is the current iteration and total number of iteration respectively and ߱௠௜௡
and ߱௠௔௫ is the upper and lower limit which are set 1.3 and 0.1 respectively.

The advantage of the integration of mutation from GAs is to prevent stagnation as the
mutation operation choose the particles in the swarm randomly and the particles can move
to difference position. The particles will update the velocities and positions after mutation.

mutation  xid   xid   ,  1  r  0  (27)

mutation  xid   xid   ,  1  r  0  (28)

where xid is a randomly chosen element of the particle from the swarm, ω is randomly
ଵ
generated within the range [0, ଵ଴ × (particle max – particle min)] (particle max and particle min are
the upper and lower boundaries of each particle element respectively) and r is the random
number in between 1 and -1

Implementation of an optimization problem is realized within the evolutionary process of a

fitness function. The fitness function adopted is derived as equation (9). The objective
function is to minimize f. It is composed of two parts; 1) the cost of the power loss in the
transmission branch and 2) the cost of reactive power supply. Since PSO is applied to
maximization problem, minimization of the problem take the normalized relative fitness
value of the population and the fitness function is defined as:

fmax  fa
fi  (29)
fmax

m
where fa  Kl K p Ploss   Qcj Kcj
j 1

5. Software design
Figure 3 depicts the main steps in the process of this chapter. The predefined processes of
optimal SVC location and Particle Swarm Optimisation calculation are illustrated in Figure 4
and Figure 5.
 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 69

Start

Input setting, system file

and capacitor file.

Setup a Y-matrix

Setup the possible choice of the SVC

sizes and costs.

Optimal SVC location calculation

subprogram *

PSO calculation subprogram **

No No solution found
Any feasible solution found ? within the
constraints

Yes
Record the best result and
set as old solution

Optimal SVC location calculation

subprogram *

Old solution replaced PSO calculation subprogram **

by new solution

Record the best result and

set as new solution
No

Is all location Yes Is new solution better

considered ? than old solution?

Yes No

Output the new Output the old setting

setting result result

End

* refer to Figure 4 and ** refer to Figure 5

Figure 3. Flow chart of main operation

70 An Update on Power Quality

Enter

Newton-Raphson power flow

calculation

Is harmonic
considered ? No

Yes
Harmonic distortion
calculation subprogram

Calculate power loss in each

line (equation 7)

Select the optimal capacitor

location

Exit

Figure 4. Flow chart of ‘Optimal SVC location calculation subprogram’ in Figure 2

 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 71

Figure 5. Flow chart of ‘Particle Swarm Optimisation calculation subprogram’ in Figure 3

72 An Update on Power Quality

Enter

Set first harmonic order

Adjust Y-matrix

Calculate Harmonic current

Next harmonic order
source

Solve V*Y=I

Is the highest No
harmonic order
considered?

Yes
Calculate the harmonic
distortion factor

Exit

Figure 6. Flow chart of ‘Harmonic distortion calculation subprogram’ in Figure 4 and Figure 5

6. Numerical example and results

In this section, a radial distribution feeder [10] is used as an example to show the
effectiveness of this algorithm. The testing distribution system is shown in Figure 7. This
feeder has nine load buses with rated voltage 23kV. Table 1 and Table 2 show the loads and
feeder line constants. The harmonic current sources are shown in Table 3, which are
generated by each customer.

Supply
source

1 2 3 4 5 6 7 8 9
Figure 7. Testing distribution system with 9 buses
 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 73

Bus 1 2 3 4 5 6 7 8 9
P(kW) 1840 980 1790 1598 1610 780 1150 980 1640
Q(MVAr) 460 340 446 1840 600 110 60 130 200
Non-linear (%) 0 55.7 18.9 92.1 4.7 1.9 38.2 4.5 4.0
Table 1. Load data of the test system

From
From Bus i R i,i 1   Xi,i1  
Bus j
0 1 0.1233 0.4127
1 2 0.0140 0.6051
2 3 0.7463 1.2050
3 4 0.6984 0.6084
4 5 1.9831 1.7276
5 6 0.9053 0.7886
6 7 2.0552 1.1640
7 8 4.7953 2.7160
8 9 5.3434 3.0264
Table 2. Feeder data of the test system

Harmonic current sources(%) in harmonic

order
Bus 5 7 11 13 17 19 23 25
1 0 0 0 0 0 0 0 0
2 9.1 5.3 1.8 1.1 0.7 0.6 0.4 0.3
3 3.1 1.8 0.6 0.4 0.2 0.2 0.1 0.1
4 6.2 3.6 1.3 0.8 0.5 0.4 0.3 0.2
5 17.7 2.9 4.5 8.2 5.4 2.9 2.9 0
6 0 0 9.6 5.8 0 0 3.6 3.0
7 0.3 0 0 0 0 0 0 0
8 0.8 0.5 0.2 0 0 0 0 0
9 15.1 8.8 3.0 1.8 1.2 1.0 0.6 0.5
Table 3. The harmonic current sources

Kp is selected to be US $168/MW in equation (9). The minimum and maximum voltages are
0.9 p.u. and 1.0 p.u. respectively. All voltage and power quantities are per-unit values. The
base value of voltage and power is 23kV and 100MW respectively. Commercially available
SVC sizes are analyzed. Table 4 shows an example of such data provided by a supplier for
23kV distribution feeders. For reactive power compensation, the maximum SVC size Qc(max)
should not exceed the reactive load, i.e. 4186 MVAr. SVC sizes and costs are shown in Table
5 by assuming a life expectancy of ten years (the placement, maintenance, and running costs
are assumed to be grouped as total cost.)
74 An Update on Power Quality

Size of SVC (MVAr) 150 300 450 600 900 1200

Cost of SVC ($) 750 975 1140 1320 1650 2040
Table 4. Available 3-phase SVC sizes and costs

j 1 2 3 4 5 6 7 8 9
Qcj (MVAr) 150 300 450 600 750 900 1050 1200 1350
Kcj ($ / MVAr) 0.500 0.350 0.253 0.220 0.276 0.183 0.228 0.170 0.207
j 10 11 12 13 14 15 16 17 18
Qcj (MVAr) 1500 1650 1800 1950 2100 2250 2400 2550 2700
Kcj ($ / MVAr) 0.201 0.193 0.187 0.211 0.176 0.197 0.170 0.189 0.187
j 19 20 21 22 23 24 25 26 27
Qcj (MVAr) 2850 3000 3150 3300 3450 3600 3750 3900 4050
Kcj ($ / MVAr) 0.183 0.180 0.195 0.174 0.188 0.170 0.183 0.182 0.179
Table 5. Possible choice of SVC sizes and costs

The effectiveness of the method is illustrated by a comparative study of the following three
cases. Case 1 is without SVC installation and neglected the harmonic. Both Case 2 and 3 use
PSO approach for optimizing the size and the placement of the SVC in the radial
distribution system. However, Case 2 does not take harmonic into consideration and Case 3
takes harmonic into consideration. The optimal locations of SVCs are selected at bus 4, bus 5
and bus 9.
Before optimization (Case 1), the voltages of bus 7, 8, 9 are violated. The cost function and
the maximum HDF are $132138 and 6.15% respectively. The harmonic distortion level on all
buses is higher than 5%.
After optimization (Case 2 and 3), the power losses become 0.007065 p.u. in Case 2 and
0.007036 p.u. in Case 3. Therefore, the power savings will be 0.000747 p.u. in Case 2 and
0.000776 p.u. in Case 3. It can also be seen that Case 3 has more power saving than Case 2.
The voltage profile of Case 2 and 3 are shown in Table 6 and Table 7 respectively. In both
cases, all bus voltages are within the limit. The cost savings of Case 2 and Case 3 are $2,744
(2.091%) and $1,904 (1.451%) respectively with respect to Case 1. Since harmonic distortion
is considered in Case 3, the sizes of SVCs are larger than Case 2 so that the total cost of Case
3 is higher than Case 2.
The maximum HDF of Case 2 of Case 3 are 1.35% and 1.2% respectively. The HDF
improvement of Case 3 with respects to Case 1 is

6.15  1.20
HDF improvement
 %  100 80.49%

6.15
The HDF improvement of Case 3 with respects to Case 2 is

1.40  1.20
HDF improvement %   14.29%
1.40
 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 75

The improvement of the harmonic distortion is quite attractive and it is clearly shown in
Figure 7. The reductions in HDF are 80.49% and 14.29% with respect to Case 1 and Case 2.

The optimal cost and the corresponding SVC sizes, power loss, minimum / maximum
voltages, the average CPU time and harmonic distortion factor are also shown in Figure 8.

Figure 8. Effect of harmonic distortion on each bus

Voltages in harmonic order

1 5 7 11 13 17 19 23 25 Vrms HDF
Bus x1 x10-2 x10 -3 x10 -3 X10 -3 x10 -4 x10-4 x10-4 x10-4 x1 %
1 0.993 4.41 2.96 1.57 1.25 9.60 8.12 7.47 4.72 0.992 5.78
2 0.987 4.43 2.98 1.58 1.26 9.69 8.19 7.53 4.76 0.987 5.85
3 0.963 4.45 2.98 1.58 1.26 9.70 8.18 7.54 4.74 0.963 6.02
4 0.948 4.47 3.00 1.59 1.27 9.76 8.21 7.59 4.75 0.947 6.15
5 0.917 4.23 2.78 1.46 1.18 9.02 7.49 6.98 4.24 0.916 5.95
6 0.907 4.14 2.71 1.41 1.14 8.61 7.14 6.65 4.05 0.907 5.86
7 0.889 4.02 2.61 1.34 1.08 8.11 6.72 6.22 3.79 0.888 5.78
8 0.859 3.80 2.43 1.23 0.98 7.31 6.05 5.57 3.40 0.858 5.60
9 0.838 3.66 2.32 1.15 0.91 6.79 5.61 5.13 3.15 0.837 5.49
Table 6. The voltage profile of Case 1
76 An Update on Power Quality

Voltages in harmonic order

1 5 7 11 13 17 19 23 25 Vrms HDF
Bus x1 x10-2 x10-2 x10-3 x10-3 x10-4 x10-4 x10-4 x10-4 x1 %
1 0.997 1.190 5.86 1.93 1.22 7.45 6.27 4.49 3.33 0.999 1.40
2 0.999 1.190 5.90 1.94 1.23 7.51 6.32 4.53 3.36 0.988 1.40
3 0.988 1.130 5.34 1.62 0.99 5.51 4.37 2.94 2.05 0.980 1.32
4 0.980 1.100 5.02 1.44 0.85 4.36 3.23 2.05 1.29 0.980 1.26
5 0.962 0.887 3.42 0.81 0.52 2.29 1.33 0.96 0.29 0.962 1.02
6 0.954 0.861 3.28 0.79 0.51 2.12 1.24 1.12 0.49 0.954 0.99
7 0.939 0.827 3.10 0.73 0.46 1.90 1.12 0.97 0.44 0.939 0.95
8 0.915 0.751 2.72 0.60 0.36 1.45 0.89 0.68 0.34 0.915 0.89
9 0.900 0.682 2.37 0.47 0.25 1.04 0.69 0.39 0.25 0.901 0.82
Table 7. The voltage profile of Case 2

Voltages in harmonic order

1 5 7 11 13 17 19 23 25 Vrms HDF
Bus x1 x10-2 x10-2 x10-3 x10-3 x10-4 x10-4 x10-4 x10-4 x1 %
1 0.998 1.05 5.08 1.64 1.03 6.41 5.45 3.95 2.98 0.998 1.20
2 1.000 1.06 5.11 1.65 1.04 6.46 5.50 3.98 3.00 1.000 1.19
3 0.991 0.99 4.54 1.33 0.80 4.42 3.53 2.38 1.69 0.991 1.11
4 0.983 0.95 4.20 1.14 0.66 3.25 2.36 1.47 0.91 0.983 1.07
5 0.963 0.81 3.08 0.75 0.52 2.35 1.36 1.05 0.28 0.963 0.90
6 0.955 0.79 2.96 0.74 0.50 2.18 1.26 1.20 0.49 0.955 0.89
7 0.944 0.76 2.81 0.68 0.45 1.95 1.14 1.04 0.44 0.940 0.86
8 0.917 0.69 2.48 0.57 0.35 1.49 0.90 0.73 0.34 0.917 0.80
9 0.902 0.63 2.18 0.45 0.25 1.05 0.69 0.40 0.25 0.902 0.74
Table 8. The voltage profile of Case 3

Case 1 Case 2 Case 3

Maximum voltage (p.u.) 0.999 0.999 1.000
Minimum voltage (p.u.) 0.837 0.901 0.902
Total power loss (p.u.) 0.007812 0.007065 0.007036
Qc(4) (p.u.) 0.024 0.036
Qc(5) (p.u.) 0.024 0.018
Qc(9) (p.u.) 0.009 0.009
Cost ($ / year) 131238 128494 129334
Average CPU Time (sec.) 0.8 1.20 3.39
Maximum HDF (%) 6.15 1.40 1.20
Table 9. Summary results of the approach
 A PSO Approach in Optimal FACTS Selection with Harmonic Distortion Considerations 77

7. Conclusion
This chapter presents a Particle Swarm Optimisation (PSO) approach to searching for
optimal shunt SVC location and size with harmonic consideration. The cost or fitness
function is constrained by voltage and Harmonic Distortion Factor (HDF). Since PSO is a
stochastic approach, performances should be evaluated using statistical value. The
performance will be affected by initial condition but PSO can give the optimal solution by
increasing the population size. PSO offers robustness by searching for the best solution from
a population point of view and avoiding derivatives and using payoff information (objective
function). The result shows that PSO method is suitable for discrete value optimization
problem such as SVC allocation and the consideration of harmonic distortion limit may be
included with an integrated approach in the PSO.

Nomenclature
fmax the maximum fitness of each generation in the population
N the number of harmonic order is being considered
Qc the size of SVC (MVAr)
Kc the equivalent SVC cost ($/MVAr)
Kl the duration of the load period
Kp the equivalent annual cost per unit of power losses ($/kW)
Ks the SVC bank size (MVAr)
yci frequency admittance of the SVC at bus i (pu)
Vi voltage magnitude at bus i (pu)
Pi, Qi active and reactive powers injected into network at bus i (pu)
Pli, Qli linear active and reactive load at bus i (pu)
Pni Qni nonlinear active and reactive load at bus i (pu)
ij voltage angle different between bus i and bus j (rad)
Gii, Bii self conductance and susceptance of bus i (pu)
Gij, Bij mutual conductance and susceptance between bus i and bus j (pu)

Superscript
1 corresponds to the fundamental frequency value
n corresponds to the nth harmonic order value

Author details
H.C. Leung and Dylan D.C. Lu
Department of Electrical and Information Engineering,
The University of Sydney, NSW 2006,
Australia
78 An Update on Power Quality

8. References
[1] Ewald Fuchs and Mohammad A. S. Masoum (2008). “Power Quality in Power Systems
and Electrical Machines“: pp 398-399
[2] Zhang, Wenjuan, Fangxing Li, and Leon M. Tolbert. "Optimal allocation of shunt
dynamic Var source SVC and STATCOM: A Survey." 7th IEEE International Conference
on Advances in Power System Control, Operation and Management (APSCOM). Hong
Kong. 30th Oct.-2nd Nov. 2006.
[3] Verma, M. K., and S. C. Srivastava. "Optimal placement of SVC for static and dynamic
voltage security enhancement." International Journal of Emerging Electric Power
Systems 2.2 (2005).
[4] Garbex, S., R. Cherkaoui, and A. J. Germond. "Optimal location of multi-type FACTS
devices in power system by means of genetic algorithm." IEEE Trans. on Power System
16 (2001): pp 537-544.
[5] Kennedy, J.; Eberhart, R. (1995). "Particle Swarm Optimization". Proceedings of IEEE
International Conference on Neural Networks. IV. pp. 1942–1948.
http://dx.doi.org/10.1109%2FICNN.1995.488968
[6] Mínguez, Roberto, et al. "Optimal network placement of SVC devices.", IEEE
Transactions on Power Systems 22.4 (2007): pp. 1851-1860.
[7] IEEE std. 519-1981, “IEEE Guide for harmonic control and reactive power compensation
of static power converters”, IEEE, New York, (1981).
[8] J. Arrillaga, D.A. Bradley and P.S. Boodger, “Power system harmonics”, John Willey &
Sons, (1985), ISBN 0-471-90640-9.
[9] Y. Baghzouz, “Effects of nonlinear loads on optimal capacitor placement in radial
feeders”, IEEE Trans. Power Delivery, (1991), pp.245-251.
[10] Hamada, Mohamed M., et al. "A New Approach for Capacitor Allocation in Radial
Distribution Feeders." The Online Journal on Electronics and Electrical Engineering
(OJEEE) Vol. (1) – No. (1), pp 24-29
 Chapter 5

Electromechanical Active Filter

as a Novel Custom Power Device (CP)

Ahad Mokhtarpour, Heidarali Shayanfar and Mitra Sarhangzadeh

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/55009

1. Introduction
One of the serious problems in electrical power systems is the increase of electronic devices
which are used by the industry as well as residences. These devices, which need high-
quality energy to work properly, at the same time, are the most responsible ones for
decreasing of power quality by themselves.

In the last decade, Distributed Generation systems (DGs) which use Clean Energy Sources
(CESs) such as wind power, photo voltaic, fuel cells, and acid batteries have integrated at
distribution networks increasingly. They can affect in stability, voltage regulation and
power quality of the network as an electric device connected to the power system.

One of the most efficient systems to solve power quality problems is Unified Power Quality
Conditioner (UPQC). It consists of a Parallel-Active Filter (PAF) and a Series-Active Filter
(SAF) together with a common dc link [1-3]. This combination allows a simultaneous
compensation for source side currents and delivered voltage to the load. In this way,
operation of the UPQC isolates the utility from current quality problems of load and at the
same time isolates the load from the voltage quality problems of utility. Nowadays, small
synchronous generators, as DG source, which are installed near the load can be used for
increase reliability and decrease losses.

Scope of this research is integration of UPQC and mentioned synchronous generators for
power quality compensation and reliability increase. In this research small synchronous
generator, which will be treated as an electromechanical active filter, not only can be used as
another power source for load supply but also, can be used for the power quality
compensation. Algorithm and mathematical relations for the control of small synchronous
generator as an electromechanical active filter have been presented, too. Power quality
compensation in sag, swell, unbalance, and harmonized conditions have been done by use

© 2013 The
© Author(s).et
Mokhtarpour Licensee InTech.
al., licensee This chapter
InTech. This is is
andistributed
open accessunder the terms
chapter of the under
distributed Creative
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Attribution Commons Attribution License (http://creativecommons.org/licenses/by/3.0),
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which permits unrestricted use,permits
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unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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80 An Update on Power Quality

of introduced active filter with integration of Unified Power Quality Conditioner (UPQC). In
this research, voltage problems are compensated by the Series Active Filter (SAF) of the
UPQC. On the other hand, issues related to the compensation of current problems are done
by the electromechanical active filter and PAF of UPQC. For validation of the proposed
theory in power quality compensation, a simulation has been done in MATLAB/SIMULINK
and a number of selected simulation results have been shown.

A T-type active power filter for power factor correction is proposed in [4]. In [5], neutral
current in three phase four wire systems is compensated by using a four leg PAF for the
UPQC. In [6], UPQC is controlled by H∞ approach which needs high calculation demand. In
[7], UPQC can be controlled based on phase angle control for share load reactive power
between SAF and PAF. In [8] minimum active power injection has been used for SAF in a
UPQC-Q, based on its voltage magnitude and phase angle ratings in sag conditions. In [9],
UPQC control has been done in parallel and islanding modes in dqo frame use of a high
pass filter. In [10-12] two new combinations of SAF and PAF for two independent
distribution feeders power quality compensation have been proposed. Section 2 generally
introduces UPQC. Section 3 explains connection of the proposed active filter. Section 4
introduces electromechanical active filter. Section 5 explains used algorithm for reference
generation of the electromechanical filter in detail. Section 6 simulates the paper. Finally,
section 7 concludes the results.

2. Unified Power Quality Conditioner (UPQC)

UPQC has composed of two inverters that are connected back to back [2]. One of them is
connected to the grid via a parallel transformer and can compensate the current problems
(PAF). Another one is connected to the grid via a series transformer and can compensate the
voltage problems (SAF). These inverters are controlled for the compensation of the power
quality problems instantaneously. Figure 1 shows the general schematic of a UPQC.

Figure 1. General schematic of a UPQC

A simple circuit model of the UPQC is shown in Figure 2. Series active filter has been
modeled as the voltage source and parallel active filter has been modeled as the current
source.
 Electromechanical Active Filter as a Novel Custom Power Device (CP) 81

Figure 2. Circuit model of UPQC

3. Connection of Electromechanical Filter

Figure 3, shows schematic of the proposed compensator system. In this research load
current harmonics with higher order than 7, has been determined as PAF of UPQC
compensator signal. But, load current harmonics with lower order than 7 and reactive
power have been compensated by the proposed electromechanical filter.

Figure 3. Proposed compensator system

4. Electromechanical Parallel Active Filter

Figure 4, shows the simple structure of a synchronous generator. Based on equation (1), a
DC field current of if produces a constant magnitude flux.

Nfif N f N si f
 fif , f
Ff N 
R
, f  Mi f
R
(1)

As in [13] N f and N s are effective turns of the field windings and the stator windings,
respectively; Ff is the magnetomotive force; R is the reluctance of the flux line direction and
M is the mutual induction between rotor and stator windings. Speed of rotor is equal to the
synchronous speed ( ns  120 f ). Thus, the flux rotates with the angular speed of
p
82 An Update on Power Quality

2 ns
s  . So, stator windings passing flux has been changed as equation (2). It is
60
assumed that in t  0 , direct axis of field and stator first phase windings conform each
other.

 s  i f M cos(t ) (2)

The scope of this section is theoretically investigation of a synchronous machine as a

rotating active filter. This theory will be investigated in the static state for a circular rotor
type synchronous generator that its equivalent circuit has been shown in Figure 5.

Figure 4. Simple structure of synchronous generator

Figure 5. Equivalent circuit of synchronous generator

Equation (3) shows the relation between magnetic flux and voltage behind synchronous
reactance of the generator.

d (t ) d(i M cos(t )) d(i cos(t ))

e
 s  f
 M f
 (3)
dt dt dt
 Electromechanical Active Filter as a Novel Custom Power Device (CP) 83

Based on equation (3), if the field current be a DC current, the stator induction voltage will
be a sinusoidal voltage by the amplitude of Mi f . But, if the field current be harmonized as
equation (4) then, the flux and internal induction voltage will be as equations (5) and (6),
respectively.

I dc   I fn sin(nt   fn )
if  (4)
n

f  [ I dc   I fn sin(nt   fn )]M cos(t ) 

i f M cos(t ) 
n
1 (5)
MI dc cos(t )  M  I fn[sin((n  1)t   fn )  sin((n  1)t   fn )]
2

1
eo 
[ MI dc sin(t )  MI f 2 cos(t   f 2 )] 
2
(6)
1 1
 [ 2 MI f (n1)n cos(nt   f (n1) )  2 MI f (n1)n cos(nt   f (n1) )]
n 2

Equation (6) shows that each component of the generator output voltage has composed of
two components of the field current. This problem has been shown in Figure 6.

Figure 6. Relation of the field current components by the stator voltage components

It seems that a synchronous generator can be assumed as the Current Controlled System
(CCS). Thus it can be used for the current harmonic compensation of a nonlinear load ( I hn )
as parallel active filter.

5. Algorithm and method

From Figure 5, relation between terminal voltage of the generator and I hn can be derived as
equation (7).

eo Vpcc  Zn I hn  Vn sin(nt   n ) (7)

n
84 An Update on Power Quality

Where, n is the harmonic order; Zn R  jnX is the harmonic impedance of the synchronous
generator and connector transformer which are known, VPCC is the point of common
coupling voltage and I hn is the compensator current that has been extracted from the
control circuit.

If similar frequency components of voltage signal eo in equation (6) and eo in equation (7)
set equal, the magnitude and phase angle of the related field current components will be
extracted as:

For n=1:

1
 MI dc sin(t )  MI f 2 cos(t   
f 2 ) V1 sin(t  1 ) (8)
2

1 1
[ MI dc  MI f 2 sin  f 2 ]2  [ MI f 2 cos  f 2 ]2 
V1 (9)
2 2

1
MI f 2 cos  f 2
1
tan [ 2 ]  1 (10)
1
 MI dc  MI f 2 sin  f 2
2

For simplicity equations (9) and (10) can be rewritten as follows:

1
 MI dc  MI f 2 sin  f 2
X (11)
2

1
Y MI f 2 cos  f 2 (12)
2

X2  Y 2 
V12 (13)

X  1 (14)
Y

From the above equations, magnitude and phase of the second component of filed current
can result in:

V1
X (15)
1  tan 2 1

X  MI dc
tan  f 2  (16)
X tan 1
 Electromechanical Active Filter as a Novel Custom Power Device (CP) 85

2( X  MI dc )
If2  (17)
M sin  f 2

For n≥2:

1 1
X MI f ( n 1)n sin  f ( n 1)  MI f ( n 1)n sin  f ( n 1) (18)
2 2

1 1
Y MI f ( n 1)n cos  f ( n 1)  MI f ( n 1)n cos  f ( n 1) (19)
2 2

Vn
X (20)
1  tan 2 n

X  0.5 Mn I f ( n 1) sin  f ( n 1)

tan  f ( n 1)  (21)
X tan  n  0.5 Mn I f ( n 1) cos  f ( n 1)

2( X  0.5 Mn I f ( n 1) sin  f ( n 1) )

I f ( n 1)  (22)
Mn sin  f ( n 1)

Where, M and  are the mutual inductance and angular frequency, respectively.
Obviously for the extraction of required components of filed current from the above
equations, first suggestion for DC and first order component of the field current are need.
Resulted field current can be injected via a PWM and current inverter to the field windings
of the synchronous generator. Figure 7, shows the control circuit of the electromechanical

Figure 7. Block diagram of the proposed active filter control

86 An Update on Power Quality

active filter. I h and I f are desired compensator current and calculated field current signal.
Detail of the proposed control circuit can be found in the equations (11) to (22). In the
present research controlled voltage source of MATLAB has been used instead of required
PWM and inverter. Constant and integrator coefficients in the PI controller have been
chosen 1000 and 200, respectively. As mentioned earlier first order load active and reactive
powers can be easily attended in the electromechanically compensated share of load current
for decrease of SAF and PAF power range of UPQC. This problem can control power flow as
well as power quality. In other word it can be possible to use a synchronous generator not
only for first order voltage generation but, also for the harmonic compensation too.

6. Results
For the investigation of the validity of the mentioned control strategy for power quality
compensation of a distribution system, simulation of the test circuit of Figure 8, has been
done in MATLAB software. Source current and load voltage, have been measured and
analyzed in the proposed control system for the determination of the compensator signals of
SAF, PAF and filed current of the electromechanical active filter. Related equations of the
controlled system and proposed model of the electromechanical active filter as a current
controlled source have been compiled in MATLAB software via M-file. In mentioned control
strategy, voltage harmonics have been compensated by SAF of the UPQC and current
harmonics with higher order than 7, have been compensated by PAF of UPQC. But, the total
of load reactive power, 25 percent of load active power and load current harmonics with lower
order than 7 have been compensated by the proposed CCS. This power system consists of a
harmonized and unbalanced three phase 380V (RMS, L-L), 50 Hz utility, a three phase
balanced R-L load and a three phase rectifier as a nonlinear load. For the investigation of the

Figure 8. General test system circuit

 Electromechanical Active Filter as a Novel Custom Power Device (CP) 87

voltage harmonic condition, utility voltages have harmonic and negative sequence
components between 0.05 s and 0.2 s. Also, for the investigation of the proposed control
strategy in unbalance condition, magnitude of the first phase voltage is increased to the 1.25
pu between 0.05 s and 0.1 s and decreased to the 0.75 pu between 0.15 s to 0.2 s. Table 1, shows
the utility voltage harmonic and sequence parameters data and Table 2, shows the load power
and voltage parameters. A number of selected simulation results will be showed further.

Voltage Order Sequence Magnitude (pu) Phase Angle (deg)

5 1 0.12 -45
3 2 0.1 0
Table 1. Utility voltage harmonic and sequence parameters data

Load Nominal Power (kVA) Nominal Voltage (RMS, L-L)

Linear 10 380V
Non linear 5 380V
Table 2. Load power and voltage parameters data

Figure 9, shows the source side voltage of phase 1. Figure 10, shows the compensator
voltage of phase 1. Figure 11, shows load side voltage of phase 1. Figure 12, shows the load
side current of phase 1. Figure 13, shows the CCS current of phase 1 that has been supplied
by the proposed active filter. Figure 14, shows the PAF of UPQC current of phase 1. Figure
15, shows the source side current of phase 1. Figure 16, shows the field current of the
proposed harmonic filter. Figure 17 and 18 show source voltage and load voltage frequency
spectrum, respectively. Figure 19 and 20 show load current and source current frequency
spectrum, respectively. Figure 21 and 22 show CCS and PAF frequency spectrum,
respectively. Table 3 shows THDs of source and load voltages and currents. Load voltage
and source current harmonics have been compensated satisfactory.
400

300

200

100
Voltage (V)

-100

-200

-300

-400
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 9. Source side voltage of phase 1 (swell has been occurred between 0.05 and 0.1 sec and sag has
been occurred between 0.15 and 0.2 sec. Also, harmonics of positive and negative sequences have been
concluded between 0.05 to 0.2 sec)
88 An Update on Power Quality

150

100

50

Voltage (V)
0

-50

-100

-150
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 10. Compensator voltage of phase 1 (compensator voltage has been determined for the sag,
swell, negative sequence and harmonics improvement)

400

300

200

100
Voltage (V)

-100

-200

-300

-400
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 11. Load side voltage of phase 1 (sag, swell, harmonics, positive and negative sequences have
been canceled)

40

30

20

10
Current (A)

-10

-20

-30

-40
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 12. Load side current of phase 1 (it is harmonized. It should be noticed that this current has been
calculated after the voltage compensation and thus voltage unbalance has not been transmitted to the
current)
 Electromechanical Active Filter as a Novel Custom Power Device (CP) 89

20

15

10

Current (A) 0

-5

-10

-15

-20
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 13. Proposed CCS current of phase 1 (this current has been injected to the grid by the
electromechanical active filter. The solid line shows output current of filter and dotted line shows
desired current of filter)

40

30

20
Current (A)

10

-10

-20

-30
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 14. PAF of UPQC current of phase 1 (this current has been injected to the grid by the parallel
active filter of UPQC)
40

30

20

10
Current (A)

-10

-20

-30

-40
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 15. Source side current of phase 1 (harmonics and reactive components of load current have
been canceled)
90 An Update on Power Quality

1400

1200

1000
Current (A)

800

600

400

200
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Time (Sec)

Figure 16. Field current of proposed harmonic filter (field current is controlled for the load active,
reactive and harmonic current compensation)

350

300

250
Amplitude (V)

200

150

100

50

0
0 100 200 300 400 500 600 700 800 900 1,0001,100 1,200 1,300 1,400
Frequency (Hz)

Figure 17. Source side voltage frequency spectrum

350

300

250
Amplitude (V)

200

150

100

50

0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Frequency (Hz)

Figure 18. Load side voltage frequency spectrum

 Electromechanical Active Filter as a Novel Custom Power Device (CP) 91

45

40

35

Amplitude (A) 30

25

20

15

10

0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Frequency (Hz)

Figure 19. Load side current frequency spectrum

35

30

25
Amplitude (A)

20

15

10

0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Frequency (Hz)

Figure 20. Source side current frequency spectrum

12

10

8
Amplitude (A)

0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Frequency (Hz)

Figure 21. Proposed current controlled system frequency spectrum

92 An Update on Power Quality

1.4

1.2

1
Amplitude (A)

0.8

0.6

0.4

0.2

0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Frequency (Hz)

Figure 22. Parallel active filter frequency spectrum

VS THD IL THD VL THD IS THD

0.1561 0.1179 .001 .0012

Table 3. Total Harmonic Distortion (THD)

7. Conclusions
It is known that use of small synchronous generators in distributed generated networks can
reduce transmitted active and reactive powers from the main source and consequently line
losses. In this research power quality compensation was done by composition of UPQC and
synchronous generators as electromechanical active filter. In other word, by proper
determination and control of synchronous generator field current it could be used as
controlled current source for power quality compensation. This was for reduction of UPQC
power rating in the distributed generated networks. Also, an algorithm was investigated for
the determination of the reference field current. Proposed CCS modeling was implemented
based on the mentioned related algorithm in MATLAB software. Control strategy had three
instantaneously stages. Voltage harmonics were compensated by SAF of the UPQC. Current
harmonics with higher order than 7 were compensated by PAF of the UPQC. Lower order
current harmonics, load reactive power and a part of load active power were compensated
by the proposed controlled current source. Total harmonic distortion of load voltage before
compensation was 0.15 which was reduced to almost zero after compensation. Also, total
harmonic distortion of the source current before compensation was 0.12 which was reduced
to almost zero after compensation.
 Electromechanical Active Filter as a Novel Custom Power Device (CP) 93

Author details
Ahad Mokhtarpour, Heidarali Shayanfar and Mitra Sarhangzadeh
Department of Electrical Engineering, Tabriz Branch, Islamic Azad University, Tabriz,
Iran

8. References
[1] Fujita H., Akagi H. The Unified Power Quality Conditioner: The Integration of
Series and Shunt Active Filters. IEEE Transaction on Power Electronics 1998; 13(2)
315-322.
[2] Shayanfar H. A., Mokhtarpour A. Management, Control and Automation of Power
Quality Improvement. In: Eberhard A. (ed.) Power Quality. Austria: InTech; 2010. p127-
152.
[3] Hannan M. A., Mohamed A. PSCAD/EMTDC Simulation of Unified Series-Shunt
Compensator for Power Quality Improvement. IEEE Transaction on Power Delivery
2005; 20(2) 1650-1656.
[4] Han Y., Khan M.M., Yao G., Zhou L.D., Chen C. A novel harmonic-free power
factor corrector based on T-type APF with adaptive linear neural network
(ADALINE) control. Simulation Modeling Practice and Theory 2008; 16 (9) 1215–
1238.
[5] Khadkikar V., Chandra A. A Novel Structure for Three Phase Four Wire Distribution
System Utilizing Unified Power Quality Conditioner (UPQC). IEEE Transactions on
Industry Applications 2009; 45(5) 1897-1902.
[6] Kwan K. H., Chu Y.C., So P.L. Model-Based H∞ Control of a Unied Power Quality
Conditioner. IEEE Transactions on Industrial Electronics 2009; 56 (7) 2493-2504.
[7] Khadkikar V., Chandra A. A New Control Philosophy for a Unified Power Quality
Conditioner (UPQC) to Coordinate Load-Reactive Power Demand between Shunt and
Series Inverters. IEEE Transactions on Power Delivery 2008; 23 (4) 2522-2534.
[8] Lee W.C., Lee D.M., Lee T.K. New Control Scheme for a Unified Power Quality
Compensator-Q with Minimum Active Power Injection. IEEE Transactions on Power
Delivery 2010; 25(2) 1068-1076.
[9] Han B., Bae B., Kim H., Baek S. Combined Operation of Unified Power-Quality
Conditioner with Distributed Generation. IEEE Transaction on Power Delivery 2006;
21(1) 330-338.
[10] Mohammadi H.R., Varjani A.Y., Mokhtari H. Multiconverter Unified Power-Quality
Conditioning System: MC-UPQC. IEEE Transactions on Power Delivery 2009; 24(3)
1679-1686.
[11] Jindal A.K., Ghosh A., Joshi A. Interline Unified Power Quality Conditioner. IEEE
Transactions on Power Delivery 2007; 22(1) 364-372.
94 An Update on Power Quality

[12] Mokhtarpour A., Shayanfar H.A., Tabatabaei N.M. Power Quality Compensation in two
Independent Distribution Feeders. International Journal for Knowledge, Science and
Technology 2009; 1 (1) 98-105.
[13] Machowski J., Bialek J., Bumby J.R. Power System Dynamics and Stability, United
Kingdom: John Wiley and Sons; 1997.
 Chapter 6

Reference Generation
of Custom Power Devices (CPs)

Ahad Mokhtarpour, Heidarali Shayanfar

and Seiied Mohammad Taghi Bathaee

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/54680

1. Introduction
One of the serious problems in electrical power systems is the increase of electronic devices
which are used by the industry. These devices, which need high-quality energy to work
properly, at the same time, are the most responsible ones for decreasing of power quality by
themselves.

Custom power devices (CP) used in distribution systems can control power quality. One of
the most efficient CPs is Unified Power Quality Conditioner (UPQC). It consists of a
Parallel-Active Filter (PAF) and a Series-Active Filter (SAF) together with a common dc link
[1-3]. This combination allows a simultaneous compensation for source side currents and
delivered voltage to the load. In this way, operation of the UPQC isolates the utility from
current quality problems of the load and at the same time isolates the load from the voltage
quality problems of utility.

Reference generation of UPQC is an important problem. One of the scopes of this research is
extending of Fourier transform for increasing of its responsibility speed twelve times as the
main control part of reference generation of the UPQC. Proposed approach named Very Fast
Fourier Transform (VFFT) can be used in balanced three phase systems for extraction of
reference voltage and current signals. Proposed approach has fast responsibility as well as
good steady state response. As it is known, Fourier transform response needs at least one
cycle data for the settling down which results in slow responsibility and week capability in
dynamic condition. In the proposed approach there are two different data window lengths.
In the sag or swell condition, control system switches to T/12 data window length but, in the
steady state condition it is switched to T/2 data window length. It causes fast responsibility
as well as good steady state response. This approach will be used for the UPQC control
circuit for extraction of the reference signals.

© 2013 The
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Shayanfar Licensee
et al., InTech.
licensee This
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96 An Update on Power Quality

Second scope of this research is to use Multy Output ADAptive LINEar (MOADALINE)
approach for the reference generation of UPQC. Simplicity and flexibility in extraction of
different reference signals can be advantage of the proposed algorithm. Third scope of this
research is reference generation of UPQC with the scope of power flow control as well as
power quality compensation. In this stage, SAF is controlled by dqo approach for voltage
sag, swell, unbalance, interruption, harmonic compensation and power flow control. Also,
PAF is controlled by composition of dqo and Fourier theories for current harmonic and
reactive power compensation.

Also for the validity of the proposed approaches, power quality compensation has been
done in a test circuit via simulation. Voltage sag, swell and harmonics will be compensated
by SAF of UPQC. Also, current harmonics and reactive power will be compensated by PAF
of UPQC. Section 2 generally introduces UPQC and its equivalent circuit. Section 3 explains
the proposed VFFT and related equations. Section 4 introduces UPQC reference generation
system based on the proposed VFFT approach. Section 5 explains proposed MOADALINE
algorithm for reference generation. Section 6 explains reference generation based on power
flow control. Section 7 simulates the research. Finally, section 8 concludes the results.

2. Unified Power Quality Conditioner (UPQC)

UPQC is composed of two inverters that are connected back to back [3-10]. One of them is
connected to the grid via a parallel transformer and can compensate the current problems
(PAF). Another one is connected to the grid via a series transformer and can compensate the
voltage problems (SAF). These inverters are controlled for the compensation of the power
quality problems instantaneously. Figure 1 shows the general schematic of a UPQC.

Figure 1. General schematic of a UPQC

A simple circuit model of the UPQC is shown in Figure 2. Series active filter has been
modeled as the voltage source and parallel active filter has been modeled as the current
source.

Figure 2. Circuit model of UPQC

 Reference Generation of Custom Power Devices (CPs) 97

3. VFFT problem statement

Fourier transform has the capability of different order components extraction of distorted
periodic voltage and current. It is possible to use voltage and current first order components
for determining the compensator signals. Based on the related equations of Fourier
transform, there is a need for at least one cycle data for settling down the response. This
problem can cause week responsibility in dynamic condition. Proposed extended Fourier
transform will be responsible for improving this problem. First order Fourier coefficients of
a sinusoidal signal can be written as equations (1) and (2).

2 2 4 
a1 
2 0 v(t )cos(t )dt 
2 0 v(t )cos(t)dt (1)

2 2 4 
b1 
2 0 v(t )sin(t )dt 
2 0 v(t )sin(t)dt (2)

Based on equations (1) and (2) it is possible to reduce settling time of the Fourier transform
responsibility to T/2; where, T is the main period of the signal. In this condition the
responsibility speed will be increased twice but, it is not reasonable speed in dynamic
condition yet. Equation (5) can be resulted from equations (3) and (4), for a sinusoidal signal
with phase angle Φ. Equation (6) can be resulted similarly.

4 

2 0 sin(t   )cos(t)dt 
sin  (3)

 3
8 8
2 0
6 sin(t   )cos(t )dt 
2  6
2
sin(t   )cos(t )dt 
6
5
(4)
8
2  6
4
sin(t   )cos(t )dt 
sin
6


4  8
2 0 sin(t   )cos(t )dt  2 06 sin(t   )cos(t)dt 
3 5 (5)
8 8
2  6
2
sin(t   )cos(t )dt 
2  6
4
sin(t   )cos(t )dt 
sin
6 6


4  8
2 0 sin(t   )sin(t )dt 
2 06 sin(t   )sin(t)dt 
3 5 (6)
8 8
2  6
2
sin(t   )sin(t )dt 
2  6
4
sin(t   )sin(t )dt 
cos
6 6

Equations (7) and (8) can be rewritten from equations (5) and (6) respectively.
98 An Update on Power Quality

 
8 8
a1 
2 
0
6 sin(t   )cos(t )dt 
2 06 (  sin(t    2 3 ))(  cos(t  2 3 ))dt 
 
8 2 )dt 8 6 sin(t   )cos(t )dt 
2  sin(t    2 3 )cos(t  
0
6
3 2 0
(7)
 
8 6 sin(t    2 )cos(t  2 )dt 
8 6
0 sin(t    2 )cos(t  2 )dt
2 3 3 2 0 3 3

 
8 8
b1
2  0
6 sin(t   )sin(t )dt 
2 06 (  sin(t    2 3 ))( sin(t  2 3 ))dt 
 
8 2 )dt 8 6 sin(t   )sin(t )dt 
    2 )sin(t  
2 0
6 sin(t (8)
2 0 3 3
 
8 8
2 06 sin(t    2 3 )sin(t  2 3 )dt  2 06 sin(t    2 3 )sin(t  2 3 )dt

This solution has advantage of reducing the data window length to T/12. In this condition,
settling time of the Fourier transform responsibility will be decreased to T/12. In other
words, the responsibility speed will be increased twelve times. It should be noticed that
this approach can be used only in balanced three phase systems. In this condition reach to
the same accuracy in response is possible as compared to that of one cycle but very faster
than one cycle. When data window length is chosen T sec, all of even components of
distorted voltage and current in the related integral of Fourier transform can be filtered
completely. But this is not possible in T/12 data window length condition. So, the problem
of this approach is the unfiltered steady state oscillations in the response. This is because
of small data window length. Thus, to complete the proposed approach for accessing the
fast response, as well as good steady state response, proper composition of T/12 and T/2
data window lengths have been used. Completed proposed approach uses T/12 data
window length in signal magnitude change instances, for accessing the fast response, and
T/2 data window length in other times, for accessing the good response without
oscillation [10].

4. UPQC reference generation based on the VFFT

Based on the previous indications, the detection of sag, swell, and load change conditions
are essential problem for proper control of the UPQC. In this research, for the detection of
sag or swell condition in the source voltage and changes in the load current, derivative of
the first order component magnitude of the voltage and current signals has been compared
with a constant value. This is based on the facts that in these conditions, the derivative of the
signal magnitude can change rapidly with an almost increasing slope amount. Figure 3,
shows the block diagram of the proposed VFFT based control approach [10].
 Reference Generation of Custom Power Devices (CPs) 99

Figure 3. Proposed VFFT based control system

4.1. Series active filter reference generation

Proposed approach can be used for the extraction of direct and indirect first order
components of the source voltage. In this control approach, series active filter can
compensate harmonics as well as voltage sag and swells. In this approach the reference
voltage magnitude can be setup to the nominal value as equation (9). Figure 4, shows the
block diagram of the SAF control circuit.

a1
v1 (t )  a12 b12 sin(t  arctan
a1 cos(t )  b1 sin(t )  )
b1
(9)
a
vref (t )  vnom sin(t  arctan 1 )  vnom sin(t  vl1 )
b1

Figure 4. SAF control system block diagram

4.2. Parallel active filter reference generation

In this research parallel active filter have the duty of the reactive power compensation, as
well as, current harmonics. For this purpose as equation (10), active first order component of
load current which is tangent component of the load current to the load voltage can be used
as the reference current. This problem has been shown in Figure 5.

Figure 5. Reference current determination

100 An Update on Power Quality

I ref (t )  I l1 cos(vl1  il1 )sin(t  vl1 ) (10)

Where, Il1 and Φil1 are the first order component magnitude and phase angle of the load
current, respectively and Φvl1 is the first order component phase angle of the load voltage.
Figure 6, shows the block diagram of the PAF control circuit.

Figure 6. Block diagram of the PAF control circuit

5. Reference generation based on MOADALINE approach

Based on MOADLINE approach each n  1 signal of y can be written as a weighted linear
combination of its components. If S(t) be n  m component matrix of y at time t and W(t) be
m  1 vector of weighted coefficient then, the signal of y can be written as equation (11).
MOADALINE can be used for determining weight vector of W which generates a special
signal of y from its components [11]. Weighted factors can be updated in each stage of an
adaptation approach for extraction of a desired signal. Equation (11) shows adaptation rule
that is based on Least Mean Square (LMS) algorithm.

y  SW
(11)
W (t  dt ) W (t )  kST (t )[S(t )ST (t )]1 e(t )

Where, e(t) is the error between desired and actual signal of y, and K is the convergence
factor. It is possible to extract the reference voltage and current from uncompensated source
voltage and load current. Fourier coefficients can be determined as vector of y. Reference
signal can be determined as W. Matrix of S is constant. After determination of
uncompensated signal Fourier coefficients, they can be compared with the desired values.
Error signal can be used in adaptation rule for updating the vector of W. Therefore reference
voltage and current can be determined. Figure 7, shows block diagram of the proposed
MOADALINE approach [11].

 an 
 
y  b n  (12)
 a0 
 
 Reference Generation of Custom Power Devices (CPs) 101

 
cos(nt0 ) cos(nt1 ) ... cos(ntm 1 )
2  
(13)
S(t )   sin( nt0 ) sin(nt1 ) ... sin(ntm 1 ) 
m1 
1 1 ... 1
 
 2 2 2 

 w(t0 ) 
 
 w(t1 ) 
W (14)
 ... 
 
 w(tm 1 )

   w(t ) 
cos(nt0 ) 0
 an  ... cos(ntm 1 )  
  2    w(t1 ) 
(15)
 bn   m  1  sin(nt0 ) ... sin(ntm 1 ) 
 
a   1 ... 1   ... 
 0    w(tm 1 )
 2 2 

cos(wt0)
W0
a1
sin(wt0)
W0

cos(wt1) + 2/(m-1) -
W1

sin(wt1)
W1
+ 2/(m-1) -

coswt(m-1) b1

W(m-1)
sinwt(m-1)
W(m-1)

Weighted
Factors
Calculation

Figure 7. Block diagram of the proposed MOADALINE approach

6. Reference generation based on power flow control

Park transform which is used for the conversion of abc to dqo frame, is useful in the steady
state and dynamic analysis of electrical systems [3]. Conversion matrix and related
equations have been shown in Equations (16) and (17).

 2 2 
 2sin(t ) 2sin(t  3 ) 2 sin(t  3 ) 
v     va   va 
 d 1  2 2     
v  t  t  t v T (16)
 q 
3  2cos( ) 2 cos( 
3
) 2cos( 
3
)  b   vb 
    
  vc   vc 
 vo   1 1 1 
 
 
102 An Update on Power Quality

 va  v 
  1  d
 vb   T  vq  (17)
 vc   
   vo 

Instantaneous active and reactive powers in dqo axis can be written as Equations (18) and
(19).

3
P ( v i  vq iq  2 v0i0 ) (18)
2 dd

3
Q ( v i  vd iq ) (19)
2 qd

Equations (20) and (21) show direct and quadratic axis voltages based on P and Q that have
been determined from equations (18) and (19). It should be noticed that the active and
reactive powers in equations (20) and (21) are transmitted powers after series active filter
toward the load. These equations show that in constant impedance loads there is a relation
between voltage and transmitted power. In other words, a particular load voltage is needed
for a particular load power and vice versa. In equations (20) and (21) it have been assumed
that the voltages are balanced and v0  0 .

2 Pid  Qiq
vd  ( 2 2 ) (20)
3 id  iq

2 Piq  Qid
vq  ( 2 2 ) (21)
3 id  iq

Therefore, setup transmission active and reactive powers in equations (20) and (21) in
considered amounts will result the related load voltage magnitude and phase angle. In
reactive power compensated condition, Q=0 and the amount of active power will be
extracted from the above equations as equation (22).

3
P ( vd 2  vq 2 )(id 2  iq2 ) (22)
2

Generally, in this approach nominal active and reactive powers of load will be substituted in
equation (20) and (21) for reference voltage extraction. But, there is a problem. If we don’t
have load nominal power data, extracted reference voltage will not have nominal
magnitude. For correct arrangement of the voltage magnitude, a PI controller is used for
minimum error between magnitudes of extracted reference voltage and the nominal
voltage.

 k p (Vsetup  Vref )  ki  ( Vsetup  Vref )dt

Perror (23)
 Reference Generation of Custom Power Devices (CPs) 103

Where, Vref and Vsetup are the nominal voltage magnitude and extracted voltage
magnitude, respectively.

Figure 8, shows the block diagram of the proposed control circuit.

Figure 8. Block diagram of the voltage control circuit

7. Results
7.1. Results of VFFT approach
For the investigation of the validity of the proposed VFFT reference generation strategy in
power quality compensation of a distribution system, simulation of the test circuit of Figure
9, has been done in MATLAB/SIMULINK software. Source voltage and load current, have
been measured and analyzed in the proposed control system for the determination of the
compensator signals of SAF and PAF.

Figure 9. General test system circuit

This power system consists of a three phase 380V (RMS, L-L), 50 Hz utility, two three phase
linear R-L load and a three phase rectifier as a nonlinear load which can be connected to the
circuit at different times. This is for the investigation of the proposed control system
capability in dynamic conditions. For the investigation of the voltage sag and swell
conditions, utility voltages have 0.25 percent sag between 0.04 sec and 0.08 sec and 0.25
percent swell between 0.08 sec and 0.12 sec. Also, for the investigation of the proposed
control strategy in the harmonic conditions, source voltage has been harmonized between
104 An Update on Power Quality

0.17 sec and 0.4 sec. Table 1, shows the utility voltage data and Table 2, shows the load
powers and related switching times. In this study series active filter has been connected to
the circuit at time zero. But parallel active filter has been connected to the circuit at time 0.25
sec. A number of selected simulation results will be shown later.

Voltage Order Magnitude (pu) Phase Angle (deg) Time (sec)

1 1 0 0-0.04, 0.12-0.4
1 0.75 0 0.04-0.08
1 1.25 0 0.08-0.12
5 0.1 -45 0.17-0.4
3 0.1 0 0.17-0.4
Table 1. Utility voltage harmonic and sequence parameters data

Load Nominal Power Nominal Voltage Switching Time

(kVA) (RMS, L-L) (Sec)
Linear 10 380V 0
Linear 10 380V 0.29
Non linear 5 380V 0.33
Table 2. Load powers and related switching times data

Figure 10, shows the source side voltage of phase 1. Figure 11 shows the compensated load
side voltage of phase 1. Figure 12 shows SAF voltage of phase 1. Figure 13 and 14 shows
first order component magnitude of the source voltage extracted by T and T/2 data windows
respectively. Figure 15 shows first order component magnitude of the source voltage
extracted by T/12 data window. Figure 16 shows the first order component magnitude of the
source voltage extracted by the proposed composition of T/2 and T/12 data windows. Figure
17 shows the load side current of phase 1. Figure 18 shows the source side current of phase
400

300

200

100
Voltage (V)

-100

-200

-300

-400
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25
Time (Sec)

Figure 10. Source side voltage of phase 1 (sag has been occurred between 0.04 sec and 0.08 sec and
swell has been occurred between 0.08 sec and 0.12 sec. Also, harmonics have been concluded between
0.17 sec to 0.4 sec)

1. Figure 19 shows the PAF current of phase 1. Figure 20 and 21 show first order component
magnitude of the load current extracted by T and T/2 data windows respectively. Figure 22
shows the first order component magnitude of the load current extracted by T/12 data
window. Figure 23 shows the first order component magnitude of the load current extracted
 Reference Generation of Custom Power Devices (CPs) 105

by the proposed composition of T/2 and T/12 data windows. Figure 24 and 25 show the
source side and load side voltages frequency spectrum, respectively. Finally Figures 26 and
27 show the load side and source side currents frequency spectrum, respectively. Table 3
shows THDs of the source and load voltages and currents. Load voltage and source current
harmonics have been compensated satisfactory.
400

300

200

100

Voltage (V)
0

-100

-200

-300

-400
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25
Time (Sec)

Figure 11. Load side voltage (sag and swell as well as harmonics have been compensated)
150

100

50
Voltage (V)

-50

-100

-150
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25
Time (Sec)

Figure 12. Compensator voltage (this is only between sag, swell, and harmonic times)
400

350

300

250
Amplitude (V)

200

150

100

50

0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25
Time (Sec)

Figure 13. Extracted source side voltage magnitude (in this state data window length is T and settling
time is 0.02 sec)
400

350

300

250
Amplitude (A)

200

150

100

50

0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25
Time (Sec)

Figure 14. Extracted source side voltage magnitude (in this state data window length is T/2 and settling
time is 0.01 sec)
400

350

300

250
Amplitude (A)

200

150

100

50

0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25
Time (Sec)

Figure 15. Extracted source side voltage magnitude by T/12 data window (in this state settling time is
0.00166 sec but, there are unfiltered oscillations in the response)
106 An Update on Power Quality

400

350

300

250

Amplitude (V)
200

150

100

50

0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25
Time (Sec)

Figure 16. Extracted source side voltage magnitude by the proposed approach (in this state
composition of T/2 and T/12 data windows have been used, settling time is 0.00166 sec and there is no
oscillation in the response)
80

60

40

20
Current (A)

-20

-40

-60

-80
0.25 0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
Time (Sec)

Figure 17. Load side current (there is a linear three phase load until 0.29 sec, another linear three phase
load has been connected to the circuit at time 0.29 sec and finally a nonlinear rectifier load has been
connected to the circuit at time 0.33 sec)
80

60

40

20
Current (A)

-20

-40

-60

-80
0.25 0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
Time (Sec)

Figure 18. Source side current (load current harmonics as well as reactive power have been
compensated)
15

10

0
Current (A)

-5

-10

-15

-20
0.25 0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
Time (Sec)

Figure 19. Compensator current (it is for reactive power compensation as well as current harmonics)
70

60

50

40
Amplitude (A)

30

20

10

0
0.25 0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
Time (Sec)

Figure 20. Extracted load side current magnitude (in this state data window length is T and settling
time is 0.02 sec)
 Reference Generation of Custom Power Devices (CPs) 107

70

60

50

40

Amplitude (A)
30

20

10

0
0.25 0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
Time (Sec)

Figure 21. Extracted load side current magnitude (in this state data window length is T/2 and settling
time is 0.01 sec)
90

80

70

60

50
Amplitude (A)

40

30

20

10

0
0.25 0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
Time (Sec)

Figure 22. Extracted load side current magnitude by T/12 data window (in this state settling time is
0.00166 sec but there are unfiltered oscillations in the response)
90

80

70

60
Amplitude (A)

50

40

30

20

10

0
0.25 0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
Time (Sec)

Figure 23. Extracted load side current magnitude by the proposed approach (in this state composition
of T/2 and T/12 data windows have been used, settling time is 0.00166 sec and there is no oscillation in
the response)

350

300

250
Amplitude (V)

200

150

100

50

0
50 100 150 200 250 300 350 400 450 500 550
Frequency (Hz)

Figure 24. Source voltage harmonic spectrum (it has third and fifth harmonics)

350

300

250
Amplitude (V)

200

150

100

50

0
50 100 150 200 250 300 350 400 450 500 550
Frequency (Hz)

Figure 25. Load voltage harmonic spectrum (harmonics have been compensated)
108 An Update on Power Quality

70

60

50

40

Amplitude (A)
30

20

10

0
0 100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)

Figure 26. Load side current harmonic spectrum

70

60

50

40
Amplitude (A)

30

20

10

0
0 100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)

Figure 27. Source side current harmonic spectrum

VS THD IL THD VL THD IS THD

0.14 0.09 .0002 .0001

Table 3. Total Harmonic Distortion (THD)

7.2. Results of MOADALINE approach

For the investigation of the validity of the mentioned control strategy of MOADALINE for
power quality compensation of a distribution system, simulation of the test circuit has been
done in MATLAB software. Source current and load voltage have been measured and
analyzed in the proposed control system for the determination of the compensator signals of
SAF and PAF. Related equations of the controlled system have been compiled in MATLAB
software via M-file. Desired values of an and bn are determined in the proposed algorithm
for extraction of the reference signals.

The power system consists of a harmonized and unbalanced three phase 380V (RMS, L-L),
50 Hz utility, a three phase rectifier as a nonlinear load, a three phase balanced R-L load
which is connected to the circuit at 0.04 sec and a one phase load which is connected to the
circuit at 0.07 sec.

For the investigation of the voltage harmonic condition, utility voltages have harmonic and
negative sequence components between 0.03 sec and 0.1 sec. Also, for the investigation of
the proposed control strategy in unbalance condition, magnitude of the first phase voltage is
increased to the 1.25 pu between 0.02 sec and 0.04 sec and decreased to the 0.75 pu between
0.06 sec to 0.08 sec. Figure 28 shows the source side voltage of phase 1. Figure 29, shows the
compensator voltage of phase 1. Figure 30, shows load side voltage of phase 1. Figure 31,
shows the load side current of phase 1. Figure 32, shows the reactive current of phase 1.
Figure 33, shows the harmonic current of phase 1. Finally Figure 34, shows the source side
 Reference Generation of Custom Power Devices (CPs) 109

current of phase 1. Load voltage and source current harmonics have been compensated
satisfactory.

Figure 28. Source side voltage of phase 1

Figure 29. Compensator voltage of phase 1

Figure 30. Load side voltage of phase 1

110 An Update on Power Quality

Figure 31. Load side current of phase 1

Figure 32. Reactive current of phase 1

Figure 33. Harmonic current of phase 1

 Reference Generation of Custom Power Devices (CPs) 111

Figure 34. Source side current of phase 1

7.3. Results of power flow control

For the investigation of the validity of the power flow control strategy in a distribution
system, simulation of the test circuit of Figure 35 has been done.

Figure 35. General test system circuit

This power system consists of a harmonized and unbalanced three phase 20 kV (RMS, L-L),
50 Hz utility, a three phase balanced R-L load and a nonlinear three phase load. For the
investigation of the voltage harmonic condition, utility voltages have harmonic and negative
sequence components between 0.15 s and 0.35 s. Also, for the investigation of the proposed
control strategy in unbalance condition, magnitude of the first phase voltage is increased to
the 1.25 pu between 0.10 s and 0.20 s and decreased to the 0.75 pu between 0.3 s to 0.4 s.
Investigation of the control circuit performance in fault condition is done by a three phase
fault in output terminal of the main source between 0.4 s to 0.5 s. Table 4 shows the utility
voltage harmonic and sequence parameters data and Table 5 shows the load power and
voltage parameters. Table 6 show states of switches of s1 and s2 . A number of selected
simulation results have been shown next.

Voltage Sequence Magnitude Phase Time

order (pu) angle duration
(degree) (sec)
5 + 0.12 -45 0.15-0.35
3 - 0.1 0 0.15-0.35
Table 4. Utility voltage harmonic and sequence parameters data
112 An Update on Power Quality

Load Nominal Nominal voltage

power (kVA) (RMS, L-L)
Linear 50 20 kV
Non linear 260 20 kV
Table 5. Load power and voltage parameters data

switch 0<t<0.4 sec 0.4<t<0.5 sec

First Second First Second
strategy strategy strategy strategy
s1 close close open open

s2 open open close close

Table 6. States of switches

Figure 36, shows the source side voltage of phase 1. Figure 37, shows the compensator
voltage of phase 1. Figure 38, shows the load side voltage of phase 1. Figure 39, shows the
load side current of phase 1. Figure 40, shows the compensator current of phase 1. Figure
41, shows the source side current of phase 1. Figure 42, shows the load active and reactive
powers. Figure 43, shows generation PAF active and reactive powers. Figure 44, shows the
consumption active and reactive powers of the series active filter. Figure 45, shows
generation active and reactive powers of the source. Figure 46, shows the difference between
load voltage magnitude and nominal value and finally Figure 47, shows the difference
between load voltage and source voltage phases.

Figure 36. Source side voltage of phase 1 (a swell has been occurred between 0.1 and 0.2 sec and a sag
has been occurred between 0.3 and 0.4 sec. Also positive and negative harmonic sequences have been
concluded between 0.15 and 0.35 sec. It has been tripped between 0.4 and 0.5 sec)
 Reference Generation of Custom Power Devices (CPs) 113

Figure 37. Compensator voltage of phase 1 (compensator voltage has been determined for the sag,
swell, interruption, negative sequence and harmonics improvement)

Figure 38. Load side voltage of phase 1 (swell, sag, positive and negative harmonic sequences have
been improved. Load voltage has been compensated in the fault condition)

Figure 39. Load side current of phase 1 (it has different order harmonics. It should be considered that
this current has been calculated after the voltage compensation, so the voltage unbalance has not been
concluded in the current)
114 An Update on Power Quality

Figure 40. Compensator current of phase 1 (compensator current has been determined for the load
current harmonics improvement as well as the reactive power)

Figure 41. Source side current of phase 1 (harmonics and reactive power components of the load
current have been canceled)

Figure 42. Load active and reactive power (load is nonlinear resistive-inductive)
 Reference Generation of Custom Power Devices (CPs) 115

Figure 43. Generation PAF active and reactive powers (reactive power and harmonics of load current
have been supplied by the parallel active filter)

Figure 44. Consumption active and reactive power of series active filter (it is considered that the
consumption power has been increased between sag times and decreased between swell times. Cause of
power oscillation has been investigated in the text. Active power has been increased in fault condition
for prevention of load interruption)

Figure 45. Generation active and reactive power of source (it is considered that the generation active
power has been increased between sag times and decreased between swell times. Reactive power has
been compensated. Cause of power oscillation has been investigated in the text. These powers are equal
to zero in fault condition)
116 An Update on Power Quality

Figure 46. Difference between load voltage magnitude and nominal value (this amount is decreased by
use of the PI controller to zero)

Figure 47. Difference between load voltage and source voltage phases (this amount decreased by use of
PI controller to zero)

8. Conclusions
In this research different approaches for reference generation of UPQC have been proposed.
Based on the general equations of Fourier transform, its response settling time is one cycle.
In this research for increasing the response speed and improving the control system
capabilities in dynamic conditions, very fast Fourier transform approach has been proposed
for balanced three phase systems. In the proposed approach, settling time of the response
could be reduced to one twelfth of a cycle. In the proposed approach, there were two data
window lengths, T/12 and T/2. In the sag, swell, and load change conditions, control system
was switched to T/12 for obtaining fast response. Then for improving the proposed
approach responsibility in filtering of unwanted steady state oscillation, control system was
switched to T/2 for obtaining no oscillated response. In these states, fast response in
dynamic conditions as well as good response in the steady state conditions would be
possible. In this research for the detection of the source voltage sag, swell, and load change
conditions, derivative of the first order magnitude of the voltage and current signal, were
compared to a constant value. This was based on the fact that in these conditions voltage or
current magnitude generally changes rapidly. Proposed control approach was simulated in
MATLAB/SIMULINK software. Voltage sag, swell, and harmonics were compensated by
 Reference Generation of Custom Power Devices (CPs) 117

SAF. But, reactive power and current harmonics were compensated by PAF. THD of load
voltage before compensation was 14.14 percent which was reduced to almost zero after the
compensation. But, THD of the source current before compensation was 9 percent which
was reduced to almost zero after the compensation.

Also the proposed reference generation algorithm based on MOADALINE has been
compiled in MATLAB software via M-File. Voltage harmonics have been compensated by
SAF of the UPQC and current harmonics have been compensated by PAF of the UPQC.
Based on the results proposed strategy not only could generate pure sinusoidal source
current and load voltage but also could compensate source reactive power satisfactory. Total
harmonic distortion of load voltage and current before compensation was 0.17 and 0.12
respectively which was reduced to almost zero after the compensation.

Another scope of this research was reference generation based on power flow control. This
approach was based on relation between active and reactive powers and load voltage. In
this approach amount of reactive power arranged to zero but amount of active power
arranged to load nominal power. Also a PI controller used for arranging the load voltage
magnitude to the nominal amount.

Author details
Ahad Mokhtarpour
Department of Electrical Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran

Heidarali Shayanfar
Department of Electrical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran

Seiied Mohammad Taghi Bathaee

Department of Electrical Engineering, K.N.T University, Tehran, Iran

9. References
[1] Fujita H., Akagi H. The Unified Power Quality Conditioner: The Integration of Series
and Shunt Active Filters. IEEE Transaction on Power Electronics 1998; 13(2) 315-322.
[2] Hannan M. A., Mohamed A. PSCAD/EMTDC Simulation of Unified Series-Shunt
Compensator for Power Quality Improvement. IEEE Transaction on Power Delivery
2005; 20(2) 1650-1656.
[3] Shayanfar H. A., Mokhtarpour A. Management, Control and Automation of Power
Quality Improvement. In: Eberhard A. (ed.) Power Quality. Austria: InTech; 2010.
p127-152.
[4] Khadkikar V., Chandra A. A Novel Structure for Three Phase Four Wire Distribution
System Utilizing Unified Power Quality Conditioner (UPQC). IEEE Transactions on
Industry Applications 2009; 45(5) 1897-1902.
[5] Kwan K.H., Chu Y.C., So P.L. Model-Based H∞ Control of a Unied Power Quality
Conditioner. IEEE Transactions on Industrial Electronics 2009; 56 (7) 2493-2504.
118 An Update on Power Quality

[6] Khadkikar V., Chandra A. A New Control Philosophy for a Unified Power Quality
Conditioner (UPQC) to Coordinate Load-Reactive Power Demand Between Shunt and
Series Inverters. IEEE Transactions on Power Delivery 2008; 23 (4) 2522-2534.
[7] Lee W.C., Lee D.M., Lee T.K. New Control Scheme for a Unified Power Quality
Compensator-Q with Minimum Active Power Injection. IEEE Transactions on Power
Delivery 2010; 25(2) 1068-1076.
[8] Han B., Bae B., Kim H., Baek S. Combined Operation of Unified Power-Quality
Conditioner with Distributed Generation. IEEE Transaction on Power Delivery 2006;
21(1) 330-338.
[9] Mohammadi H.R., Varjani A.Y., Mokhtari H. Multiconverter Unified Power-Quality
Conditioning System: MC-UPQC. IEEE Transactions on Power Delivery 2009; 24(3)
1679-1686.
[10] Mokhtarpour A., Shayanfar H.A., Bathaee. S.M.T Extension of Fourier Transform for
Very Fast Reference Generation of UPQC. International Journal on Technical and
Physical Problems of Engineering 2011; 3(4) 120-126.
[11] Mokhtarpour A., Shayanfar H.A., Bathaee. S.M.T UPQC Control Based on MO-
ADALINE Approach. International Journal on Technical and Physical Problems of
Engineering 2011; 3(4) 115-119.
 Section 3

Power Quality Improvement in End Users Stage

 Chapter 7

Power Quality Improvement Using

Switch Mode Regulator

Raju Ahmed and Mohammad Jahangir Alam

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53234

1. Introduction
Power quality describes the quality of voltage and current. It is an important consideration
in industries and commercial applications. Power quality problems commonly faced are
transients, sags, swells, surges, outages, harmonics and impulses [1]. Among these voltage
sags and extended under voltages have large negative impact on industrial productivity,
and could be the most important type of power quality variation for many industrial and
commercial customers [1-5].
Voltage sags is mainly due to the fault occurring in the transmission and distribution
system, loads like welding and operation of building construction equipment, switching of
the loaded feeders or equipments. Both momentary and continuous voltage sags are
undesirable in complex process controls and household appliances as they use precision
electronic and computerized control.
Major problems associated with the unregulated long term voltage sags include equipment
failure, overheating and complete shutdown. Tap changing transformers with silicon-
controlled rectifiers (SCR) are usually used as a solution of continuous voltage sags [6]. They
require large transformer with many SCRs to control the voltage at the load which lacks the
facility of adjusting to momentary changes. Some solutions have been suggested in the past
to encounter the problems of voltage sag [7-11]. But these proposals have not been realized
practically to replace conventional tap changing transformers.

Now a day’s various power semiconductor devices are used to raise power quality levels to
meet the requirements [12]. Several AC voltage regulators have been studied as a solution of
voltage sags [13-18]. In [13] the input current was not sinusoidal, in [14-16] the efficiency of
the regulator was not analyzed and in [17-18] the input power factor was very low and the
efficiency is also found poor. Compact and fully electronic voltage regulators are still
unavailable practically.

© 2013 The
© Author(s).
Ahmed Licensee
and Alam, InTech.
licensee This chapter
InTech. is distributed
This is an open accessunder thedistributed
chapter terms of theunder
Creative
the Commons
terms of
the CreativeLicense
Attribution Commons Attribution License (http://creativecommons.org/licenses/by/3.0),
http://creativecommons.org/licenses/by/3.0), which
which permits unrestricted use,permits
distribution,
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
and reproduction in any medium, provided the original work is properly cited.
122 An Update on Power Quality

Dynamic Voltage Restorer (DVR) is sometimes used to regulate the load side voltage [19-
21]. The DVR requires energy storage device to compensate the voltage sags. Flywheels,
batteries, superconducting magnetic energy storage (SMES) and super capacitors are
generally used as energy storage devices. The rated power operation of DVR depends on the
size and capacity of energy storage device which limits its use in high power applications.
Whereas, switching regulator needs no energy storage devices, therefore, can be used both
in low power and high power applications.

The objective of this chapter is to describe the operation and design procedure of a switch
mode AC voltage regulator. Firstly, some reviews of the regulators are presented then the
procedure of design and analysis of a switch mode regulator is described step by step.
Simulation software OrCAD version 9.1 [22] is used to analyze the regulator. The proposed
regulator consists mainly two parts, power circuit and control circuit. The power circuit
consist two bi-directional switches which serve as the freewheeling path for each other. A
signal generating control circuit is to be associated with the power circuit for getting pulses
of the switches. In the control circuit, a commercially available pulse width modulator IC
chip SG1524B is used, thus circuit is compact and more viable.

2. Review of voltage regulators

2.1. Switching-mode power supply (SMPS)
A switching-mode power supply (SMPS) is switched at very high frequency. Conversion of
both step down and step up of voltage is possible using SMPS. Uses of SMPSs are now
universal in space power applications, computers, TV and industrial units. SMPSs are used
in DC-DC, AC-AC, AC-DC, DC-AC conversion for their light weight, high efficiency and
isolated multiple outputs with voltage regulation. Main parts of a Switching-mode power
supply are:

(a) Power circuit, (b) Control circuit.

Figure 1 shows the block diagram of a SMPS. The power circuit is mainly the input, output
side with the switching device. The switching device is continuously switched at high
frequency by the gate signal from the control circuit to transfer power from input to the
output. The control circuit of a SMPS basically generates high frequency gating pulses for
the switching devices to control the output voltage. Switching is performed in multiple
pulse width modulation (PWM) fashion according to feedback error signal from the load.
High frequency switching reduces filter requirements at the input and output sides of the
converter. Simplest PWM control uses multiple pulse modulations generated by comparing
a DC with a high frequency carrier triangular wave.
The PWM control circuit is commonly available as integrated form. The designer can select
the switching frequency by choosing the value of RC to set oscillator frequency. As a rule of
thumb to maximize the efficiency, the oscillation period should be about 100 times longer
than the switching time of the switching device such as Transistor, Metal oxide
semiconductor field-effect transistor (MOSFET), Insulated gate bipolar transistor (IGBT). For
 Power Quality Improvement Using Switch Mode Regulator 123

example, if a switch has a switching time of 0.5 us, the oscillator period would be 50 us,
which gives the maximum oscillation frequency of 20 KHz. This limitation is due to the
switching loss in the switching devices. The switching loss of switching devices increases
with the switching frequency. In addition, the core loss of inductor limits the high frequency
operation.

Power circuit

Input Input Output

Switch Output
filter filter

Gating Feed back

Signal Reference Control
Generator Voltage Circuit

Control circuit
Figure 1. Block diagram of Switching-mode power supply (SMPS).

2.2. DC-DC converter

Figure 2 illustrates the circuit of a classical linear power converter. Here power is controlled
by a series linear element; either a resister or a transistor is used in the linear mode. The total
load current passes through the series linear element. In this circuit greater the difference
between the input and the output voltage, more is the power loss in the controlling device
(linear element). Linear power conversion is dissipative and hence is inefficient.

The circuit of Fig. 3 illustrates basic principle of a DC-DC switching-mode power converter.
The controlling device is a switch. By controlling the duty cycle, (the ratio of the time in on
positions to the total time of on and off position of a switch) the power flow to the load can
be controlled in a very efficient way. Ideally this method is 100% efficient. In practice, the
efficiency is reduced as the switch is non-ideal and losses occur in power circuits. Hence,
one of the prime objectives in switch mode power conversion is to realize conversion with
the least number of components having better efficiency and reliability. The DC output
voltage to the load can be controlled by controlling the duty cycle of the rectangular wave
supplied to the base or gate of the switching device. When the switch is on, it has only a
small saturation voltage drop across it. In the off condition the current through the switch
is zero.

The output of the switch mode power conversion circuit (Fig. 3) is not pure DC. This type
of output is applicable in some cases such as oven heating without proper filtration. If
constant DC is required, then output of converter has to be smoothed out by the addition
of low-pass filter.
124 An Update on Power Quality

R1
V
Vin
+
Vin Vout R2
_
Vout

t
Figure 2. Linear (dissipative) DC-DC power conversion circuit.

V Vout

Vin
BJT
+
Vin Vout R
_

t
Figure 3. Switching-mode (non dissipative) DC-DC power conversion circuit.

2.2.1. Types of DC-DC converter

There are four basic topologies of switching DC-DC regulators:

a. Buck regulator
b. Boost regulator
c. Buck-Boost regulator and
d. Cûk regulator.

The Circuit diagram of four basic DC-DC switching regulators is shown in Fig. 4. The
expression of output voltage for the four types of DC-DC regulators are as follows:

Vin
For Buck regulator, Vout  kVin , For Boost regulator, Vout 
1 k

-kVin
For Buck- Boost regulator and Cûk regulator, Vout 
1 k

Where k is the duty cycle, the value of k is less than 1. For Buck regulator output voltage is
always lower than input voltage, for Boost regulator output voltage is always higher than
input voltage. For Buck-Boost regulator and Cûk regulator output voltage is higher than
input voltage when the value of k is higher than 0.5, and output voltage is lower than input
voltage when the value of k is lower than 0.5. When k is equal to 0.5 output voltage is same
 Power Quality Improvement Using Switch Mode Regulator 125

as input voltage. In Buck-Boost and Cûk regulator, the polarity of output voltage is opposite
to that of the input voltage, therefore theses regulators are also called inverting regulators.

L L D
BJT
+
Vg + C
C Vout R BJT Vout R
_ Vin D _ Vin Vg

(a) Buck regulator (b) Boost regulator

L1 C1 L2
BJT D
+ Vg +
C Vg BJT C2 R
Vin L Vout R Vin D Vout
_ _

(c) Buck-Boost regulator (d) Cûk regulator

Figure 4. Circuit diagram of DC-DC regulator, (a) Buck regulator, (b) Boost regulator, (c) Buck-Boost
regulator, (d) Cûk regulator.

2.3. AC-AC converter

The AC voltage regulator is an appliance by which the AC output voltage can be set to a
desired value and can be maintained constant all the time irrespective of the variations of
input voltage and load. This subject is vast and the field of application extends from very
large power systems to small electronic apparatus. Naturally, the types of regulators are also
numerous. The design of the regulators depends mainly on the power requirements and
degree of stability.

The AC voltage can be regulated by the following ways.

a. Solid-state tap changer and steeples control by variac
b. Solid-tap changer using anti-parallel SCRs
c. Voltage regulation using servo system
d. Phase controlled AC regulator
e. Ferro-resonant AC regulator
f. Switch mode AC regulator

2.3.1. Solid-state tap changer and stepless control by variac

The voltage regulations by tap-changing switches are used in many industrial applications
where the maintenance of output voltage at a constant value is not very stringent, such as
ordinary battery chargers, electroplating rectifiers etc. For smaller installation, off-load tap
126 An Update on Power Quality

changing switches are used and for large installation on-load tap changing switches are
used. The switches are generally incorporated at the secondary of the transformer. For a low
voltage high current load, the switches are provided on the primary side of the transformer
due to economical reason. For line voltage correction, taps are provided on the primary of
the transformer. For three-phase transformers three pole tap changing switches are used.
In off-load tap changer, the output is momentarily cut-off from the supply. It is therefore
used for low capacity equipment and where the momentary cut-off of the supply is not
objectionable for the load. The major limitation of the off-load tap changing switches is the
occurrences of arcs at the contact points during the change-over operation. This shortens the
life of off-load rotary switches, particularly of high current ratings. In Fig. 5 (a), three four-
position switches of an off load tap changer are shown, such that the minimum of X volts
per step are available at the output.

The voltage is corrected by tap-charging switches in steps. Where stepless control is required,
variable autotransformers or variacs are used. The normal variac consists of a toroidal coil
wound on a laminated iron ring. The insulation of the wire is removed from one of the end
faces and the wire is grounded to ensure a smooth path for the carbon brush. Carbon brush is
used to limit the circulating current, which flows between the short-circuited turns.
A Buck-Boost transformer is sometimes used for AC voltage regulation when the output
voltage is approximately the same as the mean input voltage as shown in Fig. 5(b). In this
case if the output voltage is less than or greater than the desired value, it can be increased or
decreased to the desired value by adding a suitable forward or reverse voltage with the
input through the Buck-Boost transformer.

Ns
16X
16X Coarse
16X Np
Medium Buck – Boost
4X Transformer Output
Input Input = Ei  Ei/2
4X Output
= Ei (Ns/Np)
4X
Ei/2
X Fine
X
X

(a) Off load tap changing switch (b) Voltage control by combination of a
arrangement. Buck–Boost transformer and a variac.

Figure 5. Circuit diagram of AC voltage controller using (a) Off load tap changer and (b) Buck-Boost
transformer and variac.

2.3.2. Solid tap changer using anti-parallel SCRs

Anti-parallel SCRs combinations can replace the voltage sensitive relay in the tap-changing
regulator. Figure 6 shows a tap changer with three taps which can be connected to the load
 Power Quality Improvement Using Switch Mode Regulator 127

through three anti-parallel switches. When the SCR1-SCR2 switch is fired, tap 1 is connected
to the load. Similarly taps 2 and 3 can be connected to the load through the SCR3-SCR4 and
CSR5-SCR6 switches respectively. Thus, any number of taps can be connected to the load
with similar SCR switches. When one group of SCRs operates for the whole cycle and other
groups are off, the voltage corresponding to the tap of that group appears at the load.
Changeover from one loop to the other is done simply by shifting the firing pulses from one
group of SCRs to the other.
With resistive load, the load current becomes zero and the SCRs stop conduction as soon as
the voltage reverses its polarity. Therefore, when one group is fired, the other groups are
commutated automatically. With reactive loads, the situation is complicated by the fact that
the zero current angle depends on the load power factor. This means that the SCR conducts
a finite value of current at the time of reversal of line voltage. This results in either
preventing a tap change due to reverse bias on the SCR to be triggered or causing a short
circuit between the taps through two SCRs.

2.3.3. Voltage regulation using servo system

Voltage regulators using servo systems are quite common. Both single and three-phase
types are available. The rating of this type of regulator is quite high and is more economical
for high power rating. This regulator normally consist a variac driven by a servomotor, a
sensing unit and a voltage and power amplifier to drive the motor in a reversible way.
Various types of driving motor may be used for regulating the unit, such as direct current,
induction and synchronous motors. However, in all cases, the motor must come to rest
rapidly to avoid overrun and hunting. The amount of overrun may be reduced by dynamic
braking in the case of a DC motor or by disconnecting the motor from the variac by a clutch
as soon as the signal from the measuring unit ceases. The main disadvantage of this type of
regulator is the low life of the contact points of the relays.

2.3.4. Phase controlled AC voltage regulator

Voltage regulators using SCRs are quit common. The load voltage is regulated by
controlling the firing instants of the SCRs. There are various circuits for single phase and
three phase regulators using SCRs. Though the output voltage can be precisely controlled by
this method, the harmonic introduced in the load voltage are quit large and this circuit is
used for applications where the output voltage waveform need not be strictly sinusoidal.
The circuit arrangement for a single phase SCR regulator is shown in Fig. 6 and Fig. 7.

2.3.5. Ferro-resonant AC voltage regulator

The concept of the stabilization of AC voltage using a saturated transformer is rather old.
The basic circuit arrangement consists of a linear reactor or transformer T1 and a nonlinear
saturated reactor or transformer T2 connected in series as shown in Fig. 8. Since the two
elements T1 and T2 are in series, the current through them is the same. Transformer T2 is
operated under saturated. The voltage division between the two is according to their
128 An Update on Power Quality

impedances. Due to nonlinear characteristics of T2 the percentage change of voltage across it

is much smaller compared to the percentage change of input voltage. If a suitable voltage
proportional to the current is subtracted from the voltage across T2 a practically constant
output voltage can be obtained. The circuit arrangement shown is Fig. 8(a) has some
drawbacks such as, no load input current is high, and good output voltage stability cab be
achieved only at a particular load. Hence some modifications are necessary to improve its
performance. The major modification is to place a capacitor across the saturated
transformerT2 that is shown in Fig. 8(b).

SCR 1 GR 1
SCR 2
V1
SCR 3
SCR 4 GR 2
Input
V2 Lo
Output ad
SCR 5
SCR 6 GR 3
V3

Figure 6. Circuit diagram of solid tap changer using anti-parallel SCRs.

SCR2 SCR1
SCR1
SCR2

SCR1

Input Output
Input Output Input Output

(a) (b) (c)

Figure 7. Phase controlled AC voltage regulator, (a) Using back to back SCR and diode and (b) using
inverse parallel SCR (c) Using diode-bridge and single SCR

T1 ET1(P) ET1(S)
ET

Input Output Input Output

ET C ET2
T2

(a) (b)
Figure 8. Fero-resonant AC voltage regulator.

The value of the capacitor is such that it resonant with the saturated inductance of T2 at
some point. The characteristics of the circuit is such that a small change in voltage across T2
 Power Quality Improvement Using Switch Mode Regulator 129

causes the circuit to go out of resonance consequently a large change in input current and
power factor. For a change in the input voltage, the change in voltage across the resonant
circuit is small but the change in voltage at T1 is large, and by suitable proportioning of the
voltage, a good degree of stabilization is achieved for the variation of input voltage as well
as load current. The simple Ferro-resonant regulator has the following disadvantages:

a. The output voltage changes with frequency.

b. Since the core operates in saturation and output is derived from the tank circuit, the
core volume is large, the core losses are high and external magnetic field is also high.

2.3.6. Switch mode AC voltage regulator

In switch mode AC voltage regulator, the switching devices are continuously switching on
and off with high frequency in order to transfer energy from input to output. The high
operating frequency results in the smaller size of the switch mode power supplies since the
size of power transformer inductors and filter capacitors is inversely proportional to the
frequency. The SMPS are more complicated and more expensive, their switching current can
cause noise problems, and simple designs can have a poor power factor.

Four common types of switch mode converters are used in DC-DC conversion. They are
Buck, Boost, Buck-Boost and C^UK converters. Researches are trying to modify these DC
regulators to regulate AC voltages. Buck- Boost and Cûk converter configuration has been
investigated for voltage regulation [17-18]. But in every case it is found that the input power
factor is very low and the efficiency is poor.

3. Design and analysis of switching-mode AC voltage regulator

3.1. Operation principle of switching-mode AC voltage regulator
3.1.1. Operation of power circuit
Voltage sag is an important power quality problem, which may affect domestic, industrial
and commercial customers. Voltage sags may either decrease or increase in the magnitude
of system voltage due to faults or change in loads. Momentary and sustained over voltage
and under voltage may cause the equipment to trip out, which is highly undesirable in
certain application. In order to maintain the load voltage constant in case of any fluctuation
of input voltage or variation of load some regulating device is necessary.
In this chapter the principle of operation of high frequency switching AC voltage regulator,
design of its filter circuit and snubber circuit are described. Performance of the regulator is
also analyzed using simulation software OrCAD version 9.1. Switch-mode power supplies
(SMPS) incorporate power handling electronic components which are continuously
switching on and off with high frequency in order to provide the transfer of electric energy
from input to output. The design of AC voltage regulator depends on power requirement,
degree of stability and efficiency. Solid state AC regulator using phase control technique are
not new and are widely used in many application such as heating and lighting control etc.
130 An Update on Power Quality

These regulators are not suited for critical loads because the output waveforms are
truncated sine waves, which contain large percentage of distortion. The input power factor
is low. These drawbacks are largely overcome and the voltage can be efficiently controlled
by means of a solid-state AC regulator using PWM technique.

The power circuit of the proposed AC voltage regulator is shown in Fig. 9. The circuit
operation can be explained with the help of Fig. 10. During positive half cycle of the input
voltage, at mode 1, when switch-1 is on and switch-2 is off, the current passes through diode
D1, switch-1, diode D4 and through the inductor and the energy is stored in the inductor. At
mode 2, when switch-1 is off and switch-2 is on, the energy stored in the inductor is
transferred through diode D8, switch-2 and diode D5. At mode 1, power is transferred from
source and at mode 2, power is not transferred from the source, so by controlling the on and
off duration of switch-1 output power can be controlled.

During negative half cycle of the input voltage, at mode 1, when switch-1 is on and switch-2
is off the current passes through the inductor, diode D3, switch-1, and diode D2 and the
energy is stored in the inductor. At mode 2, when switch-1 is off and switch-2 is on the
energy stored in the inductor is transferred through diode D6, switch-2 and diode D7.

D1 D3

Gate signal 1
+ +
Switch 1
- -
D5 Gate signal 2 D6
TX1

0 Switch 2
Lo
+
-

D2 D4 0
+

ad
-

D7 D8
0

Figure 9. Power circuit of the proposed AC voltage regulator.

Switch 1 Switch 1

Mode 1, current path Mode 1, current path

L L
Switch 2 Switch 2

Mode 2, current path Mode 2, current path

(a) (b)
Figure 10. Operation of the power circuit of AC voltage regulator (a) Operation during positive half
cycle (b) Operation during negative half cycle
 Power Quality Improvement Using Switch Mode Regulator 131

3.1.2. Operation of control circuit

The gate signal generating circuit for a manually controlled AC voltage regulator is shown
in Fig. 11. The control circuit incorporates an Operational Amplifier (OPAMP) whose
positive input is a variable DC voltage V1, and negative input is a fixed saw-tooth signal V2.
In this circuit the OPAMP acts as a comparator, output of the OPAMP depends on the
difference of the two inputs. The negative input (saw-tooth wave) is kept constant and
positive input (DC voltage) is varied. So output pulse width depends on DC input voltage
of OPAMP i.e. when DC input is higher the output of comparator will be wider and when
DC input is lower the output of comparator will be narrower.

The outputs of OPAMP are used to turn on/off the switches of the power circuit of the
regulator to regulate the output voltage. The output of OPAMP is directly passed through
limiter-1 which is the gate signal for switch-1 and after inverting the output of the
comparator is passed through the limiter-2 which is the gate signal for switch-2. The
function of the limiter is to limit the output of comparator from 0 to 5 V. When switch-1 of
the power circuit is on then switch-2 should be off. So the gate signal generating circuit is
arranged in such a way that when gate signal of switch-1 is on then gate signal for switch-2
is off and vice versa.

0
V3 5
-1
8

12Vdc
3 0
gate signal 2
V+

+
V1 1
OUT
2 5
-
V-

V1 = 10 V2
5Vdc V2 = 0 AD648A
TD = 0 0
4

gate signal 1
TR = .125ms V4
TF = .125ms
PW = .005ms 12Vdc
PER = .255ms
0 0 0

Figure 11. Gate signal generation circuit of manually controlled AC voltage regulator.

3.2. Manually controlled AC voltage regulator

When the stability is not very stringent, manually controlled AC voltage regulator is
generally preferred from economic considerations.
The basic circuit of a manually controlled AC voltage regulator is shown in Fig. 12. When
any change in output voltage occurs due to change in input voltage or change in load, the
voltage can be regulated to the desirable value by changing the DC voltage of the gate signal
generating circuit manually. The power circuit of the proposed regulator shown in Fig. 12 is
implemented using ideal switches; later part of this chapter the ideal switches is replaced by
practical switches. The regulator proposed in this chapter is employed to regulate the output
132 An Update on Power Quality

voltage to 300V (peak) for variations of input voltage from 200V (peak) to 400V (peak), also
for variation of load from 100 ohm to 200 ohm. However, the output voltage can be set to
any desirable value according to requirement. The values of all voltages and currents
indicated in this chapter are in peak values.

The input current and output voltage waveforms of the manually controlled AC voltage
regulator as shown in Fig. 12, is shown in Fig. 13, when the input voltage is 300V and
output voltage is also 300V. The spectrum of the input current and output voltage as shown
in Fig. 13 is shown in Fig. From the waveforms it is seen that the waveforms are not smooth,
sinusoidal and from the spectrum it is seen that due to high frequency switching the
significant number and amount of harmonics occur. The switching frequency is selected to 4
KHz. Harmonics occurs at switching frequency and its odd multiple frequencies. So, filters
are required at input and output side to filter out these harmonics to get desired sinusoidal
waveforms.

SW1
S1
+ +
- -
SW2 TX1
0
S2 R6
+
-

Input 0
+
-

VOFF = 0 100
VAMPL = 300
FREQ = 50

0 0

0 5
-1
V3
0
8

SW2
3
V+

+ 12Vdc
1
5Vdc OUT
V1 2
-
V-

V1 = 10 V2
V2 = 0 AD648A 5
TD = 0
4

TR = .125ms V4
TF = .125ms 0
12Vdc SW1
PW = .005ms
PER = .255ms
0 0 0

Figure 12. Fundamental circuit of manually controlled AC voltage regulator (ideal switch
implementation).
 Power Quality Improvement Using Switch Mode Regulator 133

10A

0A

SEL>>
-15A
- I(V5)

500V

0V

-500V

0s 4ms 8ms 12ms 16ms 20ms

V2(R3)
Time

Figure 13. Input current and output voltage waveforms of the regulator shown in Fig. 12.
-I(V5): Input current, V(R3:2): Output voltage.

10A

5A

0A
- I(V5)
400V

200V

SEL>>
0V
0Hz 10KHz 20KHz 30KHz 40KHz 50KHz
V2(R3)
Frequency

Figure 14. Spectrum of input current and output voltage waveforms. -I(V5):Input current V(R3:2):
Output voltage.

3.3. Filter design

3.3.1. Output filter design
For getting smooth output voltage, a low pass LC filter of proper L and C value is needed at
the output of this regulator. The output filter circuit and the corresponding AC sweep are
V  J C V0 1
shown in Fig. 15. From this circuit we can write, V0  in or 
J(L-1 C) Vin C(L-1 C)
134 An Update on Power Quality

The input to the filter is high frequency modulated 50 Hz AC input. The switching signal
that modulates the 50 Hz signal is taken to be 4 KHz in this case. So, we will have to make a
filter that would pass signal up to 1 KHz (say) and attenuate all other frequencies. This
would result a nearly sinusoidal output voltage. In the LC filter section we choose a
capacitor of 5µF and determine the value of inductor for a cutoff from AC sweep analysis
through OrCAD simulation. We found the value of the inductor to be 30 mH.

L1 500V

30mH

300Vac Input C1 R1 250V

0Vdc
5u 100

0V
10Hz 100Hz 1.0KHz 10KHz
0 V(R1:2)
Frequency
(a) (b)

Figure 15. Output voltage filter and AC sweep analysis (a) Output voltage filter (b) AC sweep analysis.

3.3.2. Input filter design

A low pass LC filter of proper L and C value is needed at the input of the regulator to filter out
some of the harmonics from the supply system. The input filter circuit and the corresponding
AC sweep are shown in Fig. 16. Input current contains harmonics at switching frequency 4
KHz and its odd multiple. In order to remove harmonics above 1 KHz, we choose a capacitor
of 5µF and determine the value of inductor for a cutoff from AC sweep analysis through
OrCAD simulation. We found the value of the inductor to be 30 mH.

L1
20A
30mH

20Aac
0Adc R1 10A
Input
C1

5u
0A
10Hz 100Hz 1.0KHz 10KHz
0 - I(R2)
Frequency
(a) (b)
Figure 16. Input current filter and corresponding AC sweep analysis (a) Input current filter (b) AC
sweep analysis.
 Power Quality Improvement Using Switch Mode Regulator 135

3.4. Free wheeling path and surge voltage across switching devices
The power circuit of the proposed regulator with input and output filter is shown in Fig. 17.
In an inductor, current does not change instantaneously. When the switches of power circuit
switched on and off the current into the inductor of input and output filter are changed
abruptly. Abrupt change of current causes a high di/dt resulting high voltage which is equal
to Ldi/dt. These voltages appear across the switches as surge. Usually providing
freewheeling path in restricts such occurrence.

3.4.1. Surge voltage across switches

In the proposed circuit, two switches serve as the freewheeling path for each other.
However, for very short period when one switch is turned off and other is turned on, an
interval elapses due to delay in the switching time. As a result, freewheeling during this
interval is disrupted in the proposed circuit. If the current in any inductive circuit is
abruptly disrupted, a high Ldi/dt across the switch appears due to the absence of
freewheeling path. High spiky surge voltage appears across the switches during these short
intervals as shown in Fig. 18.

L1 L2
SW1
S1
30mH 30mH
+ +
- - SW2 TX1
Input
0
VAMPL = 300 S2 C2 R3
+
-

FREQ = 50 0
+
-

5u 100

C1
5u

0 0

Figure 17. The power circuit of the proposed AC voltage regulator with input and output filters.

400KV

200KV

SEL>>
0V
V(S1:3)- V(S1:4)
400KV

200KV

0V
0s 4ms 8ms 12ms 16ms 20ms
V(S2:3)- V(S2:4)
Time

Figure 18. Voltage across switches with filters and without snubbers. V(S1:3)-V(S1:4): Voltage across
switch-1, V(S2:3)-V(S2:4): Voltage across switch-2.
136 An Update on Power Quality

These spiky voltages across the switches may be excessively high, about thousand of
kilovolt and which may destroy the switches during the operation of the circuit. Remedial
measures should be taken to prevent this phenomenon to make the circuit commercially
viable. In the proposed circuit RC snubbers are used for suppressing surge voltage across
the switches. The power circuit of the proposed regulator with input output filter and
snubbers is shown in Fig. 19.
Snubber enhances the performance of the switching circuits and results in higher reliability,
higher efficiency, higher switching frequency, smaller size and lower EMI. The basic intent
of a snubber is to absorb energy from the reactive elements in the circuit. The benefits of this
may include circuit damping, controlling the rate of change of voltage or current or
clamping voltage overshoot. The waveforms of voltages across switches with input output
filters and snubbers are shown in Fig. 20.
Use of snubbers reduces the spiky voltage across the switches to a tolerate limit for practical
application of the AC voltage regulator.

L1 L2
SW1 1
S1 R5
30mH 30mH
+ +
- - SW2 TX1
Input C5
0 0.1u S2
+
-

VAMPL = 300 0 C2 R3
+
-

FREQ = 50
5u 100
R6
C1 C3 0.1u 1
5u

0 0

Figure 19. The power circuit of the proposed AC voltage regulator with input output filters and
snubbers.

400V

200V

0V
V(S1:3)- V(S1:4)
400V

200V

SEL>>
0V
0s 5ms 10ms 15ms 20ms
V(S2:3)- V(S2:4)
Time

Figure 20. Voltage across switches with filters and snubbers. V(S1:3)-V(S1:4): Voltage across switch-1,
V(S2:3)-V(S2:4): Voltage across switch-2.
 Power Quality Improvement Using Switch Mode Regulator 137

3.5. Proposed AC voltage regulator with practical switches

In the previous section, we have studied the regulator using ideal S-break switches which
have been operated by the pulses from the limiter. But for practical application, real
switches are essential which are to be controlled by the pulses having ground isolation. The
proposed AC voltage regulator circuit with practical switches is shown in Fig. 21. The ideal
S-break switch is replaced by IGBT.
In the proposed regulator chip SG1524B is used to control the gate signal. Signal from the
chip is fed to the Limiter and finally to the optocoupler. The output of the optocoupler is
used to control the on off time of the IGBTs. The function of the Limiter is to limit the output
voltage of the gate signal generating IC from 0 to 6 volts. Optocoupler is used to generate
signaling voltage with ground isolation.

R1
U1
16

S2
3

R3 20Vdc V1 0 R15 U3 R8
VREF
OSC

50k 15 A4N25A
0 C1 VIN
7 12 6 V3
0 4000pf 6 CT C_A 11 15V
RT E_A 2
1
2 ERR- 13 0
R4 ERR+ C_B 14 0 R6
4 E_B
CL+ V2 G2
COMP

1 5 R5
SHUT
GND

CL- 10Vdc
SG1524B U2A S1
0 V6 0 0 6 R16 U4 R9
10

0 R20
8

3 2 2 A4N25A
100uVdc 0 V4
1k 0 15V
C2
CD4009A
0 0.001u R7
0
0 G1

D1 D3
L1 L2
1 R10
30mH 30mH
Z1
D9
D5 S2 D6 100
S1 C6 G2 TX1 C4
V5 Z2 5u R14
C3 0.1u R11
5u G1

VAMPL = 300 0.001 D10 R13

FREQ = 50 D2 R12 C5 1
0.001 D4
D7 0.1u D8

0 0

Figure 21. Manually controlled AC voltage regulator circuit with practical switches.

3.5.1. Chip SG1524B for generation of gate signal

The Block diagram of the internal circuitry of the chip SG1524B is shown in Fig. 22. By
controlling the error signals of the error amplifier the duty cycle of the gate signal to the
138 An Update on Power Quality

regulator can be controlled. Thus it is a very suitable device for using in the regulator
circuits.

3.5.2. Results of proposed AC voltage regulator (practical switch implementation)

The waveforms of the input and output voltages of the proposed regulator are shown in Fig.
23 and Fig. 24. Fig. 23 shows the input and output voltages waveform when the input
voltage is 200V and output voltage is 300V. Fig. 24 shows the input and output voltages
waveform when the input voltage is 400V and output voltage is 300V. Fig. 25 and Fig. 26
show the input and output current waveforms corresponding to Fig. 23 and Fig. 24.

15 Reference 16
VCC Regulator REF OUT
Vref

Vref 12
COL 1
11
EMIT 1
T 13
COL 2
Vref 14
RT 6 EMIT 2
Oscillator 3
CT 7 OSC OUT
Vref
1 Vref
IN - –
2 + Comparator
IN +

9
COMP
Vref Error Amplifier
4
CURR LIM + +
5
CURR LIM - –

10 1 kΩ
SHUTDOWN
10 kΩ
8
GND

Figure 22. Block diagrm of IC chip SG1524B

400V

0V

-400V
0s 50ms 100ms 150ms 200ms
V1(V5) V(R14:2)
Time

Figure 23. Input and output voltage waveforms, Input 200V output 300V. V1(V5): Input voltage –
dotted line, V(R14:2): Output voltage – solid line.
 Power Quality Improvement Using Switch Mode Regulator 139

400V

0V

-400V
0s 50ms 100ms 150ms 200ms
V1(V5) V(R14:2)
Time

Figure 24. Input and output voltage waveforms, Input 400V output 300V. V1(V5): Input voltage –
dotted line, V(R14:2): Output voltage – solid line.

5.0A

0A

-5.0A
0s 50ms 100ms 150ms 200ms
-I(V5) -I(R14)
Time

Figure 25. Input and output current waveforms for input 200V output 300V. -I(V5): Input current -
dotted line, -I(R14): Output current – solid line.

4.0A

0A

-4.0A
0s 50ms 100ms 150ms 200ms
-I(V5) -I(R14)
Time

Figure 26. Input and output current waveforms for input 400V output 300V. -I(V5): Input current –
dotted line, -I(R14): Output current – solid line.
140 An Update on Power Quality

From the waveforms shown in Fig. 23 to Fig. 26, it is seen that the waveforms of output
voltage and input current is perfectly sinusoidal. The variation of output voltage of the
proposed regulator with the duty cycle is shown in Fig. 27. The value of input voltage is
kept constant to 300V. From Fig. 23 it is seen that the variation of output voltage with duty
cycle is almost linear. The variation of duty cycle with the variation of input voltage from
200V to 400V to maintain the output voltage constant to 300V is shown in Fig. 28.

600
Output voltage (V)

500
400
300
200
100
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Duty cycle

Figure 27. Variation of output voltage with duty cycle. Input voltage is 300V.

0.8
0.7
0.6
Duty cycle

0.5
0.4
0.3
0.2
175 225 275 325 375 425
Input voltage (V)

Figure 28. Variation of duty cycle with input voltage to maintain output voltage constant to 300V.

4. Automatic controlled AC voltage regulator

In manually controlled AC voltage regulator control, the output voltage is sensed with a
voltmeter connected at the output; the decision and correcting operation is made by a
human judgment. The manual control may not be feasible always due to various factors. In
automatic voltage regulators, all functions are performed by instruction, and give much
better performance, so far as stability, speed of correction, consistency, fatigue, etc. are
concerned.
 Power Quality Improvement Using Switch Mode Regulator 141

There are two types of automatic control voltage regulator, discontinuous control and
continuous control. The automatic control system consists of a sensing or measuring unit
and a power control or regulating unit. The sensing unit compares the output voltage or the
controlled variable with a steady reference and gives an output proportional to their
difference called the error signal. The error voltage is amplified, integrated or differentiated
or modified whenever necessary. The processed error voltage is fed to the main control unit
to have required corrective action.
In the discontinuous type of control, the measuring unit is such as to produce no signal as
long as the voltage is within certain limits. When the voltage goes outside this limit, a signal
is produced by the measuring unit until the voltage is again brought within this limit. In this
type of measuring or sensing unit, the correcting voltage is independent of percentage of
error. When the voltage is brought back to this limit, the signal from the measuring unit is
zero and the regulating unit remains at its new position until another signal is received from
the measuring unit.
In continuous control, the measuring unit produces a signal with amplitude proportional to
the difference between the fixed reference and the controlled voltage. The output of the
measuring unit is zero when the controlled voltage or a fraction of it is equal to the reference
voltage. The regulating or the controlling unit, which is associated with the continuous
measuring unit, gives a correcting voltage proportional to the output of the measuring unit.
The principle of operation of a continuous control AC voltage regulator is described in this
section.

4.1. Control and gate signal generating circuit for controlled AC voltage
regulator
Figure 29 shows the circuit of the proposed automatic controlled AC voltage regulator
including the control and gate signal generating circuit. A fraction of the output voltage
after capacitor voltage dividing and rectifying is passed through an OPAMP buffer. Buffer is
used to remove the loading effect. Output voltage of the buffer is same as its input voltage.
The output voltage of the buffer is further reduces using resistive voltage divider and taken
as the negative input of the error amplifier of the PWM voltage regulating IC SG1524B.
The positive input of the error amplifier is taken from the reference voltage of the chip, after
voltage dividing using 50K and 1 ohm resistance. The positive input of the error amplifier is
fixed and the negative input is error signal which will vary according to the output voltage.
Since the error signal is applied to the negative input of the error amplifier, the duty cycle
will be increased if the error signal is decreased and vice versa.
When the output voltage increases above the set value which is 300V either due to change in
input voltage or load, the error signal will be increased, therefore the duty cycle will
decrease. As a result less power will be transferred from the input to output, and output
voltage start to decrease until it reaches to the set value.

When the output voltage decreases below the set value either due to change in input voltage
or load then error signal will be decreased which will increase the duty cycle. As a result,
142 An Update on Power Quality

more power will be transferred from the input to output, and output voltage start to
increase until it reaches to the set value.

When the output voltage is same as the set value than the negative and positive input of the
error amplifier will be same as a result the duty cycle will remain same and output voltage
will remain unchanged. In this way the proposed regulator will maintain output voltage
constant, irrespective of the variation of input voltage and load.
16
3 S2
U1
20Vdc V1 R1 R15 U3 R8
0
VREF
OSC

50k 15 A4N25A
0 C1 VIN V3
R14 4000pf 7 12 6
0 6 CT C_A 11 15V
RT E_A 2
1
2 ERR- 13 0 R6
ERR+ C_B 14 0
E_B G2
R4 4
CL+ V2
COM P

5 R5
SHUT
GND

1 CL- 10Vdc U2A

6 U4 S1
R16
3 2 2 A4N25A
0 0 0 V4
10

0 R20
8

0 R9
0 15V
SG1524B 50k CD4009A
C2 R7
.001u 0
G1
0

11
0 -
2

V-
R18
1 LM324
OUT U5A
3

V+
R19 +
V7

4
0 20V
R10
L1 D1 D3 L2 0
1
30mH 30mH
0.1u
D9
D5 D6 C7
S1 C6 G2 S2
V5
Z1 Z3 TX1 100
0.1u R11
G1 C4 R3
FREQ = 50 5u
0.001
VAMPL = 300 R13
R12 D4 C5 D10 1 0.3u
D2 0.001 10u R17
C9
D7 0.1u D8
C3 C8 4000k

5u

0 0

Figure 29. Automatic controlled AC voltage regulator circuit with practical switches.

4.2. Results of automatic controlled AC voltage regulator

Figure 30 shows the input and output voltage waveforms of the proposed automatic
controlled AC voltage regulator when the input voltage is 250V and output voltage is 300V.
Figure 31 shows the input and output voltage waveforms of the proposed regulator when
the input voltage is 350V and output voltage is 300V. Figure 32 and Fig. 33 shows the
 Power Quality Improvement Using Switch Mode Regulator 143

waveforms of the input current and output currents corresponding to the waveforms of Fig.
30 and Fig. 31 for a load of 100 Ω.

400V

0V

-400V
V(R14:2)
400V

0V

SEL>>
-400V
0s 100ms 200ms 300ms 400ms 500ms 600ms
V1(V5)
Time
Figure 30. Input and output voltage waveforms for input 250V and output 300V. V1(V5): Input voltage-
bottom figure, V(R14:2): Output voltage – top figure.

500V

0V

SEL>>
-500V
V(R14:2)
400V

0V

-400V
0s 100ms 200ms 300ms 400ms 500ms 600ms
V1(V5)
Time
Figure 31. Input and output voltage waveforms for input 350V and output 300V. V1(V5): Input voltage-
bottom figure, V(R14:2): Output voltage – top figure.

Table 1 summarizes the result of the proposed regulator to regulate output voltage to 300V
for variation of input voltage from 200V to 350V and load from 100 ohm to 200 ohm. In this
144 An Update on Power Quality

table input current, output current, input power factor, and efficiency of the regulator are
also provided. The proposed regulator can regulate the output voltage effectively, for a
wide variation of input voltage and load with efficiency of more than 90% and input power
factor more than 0.9.

4.0A

0A

SEL>>
-4.0A
-I(R14)
5.0A

0A

-5.0A
0s 100ms 200ms 300ms 400ms 500ms 600ms
-I(V5)
Time
Figure 32. Input and output current waveforms for input 250V output 300V. -I(V5): Input current –
bottom figure, -I(R14): Output current – top figure.

5.0A

0A

SEL>>
-5.0A
-I(R14)

5.0A

0A

-5.0A

0s 100ms 200ms 300ms 400ms 500ms 600ms

-I(V5)
Time
Figure 33. Input and output current waveforms for input 350V output 300V. -I(V5): Input current –
bottom figure, -I(R14): Output current – top figure.
 Power Quality Improvement Using Switch Mode Regulator 145

Vin I in Input pf Pin Vout (V) Load Iout Pout Efficiency

(V) (A) (W) (Ω) (A) (W) (%)
200 4.81 1.00 481 295 100 2.95 435.13 90.46
225 4.30 1.00 483.09 298 100 2.98 444.02 91.91
250 3.92 1.00 489.70 300 100 3.00 450.00 91.89
275 3.60 1.00 495.00 300 100 3.00 450.00 90.91
300 3.30 1.00 493.79 300 100 3.00 450.00 91.13
325 3.10 0.99 498.85 302 100 3.02 456.02 91.41
350 2.95 0.98 508.41 305 100 3.05 465.13 91.49
250 2.07 0.96 248.73 300 200 1.50 225.00 90.46
275 1.90 0.95 248.46 300 200 1.50 225.00 90.56
300 1.75 0.95 248.20 300 200 1.50 225.00 90.65
325 1.68 0.93 253.12 302 200 1.51 228.01 90.08
350 1.60 0.91 253.77 305 200 1.53 232.56 91.64
*All voltages and currents values in this table are in peak values.

Table 1. Results of proposed automatic controlled AC voltage regulator for maintaining output 300 V.

5. Conclusion
An essential feature of efficient electronic power processing is the use of semiconductors
devices in switch mode to control the transfer of energy from source to load through the use
of pulse width modulation techniques. Inductive and capacitive energy storage elements are
used to smooth the flow of energy while keeping losses at a lower level. As the frequency of
the switching increases, the size of the capacitive and inductive elements decreases in a
direct proportion. Because of the superior performance, the SMPS are replacing
conventional linear power supplies.

In this chapter the design and analysis of an AC voltage regulator operated in switch mode
is described in details. AC voltage regulator is used to maintain output voltage constant
either for an input voltage variation or load variation to improve the power quality. If the
output voltage remains constant, equipment life time increases and outages and
maintenance are reduced.
At first the regulator is analyzed using ideal switches, then the ideal switches is replaced by
practical switches which required isolated gate signal. The procedure of smoothing the
input current and output voltage, and suppressing the surge voltage across the switches is
described. A manually controlled AC voltage regulator is analyzed then the concept of
operation of an automatic controlled AC voltage regulator is described. Finally an automatic
controlled AC voltage regulator is designed and its performance is analyzed.
The proposed regulator can maintain the output voltage constant to 300V, when input
voltage is vary from 200V to 350V also for variation of load. To maintain constant output
voltage PWM control is used. By varying the duty cycle of the control circuit have achieved
the goal of maintaining the constant output voltage across load. For generation of gate
146 An Update on Power Quality

signal of the switches an IC chip SG1524B is used which is compact and commercially
available at a very low cost. The input current of the proposed regulator is sinusoidal and
the input power factor is above 0.9. From simulation results it is seen that the efficiency of
the proposed regulator is more than 90%.

Author details
Raju Ahmed
Electrical and Electronic Engineering Department, Dhaka University of Engineering and Technology
(DUET), Gazipur, Bangladesh

Mohammad Jahangir Alam

Electrical and Electronic Engineering Department, Bangladesh University of Engineering and
Technology (BUET), Dhaka, Bangladesh

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 Edited by Dylan Dah-Chuan Lu

Power quality is an important measure of fitness of electricity networks. With

increasing renewable energy generations and usage of power electronics converters,
it is important to investigate how these developments will have an impact to existing
and future electricity networks. This book hence provides readers with an update of
power quality issues in all sections of the network, namely, generation, transmission,
distribution and end user, and discusses some practical solutions.

ISBN 978-953-51-6327-5
978-953-51-1079-8

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