International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.

51 (2015)
© Research India Publications; httpwww.ripublication.comijaer.htm

IMPLEMENTATION OF UPQC TOPOLOGY IN

DISTRIBUTION SYSTEM TO REDUCE PQ ISSUES
V. Vedhavalli*, M. Kavitha**, K. Krishnaram*** and A. Ragavendiran****.
*PG Scholar, Dr. S.J.S. Paul Memorial College of Engineering and Technology, Puducherry.
**Assistant Professor, Dr. S.J.S. Paul Memorial College of Engineering and Technology, Puducherry.
*** Assistant Professor, EGS Pillay Engineering College, Nagapattinam
****Assistant Professor, A.V.C college of Engineering, Mayiladuthurai, Tamilnadu. raga_as@yahoo.co.in

Abstract— In advancement of power electronics and digital known as UPQC and have been analyzed in this work.
control technology the proliferation of the power electronics UPQC was presented during 1998. Such solution can
devices, nonlinear loads and unbalanced loads have degraded compensate for different power quality phenomena, such as
the power quality (PQ) in the power distribution network. sags, swells, voltage imbalance, flicker, harmonics and
Custom power devices have been proposed for enhancing the reactive currents. UPQC usually consists of two voltage-
quality and reliability of electrical power.
source converters sharing the same capacitive DC link. One
The unified power quality conditioner (UPQC) is a of the converters is an active rectifier or shunt active filter
custom power device, which mitigates voltage and current-
while other is a series active filter. Also, at the point of the
related PQ issues in the power distribution systems. In this
work, the performance investigation of UPQC with harmonic load connection, passive filter banks are connected. In
source has to be analyzed. UPQC the series active power filter eliminates supply
UPQC is a combination of shunt and series active voltage flicker/imbalance from the load terminal voltage
filters, which helps to match the dc-link capacitor voltage and forces an existing shunt passive filter to absorb all the
need for both filters. The topology uses a capacitor in series current harmonics produced by a nonlinear load. The shunt
with the interfacing inductor of the shunt active filter, and active filter performs dc link voltage regulation, thus
the system neutral is connected to the negative terminal of leading to a significant reduction of capacity of dc link
the dc-link voltage to avoid the requirement of the fourth leg capacitor.[1-8]
in the voltage source inverter (VSI) of the shunt active filter.
The average switching frequency of the switches in the VSI II POWER QUALITY PROBLEMS OVERCOME BY
also reduces. Consequently the switching losses in the USING CUSTOM POWER DEVICES
inverters reduce. The main merits of UPQC are harmonic In a custom power system customer receives
elimination and simultaneous compensation of voltage and
specified power quality from a utility or a service provider
current, which improves the power quality offered for other
harmonic sensitive loads. or at-the-fence equipment installed by the customer in
coordination with the utility, which includes an acceptable
The performance of UPQC of different controller at
different operating conditions will be analyzed using combination of the following features.
Matlab/Simulink Platform. It will be analyzed that the No (or rare) power interruptions
modified topology has less average switching frequency, less ¾ Magnitude and duration of voltage reductions
THDs in the source currents, and load voltages with reduced within specified limits.
dc-link voltage as compared to the various controller. ¾ Low harmonic voltage.
Index Terms—Power Quality Problems, Custom Power ¾ Low phase unbalance.
Devices, Controllers, THD Values. In the several processes such as semiconductor
I INTRODUCTION manufacturing or food processing plants, a batch of
In recent years active methods for power quality product can be ruined by a voltage dip of very short
control have become more attractive compared with duration. Even short dips are sufficient to cause contactors
passive ones due to their fast response, smaller size, and on motor drives to drop out. There are other loads which
higher performance. For example, Static VAR are very sensitive such as hospitals, processing plants, air
Compensator (SVC) have been reported to improve the traffic control and numerous other data processing and
power factor are Power Factor Corrector (PFC) and service providers that require clean and uninterrupted
Active Power Filters (APF) have the ability of current power. Thus in this scenario in which customers
harmonics suppression and power factor correction, some increasingly demand power quality, the term power
active circuits were developed to compensate unbalanced quality attains increased significance. They are
currents as well as limit the neutral current. In general,
parallel-connected converters have the ability to improve
the current quality while the series-connected regulators
inserted between the load and the supply, improve the
voltage quality. For voltage and current quality control,
both series and shunt converters are necessary, which is

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1. SOLID STATE FAULT CURRENT LIMITER The SSTS provides continuous high-quality power
supply to sensitive loads by transferring, within a time scale
of milliseconds, the load from a faulted bus to a healthy
one. The basic configuration of this device consists of two
three-phase solid-state switches, one for the main feeder
another for the backup feeder. These switches have an
arrangement of back-to-back connected thyristors, as
illustrated in the schematic diagram of Figure 2.
Each time a fault condition is detected in the main
feeder, the control system swaps the firing signals to the
thyristors in both switches, i.e., Switch 1 in the main feeder
Figure 1 Solid state current limiter is deactivated and Switch 2 in the backup feeder is
activated. The control system measures the peak value of
Solid State Fault Current Limiter (SSFCL) which the voltage waveform at every half cycle and checks
consists two circuit branches with one branch connected whether or not it is within a pre specified range. If it is
to the solid state switch comprising of only two thyristor outside limits, an abnormal condition is detected and the
connected in inversely parallel manner and the other firing signals to the thyristors are changed to transfer the
branch, consists of two thyristor connected in inversely load to the healthy feeder.
parallel but with current limiting impedance The success of the SSTS is mainly due to its rather low
(reactor)connected in series with it. The first branch (with cost compared with other solutions. A requirement is that a
thyristor switch only) acts as a main circuit breaker and is secondary in-feed, independent from the main source (e.g. a
used to clear the fault when it occurs. The first branch is feeder to another substation), must be available. Therefore,
normally closed and conducts current during normal this solution is particularly attractive for installations that
operation. Nevertheless, when the magnitude of the already have mechanical transfer systems, where upgrading
current exceeds a pre-set level, the switches one will open to a static system does not require major changes in the
the circuit instantly interrupts the current flow. layout of the distribution system. Formerly available only
The switches from the other branches (with thyristor for low voltages, SSTS systems are now advertised for
and current limiting reactor in series) are normally open higher voltages and load ratings, which make them suitable
and have no continuously current rating during normal for high-power industrial applications. Transfer-time
condition. Its function is to conduct fault current to estimation of a SSTS is not a straightforward process due to
facilitate operation of the conventional protective device its dependence on commutation between the thyristor
on the load side of the SSFCL.[5] switches in each phase. The commutation is determined by
Parallel fault current limiters are activated only at the the system parameters and the component characteristics.
moment of fault and have the following functions: To offer ride-through capability, the load must be
transferred within the shortest possible time.
¾ Limit the peak fault current.
¾ Decrease the motors feeding into the fault. 3. DISTRIBUTION STATCOM
¾ Shunt the consumer switches while
disconnecting. The purpose of the Distribution Static Compensator
(DSTATCOM) is to cancel load harmonics fed to the
2. SOLID STATE TRANSFER SWITCH supply. The coupling of DSTATCOM is three phase, in
parallel to network and load. It work as current sources,
connected in parallel with the nonlinear load, generating the
harmonic currents the load requires also balance them in
addition to providing reactive power. In order to
compensate undesirable components of the load current the
DSTATCOM injects currents into the point of common
coupling. With an appropriated control strategy, it is also
possible to correct power factor and unbalanced loads. This
principle is applicable to any type of load considered a
harmonic source [9-12].
Their advantage is that carries the compensation current
and a small amount of active fundamental current supplied
to compensate for system losses. Shunt Active Power Filter
in current control mode is also called as DSTATCOM has
shown in Figure 3.
Figure 2 Solid state transfer switch

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5. UNIFIED POWER QUALITY CONDITIONER

The best protection for sensitive loads from sources

with inadequate quality, is shunt-series connection i.e.
unified power quality conditioner. Recent research efforts
have been made towards utilizing unified power quality
conditioner to solve almost all power quality problems for
example voltage sag, voltage swell, voltage outage and over
correction of power factor and unacceptable levels of
harmonics in the current and voltage The basic configuration
of UPQC is shown in Figure 5.
Figure 3 Distribution STATCOM
The main purpose of a UPQC is to compensate for
Disadvantages: supply voltage flicker/imbalance, reactive power, negative-
sequence current, and harmonics. In other words, the UPQC
¾ Needs separate isolated dc sources for real power has the capability of improving power quality at the point of
installation on power distribution systems or industrial
transfer.
power systems. The UPQC, therefore, is expected as one of
¾ No common DC-bus the most powerful solutions to large capacity sensitive loads
4. DYNAMIC VOLTAGE RESTORER to voltage flicker/imbalance [15].

Dynamic Voltage Restorer (DVR) injects a Unified Power Quality Conditioner for non-linear and a
voltage component in series with the supply voltage, thus voltage sensitive load has following facilities:
compensating voltage sags and swells on the load side has ¾ It eliminates the harmonics in the supply current, thus
shown in Figure 4. Control response is on the order of improves utility current quality for nonlinear loads.
3msec, ensuring a secure voltage supply under transient ¾ It provides the VAR requirement of the load, so that
network conditions. Voltage injection of arbitrary phase the supply voltage and current are always in phase,
with respect to the load current implies active power therefore, no additional power factor correction
transfer capability. This active power is transferred via the equipment is necessary.
dc link, and is supplied either by a diode bridge connected ¾ It maintains load end voltage at the rated value even in
to the ac network, a shunt connected PWM converter or by the presence of supply voltage sag.
an energy storage device. It works as a harmonic isolator ¾ The voltage injected by UPQC to maintain the load
to prevent the harmonics in the source voltage reaching the end voltage at the desired value is taken from the same
load in addition to balancing the voltages and providing dc link, thus no additional dc link voltage support is
voltage regulation [13-14]. required for the series compensator.
The UPQC consists of two three phase inverters connected
in cascade in such a manner that series APF is connected in
series with the supply voltage through a transformer and
shunt APF is connected in parallel with the load. The shunt
compensator is used for the compensation of reactive power
demanded by the load, harmonic elimination and common
DC link voltage regulation. The series compensator is
operated in PWM voltage controlled mode. It injects voltage
in quadrature advance to the supply voltage (current) such
that the load end voltage is always maintained at the desired
value. The two inverters operate in a coordinated manner.
Here the shunt active filter acts as DSTATCOM and series
active filter acts as DVR and Both the filters combined are
Figure 4 Dynamic Voltage Regulator
called as UPQC.
The only Disadvantage of DVR is incapability to mitigate
interruptions.

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m=1.58=1.6

Line Voltage =140V.Based on this, the shunt

interfacing inductance has been derived taking into
consideration of the maximum switching frequency and is

given

Figure 5 Unified Power Quality Conditioner

=28mH
Therefore three principle elements to the custom power
concepts are The dc-link capacitor value is given by,
¾ The Dynamic Voltage Restorer, it provides series
compensation by voltage injection for power system
sag and swell.
¾ The Distribution Static Compensator, it provides
continuously variable shunt compensation by current F
injection for eliminating voltage fluctuations and
obtaining correct power factor in three-phase
systems. An ideal application of it is to prevent The DVR voltage and the current of the capacitor are given
disturbing loads from polluting the rest of the by
distribution system.
¾ UPQC which provide series and shunt compensation
i.e. inject voltage in sag and swell condition and
inject current for elimination of voltage fluctuations,
correct the power factor, and to avoid pollution to
rest of the distribution system. Where,
The proper selection of necessary custom power strategies
in addition to accurate system modeling and appropriate
protection devices will increase the power quality.[16-21]
=140V
III DESIGN OF UPQC
=400V
Let us assume X as 5 KVA, by an empirical study

inductance values varies = m .The approximate =1Ω

relationship between m, minimum , and maximum

switching frequency is obtained by analysis of =1

the VSI
The interfacing inductor has been designed based on the
switching frequency of the series active filter and is given by

=1.2mH

m=

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Therefore UPQC device designed in Matlab/Simulink In power system without UPQC device has been designed
2010a based on design parameters. and simulated using MATLAB 2010a. The Effective
comparative study on with and without using UPQC Device
has been designed and presented as follows.

Figure 5 Power System without UPQC Device

IV SIMULATION RESULTS
The Simulink model for power system UPQC has been In the above circuit without using UPQC Device the power
simulated by using Matlab2010a. Table gives the simulation quality problems occurred, further by using series active
filter and shunt active filters it is used to maintain balanced
parameters in detail. and distortion free nominal voltage.
SPECIFICATIONS The Simulink Diagram is shown in Figure 6 and its
System Voltages =420v Corresponding output Voltage, Current Without UPQC
Device waveform are shown in Figure 7
=400v
f =50Hz
R=0.001Ω
L=1X
Feeder Impedance =1+j3.141Ω
Linear Transformer =0.002Ω
=0.002Ω
=0.008H
f =50Hz
DC Link Capacitor C=2200µF
Balanced Load R=10Ω
Unbalanced Load =2
=4
=6
Series VSI Parameter =1µF
=1.2
Shunt VSI Parameter =1µF Figure 7 Output waveform without using UPQC Device
=0.1
PI Controller of Series and
Shunt The Power system without UPQC Device has been simulated
=1
and load voltage, load current obtained has been shown in
Figure 1.1
I. POWER SYSTEM WITHOUT UPQC DEVICE

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1.1 THD VALUE WITHOUT UPQC 2.1 CONTROLLER OF THE SERIES ACTIVE
DEVICE FILTERS

The Controller Circuit of the Series Active

Filters has shown in Figure 10.

Figure 8 THD Value without UPQC Device

Figure 10 Controller Circuit of Series Active Filter

Total Harmonic Distortion (THD) obtained from
the power system without UPQC device is 30.27% as Once the reference quantities and the actual quantities are
shown in Figure 8. obtained from the measurements, the switching commands
for the VSI switches are generated using hysteresis band
current control method. The above control method for Series
II. POWER SYSTEM USING SERIES ACTIVE
active filters shown in Figure 5.5 here by using series active
FILTERS
filters it compensates the voltage.
The Simulink model for the Power System using Series
Active Filter has been simulated by using Matlab2010a. 2.2 HYSTERESIS CONTROLLER

The Hysteresis Controller Circuit of the Series Active Filters

as shown in Figure 11.

Figure 9 Power System using Series Active Filters

The Power system with series active filter has been

simulated. It is used to maintain balanced and distortion Figure 11 Hysteresis Controller Circuit Using Series
free nominal voltage at the Load are shown in Figure 9. Active Filters

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Hysteresis current controller scheme is based on a The Power system using Series active filters has been
feedback loop, generally with two-level comparators. The simulated and load voltage, load current obtained has been
switching commands are issued whenever the error limit shown in Figure 2.4
exceeds a specified tolerance band “±h” .The Power
system using series active filters with hysteresis controller 2.5 THD VALUE USING SERIES ACTIVE FILTERS
has been designed.

2.3 INVERTER CIRCUIT USING SERIES ACTIVE

FILTERS

Figure 13 THD Value of Series Active Filters

Total Harmonic Distortion obtained from the power system

Figure 12 Inverter Circuit Using Series Active Filters without UPQC device is 29.12% as shown in Figure 13.

In the three phase inverter SCR conducts for 180 of a III. POWER SYSTEM USING SHUNTACTIVE
cycle. Thyristor pair in each arm are turned on with the FILTERS
The Simulink model for power system Shunt Active Filter is
time interval of 180 .Series active filter using inverter
simulated by using Matlab2010a.
circuit shown in Figure 12

2.4 OUTPUTWAVEFORM OF POWER SYSTEM

USING SERIES ACTIVE FILTERS

Figure 14 Power System Using Shunt Active Filters

The shunt part of the UPQC is known as Distribution static

Figure 2.4 Output waveform of Power System using compensator .It is used to compensate load reactive power,
Series Active Filters harmonics and balance the load current thereby making

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source current balanced and distortion free with unity Total Harmonic Distortion obtained from the power system
power factor. The Shunt active filter as shown in Figure 14 without UPQC device is 7.84% as shown in Figure 16.

3.1 CONTROLLER OF SHUNT ACTIVE FILTERS

IV. POWER SYSTEM USING UPQC DEVICE
The Controller Circuit of Power System using The Simulink model for the Power System using UPQC
shunt active filters Figure 15. Device has been simulated by using Matlab 2010a.

Figure 17 Power Systems Using UPQC Device

UPQC which consists of two inverters connected back-to-

back and deals with both load current and supply voltage
Figure 15 Controller Circuit of Shunt Active Circuit
imperfections. UPQC can simultaneously act as shunt and
Once the reference quantities and the actual quantities are series active power filters. It uses balanced load with bridge
obtained from the measurements, the switching commands rectifier and unbalanced load with R load.
for the VSI switches are generated using hysteresis band
The Power system using UPQC device has been simulated. It
current control method. The above control method for
is used to maintain balanced and distortion free nominal
Shunt active filters shown in Figure 3.1 here by using
voltage at the Load are shown in Figure 17.
shunt active filters it compensates the current.
4.1 UNBALANCED LOAD VOLTAGE AND CURRENT
3.2 THD VALUE USING SHUNT ACTIVE FILTERS
The Simulink using the Power System of UPQC device
shows unbalanced Load voltage and Current.

Figure 16 THD Value of Shunt Active Filter

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Figure 20 Input Wave form of UPQC Device

Figure 18 Unbalanced Load Voltage and Current
The Power system using UPQC Device shows the
The Power system using UPQC Device shows unbalanced line current, DC voltage and shunt active filter current as
load voltage and load current of the UPQC device with shown in Figure 20.
input voltage 400V as shown in Figure 18.
4.4 OUTPUT WAVEFORM OF POWER SYSTEM
4.2 BALANCED LOAD VOLTAGE AND CURRENT USING UPQC DEVICE
The Simulink using the Power System of UPQC Device The Simulink using the Power System of UPQC device
shows Balanced Load voltage and Current. shows Output Waveform of UPQC Device.

Figure 19 Balanced Load Voltage of Power System

Using UPQC Device

The Power system using UPQC Device shows balanced

load voltage and load current of the UPQC device with
input voltage 400V as shown in Figure 19.
Figure 21 Output Waveform of UPQC Device
4.3 INPUT WAVEFORM OF UPQC DEVICE
The output waveform shows the voltage swell at source
The Simulink using the Power System of UPQC device current and voltage sag at load current of the UPQC device
shows Input Waveform of UPQC Device. in the power system. The load voltage shows the
interruptions occurred in the power system.

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4.5 THD VALUE OF POWER SYSTEM USING 5.1 THD VALUE USING FUZZY LOGIC
UPQC DEVICE CONTROLLER

Power System using UPQC Device has been simulated and The Power System using UPQC Device with Fuzzy Logic
the THD is obtained as 7.16 %. Controller the Total Harmonic Distortion is 5.85 %.

Figure 22 THD Value of UPQC Device Figure 24 THD Value of UPQC Device with Fuzzy Logic
Controller
From above Figure it shows that when compared to active
filters and without using the UPQC device in power When compared to UPQC Device with bridge rectifier in
system THD value is decreases and can be utilized in the power system THD value is decreases. Therefore by FLC
power system further by using FLC the THD value are analysis it is proved that harmonic problem and distortion
decreases. can be reduced it is shown in Figure 24.

V. POWER SYSTEM USING UPQC WITH FUZZY VI. POWER SYSTEM USING UPQC DEVICE WITH
LOGIC CONTROLLER CONVERTER BY USING FLC
The Simulink using Controller of UPQC Device has been The Simulink using Converter of UPQC Device with FLC in
simulated Matlab/Simulink 2010a. Figure 25.

Figure 25 UPQC Device with Converter using FLC

Figure 23 Controller of UPQC Device using Fuzzy
Logic Controller UPQC can simultaneously act as shunt and series active
power filters. It uses balanced load with converter with using
The Power system using UPQC Device with controller FLC Controller.
using Fuzzy Logic Controller as shown in Figure 23.

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6.1 POWER SYSTEM USING UPQC DEVICE Shunt active filter 7.84%
WITH CONVERTER BY USING FLC
UPQC device with 7.16%
Bridge Rectifier

UPQC with Fuzzy logic 5.85%

Controller

UPQC with FLC using 4.90%

Converter

Figure 26 UPQC Device with Converter using FLC. V CONCLUSION

The power system using UPQC Device with converter by The topology uses a capacitor in series with the interfacing
using FLC as shown in Figure 26. inductor of the shunt active filter, and the system neutral is
connected to the negative terminal of the dc-link voltage to
6.2 THD VALUE USING FUZZY LOGIC avoid the requirement of the fourth leg in the voltage
CONTROLLER USING CONVERTER source inverter (VSI) of the shunt active filter. The
average switching frequency of the switches in the VSI
The Power System using UPQC Device with Converter
also reduces. Consequently the switching losses in the
using Fuzzy Logic Controller the THD is 4.90 %.
inverters reduce. The Main Merits of UPQC are harmonic
elimination and simultaneous compensation of voltage and
current, which improves the power quality offered for
other harmonic sensitive loads

The Performance of UPQC of different Controller at

Different operating conditions are analyzed using
Matlab/Simulink Model. It had been analyzed that the
modified UPQC topology has less THD value in Load
Voltage with reduced dc-link voltage as compared with
Series and Shunt Active Filter.

VI REFERENCES

[1] Alexis Polycarpou Frederick University Cyprus

Figure 27 THD Value of UPQC Device with Converter
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[2] S.Khalid & Bharti Dwivedi Department of Electrical
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[3] Victor Fabián Corasaniti, Member, IEEE, Maria
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Liliana Arnera, Senior Member, IEEE, and María
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