A HIGH POWER DENSITY ZERO-VOLTAGE-SWITCHING TOTEM-POLE POWER

FACTOR CORRECTION CONVERTER

The power factor correction (PFC) circuit is an essential component in high-power supplies
with nonlinear loads, occupying nearly half the size of a typical power supply. To minimize the size
of passive components in PFC converters, the switching frequency must be increased to several
hundred kHz, a challenge even when employing gallium nitride (GaN) devices under hard-switching
conditions. This project proposes a new GaN-based totem-pole (TP) PFC converter integrated with a
bidirectional soft switching cell. Unlike critical-conduction-mode TP PFC circuit, the proposed
converter operates in continuous-conduction-mode with simple control. Design considerations and
optimization of soft-switching cell are discussed and verified with simulations. As a proof of
concept, a two-phase interleaved version of the proposed converter rated at 3700Whas been
designed. The designed prototype achieves a peak efficiency of 99.14% and surpasses the hard
switched GaN-based TP PFC converters in both power density and cost.

1
 CHAPTER-1

INTRODUCTION:

The applications of power electronics have steadily grown over the past decade in industries, such as
the automotive sector, communication/server infrastructure, and energy management systems. Due
to higher electrification in these industries and advances in semiconductor technology, the power
density and efficiency expectations of power converters have increased tremendously. As front-end
power factor correction (PFC) circuits are common across high-power converters, it has always been
of interest to shrink the size and improve the efficiency of this stage [1], [2], [3], [4], [5]. When
efficiency for high-power applications is a concern, bridge-less PFC topologies are preferred over
diode-bridge PFC converters. The basic and highly efficient PFC converter is the bridge-less boost
PFC converter presented in [6]. To reduce electromagnetic interference (EMI) and current stress on
the inductors, clamping diodes are added between the negative rail and the ac line [7], [8]. Even
though the efficiency is higher, the number of components compromises its power density.

The introduction of wide-bandgap devices, such as gallium nitride (GaN)-based power devices, has
paved the way for simplified power architectures. The system-level cost and power density
advantages brought by GaN devices have been observed and proven in hard-switching half-bridge
power stages [9], [10], [11], [12], [13]. This has led designers to move from classical diode-bridge
based or semibridgeless topologies to totem-pole (TP) PFC circuits [14], [15].With the absence of a
P-N junction from source to drain in GaN power devices, both the switching losses and conduction
losses can be reduced with synchronous switching, allowing for high efficiency and a compact
converter size. The continuous-conduction-mode (CCM) control in TP PFCs is very similar to that in
conventional PFCs, with the exception of the necessary soft-start scheme at near zero-crossings due
to the large parasitic capacitance of line frequency FETs or diodes. To further reduce the size of
passive components, it is necessary to increase the switching frequency. While the PFC boost
inductance size decreases with higher switching frequency, the input current ripple frequency must
exceed 400 kHz to achieve a smaller differential-mode (DM) filter volume than that obtained at 135
kHz, considering that EMI standards begin at 150 kHz for conducted emission. However, operating
a hard-switched half-bridge leg with 600V FETs at such frequencies is infeasible even with GaN

2
devices due to thermal constraints. To increase the input current ripple frequency, a multiphase
critical-conduction-mode (CrM) TP PFC converter has been proposed and extensively studied in
[16] and [17]. The zero-voltage-switching (ZVS) feature allows for increasing the switching
frequency, and the input current ripple frequency can be multiplied with the number of interleaving
legs. Nonetheless, this topology poses significant challenges. For high output power, many
interleaving legs are needed since the peak currents in inductors reach twice the average input
current.

Due to the energy crisis and the environmental pollution caused by the consumption of fossil fuel,
the development of renewable energy generation has been an increasingly critical topic. Since
renewable energies have the intrinsic intermittence and fluctuation, in order to improve the reliability
and the quality of power supply, Nano-grids have been proposed to facilitate the connection of
renewable power sources to the traditional AC power system. On the one hand, now most renewable
power conversion systems are connected into AC Nano-grids. On the other hand, more and more
loads show DC characteristics for example, the variable frequency drives, the LED lighting
applications, the computer power supplies and the data centers which constitute a significant portion
of the energy consuming loads. If the renewable energies can be directly utilized via the DC Nano-
grids, the total energy efficiency will be obviously improved. Therefore, the researches on the DC
Nano-grids are drawing more and more attention especially for the control of AC/DC topologies
which interface with the DC Nano-grid and the traditional AC power systems.
In addition to a high output voltage regulation, high power factor correction and low input-current
harmonics are becoming mandatory design criteria for the switching power supplies. The buck,
boost and buck boost converters can be used as active power factor corrector and they change the
wave shape of current drawn by a load to improve the power factor. Basic configurations of
converters for achieving power factor correction and voltage regulations were described. The boost
dc-dc converter, due to its smooth continuous input current, high efficiency and relative simplicity,
became designer’s choice as a PFC power stage. The major drawback is that it can neither limit the
input inrush current nor provide output short circuit protection. Power factor correction circuits for
single phase and low power applications can be derived using single stage approach and two stage
approach. The single stage topologies are cost effective and can provide high PFC and fast output
voltage regulation compared to two stage topologies

3
Interleaved boost converter require complicated control method for soft switching performance.
Some applications, especially battery oriented equipment, require high voltage boosting. The tapped
inductor boost converter can provide a comparable voltage step up. Improved current doublers
rectifier suggested in requires a transformer with high turns ratio for high step down voltage
conversions. High step up dc-dc converters can be used for renewable energy applications. A
bridgeless buck-boost converter was introduced. Buck-boost converters with two independently
controlled switches can provide lower stresses on the components. Coupled inductors can be
introduced into the converters to obtain wide dc-dc conversion range. A tapped inductor buck
converter with soft switching was introduced. Buck-boost converters are widely used for universal-
input PFC applications. The integrated buck boost- quadratic buck converter can be used for extreme
low output dc voltage applications. However the circuit is more complex and requires increased
number of components. Tapped inductor buck converter introduced in have wide step-down
conversion ratio. Boost converter with tapped inductor can provide wide step-up conversion ratio.
The WIWO converter is an integration of buck and boost converters via coupled inductor. By
replacing the inductor with coupled inductors, the WIWO converter not only retains the functions of
both buck and boost converters, but also extends the conversion range. Therefore, wide-step-up and
wide-step-down dc-dc conversions can be achieved
In electromagnetic systems, only the magnetic energy is likely to be stored in enough density to be
converted into another form of energy, in large quantities. Thus, in such system, the magnetic circuit
is the central element of the converter as it assumes the storage and the transformation. The coils can
serve as a controlled switch in the context of the magnetic regulation. This one is a method of
regulating a power electronics converter that uses the properties of saturable inductors. In fact, an
inductance in its linear functioning zone B(H) which is a relation between flux density and the
magnetic field, its generally used so that it doesn't change its value, which is particularly important
for maintaining fixed cutoff frequency of a filter. Coils have an essential impact in different
applications. They are used as electric current transformers to transform high current values in the
kilo-ampere range to low ones or contrary. They are also inserted in power electrical network as
galvanic isolation transformers. We can also found coils used to transform a neutral system, in which
the transformer neutral and the materials masses are common and connected to the ground, into
isolated ground systems for supplying loads and apparatus sensitive to disturbances. Another
important family of applications for coils is their used for various functions consisting to eliminate
parasites of analog signals providing from power generators, thus playing the role of impedance. In
4
environmental application, they are also used in magnetic and electronic ballasts for discharge lamp
lighting i.e. the fluorescent lamps, metal halide lamps, etc.

The majority of current light systems are using high brightness light-emitting diodes (LEDs) as the
light source. That is owing to many reasons that include their longer lifetime, higher energy savings,
smaller form factors, as well as higher quality and durability compared to other technologies. The
complete system comprises the electrical part (light engine), the mechanical part (luminaire), and the
optical part (reflector and lens). The bottleneck for the size, weight, and cost reduction, as well as
higher reliability and efficiency, is the light engine. It consists of an LED module (the LED array
and the substrate material it is mounted on) and a driver (electrical engine). While the LED module
is responsible for the limit in energy efficacy

Fig. 1. Conventional LED driver structure

The conventional solution for LED driver systems, which is comprised of a two-stage converter
structure. The ac mains are first interfaced with a power factor correction (PFC) converter that
rectifies the mains voltage and regulates the input current to satisfy the regulations on input current
displacement and harmonics set by international standards. A following dc-dc stage converts the
intermediate dc-bus voltage to the voltage and current levels that apply to the LED load electrical
characteristics. An energy-storage capacitor is inserted to filter the double-the-line 100/120 Hz
frequency component on the output side. Hard-switched pulse-width-modulated (PWM) converters
have been the primary candidate for both LED driver stages. They can provide high power factor
and efficiency with simple control methods. Prior art report solutions based on different topologies,
including buck, boost-flyback, buck boost-flyback, SEPIC-flyback, and flyback topologies.
However, in addition to the high conducted electromagnetic interference (EMI) from the rectangular
waveforms, they are typically designed to operate at low frequencies in the range of few hundred
kHz. That helps limit the switching losses, yet results in larger sizes for the passive converter
components. On the other hand, high-frequency designs (1 MHz and above) have less efficiency and
may incorporate a heat sink for thermal management, which counteracts the gain in power density.

5
Accordingly, soft-switching resonant converters have received increased attention in the recent
years. They incur substantially lower switching losses compared to their PWM counterparts. That
makes them a primary candidate for achieving high efficiencies at high frequencies, resulting in
reduced sizes for the passive components and, therefore, higher power densities. In addition, high-
frequency operation offers higher loop-gain bandwidths and faster transient responses. This has led
to the investigation of their adoption into the converter stages in different applications including the
ac-dc and the dc-dc stages. One of such applications is the LED driver, where there is a high demand
for small-size and compact solution for several applications, such as in-track LED drivers. Prior art
introduced different resonant LED driver structures, including resonant-SEPIC, class-E, class-E-
LLC, class-DE and LLC topologies. In addition, combined PWM-resonant solutions were reported,
such as the fly back-class-E, boost LLC and buck-boost-resonant converters. Nevertheless, the
reported solutions operate with relatively low switching frequencies and have limited power
densities. Accordingly, the potential of high-frequency resonant converters for high-power-density
LED driver applications can be further investigated.
Pulse-width-modulated (PWM) converters have been the primary candidate for the AC-DC stage in
offline converters, including buck, boost, buck-boost, fly back, and SEPIC converters. They can
provide high power factor and are easy to control. However, their operation is based on hard
switching. Accordingly, they typically operate at low frequencies in order to limit the switching
losses. This in turn results in large sizes for the passive components needed to store and process the
energy transferred to the load every switching cycle. On the other hand, high-frequency designs have
less efficiency and may incorporate a heat sink for thermal management, which counteracts the gain
in power density. Accordingly, soft-switching resonant converters have been receiving much
attention in the recent years. Resonant converters have substantially lower switching losses than their
PWM counterparts. Thanks to their zero-voltage-switching (ZVS) and/or zero-current-switching
(ZCS) characteristics, which make them a good candidate for achieving high efficiencies at high
frequencies. That in turn results in reduced sizes for the passive components, and thus higher power
densities, higher loop-gain bandwidths, and faster transient responses.

6
CHAPTER-2

LITERATURE SURVEY:

LITERATURE SURVEY
[1] Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques,
Topologies, and Applications, Mojtaba Forouzesh, YamP. Siwakoti, Saman A. Gorji, Frede
Blaabjerg, and Brad Lehman-2017
DC–DC converters with voltage boost capability are widely used in a large number of power
conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from
milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in
which fundamental energy storing elements and/or transformers in conjunction with switch (es) and
diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump),
voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each
has its own merits and demerits depending on application, in terms of cost, complexity, power
density, reliability, and efficiency. The permutations and combinations of the various voltage-
boosting techniques with additional components in a circuit allow for numerous new topologies and
configurations, which are often confusing and difficult to follow. Therefore, to present a clear
picture on the general law and framework of the development of next-generation step-up dc–dc
converters, this paper aims to comprehensively review and classify various step-up dc–dc converters
based on their characteristics and voltage-boosting techniques.
TECHNIQUES
 Voltage-boosting techniques

ADVANTAGES
 High reliability
 Low cost

DISADVANTAGES
 Higher complexity process
 Increase power density

7
[2] High Step-Up/Step-Down Soft-Switching Bidirectional DC-DC Converter with Coupled-
Inductor and Voltage Matching Control for Energy Storage Systems, Hongfei Wu, Kai Sun,
Liqun Chen, Lei Zhu, Yan Xing-2016
A soft-switching bidirectional DC-DC converter (BDC) with a coupled-inductor and a voltage
doublers cell is proposed for high step-up/step-down voltage conversion applications. A dual-active
half-bridge (DAHB) converter is integrated into a conventional buck-boost BDC to extend the
voltage gain dramatically and decrease switch voltage stresses effectively. The coupled inductor
operates not only as a filter inductor of the buck-boost BDC, but also as a transformer of the DAHB
converter. The input voltage of the DAHB converter is shared with the output of the buck-boost
BDC. So PWM control can be adapted to the buck-boost BDC to ensure that the voltage on the two
sides of the DAHB converter is always matched. As a result, the circulating current and conduction
losses can be lowered to improve efficiency. Phase-shift control is adapted to the DAHB converter to
regulate the power flows of the proposed BDC. Moreover, zero-voltage-switching is achieved for all
of the active switches to reduce the switching losses. The operational principles and characteristics
of the proposed BDC are presented in detail. A novel high step-up/step-down soft-switching BDC
with coupled-inductor and voltage matching control is proposed for energy storage applications. The
drawbacks of the conventional nonisolated buck-boost BDC and isolated BDCs are overcome while
the advantages of these BDCs are combined by integrating the buck-boost BDC and a dual-active
half-bridge (DAHB) BDC together.
TECHNIQUES
 Dual-active half-bridge (DAHB) converter

ADVANTAGES
 Improve efficiency
 Lower conduction losses

DISADVANTAGES
 Limited voltage conversion ratio
 Severe reverse-recovery problem

[3] Analysis and Simulation of a Novel Coupled Inductor Bidirectional DC-DC Converter,
Murilo Brunel da Rosa, Menaouar Berrehil El Kattel, Robson Mayer, Maicon Douglas
Possamai-2016

8
A novel bidirectional coupled inductor non-isolated DC-DC converter. It is relatively feasible for
low-input-voltage applications for interfacing energy storage elements, such as batteries, and ultra
capacitors with the high voltage DC bus in hybrid electric vehicles and electric vehicles. The
converter can operates as step-up or step-down voltage in both directions, as well, the turns ratio
confers a great voltage gain without using transformer, these give versatility and a lot of
applications. The use of coupled inductors usually presents practical limitations in its construction
which affect the operation of the converter, causing high voltage spike across the switches at their
turn-off by the leakage inductances, especially in applications where the input voltage is low and the
output voltage is high, this needs high turns ratio increasing the voltage stress in the semiconductors,
decreasing efficiency. To minimize this problem a dissipative snubber can be applied to reduce
losses and mitigate the voltage-spike across the devices, some authors use auxiliary capacitors and
switches to transfer the energy stored in the leakage inductance and provide soft switching. This
paper, aims to provide a basic analysis of the novel bidirectional DC-DC converter with coupled
inductor operating in continuous conduction mode (CCM) in first section, in second one a
mathematical analysis for both directions of the energy flow and a simulation, and comparison with
mathematics analysis in the third section.
TECHNIQUES
 Novel bidirectional coupled inductor non-isolated DC-DC converter

ADVANTAGES
 Maximize the efficiency
 Greater versatility

DISADVANTAGES
 Affect the operation of the converter
 Limit the construction process

[4] Analysis, modeling, and implementation of a new transformer less semi ‐quadratic Buck–
boost DC/DC converter, Sara Hasanpour, Ali Mostaan, Alfred Baghramian, Hamed Mojallali-
2019
In the proposed SQBuBoC, two power switches with simultaneous operation are used and a higher
step‐up/step‐down voltage conversion ratio is achieved compared with the traditional buck ‐boost,

9
Cuk, single‐ended primary‐inductor converter, and Zeta converters. The positive polarity of the
output voltage, along with low ripple continuous input current and common ground between the
source and the output voltages are some features that make the suggested topology more suitable for
many applications with wide range of output voltage such as photovoltaic systems. Moreover, the
total voltage stress across the power switches in this converter is lower than the cascade boost, and
the traditional buck‐boost converters led to power MOSFETs selection with lower drain ‐source ON
resistance (Rds) and efficiency improvement. In addition, to study the low frequency behavior of the
SQBuBoC by means of the state‐space averaging technique, the small and large signal models of this
converter in CCM are presented. A new configuration of nonisolated doubled ‐switch buck ‐boost
converter (SQBuBoC) is presented to solve the aforementioned drawbacks of the conventional buck‐
boost converters. Continuous input current with low ripple, semi‐quadratic high step ‐up and step ‐
down voltage conversion ratio with wide range of the output voltage, simple structure, noninverting
voltage conversion ratio, and common ground between the input and output voltages are substantial
merits of the proposed SQBuBoC
TECHNIQUES
 Transformer less semi‐quadratic buck‐boost converter (SQBuBoC)

ADVANTAGES
 High efficiency improvement
 Good performance

DISADVANTAGES
 Low ripple continuous input current
 Low power industrial application

[5] Quadratic Buck-Boost Converter with Zero Output-Voltage Ripple at a Selectable

Operating Point, J.C. Mayo-Maldonado, J.E. Valdez-Resendiz, P.M. Garcia-Vite, J.C. Rosas-
Caro-2018
A new DC-DC converter topology with the following features: (i) quadratic voltage gain, which
allows the converter to work over a wide voltage range with a minimal variation of duty cycle and
without the use of extreme duty cycles; (ii) output voltage ripple mitigation, which can be
accomplished with respect to a fixed but otherwise arbitrary duty cycle by proper selection of
components and switching signals. Since the proposed converter can be designed to have zero output

10
voltage ripple for the nominal gain (duty cycle), this allows the use of small values of capacitances.
Low output voltage ripple permits the use of small values of capacitances, which reduces the cost
and improve the dynamic performance of the converter. In despite of the natural variations on the
duty cycle during operation (to regulate the output voltage) and the tolerance on passive components
parameters, it is shown that the freedom to choose the duty cycle at which the voltage ripple is zero,
leads to a reduced voltage ripple in the full operation range. Besides the fact that high-gain and
ripple cancellation topologies are commonly studied separately a common shortcoming in
interleaved converters is the restriction of their operating point, i.e. the point at which the current-
ripple is perfectly cancelled out. This restriction implies that the duty cycle and consequently the
converter gain cannot be freely chosen, hence the current-ripple cancellation might be poor when the
converter is required to operate outside a closed region.
TECHNIQUES
 DC-DC converter topology

ADVANTAGES
 High duty cycle
 High gain and ripple cancellation

DISADVANTAGES
 Increase converter losses
 Increase voltage stress across devices

[6] A New Buck-Boost Converter with Low Voltage Stress and Reduced Conducting
Components, Hyo-Soo Son, Jae-Kuk Kim, Jae-Bum Lee, Sang-Su Moon, Ji-Hoon Park-2017
A new buck-boost converter presents unlike the single-switch buck-boost (SSBB) converter, the
proposed converter has low voltage stresses on semiconductors. Moreover, although both the
conventional two-switch buck-boost (TSBB) and the proposed converters have the same number of
passive and active components and the proposed converter can reduce the conduction loss as a result
of having fewer conducting components. Therefore, the proposed converter obtained a higher
efficiency than the TSBB converter. A 48 V output voltage and 150 W output power prototype was
fabricated to verify the effectiveness of the proposed converter. The proposed converter is composed
of a single inductor and two switches and diodes, the same as the TSBB converter. Moreover, the
proposed converter can operate in three different modes, the buck, boost, and buck-boost modes, and

11
it can control the switches independently. Moreover, the voltage stresses on the semiconductors of
the proposed converter can be lower than that of the SSBB converter. In addition, the proposed
converter can reduce the conducting components more than the TSBB converter in the buck and
buck-boost modes. As a result, the proposed converter has a higher efficiency than the TSBB
converter. Moreover, by operating in the buck or boost mode, the efficiency of the proposed
converter is higher than that of the SSBB converter.
TECHNIQUES
 Single-switch buck-boost (SSBB) converter

ADVANTAGES
 High duty ratio
 Regulate the output voltage

DISADVANTAGES
 Reduce the conduction loss
 High voltage stresses as the input voltage

[7] A Single-Switch Quadratic Buck-Boost Converter with Continuous Input Port Current and
Continuous Output Port Current, Neng Zhang, Guidong Zhang, Khay Wai See, Bo Zhang-
2017
A single-switch quadratic buck-boost converter with continuous input port current and continuous
output port current is proposed in this paper. Compared with the traditional buck-boost converter, the
proposed converter can obtain a wider range of the voltage conversion ratio with the same duty
cycle. Moreover, the proposed converter can operate with continuous input port current and
continuous output port current compared to the existing counterparts with inherently discontinuous
input port current and discontinuous output port current. The operating principle and steady-state
performance of the proposed converter under continuous inductor current mode is analyzed in detail.
Then, the comparison between the proposed converter and the existing quadratic buck-boost
converters has been conducted to demonstrate the unique features of the proposed one. Finally,
experimental results from a prototype built in the lab are recorded to verify the effectiveness and
validity of the proposed quadratic buck-boost converter. Meanwhile, similar as the traditional
quadratic buck-boost converter, the input port current and the output port current of this converter

12
are naturally discontinuous. Hence, it is of interest to develop novel quadratic buck-boost converters
with single switch and continuous input port current and continuous output port current.
TECHNIQUES
 Single-switch quadratic buck-boost converter

ADVANTAGES
 High effective process
 Good performance

DISADVANTAGES
 Complicate the design of the input and output filters
 It require a wide input-output voltage conversion

[8] A Novel Structure for Single Switch Non- Isolated Transformer less Buck-Boost dc-dc
Converter, Mohammad Reza Banaei, Hossein Ajdar Faeghi Bonab-2016
A novel transformer less buck-boost dc-dc converter is proposed in this paper. The presented
converter voltage gain is higher that of the conventional boost, buck boost, CUK, SEPIC and ZETA
converters and high voltage can be obtained with a suitable duty cycle. In this converter, only one
power switch is utilized. The voltage stress across the power switch is low. Hence, the low on-state
resistance of the power switch can be selected to decrease conduction loss of the switch and improve
efficiency. The presented converter has simple structure, therefore the control of the proposed
converter will be easy. The principle of operation and the mathematical analyses of the proposed
converter are explained. The validity of the presented converter is verified by the experimental
results. The presented converter operates as a universal power supply and it is appropriate for low
voltage and low power applications and the proposed converter input current is discontinues. The
proposed buck-boost converter is utilized in many applications like fuel-cell systems, car electronic
devices, LED drivers and gadgets such as mobile phones and notebooks. In this paper, the
mathematical analyses of the proposed converter are explained. Besides, to verify the feasibility of
the converter, experimental results are provided.
TECHNIQUES
 Transformer less buck boost dc-dc converter

ADVANTAGES

13
  Simple structure
 Improve efficiency process

DISADVANTAGES
 Low voltage and low power application
 It cause high voltage spikes

[9] A Novel Single-Switch Cascaded DC-DC Converter of Boost and Buck- Boost Converters,
Jian Fu; Bo Zhang; Dongyuan Qiu; Wenxun Xiao-2010
A novel single-switch dc-dc converter with voltage gain D/(1-D)2 by cascading a Boost converter
and a Buck-boost converter. The proposed converter has the advantages of simple circuit structure
and extended voltage conversion ratio. The operating principle and steady-state analysis of the
proposed converter are discussed in detail. Finally, a prototype is implemented to verify theoretical
analysis. In recent year, high voltage gain dc-dc converters play more and more important role in
many industry applications such as uninterrupted power supplies, power factor correctors,
distributed photovoltaic (PV) generation systems and fuel cell energy conversion systems. In these
applications, a classical boost converter is normally used, but the extremely high duty cycle will
result in large conduction loss on the power devices and serious reverse recovery problems. Thus,
the conventional boost converter would not be acceptable for realizing high step-up voltage gain
along with high efficiency. To achieve a high conversion ratio without operating at extremely high
duty ratio, some converters based on transformers or coupled inductors or tapped inductors have
been provided. However, the leakage inductance in the transformer, coupled inductor or tapped
inductor will cause high voltage spikes in the switches and reduce system efficiency. In order to
solve the voltage spike, snubber circuits, such as resistor---capacitor---diode snubber, nondissipative
snubber and active clamp circuit, can be applied, but increase the complexity of converter structure
TECHNIQUES
 Single-switch dc-dc converter

ADVANTAGES
 High duty cycle
 Achieve a high conversion ratio

14
DISADVANTAGES
 Reverse recovery problems
 Large conduction loss

[10] A New Circuit Design of Two-Switch Buck- Boost Converter, H.Y. Jung, S.H. Kim, B.
Moon-2018
A conventional two-switch buck–boost (TSBB) converter can operate in buck, boost, buck– boost
modes. This paper introduces a new topology for a two-switch buck–boost converter with the same
operation modes. However, the proposed TSBB converter has fewer conductions and switching
components than a conventional TSBB converter, which reduces the power losses. Several types
converters have been proposed to solve the inverting output problem, such as single-end primary
inductor converter (SEPIC), zeta converter, and two-switch buck-boost (TSBB) converter. These
converters have a positive or non-inverting output voltage. However, compared with a basic
inverting buck-boost converter (the SSBB), all three of these non-inverting converters require
additional power components. The zeta converter and the SEPIC converter have an additional
inductor and capacitor, while the TSBB converter has an additional MOSFET and diode. Because
the zeta converter and SEPIC converter have an additional inductor and capacitor, they have larger
size, resulting in higher losses in the energy conversion and low power density. Hence, these
converters are not suitable for larger power applications. The voltage stresses can also be lower than
that of the SSBB converter, or the number of conducting components can be reduced compared to a
conventional TSBB converter in each mode. As a result, the proposed TSBB converter has lower
power losses and higher efficiency than a conventional TSBB converter.
TECHNIQUES
 Conventional two-switch buck–boost (TSBB) converter

ADVANTAGES
 Maintaining long device life
 Reducing energy consumption

DISADVANTAGES
 Fewer conductions and switching components
 Low performance

15
 CHAPTER-3

EXISTING SYSTEM:

The converters that employ integration between a PFC boost rectifier (input stage) with a half-
bridge inverter (dc-link stage) and an output circuit containing the LEDs load (output stage) can be
highlighted. One of the main features of half-bridge-based circuits is the zero-voltage switching
(ZVS) operation. However, the simplest way to compensate for input voltage and output power
variations is by varying the switching frequency or by a PFM-APWM hybrid modulation

3.1 EXISTING BLOCK DIAGRAM:

Power Controller ZVS

Supply unit unit

DC-DC Converter

OUTPUT Low Pass Filter

Fig.2 Existing Block Diagram

16
CHAPTER-4

PROPOSED SYSTEM:

4.1 BLOCK DIAGRAM:

Arduino UNO
Input Rectifier Microcontroller
unit

DC-DC DC Link
Converter Capacitor

Enhanced PWM TP PFC DC-DC

unit Converter

Load Output

Fig.3 Proposed Block Diagram

17
OVERALL PROCESS FLOW DIAGRAM

Input Source Switching Network Frequency Analysis

analysis

Dual Frequency E- Resonant Tank Circuit

Class Converter

Adaptive Algorithm
with ZVS/ZCS

Output TP PFC DC-DC

Converter

4.2 PROPOSED PROCESS EXPLANATION

4.2.1 Single-stage converter topologies
Single-phase single-stage power-factor-corrected converter topologies are reviewed in this paper.
The topologies discussed in the paper are related to ac–dc and ac–ac converters that are classified on
the basis of the frequency of the input ac source, the presence of a dc-link capacitor, and the type of
control used (resonant or pulse width modulation). The general operating principles and strengths

18
and weaknesses of the converters, which the authors have investigated over the last decade, are
discussed in detail, and their suitability in practical applications is stated. Considering practical
design constraints, it is possible to effectively employ many single-stage converter topologies in a
wide range of applications.

Fig.4 Single-phase diode bridge rectifier with capacitive output filter

It was very common in the past to use a simple, single-phase diode bridge rectifier with a capacitive
output filter as the first stage of the converter as is shown in Fig. 1. The diode bridge rectifies the ac
input voltage and the capacitor smoothes out the resulting voltage to make it an almost pure dc
waveform. The current drawn from the ac utility source, however, is very nonsinusoidal because the
bridge diodes conduct current only when the rectified input voltage is equal to or greater than the dc
capacitor voltage. It is only then that current flows to charge the capacitor. For any electrical
equipment drawing power from the utility, the input power factor is an indication how effectively
this is accomplished. If vast numbers of such converters were to be used in industry, the harmonics
that would be injected in the utility would be so large that they would create a need for increased
volt-ampere ratings of utility equipment (i.e., transformers, transmission lines, and generators) and
distort the utility voltage. Since a severely distorted ac utility voltage can damage sensitive electrical
equipment, regulatory agencies around the world have established standards on the current harmonic
content produced by electrical equipment
Stricter regulatory agency standards on harmonic content have led to the demise in popularity of the
simple diode-bridge rectifier as the front-end converter in electrical equipment operating off of an ac
supply. More and more, electrical equipment manufacturers are being forced to improve or “correct”
the input power factor of products supplied by an ac utility source.
Converters Operating with a Low-Frequency AC Source and Without a DC-Link Capacitor
An ac source can produce an ac voltage with low frequency such as the standard 50/60-Hz utility
voltage frequency, or an ac voltage with high frequency such as 100 kHz. In both cases, the most
efficient utilization of power will occur when the current f lowing out of the source is sinusoidal and
19
in phase with the source voltage. Given the nature of the two types of sources, however, techniques
that are appropriate for one type of source are not appropriate for the other. According to the
classification diagram shown in Fig. 4, single-stage converters operating with a low frequency ac
source can be further divided into two types—converters with very small or no dc-link capacitor and
converters with a large dc-link capacitor. Converters of the first type generally have the output of a
front-end diode bridge rectifier fed directly into the input of a converter, but the diode rectifier does
not have a large capacitive output filter. Since this capacitor does not exist, current can flow from the
input source to the converter throughout the line cycle instead of being restricted to flowing only
during the limited portion of the cycle when the input voltage is greater than the capacitor voltage, as
is the case with the converter shown in Fig. Without a large capacitor placed at the diode bridge
output, the single converter can be made to operate in a way that shapes the input current so that an
excellent input power factor can be achieved. Moreover, the absence of a large dc-link capacitor also
reduces the size and weight of the converter.
4.3 Power factor correction
Power factor correction shapes the input current of off-line power supplies to maximize the real
power available from the mains. Ideally, the electrical appliance should present a load that emulates
a pure resistor, in which case the reactive power drawn is zero. Input current, free of harmonics, is a
perfect replica of the input voltage (usually a sine wave) and in phase with it. In this case the current
drawn from the mains is a minimum for the real power required to perform the needed work, and
this minimizes losses and costs associated not only with the distribution of the power, but also with
the generation of the power and the equipment involved in the process. The freedom from harmonics
also minimizes interference with other devices being powered from the same source.
For single-phase electronic applications, typical active PFC approach uses an input current shaping
converter in front of a dc-dc converter. The two converters are controlled independently to achieve
high quality input current shaping and fast output voltage regulation. This system is known for its
superior performance, but the cost may not be justified for lower power applications. It is possible to
construct a single converter, containing a single transistor, which performs all of the functions
accomplished by the system

20
 Fig. 5. Single phase power converter using a high
quality rectifier, energy storage capacitor and a dc-dc converter
4.4 PROPOSED TOPOLOGY
The proposed topologies are based on the boost-PFC and current-source charge-pump power-factor-
correction (CSCPPFC) structures. These circuits have operational characteristics of current source
between the dc-link stage (half-bridge and capacitor CDC) and input stage (full-bridge rectifier,
coupled inductor L1/L2, charge-pump capacitors Cin1 and Cin2, and filter capacitors Cf1 and Cf2).
Knowing that the output current of the half-bridge inverter can be represented by an alternating
waveform at switching frequency, by employing a full-bridge rectifier with a capacitive filter Co or a
doublers rectifier configuration in the system output, it is possible to impose a continuous current
with low flicker factor on the LEDs. Moreover, due to the action of the magnetizing inductance Lm
of coupled inductor L1/L2, there is no need for an inductive filter in series with the input power
supply to eliminate high-frequency harmonics, thus contributing to reducing the number of magnetic
elements contained in the circuit.
The integration between the input and dc-link stages, which characterizes a single-stage system, is
performed by the output stage (full-bridge rectifier, capacitor Co, LEDs array, and inductor Lo). The
charge-pump capacitors Cin1 and Cin2 operate in order to limit the dc-link voltage and provide
energy to the LEDs, mainly when the input supply voltage amplitude approaches a region near to
zero. Hence, the output current crest factor is reduced, thus ensuring a low current ripple on the
LEDs.

21
Fig.6 Proposed single-stage LED drivers based on the boost-PFC and CSCPPFC structures: (a) with
only one magnetic element
The four topologies proposed in have similar operating characteristics. Although the proposed
topology shown in Fig (a) presents only one magnetic element, the LEDs current limitation and the
input current quality depends on coupled inductor leakage inductances Lk1 and Lk2. In this sense, in
order to limit the LEDs current and keep the input current within the standards required by IEC
61000-3-2 Class C the coupled inductor leakage inductance cannot be too low. It is known that the
coupled inductor leakage inductance depends on many factors, including its constructive aspects.
Therefore, if the coupled inductor is designed aiming at an increased leakage inductance, it is
possible to implement the proposed lighting system with a single magnetic element

Fig 6.1 Proposed single-stage LED drivers based on the boost-PFC and CSCPPFC structures (b)
with one coupled inductor and one series inductor
To prevent the system dependency on the leakage inductance of the coupled inductor, the converter
shown in Fig (b) is proposed. In such topology, an inductor Lo is included in series with the output
rectifier, which acts similarly to the leakage inductance of Fig (a), but it represents an additional
element in the system. On the other hand, the coupled inductor design can be carried out in a
traditional way, giving more flexibility to the system design. In addition to Fig (a) and (b), the circuit
presented in Fig (c) provides isolation between the LEDs and the mains, which may be a
requirement of some applications, and the topology depicted in Fig (d) employs a voltage doublers
circuit configuration. In the last case, the instantaneous value of the current through Lo is twice that
observed on the other circuits, but two less diodes are required. Fig presents an equivalent
representation of the proposed converter considering the integration between the input boost- PFC
and output half-bridge stages, in which it is assumed that the magnetizing current of the coupled
inductor and the current on Lo can be represented by ac current sources at their respective
22
operational frequencies. In this article, only the circuit of Fig (b) is analyzed in detail, where its
steady-state operation stages are investigated in order to obtain the fundamental equations and then
derive the expressions that yield the complete quantitative description of the system, including the
PF and the THDi

Fig.6.2 Proposed single-stage LED drivers based on the boost-PFC and CSCPPFC structures (c)
with one coupled inductor and isolated output

Fig.6.3 Proposed single-stage LED drivers based on the boost-PFC and CSCPPFC structures (d)
using a voltage doubler rectifier configuration
Operation Mode
Considering one semi cycle of the input voltage, the proposed converter exhibits two distinct
operation modes, defined as mode 1 and 2, as shown in Fig. Mode 1 occurs during the time interval
in which the dc-link voltage VDC is higher than the voltage on Cin1 (vCin ≤ VDC). In this mode,
the input current value does not change significantly and is considered constant, as shown in Fig (a).
Its value is exactly equal to half the current on Lm (imag), as defined in (1). This situation occurs as
a consequence of the action of the charge-pump capacitors Cin1 and Cin2, which assist the system

23
by providing energy to the dc-link and to the LEDs, and thus, the input current peak value is
reduced. It is noteworthy that with a reduced capacitance Cin, VDC increases and the input current
(iin) waveform converges to a sine wave. Considering the hypothetical case of Cin = 0, both the dc-
link voltage and crest factor of the current through Lo become too high and the proposed system
performance is impaired

where Imag is the maximum Lm current value and ωg is the angular frequency of the input source
defined as ωg = 2 π fg. During the period in which the maximum voltage on Cin1 is lower or equal
to VDC (VCin-max ≤VDC), the converter operates in mode 2. In this mode, the input current iin is
considered a sine wave, as indicated in

where θ can be computed as

Where q is equal to VDC/Vp, D is the duty cycle, and Vp is the input voltage peak value. In (3), it is
verified that the higher VDC, the greater will be θ. When VDC equals twice Vp, iin is a pure sine
wave. However, the LEDs current ripple is very expressive in such conditions, thus producing a high
flicker. In order to clarify the converter behavior in each mode, the diagrams are presented. It can be
seen that during mode 1, the energy delivered to the system is mainly supplied by the input voltage
source. In this condition, the energy stored in the charge-pump capacitors is low and the bus
capacitor and the input voltage provide energy to the load. In mode 2, the maximum voltages on
Cin1 and Cin2 become equal to the dc bus voltage, thus increasing the energy stored in these
capacitors. This energy, when delivered to the load, decreases the Lo resonant inductor current crest
factor, and consequently, the LEDs current ripple.

24
 Fig.7 Mode 1 operation

Fig.8 Mode 2 operation

OPERATING STAGES
All possible stages of the converter operating in steady state at switching frequency for positive
values of iLo(t). Some important operational characteristics can be observed from the detailed
analysis of each stage as follows. 1) Due to the direct connection between the input and output
stages, the power supply provides energy to the system without interruption, thus contributing to
improving the PF, THDi, and overall efficiency.
Coupled Inductor for Voltage Booster
Coupled inductor technique is an upcoming technique to step up the voltage for digital signal
processing, central processing unit (CPU), dc-dc converter necessities which are intended for
achieving good steady state and transient performance. The dc-dc converter voltage gain improves
the use of coupled inductor without increasing duty cycle. The basic coupled inductor operation is
shown in Fig.

25
 Fig.9. Core design of the integrated inductors
Automotive use of multiphase coupled inductor consists of four coupled inductors which is
functional for four segment interleaved 1KW bidirectional 14V to 42V dc-dc converter. Coupled
inductor minimizes the circuit structure and optimizes the faster transient response for medium
voltage applications of two and four wheeler vehicles. The two windings build on the two external
legs of the core. Space break is necessary on every external leg to stay away from dispersion of the
core. Commercially no space gap is provided on the middle leg, so that both inductors can be
decoupled. The magnetic flux swell decreases in the middle leg because of that core loss decreases
and efficiency increases. Core structure is used in order to reduce the magnetic swell in the middle
leg and hence to set improved efficiency, it is the best practice to use the core structure, which
consists of air gap in three legs. Though, this type of attractive core is not a standard manufacturing
practice. The air gap between the three legs is less and a result is low reluctance. Due to this better
static and dynamic performance can be achieved. The air gap takes place between two legs does not
affect the mechanical stability of cores

Fig.10.Advanced core configuration of the integrated inductors

In this core structure, the middle leg is no longer a less reluctance path for the fluxes because of the
air gap. If the second winding L2 is gets open circuited, the flux produced by the primary winding
26
goes to three legs. Similarly, when the primary winding L1 gets open circuited secondary winding
flux goes through the three windings. Based on the direction, current inductors are coupled directly
and inversely. Mutual inductance is more in direct coupling, and it is less in reverse coupling. For
inductor coupled buck converter the output wave forms is shown in Fig L1 and L2 are primary and
secondary winding inductances. M is the mutual inductance.

Fig.11. Direct and indirect coupling of inductors

Direct coupling voltages are calculated as

Similarly, indirect coupling voltages

27
 Fig.12. Voltage wave forms of direct and indirect coupled inductors
OPERATIONAL PRINCIPLES OF THE PROPOSED CIBuBoC
Fig. shows the equivalent circuit of the proposed CIBuBoC. This converter consists of two power
switches (S1 and S2), an input inductor (L1), a CL, three diodes (D1, D01 and D02) and three
capacitors (C1, C01 and C02). Two power switches of the converter are operated simultaneously.
Based on the equivalent circuit, the conductivity of the diodes D1, D01 and D02 are opposite of the
switches S1 and S2. It is clear from this figure that the proposed CIBuBoC has continues input
current, simple structure, positive polarity in the output voltage and common ground between the
input and output voltages. To simplify the steady-state analysis, some assumptions are considered as
follows:
1- All semiconductor components are ideal.
2- All capacitors are large enough such that their voltages are considered to be nearly constant
values during a switching cycle.
3- The CL is modeled as an ideal transformer including magnetizing inductor (Lm) and merged
leakage inductor in the primary-side (Lk) with coupling-coefficient K=Lm/(Lm+Lk).
4- Input inductor and magnetizing inductor of CL are considered large enough, and therefore,
the current ripples across of them are neglected.

There are only two operating modes in each switching cycle of the proposed CIBuBoC. The current
flow path of the proposed converter for operating modes is shown in Fig. Also, key waveforms of
components voltages and currents of the CIBuBoC in CCM for one switching cycle are depicted

28
 Fig Circuit diagram
First mode [t0-t1]: At the beginning of this mode at t=t0, the power switches S1 and S2 are turned
on simultaneously, whereas all diodes are reversely biased and turned off. As it is shown in Fig. 2a,
the voltages of input source and capacitor C1 are applied to the input inductor (L1) and the primary
side of CL (Lm and Lk), respectively. Therefore, these inductors receive energy and the current of
them (iL1, iLm and iLk) are increased linearly. In this time interval, the output capacitors C01 and
C02 supply the load in series. The below equations are written in this mode:

29
 Fig. 2: Current-flow path of operating modes during one switching period at CCM operation. (a)
Mode I.

Fig. 2: Current-flow path of operating modes during one switching period at CCM operation. (a)
Mode II

Second mode [t1-t2]: In this mode as it is shown in Fig. the power switches S1 and S2 are turned
off. Therefore, all diodes including D1, D01 and D02 are turned on, simultaneously. During this time
interval, the capacitor C1 is charged by the input inductor current. The energy of magnetizing
inductor Lm is transferred to the output through the output diodes D01 and D02. Then, the currents
of these inductors (iL1 and iLM ) are decreased. Since the magnetizing and leakage inductors current
are equal in the mode I, the output diode D02 current increases into Zero Current Condition (ZCS).
The capacitor C1 clamps the voltage across the power switch S1. The below equations are expressed
in this mode:

STEADY-STATE ANALYSIS OF THE PROPOSED CIBuBoC

Voltage Gain
To simplify the determination of steady-state capacitor voltages and voltage gain of the proposed
CIBuBoC, the leakage inductor is ignored. By applying the volt-second balance principle on the
inductors L1 and LM and using the following equations are given as:

30
Where, D is the duty cycle of power switches and n=n1/n2 is the turn’s ratio of the CL. By the help
of the voltage of middle capacitor C1 is achieved as:

The voltage stresses across the output capacitors VC01 and VC02 in CCM are expressed as:

The output voltage is obtained from the sum of the output capacitors voltages as follows:

Consequently, the static voltage conversion ratio of the proposed CIBuBoC is achieved as:

The ideal voltage conversion ratio of the proposed CIBuBoC is increased exponentially versus the
duty cycle as semi-quadratic form. Also, it is increased proportionally versus turn’s ratio of CL,
which results in an ultra-voltage gain ratio. It is clearly obvious that, the performance boundary
between the step-down and step-up modes of converter depends directly on the turn’s ratio of CL.
Increasing the number of turn’s ratio of CL leads to reduced step-down range and increased step-up
range, which can be considered as benefits of the CIBuBoC.
Voltage Stresses of Semiconductors
One of the most important factors in proper selection of the circuit components is voltage stresses
across the semiconductor components. Given the assumption of ignoring ripple of the circuit
capacitors and using the maximal voltage stresses on semiconductor components consisting of the
power switches S1 and S2 and diodes D1, D01 and D02 on their off-state mode are obtained as
follows:

31
It is obvious from that, the maximal voltage stresses inversely depends on the turns ratio of CL.
Therefore, by increasing the number of turn’s ratio, the voltage stresses are reduced significantly,
and the efficiency is improved.
Current Stresses of Semiconductors
Assuming a lossless system and neglecting the current ripples of input and magnetizing inductors,
the average value of the input inductor current is obtained as follows:

Here, M is the static voltage conversion ratio expressed and Io is the output load current. Using the
ampere-second balance on the output capacitors C01 and C02, the maximal current passing through
the diodes D1, D01 and D02 are given as follows:

Applying Kirchhoff's current law in the primary side of CL, the maximal current of the magnetizing
inductor is calculated as:

EFFICIENCY ANALAYSIS
Normally, the main power losses are caused by the parasitic elements of each one of converter
components. In fact, the power losses in DC/DC converters are divided into four groups including
power switch devices (MOSFETs), magnetic components (inductors and CL), diodes and capacitors.
By assuming CCM operation along with ignoring the current ripple across the inductors (L1 and
LM) and the voltage ripple of capacitors (C1, C01, and C02), the total power dissipation of the
proposed CIBuBoC is obtained as follows:

32
Power loss of MOSFETs:
The power losses of MOSFETs are divided into two main parts: conduction and ON/OFF states
losses. The MOSFETs conduction losses are expressed as:

Where, Rds(on) is the field effect transistors on-resistor and also Ids1(RMS) and Ids2(RMS) are the
RMS values of the power MOSFETs S1 and S2 on-state current respectively. By substituting The
MOSFETs conduction losses are obtained as the following:

Also, the turn-off /on states losses of the power MOSFETs S1 and S2 associated with their drain-
source voltage stresses, are calculated as:

Where, td(off) and td(on) are turn-on and turn-off times of the MOSFETs.
Power loss of Magnetics components
The magnetic components L1 and CL losses are calculated using the RMS values of their currents as
follow

Power loss of diodes

Diodes of the proposed converter in the on-state present a forward resistance loss and forward drop
voltage loss are expressed as:

By means of the RMS and averaged values of diodes current, equation are calculated as:

33
Power loss of capacitors
The power losses in the capacitors are caused by the equivalent series resistance (resr). The RMS
values of their currents can be simply expressed as follows:

Consequently, the efficiency of the proposed CIBuBoC is defined as:

Moreover, the voltage conversion ratio by consideration and the parasitic elements can be estimated
as follow

SMALL SIGNAL MODELING OF THE PROPOSED CIBuBoC

Small signal derivation and analysis of low-frequency behavior of the CIBuBoC are provided in this
section. For this purpose, the state-space averaging technique is used to model the converter. For
achieving the maximum practical situation, the magnetizing and leakage inductances (Lm and Lk ) of
CL are considered as separate state variables. Also, for non-conservative of the model, the parasitic
resistance rL is also considered for the input inductor, because of high input current level of high
step-up converters. With the above considerations, the state vector of the proposed CIBuBoC is
defined as:

The state equations are obtained from the proposed converter equivalent circuits for switches-ON
and switches-OFF states as given in Fig
Switches-ON state (0<t<dTs):

34
Switches-OFF state (dTs<t<Ts):

Where, k is the coupling coefficient of the CL. The state-space form using the weighting factors (d
and (1-d)) of Switches-ON/OFF states is expressed as:

In order to linearized and derive small signal modeling, small perturbations are superimposed to the
duty cycle, input voltage and the converter variable states as:

35
Where, lower case variables (^) represent a small value of parameters and capital variables represent
steady-state values that is much bigger than the case variables. Substituting neglecting steady-state
terms and applying Laplace transformation, the output-to-input voltage (Gvov) and the output
voltage-to-duty ratio (Gvod) transfer functions are calculated as follows:

KEY PARAMETER DESIGN GUIDANCE OF THE CIBuBoC

The turn’s ratio of the CL that acts as an inductor is determined by the static gain ratio as:

Note that, the value of the duty cycles and the number of turn’s ratio of the CL are very effective in
reducing the stress of circuit components. According to the best selection for the duty cycle to have
minimum stress on the MOSFETs is larger than 0.5. Circuit design in CCM with low input current
ripple is desired to apply the proposed CIBuBoC for renewable DC low-voltage sources with proper
performance. Normally, the input current ripple is considered 20% of the average input current
(allowable current ripple). Then, the minimum value of the input inductor L1 is designed as follows:

Where, fs is the switching frequency of the power switches S1 and S2. In order to reduce the
volume of the CL located in the middle stage of converter, the maximum allowable current ripple
can be selected larger than 20%

In the proposed converter, by considering the maximum tolerant voltage ripple as 1% of the steady-
state output voltage, appropriate value of the output capacitors C01 and C02 are written as:

36
4.2 CIRCUIT DIAGRAM-PROPOSED SYSTEM:

Fig.9 circuit diagram for proposed block diagram.

37
 CHAPTER-5

HARDWARE REQUIREMENTS/DESCRIPTION:

• Power Supply unit

• PIC Microcontroller unit
• DC-DC Converter
• DC Link Capacitor
• Single Stage Boost Converter
• Enhanced PWM
5.1 POWER SUPPLY
BLOCK DIAGRAM EXPLANATION:
The ac voltage, typically 220V rms, is connected to a transformer, which steps that ac voltage
down to the level of the desired dc output. A diode rectifier then provides a full-wave rectified
voltage that is initially filtered by a simple capacitor filter to produce a dc voltage. This resulting dc
voltage usually has some ripple or ac voltage variation.
A regulator circuit removes the ripples and also remains the same dc value even if the input
dc voltage varies, or the load connected to the output dc voltage changes. This voltage regulation is
usually obtained using one of the popular voltage regulator IC units.

TRANSFORMER RECTIFIER FILTER IC REGULATOR LOAD

Fig.10 Block diagram (Power supply)

38
 Fig.11 Power supply circuit diagram
WORKING PRINCIPLE
5.2 TRANSFORMER
The potential transformer will step down the power supply voltage (0-230V) to (0-6V) level.
Then the secondary of the potential transformer will be connected to the precision rectifier, which is
constructed with the help of op–amp. The advantages of using precision rectifier are it will give peak
voltage output as DC; rest of the circuits will give only RMS output.

5.3 Bridge Rectifier

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave
rectification. This is a widely used configuration, both with individual diodes wired as shown and
with single component bridges where the diode bridge is wired internally.

Fig.12 Bridge rectifier

5.4 Bridge Rectifier, RC Filter

39
A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave
rectification. This is a widely used configuration, both with individual diodes wired as shown and
with single component bridges where the diode bridge is wired internally.

Fig.13 Bridge Rectifier with RC Filter

5.5 Bridge Rectifier, LC Filter

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave
rectification. This is a widely used configuration, both with individual diodes wired as shown and
with single component bridges where the diode bridge is wired internally.

Fig.14 Bridge Rectifier with LC Filter

5.6 BRIDGE RECTIFIER OPERATION:

When four diodes are connected as shown in figure, the circuit is called as bridge rectifier. The input
to the circuit is applied to the diagonally opposite corners of the network, and the output is taken
from the remaining two corners.

40
Let us assume that the transformer is working properly and there is a positive potential, at point A
and a negative potential at point B. the positive potential at point A will forward bias D3 and reverse
bias D4.
The negative potential at point B will forward bias D1 and reverse D2. At this time D3 and D1 are
forward biased and will allow current flow to pass through them; D4 and D2 are reverse biased and
will block current flow.
The path for current flow is from point B through D1, up through RL, through D3, through the
secondary of the transformer back to point B. this path is indicated by the solid arrows. Waveforms
(1) and (2) can be observed across D1 and D3.
One-half cycle later the polarity across the secondary of the transformer reverse, forward biasing D2
and D4 and reverse biasing D1 and D3. Current flow will now be from point A through D4, up
through RL, through D2, through the secondary of T1, and back to point A. This path is indicated by
the broken arrows. Waveforms (3) and (4) can be observed across D2 and D4. The current flow
through RL is always in the same direction. In flowing through RL this current develops a voltage
corresponding to that shown waveform. Since current flows through the load during both half cycles
of the applied voltage, this bridge rectifier is a full-wave rectifier.
One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given

transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional

full-wave circuit.

This may be shown by assigning values to some of the components shown in views A and B. assume

that the same transformer is used in both circuits. The peak voltage developed between points X and

y is 1000 volts in both circuits. In the conventional full-wave circuit shown—in view A, the peak

voltage from the center tap to either X or Y is 500 volts. Since only one diode can conduct at any

instant, the maximum voltage that can be rectified at any instant is 500 volts.

The maximum voltage that appears across the load resistor is nearly-but never exceeds-500 v0lts, as

result of the small voltage drop across the diode. In the bridge rectifier shown in view B, the

maximum voltage that can be rectified is the full secondary voltage, which is 1000 volts. Therefore,

the peak output voltage across the load resistor is nearly 1000 volts. With both circuits using the

41
same transformer, the bridge rectifier circuit produces a higher output voltage than the conventional

full-wave rectifier circuit.

5.7 THE USE AND FUNCTION OF BRIDGE RECTIFIER:

A bridge rectifier is a tool used to rework alternating present (AC) into direct current (DC).
Moreover, a bridge rectifier is utilized in model railroads to supply the correct direct current to run
the motors and other accessories. Placed within the decoder, the bridge rectifier has many functions.
Let’s describe the features of a bridge rectifier:
* Present many N-channels which suggests that the facility inputs and the detrimental output of the
rectifier are well connected.
* Present a multiplicity of P-channel which implies that there’s a connection between each energy
inputs and the output of the rectifier.
* Facilitate third quadrant operation gate voltage management which implies that for mentioned
multiplicity of stated N-channel MOSFET means and stated multiplicity of mentioned P-channel
signifies that includes at the very least a component to assure fast MOSFET turn off.
With a purpose to operate the railroad, generate the minimal warmth required and get the highest
present capacity, you want to configure the bridge rectifier. Via a diode, the mentioned part turns off
the fast MOSFET.
5.8 IC VOLTAGE REGULATORS
Voltage regulators comprise a class of widely used ICs. Regulator IC units contain the circuitry for
reference source, comparator amplifier, control device, and overload protection all in a single IC. IC
units provide regulation of either a fixed positive voltage, a fixed negative voltage, or an adjustably
set voltage. The regulators can be selected for operation with load currents from hundreds of milli
amperes to tens of amperes, corresponding to power ratings from milli watts to tens of watts.
A fixed three-terminal voltage regulator has an unregulated dc input voltage, Vi, applied to one input
terminal, a regulated dc output voltage, Vo, from a second terminal, with the third terminal
connected to ground.The series 78 regulators provide fixed positive regulated voltages from 5 to 24
volts. Similarly, the series 79 regulators provide fixed negative regulated voltages from 5 to 24 volts.
 For ICs, microcontroller, LCD --------- 5 volts
 For alarm circuit, op-amp, relay circuits ---------- 12 volts

42
 Circuit Diagram (power supply).

CHAPTER -6
PIC MICROCONTROLLER
4.2 MICROCONTROLLER
A microcontroller is a very small computer on a single integrated circuit (IC). All computers have
several things in common:
• CPU (central processing unit) that executes programs.
• RAM (random-access memory) where it can store variables.
• Input and output devices for interaction.
Desktop computers are “general purpose computers” that can run any of thousands of programs.
Microcontrollers are “special purpose computers.” Microcontrollers do one thing well.
Microcontrollers are often embedded onto a single printed circuit board. This board provides all of
the circuitry necessary for a useful control task. The intention is that the board is immediately useful
to an application developer, without them needing to spend time and effort in developing the
controller hardware.

4.2.1 ARDUINO UNO

43
The Arduino Uno is a microcontroller board based on the ATmega328 (datasheet). It has 14 digital
input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic
resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains
everything needed to support the microcontroller; simply connect it to a computer with a USB cable
or power it with a AC-to-DC adapter or battery to get started. The Uno differs from all preceding
boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the
Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter
"Uno" means one in Italian and is named to mark the upcoming release of Arduino 1.0. The Uno and
version 1.0 will be the reference versions of Arduino, moving forward. The Uno is the latest in a
series of USB Arduino boards, and the reference model for the Arduino platform
Features
 1.0 pinout: added SDA and SCL pins that are near to the AREF pin and two other new pins placed
near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the
board. In future, shields will be compatible both with the board that use the AVR, which operate
with 5V and with the Arduino Due that operate with 3.3V. The second one is a not connected pin,
that is reserved for future purposes.
 Stronger RESET circuit.
 Atmega 16U2 replace the 8U2.
4.2.2 AURDINO PIN DESCRIPTION

Fig 17 Arduino Pin description

Power
The Arduino Uno can be powered via the USB connection or with an external power supply. The
power source is selected automatically. External (non-USB) power can come either from an AC-to-
DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm centre-
positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and Vin
44
pin headers of the POWER connector. The board can operate on an external supply of 6 to 20 volts.
If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may
be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The
recommended range is 7 to 12 volts. The power pins are as follows:
 VIN. The input voltage to the Arduino board when it's using an external power source (as opposed
to 5 volts from the USB connection or other regulated power source). You can supply voltage
through this pin, or, if supplying voltage via the power jack, access it through this pin.
 5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied
with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the
board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage
your board. We don't advise it.
 3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
 GND. Ground pins.

Fig 18 pin details

4.2.3 AURDINO PIN LAYOUT

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 Fig 19 Arduino pin layout

Memory
The ATmega328 has 32 KB (with 0.5 KB used for the bootloader). It also has 2 KB of SRAM and 1
KB of EEPROM
Input and Output
Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode(),
digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a
maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms.
In addition, some pins have specialized functions:
 Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These pins
are connected to the corresponding pins of the ATmega8U2 USB-to-TTL Serial chip.
 External Interrupts: 2 and 3. These pins can be configured to trigger an interrupt on a low value, a
rising or falling edge, or a change in value. See the attachInterrupt() function for details.
 PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite() function.
 SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication using the
SPI library.
 LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the
LED is on, when the pin is LOW, it's off.
The Uno has 6 analog inputs, labelled A0 through A5, each of which provide 10 bits of resolution
(i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to

46
change the upper end of their range using the AREF pin and the analogReference() function.
Additionally, some pins have specialized functionality:
TWI: A4 or SDA pin and A5 or SCL pin. Support TWI communication using the Wire library
There are a couple of other pins on the board:
AREF. Reference voltage for the analog inputs. Used with analogReference().
Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to
shields which block the one on the board.
Communication
The Arduino Uno has a number of facilities for communicating with a computer, another Arduino,
or other microcontrollers. The ATmega328 provides UART TTL (5V) serial communication, which
is available on digital pins 0 (RX) and 1 (TX). An ATmega16U2 on the board channels this serial
communication over USB and appears as a virtual com port to software on the computer. The '16U2
firmware uses the standard USB COM drivers, and no external driver is needed. However, on
Windows, a .inf file is required. The Arduino software includes a serial monitor which allows simple
textual data to be sent to and from the Arduino board. The RX and TX LEDs on the board will flash
when data is being transmitted via the USB-to-serial chip and USB connection to the computer (but
not for serial communication on pins 0 and 1). A Software Serial library allows for serial
communication on any of the Uno's digital pins. The ATmega328 also supports I2C (TWI) and SPI
communication
Automatic (Software) Reset
Rather than requiring a physical press of the reset button before an upload, the Arduino Uno is
designed in a way that allows it to be reset by software running on a connected computer. One of the
hardware flow control lines (DTR) of the ATmega8U2/16U2 is connected to the reset line of the
ATmega328 via a 100 nanofarad capacitor. When this line is asserted (taken low), the reset line
drops long enough to reset the chip. The Arduino software uses this capability to allow you to upload
code by simply pressing the upload button in the Arduino environment. This means that the boot
loader can have a shorter timeout, as the lowering of DTR can be well-coordinated with the start of
the upload. This setup has other implications. When the Uno is connected to either a computer
running Mac OS X or Linux, it resets each time a connection is made to it from software (via USB).
For the following half second or so, the boot loader is running on the Uno. While it is programmed
to ignore malformed data (i.e. anything besides an upload of new code), it will intercept the first few
bytes of data sent to the board after a connection is opened. If a sketch running on the board receives
47
one-time configuration or other data when it first starts, make sure that the software with which it
communicates waits a second after opening the connection and before sending this data. The Uno
contains a trace that can be cut to disable the auto-reset. The pads on either side of the trace can be
soldered together to re-enable it. It's labelled "RESET-EN". You may also be able to disable the
auto-reset by connecting a 110 ohm resistor from 5V to the reset line; see this forum thread for
details.
USB Over current Protection
The Arduino Uno has a resettable polyfuse that protects your computer's USB ports from shorts and
over current. Although most computers provide their own internal protection, the fuse provides an
extra layer of protection. If more than 500 mA is applied to the USB port, the fuse will automatically
break the connection until the short or overload is removed.

6.5 DC TO DC CONVERTER
A DC-DC converter is a power electronics device that accepts a DC input voltage and also provides
a DC output voltage. The output voltage of DC to DC converter can be greater than the input voltage
or vice versa. The converter output voltages are used to match the power supply required to the
loads. The connection and disconnection of power supply to the load can be controlled using a
switch in the simple DC to DC converter circuit. DC to DC converter circuits consists of a transistor
or diode switch, energy storage devices like inductors or capacitors and these converters are
generally used as linear voltage regulators or switched mode voltage regulators. DC to DC
converters are used to provide DC regulated power supply, constant DC power supply to the
electrical and electronics project circuits.
DC to DC converters have a wide range of applications in power supplies for devices with
batteries such as cell phones and laptops, connecting PV sources to the electricity grid or a battery
bank, in battery connections in hybrid electric cars, and in providing the desired impedance for
Maximum Power Point Tracking in solar PV modules. In batteries, switched mode DC to DC
converters are needed for charging at the required potential. Solar hybrid cars are powered by solar
cells. The DC power obtained from solar cells is used to charge a battery onboard the car. The
voltage obtained from the solar panel has to be scaled to the battery voltage using DC to DC
converters. Solar photovoltaic systems require the implementation of Maximum Power Point
Tracking algorithms in order to extract the maximum power out of a solar array. MPPT is achieved

48
by “the insertion of a power converter between the PV array and load, which could dynamically
change the impedance of the circuit by using a control algorithm”

Fig.17 DC-DC Converter

TECHNOLOGY
Switched mode DC to DC converters enable the transfer of power from input to output,
increasing or decreasing the output voltage and providing the required impedance to the input. The
basic circuit topology of a switched mode DC to DC converter includes an inductor-capacitor circuit
with a switch that is externally controlled and a diode to determine the direction of current flow.
Operation of the DC to DC converter is dependent on the transient nature of the inductor current
caused by flipping the switch. The switch is controlled by a PWM signal. Depending on the
frequency and the duty cycle of the PWM, the desired level of impedance can be achieved and the
voltage modified. The ratio of output voltage to input voltage is determined by the duty cycle of the
PWM signal.
The different circuit topologies for switched mode DC to DC converters are buck, boost and
a combination of buck and boost converters. The buck converter is used to step down the voltage.
The boost converter is used to step up the voltage. A single circuit can perform both buck and boost
functions and in the case of a battery can operate “as a buck converter in the battery charge mode
and as a boost converter when the battery must supply the load (RL) or when the load energy
demand is higher than the energy generated” by an external source such as a solar cell.
6.5.1 DIFFERENT TOPOLOGIES OF DC-DC CONVERTER

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DC-DC converters are quite extensively used in alternative energy systems to provide regulated and
controlled energy from an unpredictable and uncontrolled source of renewable energy. A DC power
supply used for many applications that require a constant voltage. The DC supply sources are
Photovoltaic cells, thermocouples, and capacitors. A DC to DC converter converts the supply
voltage to another DC voltage level required by the load. There are different forms of conversion in
the power converters: Electronic conversion, Magnetic conversion.
Electronic Conversion
DC to DC converters adopts switching technology in electronic circuits. The switched DC-DC
converter transforms the DC voltage rate by briefly storing the input energy and then releasing it at
specific voltage output. Power conversion achieved through the components of the magnetic field,
such as an inductor, transformers, or elements of the electrical field such as capacitors. This method
of conversion can increase or decrease the voltage level. Conversion switching is more energy-
efficient than control of linear voltage, which dissipates unnecessary heat power. A switched-mode
converter's high efficiency decreases the necessary heat sinking and improves portable equipment's
battery endurance. Efficiency has increased with using power FETs that can more rapidly switch to
higher frequencies with lower flipping errors, use less sophisticated drive electronics than power
rectifier diodes. Another improvement in DC-DC converters is to use a power FET to replace the
flywheel diode with synchronous rectification that has a much lower ' on-resistance,' which reduces
the loss of switching . The performance of the converter improved by the use of power FETs, which
can shift more effectively at higher frequencies with lower switching losses than power bipolar
transistors and less complicated drive structures. Many DC-DC converters intended to move
unidirectional from input to output. Switching regulator topologies also be designed for bidirectional
power flow by replacing all diodes with separately different control. In regenerative automobile
braking, for example, where energy transferred when driving to the wheels, but when the tires
provided for braking. Therefore, a bi-directional conversion is more advantageous
Magnetic Conversion
In these DC-DC converters, the energy in a frequency range of 300 KHz to 10MHz is regularly
collected and released in an inductor or transformer from a magnetic field. By adjusting the charge
voltage's duty cycle, the amount of power transferred to a load can control more efficiently. This
control can also apply to the input current, the output current, or to keep constant power. The
transformer-based converter can insulate the input and output. In general, the DC-DC converter
applies to the converters mentioned below. Such circuits are the backbone of the switched-mode
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power supply. In general there are two types of DC-DC converters in the applications of renewable
energy applications.
6.5.2 DC LINK
The calculated dc-link capacitor current is made for a sinusoidal current iP at the output of the
inverter bridge. But by the pulse width modulated voltage however also harmonic current in the filter
circuit occurs. This currents and the fundamental currents together forms the output current of the
inverter bridge. The additional load in the dc-link capacitors of these higher-frequency currents must
to be determined with the help of the Fourier analysis.
A DC link is a connection which connects a rectifier and an inverter. These links are found in
converter circuits and in VFD circuits. The AC supply of a specific frequency is converted into DC.
This DC, in turn, is converted into AC voltage. The DC link is the connection between these two
circuits. The DC link usually has a capacitor known as the DC link Capacitor. This capacitor is
connected in parallel between the positive and the negative conductors. The DC capacitor helps
prevent the transients from the load side from going back to the distributor side. It also serves to
smoothen the pulses in the rectified DC.
The calculated dc-link capacitor current is made for a sinusoidal current iP at the output of the
inverter bridge. But by the pulse width modulated voltage however also harmonic current in the filter
circuit occurs. This currents and the fundamental currents together forms the output current of the
inverter bridge. The additional load in the dc-link capacitors of these higher-frequency currents must
to be determined with the help of the Fourier analysis.

51
 Fig.18 DC link
A DC link is a connection which connects a rectifier and an inverter. These links are found in
converter circuits and in VFD circuits. The AC supply of a specific frequency is converted into DC.
This DC, in turn, is converted into AC voltage. The DC link is the connection between these two
circuits. The DC link usually has a capacitor known as the DC link Capacitor. This capacitor is
connected in parallel between the positive and the negative conductors. The DC capacitor helps
prevent the transients from the load side from going back to the distributor side. It also serves to
smoothen the pulses in the rectified DC.

Fig.19 DC link circuit diagram

6.5.3 CURRENT SOURCE DC-LINK

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 Fig.20 Current source DC Link

6.5.4 DC LINK CAPACITOR

Fig.21 DC link capacitor

53
 A DC link is a connection which connects a rectifier and an inverter. These links are found in
converter circuits and in VFD circuits. The AC supply of a specific frequency is converted into DC.
This DC, in turn, is converted into AC voltage. The DC link is the connection between these two
circuits. The DC link usually has a capacitor known as the DC link Capacitor. This capacitor is
connected in parallel between the positive and the negative conductors. The DC capacitor helps
prevent the transients from the load side from going back to the distributor side. It also serves to
smoothen the pulses in the rectified DC.
6.5.5 PWM PROCESS
Pulse width modulation (PWM) is a powerful technique for controlling analog circuits with a
processor's digital outputs. It is a very useful technique and has wide applications in measurement
and communications areas for power control and conversion. This technique is used to decrease the
Total Harmonic Distortion (THD) of load current. The total harmonic distortion, or THD, is defined
as the ratio of the sum of the powers of all harmonic components to the power of the fundamental. In
this technique for controlling the switches of inverter for the sinusoidal PWM output, a reference
signal (modulating or control signal) which is usually a sinusoidal wave and a carrier signal which is
a triangular wave is needed for controlling the switching frequency. Switching may be unipolar or
bipolar type. At present lot of research in area of multilevel inverters are going on. Such inverters
have number of voltage levels more and hence their harmonic content is lesser and output is of
improved quality. The design of such inverters is very complex. Multilevel inverters are neutral
point clamped, flying capacitor or cascaded H bridge type inverters. Of all Cascaded H bridge type
inverter is the best inverter topology.
Pulse width modulated (PWM) inverters are mostly used power electronic circuits in practical
applications. These inverters are able to produce ac voltages of variable magnitude and frequency.
The quality of the output voltage of PWM inverter is better as compared to square wave inverters.
The PWM inverters are commonly used in variable speed ac drives. Wide speed variation of drive
can be obtained by varying the frequency of the applied ac voltage. There should be linear
relationship between applied voltage and frequency. The PWM inverters could be implemented for
use in single phase and three phase types. There are different kinds of PWM techniques, depending
on the methods of implementation. However, in all these techniques, the generated output voltage
after filtering, obtain a good quality sinusoidal voltage waveform having desired fundamental
frequency and magnitude respectively.

54
A technique of modulation in which the width of the pulse or the duration of the pulse is controlled
is known as “pulse width modulation”. The main advantage of this modulation technique is the
control of the power that is given to Electrical devices. The switching ON and OFF between the
supply and the load at a faster rate controls the average value of the voltage or current. The power
supplied to the load will be longer if the switch is ON for longer time than the period during which it
is OFF. The “duty cycle” needs to be low if the power is low (i.e., if the power is OFF most of the
time) or vice versa. Low losses in switching devices are the main advantage of using this modulation
technique.

Fig.22 Pattern of PWM with its fundamental Vmod

A periodic waveform with a voltage fundamental and pattern frequency being the same represents a
PWM pattern. The fundamental amplitude (Vmod) as shown in figure-6 and the pattern amplitude
are proportional to each other.

Fig.23 PWM pattern changing Vmod

The fundamental Vmod being generated at the same power source frequency by the PWM pattern
guarantees proper working of the Rectifier. It is possible to control the Rectifier to operate in all the
four quadrants by changing the fundamental amplitude and phase shift according to the mains.
(Lagging power factor Inverter, leading power factor Inverter, Lagging power factor Rectifier,
leading power factor Rectifier).

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6.5.6 Enhanced PS-PWM
This very simple technique performs the line-to-line voltages switching exclusively between
adjacent levels. The EPSPWM uses two sets of two dynamically allocated phase shifted carriers,
only depending on the pole voltage reference signals location. Therefore, the quality of the line-to-
line and phase output voltages, in addition to the output current, is improved at all levels of
modulation when compared to the traditional PS-PWM.
The new modulator requires the use of two sets of carriers. For the general case of n legs connected
in parallel per phase, carrier Set 1 is made up of n phase-shifted carriers (vc11, vc12,. . . , and vc1n )
with a relative phase shift of 360◦/n. A second set of carriers (vc21, vc22, . . . , and vc2n)—Set 2—is
also evenly phase shifted, but the whole set is phase shifted by 360◦/(2n)with regards to Set 1. Table
I shows the relative phase shifting among the carriers. The phase shift depends on the number of
carriers, i.e., the number of legs in paralle l. The carrier set selection is dynamically assessed
depending on the instantaneous value of the modulating reference signals (vrefa , vrefb, . . . , and
vrefm). For that purpose, and considering a linear-modulation operation, the carrier/reference signal
domain (which ranges from −1 to +1) is broken down into n equally sized zones of 2/n peak-to-peak
value that are numbered upwards, as it is shown in Fig. 4. In order to quantize them, the following
expression is used:
The enhanced phase-shifted PWM (EPS-PWM) was originality proposed in taking into account
conventional multiphase voltage source inverters with interleaved parallel connected legs. There was
presented a general method, valid for any number of parallel legs, also for any number of phases. In
this paper, this method was used specifically considering a three-phase system and two connected
parallel legs for each phase. This consideration is valid, as long as the phase leg representation (as
seen in Fig. 2) can be visualized as a two parallel-connected legs phase.
As well as in the PS-PWM strategy, in the EPS-PWM method the gating signals of the two
connected parallel legs (qx1 and qx2) are obtained comparing the pole voltages, as with a double-
carrier PWM. Although, EPS-PWM method uses two sets of carriers: Set 1 is made up of two phase-
shifted carriers vt1 and vt2, that have the interleaving angle equal to 0 and 180 , respectively; Set 2 is
made up of other two phase-shifted carriers vt3 and vt4, that have the interleaving angle equal to 90
and 270 respectively. The selected set of carriers depends on the instantaneous normalized value of
the reference pole voltages

56
Fig shows a generalized operating principle of the PSPWM strategy, explaining how the
comparisons are made up. The zone detector block defines which set of carriers should be chosen for
each phase, taking into account the expression:

The variable selx stores the information about which carrier set must be used for each phase, and
controls the multiplexers that dynamically route carrier Set 1 or Set 2.

CHAPTER-7
SOFTWARE EXPLANATION:

7.1 EMBEDDED
An embedded system is an application that contains at least one programmable computer (typically
in the form of a microcontroller, a microprocessor or digital signal processor chip) and which is used
by individuals who are, in the main, unaware that the system is computer-based.

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7.2 EMBEDDED C
7.2.1 INTRODUCTION TO EMBEDDED C
Looking around, we find ourselves to be surrounded by various types of embedded systems. Be it a
digital camera or a mobile phone or a washing machine, all of them has some kind of processor
functioning inside it. Associated with each processor is the embedded software. If hardware forms
the body of an embedded system, embedded processor acts as the brain, and embedded software
forms its soul. It is the embedded software which primarily governs the functioning of embedded
systems.
During infancy years of microprocessor based systems, programs were developed using assemblers
and fused into the EPROMs. There used to be no mechanism to find what the program was doing.
LEDs, switches, etc. were used to check correct execution of the program. Some ‘very fortunate’
developers had In-circuit Simulators but they were too costly and were not quite reliable as well.
As time progressed, use of microprocessor-specific assembly-only as the programming language
reduced and embedded systems moved onto C as the embedded programming language of choice. C
is the most widely used programming language for embedded processors/controllers. Assembly is
also used but mainly to implement those portions of the code where very high timing accuracy, code
size efficiency, etc. are prime requirements.
Initially C was developed by Kernighan and Ritchie to fit into the space of 8K and to write
operating systems. Originally it was implemented on UNIX operating systems. As it was intended
for operating systems development, it can manipulate memory addresses. Also, it allowed
programmers to write very compact codes. This has given it the reputation as the language of choice
for hackers too.
As assembly language programs are specific to a processor, assembly language didn’t offer
portability across systems. To overcome this disadvantage, several high level languages, including
C, came up. Some other languages like PLM, Modula-2, Pascal, etc. also came but couldn’t find
wide acceptance. Amongst those, C got wide acceptance for not only embedded systems, but also for
desktop applications. Even though C might have lost its sheen as mainstream language for general
purpose applications, it still is having a strong-hold in embedded programming. Due to the wide
acceptance of C in the embedded systems, various kinds of support tools like compilers & cross-
compilers, ICE, etc. came up and all this facilitated development of embedded systems using C.
7.2.2 EMBEDDED SYSTEMS PROGRAMMING
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Embedded systems programming is different from developing applications on a desktop
computers. Key characteristics of an embedded system, when compared to PCs, are as follows:
 Embedded devices have resource constraints limited ROM, limited RAM, and limited stack
space, less processing power
 Components used in embedded system and PCs are different; embedded systems typically
uses smaller, less power consuming components. Embedded systems are more tied to the
hardware. Two salient features of Embedded Programming are code speed and code size.
 Code speed is governed by the processing power, timing constraints, whereas code size is
governed by available program memory and use of programming language. Goal of
embedded system programming is to get maximum features in minimum space and minimum
time.
Embedded systems are programmed using different type of languages:
 Machine Code
 Low level language, i.e., assembly
 High level language like C, C++, Java, Ada, etc.
 Application level language like Visual Basic, scripts, Access, etc.

Assembly language maps mnemonic words with the binary machine codes that the processor uses to
code the instructions. Assembly language seems to be an obvious choice for programming embedded
devices. However, use of assembly language is restricted to developing efficient codes in terms of
size and speed. Also, assembly codes lead to higher software development costs and code portability
is not there. Developing small codes are not much of a problem, but large programs/projects become
increasingly difficult to manage in assembly language. Finding good assembly programmers has also
become difficult nowadays. Hence high level languages are preferred for embedded systems
programming.
Use of C in embedded systems is driven by following advantages
It is small and reasonably simpler to learn, understand, program and debug.
C Compilers are available for almost all embedded devices in use today, and there is a
large pool of experienced C programmers.
Unlike assembly, C has advantage of processor-independence and is not specific to
any particular microprocessor/ microcontroller or any system. This makes it
convenient for a user to develop programs that can run on most of the systems.

59
 As C combines functionality of assembly language and features of high level
languages, C is treated as a ‘middle-level computer language’ or ‘high level assembly
language’
It is fairly efficient
It supports access to I/O and provides ease of management of large embedded projects.

Many of these advantages are offered by other languages also, but what sets C apart from others like
Pascal, FORTRAN, etc. is the fact that it is a middle level language; it provides direct hardware
control without sacrificing benefits of high level languages.
Compared to other high level languages, C offers more flexibility because C is relatively small,
structured language; it supports low-level bit-wise data manipulation.
Compared to assembly language, C Code written is more reliable and scalable, more portable
between different platforms. Moreover, programs developed in C are much easier to understand,
maintain and debug. Also, as they can be developed more quickly, codes written in C offers better
productivity. C is based on the philosophy ‘programmers know what they are doing’; only the
intentions are to be stated explicitly. It is easier to write good code in C & convert it to an efficient
assembly code rather than writing an efficient code in assembly itself. Benefits of assembly language
programming over C are negligible when we compare the ease with which C programs are
developed by programmers.
Objected oriented language, C++ is not apt for developing efficient programs in resource constrained
environments like embedded devices. Virtual functions & exception handling of C++ are some
specific features that are not efficient in terms of space and speed in embedded systems. Sometimes
C++ is used only with very few features, very much as C.
Ada, also an object-oriented language, is different than C++. Originally designed by the U.S. DOD,
it didn’t gain popularity despite being accepted as an international standard twice (Ada83 and
Ada95). However, Ada language has many features that would simplify embedded software
development.
Java is another language used for embedded systems programming. It primarily finds usage in high-
end mobile phones as it offers portability across systems and is also useful for browsing applications.
Java programs require Java Virtual Machine which consumes lot of resources. Hence it is not used
for smaller embedded devices.

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Dynamic C and B# are some proprietary languages which are also being used in embedded
applications.
Efficient embedded C programs must be kept small and efficient; they must be optimized for code
speed and code size. Good understanding of processor architecture embedded C programming and
debugging tools facilitate this.
7.2.3 DIFFERENCE BETWEEN C AND EMBEDDED C
Though C and embedded C appear different and are used in different contexts, they have more
similarities than the differences. Most of the constructs are same; the difference lies in their
applications.
C is used for desktop computers, while embedded C is for microcontroller based
applications. Accordingly, C has the luxury to use resources of a desktop PC like memory, OS, etc.
While programming on desktop systems, we need not bother about memory. However, embedded C
has to use with the limited resources on an embedded processor. Thus, program code must fit into
the available program memory. If code exceeds the limit, the system is likely to crash.
Compilers for C typically generate OS dependant executables. Embedded C requires compilers to
create files to be downloaded to the microcontrollers/microprocessors where it needs to run.
Embedded compilers give access to all resources which is not provided in compilers for desktop
computer applications.
Embedded systems often have the real-time constraints, which is usually not there with desktop
computer applications.
Embedded systems often do not have a console, which is available in case of desktop applications.
So, what basically is different while programming with embedded C is the mindset; for embedded
applications, we need to optimally use the resources, make the program code efficient, and satisfy
real time constraints, if any. All this is done using the basic constructs, syntaxes, and function
libraries of ‘C’.
7.3 KEIL C51 C COMPILERS

 Direct C51 to generate a listing file

 Define manifest constants on the command line

 Control the amount of information included in the object file

 Specify the level of optimization to use

61
  Specify the memory models

! Specify the memory space for variables. The Keil C51 C Compiler for the 8051 microcontroller is
the most popular 8051 C compiler in the world. It provides more features than any other 8051 C
compiler available today.

The C51 Compiler allows you to write 8051 microcontroller applications in C that, once compiled,
have the efficiency and speed of assembly language. Language extensions in the C51 Compiler give
you full access to all resources of the 8051.

The C51 Compiler translates C source files into reloadable object modules which contain full
symbolic information for debugging with the µVision Debugger or an in-circuit emulator. In
addition to the object file, the compiler generates a listing file which may optionally include symbol
table and cross reference information.

7.3.1 FEATURES
 Nine basic data types, including 32-bit IEEE floating-point,
 Flexible variable allocation with bit, data, bdata, idata, xdata, and pdata memory types,
 Interrupt functions may be written in C,
 Full use of the 8051 register banks,
 Complete symbol and type information for source-level debugging,
 Use of AJMP and ACALL instructions,
 Bit-addressable data objects,
 Built-in interface for the RTX51 Real-Time Kernel,
 Support for dual data pointers on Atmel, AMD, Cypress, Dallas Semiconductor, Infineon,
Philips, and Triscend microcontrollers,
 Support for the Philips 8xC750, 8xC751, and 8xC752 limited instruction sets,
 Support for the Infineon 80C517 arithmetic unit.

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 CHAPTER-10
CONCLUSION:
This article addressed the feasibility of using a single-stage converter for electronic lighting systems
with LEDs based on the CS-CPPFC concept. The proposed topology has a reduced magnetic
elements count, while keeping compliance with IEC 61000-3-2 Class C for any processed output
power level. Although the developed mathematical model presents complex solutions, simplified
solutions were presented in this article, providing a good understanding of the system operational
characteristics. Although the proposed solution requires a more complex circuit than the
conventional topology, it was demonstrated that it is capable of operating under both universal input
voltage range and 10%–100% dimming. This is a remarkable feature considering that a simple PI
compensator is required and electrolytic capacitors are not necessary. From experimental tests
carried out with a 43 W prototype, it was demonstrated that operation with high PF and limited
THDi is guaranteed for a wide range of operating conditions, and therefore, the proposed converter
can be considered a good alternative for lighting systems using power LEDs.

CHAPTER-11
63
REFERENCE:
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 CHAPTER-12
WEBLINKS
1. www.google.com
2. www.wikipedia.com

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