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i
ACKNOWLEDGEMENT
The satisfaction that accompanies the completion of any task would be incomplete
without the mention of the people who made it possible, the people whose constant
guidance and encouragement paved the way for my efforts to be successful. I consider it a
privilege to express my gratitude and respect to all those who guided me in the
completion of this thesis.
I express my sincere gratitude to our beloved Principal, Dr. A. N. N. Murthy,
D.S.C.E, Bangalore, for his kind co-operation, constant encouragement and support
throughout this study.
I am extremely grateful to our beloved H.O.D., Dr. K. Shanmukha Sundar who
is also my guide, Department of Electrical and Electronics, D.S.C.E, Bangalore, for
their invaluable guidance, encouragement, inspiration and co-operation.
I also express my heartfelt thanks to my family for their continuous support.
Rakesh kumar goudanaikar. (1DS12EPE13)
M.Tech (Power Electronics)
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ABSTRACT
From the literature survey, it is observed that the need of ac photovoltaic modules
in photovoltaic (PV) power-generation market has increased. However, the important
aspect is a requirement of a high voltage gain converter for the modules grid connection
through a dcac inverter. A high step up DC-DC converter, a high step up DC-DC
converter using PID controller, a interleaved high step up DC-DC converter using PID
controllers are proposed and presented in this thesis. The PID controller is used in
feedback in order to speed-up the response. The converter achieves a high step-up
voltage-conversion ratio without extreme duty ratio and the numerous turns-ratios of a
coupled inductor. The leakage inductor energy of the coupled inductor is efficiently
recycled to the load. The advantages such as reduced current stress in both the
switching devices and passive elements, reduced output current ripple, increase in output
voltage and overall efficiency and so on are achieved by virtue of the interleaving
connection. The high step up DC-DC converter, a high step up DC-DC converter using
PID controller, interleaved high step up DC-DC converter using PID controllers is
modeled using SIMULINK and hardware model of high step up DC-DC converter is
build .The simulation and hardware results are presented in this thesis to authenticate the
proposed scheme.
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TABLE OF CONTENTS
Page no
ACKNOWLEDGEMENT i
ABSTRACT ii
LIST OF FIGURES iv
LIST OF TABLES viii
CHAPTER 1 INTRODUCTION
1.1 Overview 1
1.2 Motivation 2
1.3 Organization of the Thesis 3
1.4 Summary 3
CHAPTER 2 LITERATURE SURVEY
2.1 Literature Review 4
2.2 Problem Formulation 8
2.3 Summary 9
CHAPTER 3 HIGH VOLTAGE GAIN, HIGH STEP UP DC-DC
CONVERTER
3.1 Introduction 10
3.2 Proposed Converter 10
3.2.1 Operating Principles of the Proposed Converter 12
3.3 PID Controller 15
3.4 Interleaved High Step up DC-DC Converter with
PID Controller
18
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3.4.1 Operating Principles of the Interleaved High Step
up DC-DC Converter with PID Controller
20
3.5 Summary 25
CHAPTER 4 STEADY STATE ANALYSIS AND CIRCUIT
DESIGN OF PROPOSED CONVERTER
4.1 Steady-State analysis of Proposed Converters 26
4.2 Design of Proposed Converter 28
4.3 Summary 29
CHAPTER 5 SIMULINK MODELS OF THE PROPOSED
SYSTEM
5.1 Simulink Model of Solar Panel 30
5.2 Simulink Model of High Step up DC-DC Converter 31
5.3 Simulink Model of High Step up DC-DC Converter
With PID Controller
32
5.4 Simulink Model of Interleaved High Step up DC-DC
Converter with PID
34
5.5 Simulink Model of Single Phase Full Bridge Inverter 35
5.6 Summary 36
CHAPTER 6 HARDWARE MODEL OF PROPOSED
CONVERTER
6.1 Block Diagram of Hardware Kit 37
6.2 Full Wave Bridge Rectifiers 37
6.3 Microcontrollers 39
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6.4 High Step up DC-DC Converter 40
6.5 Summary 41
CHAPTER 7 RESULTS AND DISCUSSIONS
7.1 Simulation Result of Solar Panel 42
7.2 Simulation Results of High Step up DC-DC Converter 42
7.3 Simulation Results of High Step up DC-DC Converter
With PID Controller
49
7.4 Simulation Results of Interleaved High Step up DC-DC
Converter with PID Controller
54
7.5 Hardware Results of Proposed Converter 57
7.6 Comparison of Simulation and Hardware Results 59
7.7 Comparison with Conventional Methods 59
7.7 Summary 61
CHAPTER 8 CONCLUSION AND SCOPE FOR FUTURE WORK 62
REFERENCES
PUBLICATIONS
APPENDIX
63
65
84
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LIST OF FIGURES Page no
Figure 3.1 Circuit of proposed converter 11
Figure 3.2 Some typical waveforms of proposed converters at CCM operation 12
Figure 3.3 Mode I of proposed converter in Continuous Conduction Mode
Operation
13
Figure 3.4 Mode II of proposed converter in Continuous Conduction Mode
Operation
13
Figure 3.5 Mode III of proposed converter in Continuous Conduction Mode
Operation
14
Figure 3.6 Mode IV of proposed converter in Continuous Conduction Mode
Operation
15
Figure 3.7 Mode V of proposed converter in Continuous Conduction Mode
Operation
15
Figure.3.8 Feedback using PID controller. 16
Figure 3.9 The Interleaved high step up DC-DC converter with PID controller 19
Figure 3.11 Mode 1 operation of Interleaved high step up DC-DC converter. 21
Figure 3.12 Mode 2 operation of Interleaved high step up DC-DC converter. 22
Figure 3.13 Mode 3 operation of Interleaved high step up DC-DC converter. 23
Figure 3.14 Mode 4 operation of Interleaved high step up DC-DC converter. 24
Figure 3.15 Mode 5 operation Interleaved high step up DC-DC converter. 25
Figure 5.1Simulink model of solar panel 30
Figure 5.2Simulink model of high step up DC-DC converter 32
Figure 5.3Simulink model of high step up DC-DC converter with PID controller 33
Figure. 5.4Simulink model of interleaved high step up DC-DC converter with
PID controller.
35
Figure 5.5Simulink model of single phase bridge inverter. 36
Figure 6.1 Block diagram of hardware kit of proposed converter. 37
Figure 6.2 Full Wave Bridge Rectifiers 38
Figure 6.3Shows (a) Positive half cycle (b) Negative half cycle 38
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Figure 6.4 Photograph of Full wave bridge rectifiers. 38
Figure 6.5 Photograph of microcontroller. 40
Figure 6.6 Shows photograph of hardware model proposed converter 40
Figure 7.1 Solar panel output voltages. 42
Figure 7.2 Input voltage of high step up DC-DC converter. 43
Figure 7.3 Voltage and current across diode D1, D2, D3 and S1. 44
Figure 7.4 Voltage across capacitors C1 and C2. 45
Figure 7.5 Output voltage of high step up DC-DC converter. 46
Figure 7.6 Voltage and current across diode D1, D2, D3 47
Figure 7.7 Output voltage of high step up DC-DC converter 48
Figure 7.8 Converter input voltage. 49
Figure 7.9 Voltage and current across diode D1, D2, D3 and S1. 51
Figure 7.10 Voltage across capacitors C1 and C2. 52
Figure 7.11 Converter output with and without PID controller 53
Figure 7.12 Voltages across diode D1, D2, D3, D4. 55
Figure 7.13 Voltages across capacitors C1, C2, C3, and C4. 55
Figure 7.14 Output voltage of proposed converter. 56
Figure 7.15 Gate pulses to switch S1. 57
Figure 7.16 Voltage across diode D2, D3. 57
Figure 7.17 Voltage gain as a function of the duty ratio of the proposed
converter.
60
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LIST OF TABLES Page no
Table 3.1 Effect of independent P, I, and D during the tuning. 19
Table 5.1 Switching states 38
Table 7.1 Converter output comparison 53
Table7.2 Comparison of simulation and hardware results 59
Table 7.3 Voltage gain comparison 60
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CHAPTER 1
INTRODUCTION
This chapter provides a brief introduction about the role of power electronic
converters renewable energy system, advantages of using power electronics converter in
renewable energy system .It also covers motivation for the project and organization of the
thesis.
1.1 OVERVIEW
Solar energy is growing at double-digit rates worldwide. And it will continue to
do so in coming years across all its different applications be them residential, in small
and large buildings, or in power plants. Driving the rise of solar power is the ever-
improving performance of photovoltaic (PV) systems. It a prime source of clean,
renewable energy that is making a major contribution to reducing the carbon footprint and
building the environmental sustainability of power generation. PV systems generate will
not be plagued by pollution, greenhouse gases, and depletion of resources.
A traditional centralized photovoltaic array is a serial connection of various panels
to achieve high dc link voltage for main electricity by means of dc to ac inverter a small
number of components to fit the dimension of the bezel of the ac unit, drawback is
efficiency levels are lower than those of traditional PV converters. The main purpose of
the converter in photovoltaic generation system is to obtain maximum efficiency at lower
cost .Converters are said to be heart of photovoltaic generation system. The power
converters are to be designed carefully in such a way that they provide high energy
efficiency, ensuring reliability and safety of the overall solar system, required for
different application.
The DC-DC converter requires large boost conversion from the panels low
voltage to the voltage level of the appliance. Some converters increase turns ratio of the
coupled inductor obtain higher voltage than conventional boost converter. Some
converters are effective combination fly back and boost converters .They are a range of
converters combination developed to accomplish high voltage gain by using coupled
inductor technique. Combinations of auxiliary resonant circuit, active snubber
synchronous rectifiers, or switched capacitor based resonant circuits and so on, these
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circuits made active switch into zero voltage switching (ZVS) or zero current switching
(ZCS) operation and improved converter efficiency.
Interleaved connection is a method in which the additional circuit is added in
between the input and output of the main circuit in order achieve the increase in overall
efficiency and output voltage of the converter and also reduce in input ripple and output
ripple.
Interleaving is not a new technique earlier it was only used in the buck converter
topology and there have been many papers telling the role of multiphase buck converters,
particularly for higher performance higher power applications. On the other hand, all the
merits of interleaving, like higher efficiency, increase in output voltage and reduced input
and output ripple for voltage/current can also be achieved in the boost topology. The
majority of controllers that are used in buck converter applications apply equally well
when configured for use in an interleaved boost application.
Now a days the interleaved high step up DC-DC converter has been widely used
in photovoltaic generation, electric vehicles and power factor correction due to its high
power density and fast dynamic response.
1.2 MOTIVATION
The motivation for this thesis is to design a power converter which provides
output with maximum energy efficiency at low cost, ensuring reliability and safety of the
overall solar PV system, required for different applications.
In most of the existing converters proposed by various authors with higher voltage gain
then conventional converters have certain drawbacks such has they have extreme increase
in turns ratio of coupled inductor to achieve high voltage gain which leads to increase in
weight, size of converter and also results heating issues. The PV panels having converters
fixed on them have efficiency level lower than conventional converters. Some of the
converters are successful combination 2 or more converters such as boost and flyback
converters, and various other converters. These combinations are developed to
accomplish high voltage gain by using coupled inductor technique but their efficiency and
voltage gain of converter are constrained by either the parasitic effect of the power
switches or the reverse-recovery issue of the diodes. Besides, the efficiency of converters
is affected by the equivalent series resistance (ESR) of the capacitor and the parasitic
resistances of the inductor.
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These drawbacks are overcome by the proposed converter with additional advantages, it
achieves high step up voltage conversion ratio without extreme increase in duty ratios and
the various turns ratios of a coupled inductor ,the leakage inductor energy of the coupled
inductor is efficiently recycled to the load .
1.3 ORGANIZATION OF THE THESIS
The thesis is comprised of the following chapters. Following is a briefing of each chapter
Chapter 1: A brief introduction about proposed converter, Motivation for the project, and
organization of the thesis are discussed in this chapter.
Chapter 2: Literature survey on previous research works and problem formulation of the
project are discussed in this chapter.
Chapter 3: A brief introduction about DC-DC converter, different types of DC-DC
converters and control of DC-DC converters. Here the proposed converter
and its continuous conduction mode of operation are explained.
Chapter 4: This chapter discusses about the steady-state analysis for continuous
conduction modes of operation, circuit design of the converter are explained.
Chapter 5: This chapter summarizes the simulation circuit diagram and the output results
for continuous conduction modes of operation of a proposed converter.
Chapter 6: This chapter discusses the block diagram and its description, hardware kitsnap, hardware requirements, software requirements and circuit diagram of
hardware are explained.
Chapter 7: This chapter discusses about the results obtained from simulation and
hardware implementation.
Chapter 8: Here conclusion of this thesis and the scope for the future work was explained
in detail..
1.4 SUMMARY
A brief introduction of role of power electronic converters renewable energy
system is given in this chapter. The advantages of using power electronics converter in
renewable energy system, reduction of ripple content using interleaved connection is
given in this chapter. The motivation for the project and organization of thesis are
discussed in this chapter.
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CHAPTER 2
LITERATURE SURVEY
In this chapter the previous research works done on converters by different
authors, their drawbacks are discussed in literature review section and problem
formulation is discussed in brief.
2.1 LITERATURE REVIEW
In this section previous research done by authors on converters and their
drawbacks are discussed in brief.
T. Shimizu, K. Wada, and N. Nakamura [1] proposed a Flyback-type single-
phase utility interactive inverter with power pulsation decoupling on the dc input for an ac
photovoltaic module system in this paper they stated that a conventional system which
uses a PV array which consist of many PV modules connected in series to achieve
sufficient dc input voltage for producing ac voltage from an inverter circuit. But
sometimes the power generated from the PV array is decreased extremely when a few PV
modules are partly enclosed by shadows, thereby decreasing current generation. So to
overcome this drawback, a low power DCAC inverter was individually placed on each
PV module to produce the maximal power from itsequivalentphotovoltaic module.
Particularly in case of a single phase utility interactive inverter, an electrolytic
capacitor with high capacitance is connected on the dc input bus to decouple the power
pulsation initiated by single phase power production to the utility line. Sometimes,
particularly in the course of summer, the ac module inverters have to function under a
high atmospheric temperature and due to the electrolytic capacitor having a remarkably
short lifespan when used in a high-temperature environment, the lifespan of the inverter isalso reduced. We can also use film capacitorsas an alternative of electrolytic capacitors if
we are ready to pay for extreme large volume inverter. But this is not a reasonable
solution for ac module systems.
Their thesis come up with a novel flyback type utility interactive inverter circuit
design well suited for ac module systems, were its lifespan during high atmospheric
temperature is taken into consideration. A most distinct character of the proposed system
is the decoupling of power pulsation is accomplished by a supplementary circuit that
permits use of film capacitors with low capacitance for both the dc input line and the
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decoupling circuit, and due to which the supplementary circuit is likely to increase the
lifespan of the inverter. The proposed inverter circuit fulfills the requirement of
lightweight, small volume and stable ac current insertion into the utility line.
C. Rodriguez and G. A. J. Amaratunga [2] proposed Long-lifetime power
inverter for photovoltaic ac modules, it states that there are three conversion stages form
the power topology. The first one is a full bridge rectifier associated to a high-frequency
transformer; the full bridge amplifier rectifies the voltage of the photovoltaic panel nearly
to 475V. The first stage is controlled by a phase shift PWM controller that enables zero-
voltage switching, thereby reducing losses. The Second stage, the buck converter is in
series with rectifier and is handled by using current mode in order to shape the current
injection into a rectified sine wave. The last stage, a full bridge is conducted at line
frequency to spread out the current injection. In amplification stage the voltage at the PV
terminals kept constant by a proportional compensator. In current injection stage the dc-
link voltage is kept constant by the PD compensator that controls the magnitude of the
grid current.
S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg [3] proposed A review of single-
phase grid-connected inverters for photovoltaic modules, it describes about the inverter
designs for connecting PV modules to a single-phase grid. The inverters are classified
into four classes:
1) Number of power processing stages in cascade;
2) Types of power decoupling between the PV modules and the single-phase grid;
3) Whether they use a transformer (either line or high frequency) or not
4) The type of grid-connected power stage.
Variety of inverter designs are presented and compared with demands, lifespan,
component size, cost and ratings. To conclude few topologies are considered as the best
for both single PV module and multiple PV module applications.
The drawback of [1]-[3] converters are their efficiency levels which are lower
compared of conventional Photovoltaic inverters. The capacity of a single PV panel is
from 100 W to 300 W, and the MPP voltage range is from 15 V to 40 V, which is input
voltage of the ac unit, but under lower input condition, it is hard for the ac unit to achieve
high efficiency.
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T. Umeno, K. Takahashi, F. Ueno, T. Inoue, and I. Oota [4] proposed A new
approach to low ripple-noise switching converters on the basis of switched- capacitor
converters, it states about the quickly dropping power supply voltages and tight voltage
regulation requirements for integrated circuits challenges power supply designers. A
novel interleaved discharging (ID) approach is presented to decrease the output ripple instep-down switched-capacitor (SC) dcdc converters.
B. Axelrod, Y. Berkovich, and A. Ioinovici [5] proposed Switched-capacitor/
switched-inductor structures for getting transformer less hybrid dcdc PWM converters,
it describes about a few switching designs, created by any two inductors and two-three
diodes (L-switching) , or two capacitors and two-three diodes (C-switching)are proposed.
The designs can be of two types: step-down and step-up. These blocks are inserted in
classical converters such has bucked, boost, buck boost, Cuk, Sepic. The step-down C
or L switching designs are connected with the buck, buck boost, Cuk, Sepic converters to
get a step-down function.
When the switch of the converter is on, the capacitors in the C-switching blocks
are discharged in parallel or the inductors in the L switching blocks are charged in series.
When the switch is turned off, the capacitors in the C-switching blocks are charged in
series or the inductors in the L switching blocks are discharged in parallel. The step-up
C or L switching structures are connected with the boost, buck boost, Cuk, Sepic
converters, to get a step up function.
Q.Zhao and F.C.Lee proposed [6] High-efficiency, high step-up DCDC
converters, it states about the applications were high voltage is required. Few DCDC
converters can give high step-up voltage gain, but with the drawback of either a high duty
ratio or a huge amount of circulating energy. DCDC converters with coupled inductors
can produce high voltage gain, but their efficiency is reduced by the losses related with
leakage inductors.
Converters with active clamps recover leakage energy at the cost of increasing
topology complication. A clan of high-efficiency and high step up converters with quiet
simple designs is proposed. The proposed converters, that uses diodes and coupled
windings rather than switches to achieve functions similar to active clamps and perform
better than active clamp. High efficiency is obtained due to recycle of the leakage energy
and the output rectifier reverse recovery issue is mitigated.
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The drawback of [4]-[6] converters is they have extreme increase in turns ratio of
coupled inductor to obtain higher voltage gain than conventional boost converter which
makes the converter heavy in weight ,larger in size and leads to heating problems.
R. J. Wai, C. Y. Lin, R. Y. Duan, and Y. R. Chang [7] proposed High -efficiency
DCDC converter with high voltage gain and reduced switch stress, In this thesis, a high
efficiency DC-DC converter with high voltage gain and reduced switch stress is designed.
Generally describing, the use of a coupled inductor is for raising the step up ratio of the
conventional converter. Due to, the switch surge voltage caused by the leakage inductor
will result in the need of high voltage rating devices. In the proposed design, a three
winding coupled inductor is used for producing a high voltage gain without high
switching duty cycle and strengthen the utility rate of magnetic core. In addition, the
energy in the leakage inductor is discharged directly to the output terminal for eliminating
the circumstance of circulating current and the generation of switch surge voltage.
Moreover, the delay time developed with the cross currents of primary and secondary of
the coupled inductor is altered to mitigate the reverse-recovery current problem of the
output diode. Furthermore, the closed-loop control method is used in the proposed design
to avoid the voltage drift problem of the power source under the variation of loads.
S. M. Chen, T. J. Liang, L. S. Yang, and J. F. Chen [8] proposed A cascaded high
step-up DC-DC converter with single switch for micro-source applications,This thesis
proposes a new high step-up dcdc converter designed particularly for controlling the dc
interface between different micro-sources and inverter to electricity grid. The
configuration of the proposed converter is a quadratic boost converter with the coupled
inductor in the second boost converter. The converter obtains high step-up voltage gain at
low duty ratio and low voltage stress on the switch. In addition, the energy stored in the
leakage inductor of the coupled inductor can be reused to the output capacitor.
T. J. Liang, S. M. Chen, L. S.Yang, J. F. Chen, and A. Ioinovici [9], Ultra large
gain step-up switched-capacitor dcdc converter with coupled inductor for alternative
sources of energy, In this thesis, an ultra-large voltage conversion ratio converter is
introduced by connecting a switched-capacitor circuit with a coupled inductor. The
proposed converter can be observed as parallel connection to the load of a conventional
boost converter and many forward converters, each having a switched capacitor circuit.
Every stages are turned on by the boost switch.
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There is a requirement of a single switch, with minimal duty ratio values. The
leakage energy of the coupled inductor is recycled to the load. The incoming current
effect of switched capacitors is muted by the leakage inductance of the coupled-inductor.
The above characteristics are responsible for the high efficiency performance.
G. Yao, A. Chen, and X. He [10] proposed Soft switching circuit for interleaved
boost converters, In this thesis, a zero-voltage switching (ZVS) zero-current switching
(ZCS) interleaved boost converter is proposed. An active circuit branch connected in
parallel with main switches is combined and it consists of an auxiliary switch and a
snubber capacitor. By utilizing the interleaved converter topology, zero current switch on,
zero voltage switch off of the main switches can be obtained and the reverse recovery
losses can be decreased. However, the auxiliary switches are zero voltage transmission
during the complete switching transition
The drawback of [7]-[10] is these converters successfully combine fly back and
boost converters, as a range of converter combinations are developed to accomplish high
voltage gain by means of the coupled-inductor technique .The voltage gain, efficiency of
the DC-DC boost converter are inhibited by both the parasitic effect of the switches ,the
reverse-recovery problem of the diodes. Besides, the equivalent series resistance (ESR) of
the capacitor and the parasitic resistances of the inductor also affect overall efficiency.
2.2 PROBLEM FORMULATION
A conventional centralized photovoltaic array is a series connection of various
panels to achieve high dc link voltage for main electricity from a DCAC inverter.
Regrettably, once there is a limited shadow on a few panels, the systems energy yield
becomes considerably low. An ac unit is a micro inverter configured on the rear bezel of a
PV panel; this alternative solution not only immunizes against the yield loss by shadow
effect, but also provides flexible installation options in accordance with the users budget.
Many prior research works have proposed a single-stage DC AC inverter with fewer
components to fit the dimensions of the bezel of the ac module, but their efficiency levels
are lower than those of conventional PV inverters.
Particularly in the case of a single phase utility interactive inverter, an electrolytic
capacitor with high capacitance has been connected on the dc input bus to decouple the
power pulsation initiated by single phase power generation to the utility line. Sometimes,
particularly in the course of summer, the ac module inverters have to function under a
high atmospheric temperature and due to the electrolytic capacitor having a remarkably
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short life span when used in a high-temperature environment, the lifespan of the inverter
is also reduced. We can also use film capacitorsas an alternative of electrolytic capacitors
if we are ready to pay for extreme large volume inverter. But this is not a reasonable
solution for ac module systems. In order to overcome this defect, power decoupling
schemes for the inverters have been proposed. On these inverters, two output capacitorsare used and the bias voltage induced to these capacitors is modulated so as to reduce the
power pulsation on the dc input capacitor and to generate sinusoidal voltage at the ac
output terminal.
Another fundamental problem with ac-module inverters is the poor reliability of
components at high temperatures. It is well known that aluminum electrolytic capacitors,
among others, are the weakest links in power electronic designs, because the AC module
inverter operates at high temperatures.
This thesis proposes a DC-DC converter without high duty cycles ratio and the
more turns ratios of a coupled inductor, this converter obtains a high step up voltage
conversion ratio, the leakage inductor energy of the coupled inductor is efficiently
resupplied to the load. These features explain the modules high-efficiency performance.
It also consists of a PID controller which is used to improve the steady state performance
of the converter and rise time of the converter.
2.3 SUMMARY
The literature survey of previous research works done on different converters by
different authors, there drawbacks are discussed in this chapter and how the drawbacks
are overcome are discussed problem formulation section.
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Figure 3.1 Circuit of proposed converter
The proposed converter has two features:
1) The connection of the two pairs of inductors, capacitor, and diode gives a large step-up
voltage-conversion ratio;
2) The leakage-inductor energy of the coupled inductor can be recycled, thus increasing
the efficiency and restraining the voltage stress across the active switch.
In order to simplify the circuit analysis of the proposed converter, the following
assumptions are made.
1) All components are ideal, except for the leakage inductance of coupled inductor T1,
which is being taken under consideration. The on-state resistance RDS(ON) and all parasitic
capacitances of the main switch S1 are neglected, as are the forward voltage drops of
diodes D1D3.
2) The capacitors C1 C3 are sufficiently large that the voltages across them are
considered to be constant.
3) The ESR of capacitorsC1C3and the parasitic resistance of coupled inductor T1 are
neglected.
4) The turns ratio n of the coupled inductor T1windings is equal to N2/N1.
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3.2.1 OPERATING PRINCIPLES OF THE PROPOSED CONVERTER
In this section the five operating modes of the proposed converter are explained in brief
The operating principle of continuous conduction mode (CCM) is presented in
detail. The current waveforms of major components are given in Fig. 3.2. There are five
operating modes in a switching period. The operating modes are described as follows.
Mode I [t0, t1]: In this transition interval, the magnetizing inductor Lmcontinuously
charges capacitor C2through T1when S1is turned ON. The current flow path is shown in
Fig. 3.3; switch S1and diode D2 are conducting. The current iLm is decreasing because
source voltage VIN crosses magnetizing inductor Lm and primary leakage inductor Lk1;
magnetizing inductor Lm is still transferring its energy through coupled inductor T1 to
charge switched capacitor C2, but the energy is decreasing; the charging current i D2and
iC2are decreasing. The secondary leakage inductor current iLK2is declining as equal to iLm
/ n. Once the increasing iLk1equals decreasing iLmat t = t1, this mode ends.
Figure 3.3 Mode I of proposed converter in Continuous Conduction Mode Operation
Mode II[t1,t2]: During this interval, source energy Vinis series connected with N2,
C1 , and C2 to charge output capacitor C3and load R; meanwhile magnetizing inductor
Lm is also receiving energy from V in. The current flow path is shown in Fig. 3.4, where
switch S1 remains ON and only diode D3 is conducting. The iLm, iLk1, and iD3 are
increasing because the VIN is crossing Lk1, Lm, and primary winding N1; Lmand Lk1are
storing energy from VIN; meanwhile VIN is also serially connected with secondary
winding N2 of coupled inductor T1, capacitors C1, and C2, and then discharges their
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energy to capacitor C3and load R. The iin, iD3 and discharging current |i C1| and |iC2| are
increasing. This mode ends when switch S1is turned OFF at t = t2.
Figure 3.2 Some typical waveforms of proposed converters at CCM operation.
Figure 3.4 Mode II of proposed converter in Continuous Conduction Mode Operation
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Mode III [t2, t3]: During this transition interval, secondary leakage inductor Lk2
keeps charging C3when switch S1is OFF.
Figure 3.5 Mode III of proposed converter in Continuous Conduction Mode Operation
The current flow path is shown in Fig. 3.5, where only diode D1 and D3 are
conducting. The energy stored in leakage inductor Lk1flows through diode D1to charge
capacitor C1 instantly when S1 is OFF. Meanwhile, the energy of secondary leakage
inductor Lk2 is series connected with C2 to charge output capacitor C3 and the load.
Because leakage inductance Lk1and LK2are far smaller than Lm, iLk2 rapidly decreases,
but iLm is increasing because magnetizing inductor Lm is receiving energy from Lk1.
Current iLk2decreases until it reaches zero; this mode ends at t = t3.
Mode IV [t3, t4]: During this transition interval, the energy stored in magnetizing
inductor Lm is released to C1and C2simultaneously. The current flow path is shown in
Fig. 3.6. Only diodes D1 and D2 are conducting. Currents iLk1 and iD1 are continually
decreased because the leakage energy still flowing through diode D1 keeps charging
capacitor C1. The Lm is delivering its energy through T1and D2 to charge capacitor C2.
The energy stored in capacitor C3 is constantly discharged to the load R. These energy
transfers result in decreases in iLk1and iLmbut increases in iLk2 . This mode ends when
current iLk1is zero, at t = t4.
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Figure 3.6 Mode IV of proposed converter in Continuous Conduction Mode Operation
Mode V [t4, t5]: During this interval, only magnetizing inductor Lm is constantlyreleasing its energy to C2. The current flow path is shown in Fig. 3.7, in which only diode
D2 is conducting. The iLm is decreasing due to the magnetizing inductor energy flowing
through the coupled inductor T1 to secondary winding N2 and D2 continues to charge
capacitor C2. The energy stored in capacitor C3 is constantly discharged to the load R.
This mode ends when switch S1 is turned ON at the beginning of the next switching
period.
Figure 3.7 Mode V of proposed converter in Continuous Conduction Mode Operation
3.3 PID CONTROLLER
Feedback is used in control systems to change the dynamic behavior of the
system, even if it is mechanical, electrical, or biological, and to maintain stability. The
control method of the proposed converter is based on a Proportional-Integral-Derivative
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