high voltage gain,high step up dc-dc converter

8/11/2019 high voltage gain,high step up dc-dc converter

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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 3.15 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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HIGH VOLTAGE GAIN, HIGH STEP UP DC-DC CONVERTER

MTECH, EPE, DSCE BANGALORE 1

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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MTECH EPE DSCE BANGALORE 15

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

high voltage gain,high step up dc-dc converter

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