DESIGN A M ) IMPLEMENTATION OF A SINGLE PHASE

BI-DIRECTIONAL DC-DC CONVERTER

MEGAT AZAHARI BIN CTIIJI.AN

This thesis is submitted as partial fulfillment of the requirements for the award of the

Master of Engineering (Electrical Energy and Power System)

Faculty of Engineering

University of Malaya

AUGUST 2007

UNIVERSITY MALAYA

ORIGINAL LITERARY WORK DECLARATION

Name of Candidate:

MEGAT AZAHARI BIN CHULAN (I.C/PassportNo: 670930-08-6115)

Registration/Matric No:

KGD 030015

Name of Degree:

MASTER OF ENGINEERING

Title of Project Paper/Research Report/Dissertation/Thesis ("this Work"):

DESIGN AND IMPLEMENTATION OF A SINGLE PHASE BI-DIRECTIONAL

DC-DC CONVERTER

Field of Study:

ELECTRICAL ENERGY AND POWER SYSTEM

I do solemnly and sincerely declare that:

(1) I am the sole author/writer of this work.

(2) This Work is original.

(3) Any use of any work in which copyright exists was done by way of fair dealing for

permitted purposes and any excerpt or extract from, or reference to or reproduction of

any copyright work has been disclosed expressly and sufficiently and the title of the

Work and its authorship have been acknowledged in this Work.

n

(4) I do not have any actual knowledge nor ought I reasonably to know that the making

of this work constitutes an infringement of any copyright work.

(5) I hereby assign all every rights in the copyright to this Work to the University of

Malaya ("UM"), who henceforth shall be the copyright in this Work and that any

reproduction or use in any form or by any means whatsoever is prohibited without

the written consent of UM having been first had and obtained.

(6) I am fully aware that if in the course of making this Work I have infringed any

copyright whether intentionally or otherwise, I may be subject to legal action or any

other action as may be determined by UM.

Candidate's Signature Date

Subscribed and solemnly declared before,

Witness's Signature Date

Name:

Designation:

ACKNOWLEDGEMENT

First of all, I would like to thank Allah Almighty for blessing and giving me strength to

accomplish this thesis. I also would like to acknowledge Dr. Saad Mekhilef for his

continuous guidance, help and encouragement throughout the work. Without his

commitment, this dissertation would not have been possible. He has helped me to

concentrate all my efforts on this work and encouraged me to have the confidence in my

project.

Many of my accomplishments would not been realize without his dedication to work hard.

Thank to Universiti Tun Hussein Onn Malaysia (UTHM) in providing me the financial

assistant along the period of my study in this university.

Special thanks and appreciation goes to all my friends especially Suhaimi, Zaihan, Fadzil,

Liliwati, Mr. Rahim and people either in UM and UTHM for their help at various occasion.

Lastly, my warmest thanks go to my mother and my family for their support. My highest

appreciation goes to my loving wife, Saemah Ariffin, and all my loving children, Megat

Hafiz, Siti Radhiah, Siti Shahirah, Nurshahida and Megat Haziq for their unconditional

support and love that continuously fed my strength desire to succeed.

iv

ABSTRACT

High frequency bi-directional dc-dc converters are currently widely used in a diversity of

power electronic applications. In order to interconnect the various DC sources at different

voltage levels, one requires bi-directional DC/DC converters capable of converting the

voltage from one level to another whilst also able to control the direction of power flow

through the converter. The use of a bi-directional dc-dc converter in motor drives devoted

to Electric Vehicles (EV) allows a suitable control of both motoring and regenerative

braking operations. A bi-directional arrangement of the converter is needed for the reversal

of the power flow, in order to recover the vehicle kinetic energy in the battery by means of

motor drive regenerative braking operations.

A full-bridge, single phase inverter and converter that uses Pulse Width Modulation (PWM)

to control the power switches was constructed. The concept of PWM with different

strategies for converter is described. The PWM was produced with a simple circuit and

using several chips and devices that are easily available in the market. The P W M signals

are simulated using OrCAD simulation tools. MOSFET IRF520 is used for high frequency

switching in both sides inverter and converter. An isolation transformer (ratio 1:1) is used

between inverter outputs and input of bi-directional of DC-DC converter.

The proposed converter has the advantages of high switching frequency, high efficiency,

simple circuit, low cost and bi-directional power flow. The detailed design and operating

principles are analyzed and described. The simulation and experimental waveforms for the

proposed converter are shown to verify its feasibility.

v

TABLE OF CONTENTS

DECLARATION ii

ACKNOWLEDGEMENT iv

ABSTRACT v

TABLE OF CONTENTS vi

LIST OF FIGURES x

LIST OF SYMBOL xiii

LIST OF ABBREVIATIONS xiv

LIST OF APPENDICES xv

CHAPTER 1 INTRODUCTION 1

1.0 Introduction to Power Electronics 1

1.1 Significance of Power Electronics 2

1.2 Basic switch application 3

1.3 Power Semiconductor Devices 4

1.4 Power Converters 8

1.5 Pulse Width Modulation 10

1.6 Snubber circuit for power semiconductor devices 12

1.7 Objectives of the Project 13

1.8 Outline of the thesis 13

vi

CHAPTER 2 LITERATURE REVIEW 15

2.0 Introduction 15

2.1 Pulse width modulated controller 15

2.2 Digital P W M Controller 16

2.3 Soft-Switching technique 17

2.4 Reduce current stresses 18

2.5 Converter topologies 20

2.6 Zero Voltage Switching and Zero Current Switching 21

2.7 High switching frequency 22

CHAPTER 3 PULSE WIDTH MODULATION 25

3.0 Introduction 25

3.1 Digital PWM Technique 27

3.2 Sinusoidal PWM 28

3.2.1 Natural Sampling Technique 30

vii

CHAPTER 4 BI-DIRECTIONAL DC-DC C O N V E R T E R 33

4.0 Introduction 33

4.1 Power semiconductor switching device 34

4.2 Switching mode operation 36

4.2.1 Operation Scheme 36

4.2.2 Design of inverter using OrCAD simulation tools 37

4.3 Reverse recovery characteristics 39

4.4 Snubber circuit 43

4.4.1 Snubber Chosen 44

4.5 IRF 520, N-Channel Power M O S F E T 45

CHAPTER 5 D E V O L O P M E N T OF P W M 46

5.0 Introduction 46

5.1 Generating P W M 46

5.2 Design and implement of P W M 47

5.2.1 Precision Waveform Generator (ICL8038) 49

5.2.2 Modulating Signal 49

5.2.3 High Frequency Carrier Signal 52

5.3 Buffer 52

5.4 Comparator LM311 53

5.5 Pulse Divider 55

5.6 Gate Driver 57

viii

CHAPTER 6 HARDWARE IMPLEMENTATION 59

6.0 Bi-Directional DC-DC Converter Circuit 59

6.1 Mode operation of the converter 61

6.2 LC Filter 62

6.3 Isolation transformer 64

6.3.1 Design of isolation Transformers 65

CHAPTER 7 SIMULATION AND EXPERIMENTAL RESULTS 66

7.0 Introduction 66

7.1 P W M OrCAD Simulation Results 67

7.2 P W M experimental results 70

7.3 Inverter simulation results 72

7.4 Experimental Results 74

7.4.1 Inverter 74

7.4.2 One directional DC-DC converter 75

7.4.3 Bi-directional DC-DC converter 76

7.5 Input and output using batteries 79

CHAPTER 8 CONCLUSION 81

8.0 Concluding Remarks 81

8.1 Author 's Contribution 81

8.2 Suggestions of Area for Future Works 82

List of References 8 3

Appendix A 93

LIST OF FIGURES

No. of figures Titles Pages

Figure 1.1 Two-quadrant switches of bi-directional current 3

Figure 1.2 Power MOSFET characteristics and its integral body 3

diode

Figure 3.1 PWM signals of varying duty cycles 26

Figure 3.2 Ideal sinusoidal P W M 29

Figure 3.3 Regular symmetric sampling strategy 31

Figure 3.4 Regular Asymmetrical sampling strategy 32

Figure 4.1 Block diagram of overall interconnection for PWM and 33

Converter

Figure 4.2 A Bi-directional DC-DC Converter 34

x

Figure 4.3 PWM switching timing pattern 35

Figure 4.4 Scheme for converting DC to AC 36

Figure 4.5 Schematic diagram of Full bridge inverter 38

Figure 4.6 Schematic diagram of PWM 38

Figure 4.7 Output of inverter design 39

Figure 4.8 Reverse recovery characteristics 40

Figure 4.9 Reverse recovery circuit and waveform 41

Figure 4.10 Series connected snubber 44

Figure 4.11 Model of IRF520 45

Figure 5.1 Function Diagram 48

Figure 5.2 General Schematic Precision Waveform Generators 48

Figure 5.3 Complete Circuit Precision Sine Waveform Generator 50

Figure 5.4 Modulating Signals 51

Figure 5.5 High Frequency Carrier Signal 52

Figure 5.6 Ideal Buffer schematic 52

Figure 5.7 Buffer amplifier 53

Figure 5.8 Schematic of the comparator stage 53

Figure 5.9 Practical input comparator sine wave and triangle wave 54

Figure 5.10 Practical output comparator LM311 PWM generation 54

Figure 5.11 Practical output comparator LM311 PWM generation 55

(50 kHz)

Figure 5.12 PWM and divider/switcher pulse 56

Figure 5.13 Practical output switcher and P W M through AND gate 56

Figure 5.14 Output AND gate is obtained PWM (4V) 57

xii

Figure 5.15 Schematic diagram of gate driver 58

Figure 5.16 High frequency switching P WM 5 8

Figure 6.1 Schematic of Bi-directional DC-DC Converter 59

Figure 6.2 Output of PWM switching pattern 60

Figure 6.3 Mode operation 1 &2 61

Figure 6.4 Mode Operation 4&5 62

Figure 6.5 Pie Filter for Inverter 63

Figure 6.6 Transformer current and transformer voltage 64

Figure 7.1 Schematic diagram of single phase bidirectional 66

converter

Figure 7.2 Schematic diagram of PWM generation 67

Figure 7.3(a) Sine waveform and triangle waveform 68

Figure 7.3(b) P W M signals after comparator LM311 68

Figure 7.3(c) P W M signals switching pattern 69

Figure 7.4 Sine waveform and triangle waveform 70

Figure 7.5 PWM signal 70

Figure 7.6 P W M signal before gate driver 71

Figure 7.7 PWM signal after gate driver 71

Figure 7.8 Complete P W M for full bridge switching 72

Figure 7.9 Output inverter before filter 73

Figure7.10 Output inverter after LC filter 73

Figure 7.11 Output inverter from unfiltered output 74

Figure 7.12 Output inverter from filtered output 74

Figure 7.13 Inverter and converter outputs 75

xii

Figure 7.14 Inverter, voltage and current output 76

Figure 7.15 Inverter and Bi-directional DC-DC converter output 77

Figure 7.16 Input and output Bi-directional DC-DC converter 77

Figure 7.17 Output of Bi-directional DC-DC converter 78

Figure 7.18 Output Current of Bi-directional DC-DC converter 78

Figure 7.19 Bidirectional converter with external supply 79

Figure 7.20 Initial result 80

Figure 7.21 Result when applied external voltage supply 80

LIST OF S Y M B O L S

Symbols:

(i Micro (10"6)

xiii

I Sum

<d Omega

(p Phase displ

C Capacitanc<

f Frequency

k Kilo (103)

L Inductor

m mili (10*3)

M Mega (106)

LIST OF ABBREVIATIONS

Abbreviations

AC Alternating Current

ADC Analog to Digital Converter

ASIC Application Specific Integrator

BJT Bipolar Junction Transistor

CFI Current Fed Inverter

CVCF Constant Voltage and Constant Frequency

DC Direct Current

DCM Discontinuous Conducting Mode

DSP Digital Signal Processor

EV Electric Vehicles

GAL General Array Logic

GTO Gate Turn-Off

HVDC High Voltage Direct Current

IGBT Insulated Gate Bipolar Transistor

KV Kilo-Volt

MOD Modulus

MOS Metal Oxide Semiconductor

MOSFET Metal Oxide Semiconductor Field Effect Transistor

NS Natural Sampling

PAL Programmable Array Logic

PWM Pulse Width Modulation

PPM/°C Part Per Million

RAS Regularly Asymmetric Sampling

RMS Root mean square

RSS Regular Symmetric Sampling

SPWM Sinusoidal Pulse Width Modulation

THD Total Harmonic Distortion

TTL Transistor-transistor Logic

U/D Up Down

UP University Program

UPS Uninterruptible Power Supply

VFI Voltage Fed Inverter

ZCS Zero Current Switching

z v s Zero Voltage Switching

LIST OF APPENDIX

No. of appendix Title

Appendix A Pictures of hardware implementation

CHAPTER 1

INTRODUCTION

CHAPTER 1

INTRODUCTION

1.0 Introduction to Power Electronic

1.0.1 History of Power Electronic devices

Power Electronics began with the introduction of the mercury arc rectifier in 1900. This

was followed by the first electronic revolution which began in 1948 with the invention of

the silicon transistor.

The second electronic revolution began in 1958 with the development of the thyristor.

This caused the beginning of a new era for power electronics, since many power

semiconductor devices and power conversion techniques were introduced using

thyristors. Next, was the microelectronics revolution which gave the ability to process a

huge amount of data in a very short time. The power electronics revolution which merges

power electronics and microelectronics provides the ability to control large amounts of

power in a very efficient manner. Power electronics have already found an important

placc in modern technology and are now used in a great variety of high-power products,

including motor controls, power supplies and High Voltage Direct Current (VHDC)

systems [1],

1

1.0.2 Definition of Power Electronics

Power Electronics is defined as the application of solid-state electronics for the control

and conversion of electric power. Power Electronics is based on the switching of power

semiconductor devices whose power handling capabilities and switching speeds have

improved tremendously over the years. It is presently playing an important role in

modern technology and is used in a variety of high power products e.g. motor controls,

heat controls, light controls and power supplies. [2]

1.1 Significance of Power Electronics

The demands for control of electric power exist for many years. The generation,

transmission, and distribution of electric power are almost Alternating Current (AC)

today. But in industry, transportation, agriculture, and everyday life often demand Direct

Current (DC) power. In any technically and economically defined situation, it is

necessary to provide the most suitable form of energy to meet the demand of user [3].

Power Electronics can process the power in two forms, AC and DC. For AC, it can be

processed by magnitude and frequency and for DC by magnitude only [4],

2

1.2 Basic switch application

r r r i K-K13

Current- 03710

bidirectional two-quadrant switch nnti

cf-rja relari

m=l

Voltage-bidirectional tv/o-quadrant sv/itch •rclnra

(a) Current (b) voltage

Figure 1.1: Two-quadrant switches of bi-directional current.

/

on (transistor conducts)

on v

on (diode conducts)

H G: (a) Characteristics (b) Integral body diode

Figure 1.2: Power MOSFET characteristics and its integral body diode

1.2.1 Voltage and Current bi-directional two-quadrant switches

There are several characteristics of power MOSFET [2]:

1) Usually an active switch, controlled by terminal C (gate).

2) Normally operated as two quadrant switch.

3) Can conduct positive or negative on-state current

4) Can block positive off-state voltage

5) Provided that the intended ON-state and OFF-state operating points lie on

the composite i-v characteristic, then switch can be realized as shown in

Figure 1.2.

Controllable switches can be turned on and off by low-power control signals (e.g. BJT,

MOSFET, IGBT, GTO).

E3 Power Semiconductor Devices

Power semiconductor devices are divided into five different groups:

I) power diodes

II) thyristors

III) power Bipolar Junction Transistors (BJTs)

IV) power Metal Oxide Semiconductor Field Effect Transistor (MOSFETs)

V) insulated Gate Bipolar Transistors (IGBTs)

1.3.1 Power Diodes

A diode is a two terminal device consisting of an anode and a cathode. The diode

conducts when its anode voltage is more positive than that of the cathode. If the cathode

voltage is more positive than its anode voltage, the diode is said to be in the blocking

mode. There are three types of power diode:

i) General purpose

4

ii) High speed (or fast recovery) - used for high frequency

switching of power converters

iii) Schottky - have low on state voltage and very small recovery

time, typically nanoseconds

1.3.2 Thyristors

A thyristor is a three terminal device consisting of an anode, a cathode and a gate. It is

physically made up of four layers of alternate p-type and n-type silicon semiconductor.

The terminals connected to the ending p-type and the n-type layers are the anode and

cathode respectively. This configuration will give three p-n junctions. When the anode is

held more positive than the cathode, two of the p-n junctions are forward biased, offering

very little resistance, and one is reverse biased, offering high resistance.

When a small current is passed through the gate to cathode circuit, and the anode is at a

higher potential than the cathode, the thyristor conducts current from anode to cathode.

In other words when triggered the thyristor has approximately the same characteristics as

a single diode. Once the thyristor has been turned on, the gate circuit looses control of

the thyristor and the forward voltage drop across the device is very small (in the region

of 0.5 to 2V).

Once on, the device loses control over the anode current, and the only way to turn it off

is to reduce the anode current below some value referred to as the holding value. This

can be achieved in one of two ways:

5

i) by making the anode potential equal or less than the cathode

potential, due to the sinusoidal nature of an ac voltage which is

. called line commutation

ii) By using of an auxiliary as in the case of forced-commutation.

1.3.3 Power Bipolar Junction Transistors (BJTs)

These are three terminal devices consisting of emitter, base and collector which operates

as a switch in the common emitter configuration. These devices are turned-on when the

base-emitter junction is forward biased with the base current sufficiently large to drive

the device into saturation. Under these conditions, the collector-emitter voltage drops in

a range of 0.5 to 1,5 V. If the base-emitter junction is reversed biased the device switches

to the off or non-conducting state.

1.3.4 Power MOSFETs

The power MOSFET is the high power version of the low power with typical ratings of

tens of amperes and hundreds of volts. Both "n-channel" and "p-channel" devices are

being made, but the former are available in higher ratings because the electrons have a

higher mobility than holes inside the silicon crystal. Although the working principle of a

power MOSFET is the same as that of its low power version, there are significant

differences in the internal geometry.

6

MOSFETs have a "planar" structure. This means that all the terminals of the device are

on one side of the silicon pellet. Therefore the internal current flow paths are parallel to

the surface of the pellet. Power MOSFETs have a vertical structure, meaning that the

current flow is across the pellet, between its power terminals, which make contact on

opposite sides of it. This results in lower internal voltage drop and higher current

capability. A power MOSFET can be used either as a static switch or for analog

operation. The main considerations in this choice are:

1) Power MOSFET is a voltage controlled device, which requires

negligible current in its control terminal to maintain the ON state.

2) Power MOSFETs have relatively shorter switching times. Therefore

they can be used at higher switching frequencies.

3) The internal junction structure of a power MOSFET is such that there exists

a diode path in the reverse direction across the main terminals of the

switch. Therefore it is, in effect, parallel combinations of two static

switches are controlled switch for forward current flow and an uncontrolled

diode switch for reverse currents.

The device is turned-off when the gate voltage is removed power. MOSFET possesses

faster switching speeds than power BJTs.

1.3.5 Insulated Gate Bipolar Transistor (IGBTs)

The IGBT is a three terminal device consisting of gate, emitter and collector. It combines

the low on-state voltage drop characteristics of the BJT with the excellent switching

characteristics and high input impedance of the MOSFET. They are available in current

7