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