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 M A L A Y A
ORIGINAL LITERARY W O R K D E C L A R A T I O N
Name of Candidate:
M E G A T A Z A H A R I BIN C H U L A N (I.C/PassportNo: 670930-08-6115)
Registration/Matric No:
K G D 030015
Name of Degree:
M A S T E R OF E N G I N E E R I N G
Title of Project Paper/Research Report/Dissertation/Thesis ("this Work"):
DESIGN AND I M P L E M E N T A T I O N OF A SINGLE PHASE BI-DIRECTIONAL
DC-DC C O N V E R T E R
Field of Study:
ELECTRICAL E N E R G Y A N D P O W E R S Y S T E M
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(1)
I am the sole author/writer of this work.
(2)
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(3)
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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 U M 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
Name:
Designation:
Date
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 U M and U T H M 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 D C 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 P W M with different
strategies for converter is described. The P W M 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. M O S F E T 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
T A B L E OF C O N T E N T S
DECLARATION
ii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
T A B L E OF C O N T E N T S
vi
LIST OF FIGURES
x
LIST OF S Y M B O L
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
L I T E R A T U R E 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 W I D T H M O D U L A T I O N
25
3.0
Introduction
25
3.1
Digital P W M Technique
27
3.2
Sinusoidal P W M
28
3.2.1
30
Natural Sampling Technique
vii
BI-DIRECTIONAL DC-DC CONVERTER
CHAPTER 4
33
4.0
Introduction
33
4.1
Power semiconductor switching device
34
4.2
Switching m o d e operation
36
4.2.1 Operation Scheme
36
4.2.2 Design of inverter using O r C A D simulation tools
37
4.3
Reverse recovery characteristics
39
4.4
Snubber circuit
43
4.4.1
44
4.5
Snubber Chosen
IRF 520, N-Channel Power M O S F E T
CHAPTER 5
DEVOLOPMENT OF PWM
45
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 W a v e f o r m 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 E X P E R I M E N T A L R E S U L T S
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
Input and output using batteries
79
7.5
CHAPTER 8
81
CONCLUSION
8.0
Concluding Remarks
81
8.1
Author's Contribution
81
8.2
Suggestions of Area for Future Works
82
List of References
83
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 M O S F E T characteristics and its integral body
3
diode
Figure 3.1
P W M 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 P W M and
33
Converter
Figure 4.2
A Bi-directional DC-DC Converter
34
x
Figure 4.3
P W M switching timing pattern
35
Figure 4.4
Scheme for converting D C to AC
36
Figure 4.5
Schematic diagram of Full bridge inverter
38
Figure 4.6
Schematic diagram of P W M
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 P W M generation
54
Figure 5.11
Practical output comparator LM311 P W M generation
55
(50 kHz)
Figure 5.12
P W M and divider/switcher pulse
56
Figure 5.13
Practical output switcher and P W M through A N D gate
56
Figure 5.14
Output A N D gate is obtained P W M (4V)
57
xii
Figure 5.15
Schematic diagram of gate driver
58
Figure 5.16
High frequency switching P WM
58
Figure 6.1
Schematic of Bi-directional DC-DC Converter
59
Figure 6.2
Output of P W M 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 P W M 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
P W M signal
70
Figure 7.6
P W M signal before gate driver
71
Figure 7.7
P W M 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 D C - D C converter output
77
Figure 7.16
Input and output Bi-directional D C - D C converter
77
Figure 7.17
Output of Bi-directional D C - D C converter
78
Figure 7.18
Output Current of Bi-directional D C - D C 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
L I S T OF S Y M B O L S
Symbols:
(i
Micro (10" 6 )
I
Sum
<d
Omega
(p
Phase displ
C
Capacitanc<
f
Frequency
k
Kilo (10 3 )
L
Inductor
m
mili (10*3)
M
Mega (10 6 )
xiii
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
zvs
Zero Voltage Switching
LIST OF A P P E N D I X
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
m=l
rrri
K-K13
03710
Currentbidirectional
two-quadrant
switch
nnti
cf-rja
relari
Voltagebidirectional
tv/o-quadrant
sv/itch
(a) Current
•rclnra
(b) voltage
Figure 1.1: Two-quadrant switches of bi-directional current.
/
on
(transistor
conducts)
on
on
(diode
v
H
conducts)
(a) Characteristics
G:
(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)
1.3.3
By using of an auxiliary as in the case of forced-commutation.
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