UNIVERSITI PUTRA MALAYSIA

DESIGN AND CONSTRUCTION OF A DC·TO·DC CONVERTER FOR ELECTRIC VEHICLE APPLICATION

EYAD MOH'D RADWAN

FK 1998 11

DESIGN AND CONSTRUCTION OF A DC·TO·DC CONVERTER FOR ELECTRIC VEmCLE APPLICATION

By

EYAD MOH'D RADWAN

Thesis Submitted in Fulfillment of the Requirements for the Degree of Master of Science in the Faculty of Engineering

Universiti Putra Malaysia October 1998

AKNOWLEDGMENTS

Thanks to God (ALLAH), f or helping me to complete this work .

I wish to express my prof ound gratitude to my supervisor, D r. Jr. Norman Mariun,

Lecturer in the Electrical and Electronic Engineering, Universiti Putra Malaysia, f or

his supervision, guidance, encouragement, support and helpful discussions during

all of this work.

I would also like to express my grateful thanks to all of my committee

supervisors, Dr. Ishak Aris, Assoc. Prof . Muk htar Ahmad, and to all the Eng ineering

Faculty staff . Thanks are al so extended to al l the CASC laboratory m embers, and to

all of my f riends, here in Malaysia and back in J ordan. Finally I would l ike to

f orward my appreciation to my f ather, m other, my brothers, and sisters in J ordan for

their support and belief in me.

11

TABLE OF CONTENTS

Page

ACKN"OWLEDGMENTS........................................................... 11 LIST OF TABLES....... .................. ...... ...... ... ...... ...... ... ... .... ..... v LIST OF FIGURES................................................................... VI LIST OF ABBREVIATIONS..................................................... . . . IX ABSTRACT.... ......... ......... .... ........ ... ....... ... ........ .... ... ........ ...... XlII ABSTRAK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. XV

CHAPTER

I INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 1

II �IT�Fli\T��VI��. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 5 The �lectric Vehicle System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

System Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Body Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 �v Propulsion Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Battery Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Direct Current Machine Drives and Control. . . . . . . . . . . . . . . . . . . . . . . 17 �quivalent Circuit of DC Motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 DC Motor Drives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Chopper Operation with DC Motor as a �oad. . . . . . . . . . . . . 43 The �ffect of Using �C Filter on the Output Voltage Ripple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .... . . .. 47

ill MAT�RIALS AND M�THODS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 50 High Power Circuit Motor Control Design. . . . . . . . . . . . . . . . . . . . . . . . 51

Power Switches Multiple Discretes and High power Modules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 53 Heat Sink Design Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Motor Inductance Clamp Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Current Sensing Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

�ow Currents Control Circuit Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 MC33033p Brushless DC Motor Controller. . . . . . . .. . . . . . . . . . 73 IGBT Gate Drive Circuit Design. . . . . . . . . . . . . . . . . .. . . . . . .. . . . . 75

IV �S� TS AND DISCUSSION ... . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 �ow Currents Circuit. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 High Current Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Results of Simulation Program. . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . 95

V CONC�USION AND F� STUDI�S . . . . . . . . . . . . . . . . . ... . . . . 101

iii

REFERENCES.. . . . . . .. . .. . . .. . ... . . . . . . . . . . . . . . .. . .. . . .. . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

APPENDICES . . . . . . . . . '" . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . '" . . . . 107 APPENDIX A: Simulation Program . . . . . . . . . .. . . . . . . . . , . . . . . . . . . . . . . 108 APPENDIX B: Components Data Sheets . . . . . . . . . . . . . . . . . . . . . . . . . . 111

VITA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

IV

LIST OF TABLES

Table Page

2.1 Comparison of Different EV Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 1

2.2 Electric Vehicle Motor Application Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12

2.3 Comparison of Power Switching Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 14

4. 1 The Performance Characteristics of a Series Wound DC Motor Under Steady State Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " 97

v

LIST OF FIGURES

Figure Page

2 . 1 Functional Block Diagram ofEV Propulsion System . . . . . . . . . . . . . . . . 9

2.2 DC Motor Equivalent Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.3 The Equivalent Circuit of Separately Excited DC Motor. . . . . . . . . . . . 25

2.4 Magnetisation Curve for Separately Excited DC Motor. . . . . . . . . . . . . 25

2 .5 Characteristics of Separately Excited DC motor . . . . . . . . . . . . . . . . . . . . . 26

2.6 Series DC Motor Equivalent Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.7 Series DC Motor Characteristics Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2. 8 Single Phase Inverter Fed Separately Excited DC Motor. . . . . . . . .. . . 3 1

2.9 Chopper Circuit, Power Control Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2 . 10 Chopper Circuit, Regenerative Braking Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.11 Chopper Circuit, Rheostatic Braking Mode. . . . . . . . . . . . . . . . . .. . . . . . . . . . 35

2. 12 Chopper Circuit, Regenerative and Rheostatic Braking Mode . . . . . . . 35

2 .13 Basic Circuit of Step Down Converter . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 3 9

2 . 14 The Input Signal to the Low Pass Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2. 15 The low Pass Filter Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

2. 16 The Load Current Growth During the Progress of the Switching Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

vi

2. 17 a,b The Equivalent Circuit for Chopper ON and OFF Times R espectively. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

2. 1 8 D iscontinuous Current Waveform. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

2. 19 Continuous Conduction Mode. " . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3 . 1 Current D ensity V s. V oltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

3.2 VON V s. Ie for D ifferent IGBTs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

3.3 Use of Heat Spreader Providing Thermal Coupling Between D iscretes. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 55

3 .4 The Common Emitter In ductance as a Result of the Wiring. . . . . . . 57

3.5 The in Line Arr angement of the IGBT on a Common Heat Sink. . . 57

3.6 Diode Model Connection. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 62

3.7 Percent Current Unbalance V s. Total Current for IR GPC50F, �V Diode=0.69v . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

3.8 Junction Temperature V s. Total Current for IR GPC50F, � V Diode = 0.69v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 63

3.9 Thermal Power Flow Model for a Static Switch Mounted on a Heat Sink. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

3 . 10 Switch Current and V oltage Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

3. 1 1 The Shoot Through Current Path . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

3 . 12 Current Measurement by Means of Shunt Resistor and Op-amp . . . . 72

3 . 13 Motor Control Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

3 . 14 PWM Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . .. . . . . . . . . . . . . . . 77

3 . 15 Typical Gate Charge V s. Gate to Emitter V oltage . . . . . . . . . . . . . . . . . . . . . 8 1

3 . 16 The Complete Circuit D esign for EV Motor € ontroller. . . . . . . . . . . . . . 82

4. 1 The PWM Controller Output at 10KHZ, Duty Cycle 0.5 . . . . . . . . . . . . . 84

vii

4.2 The Tum ON Waveform at the Gate of the IGBT Under No Load Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 86

4.3 The Tum ON Waveform at the Gate of the IGB T Under Load Condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

4.4 The Tum OFF Waveform at the Gate of the IGB T Under No Load Condition. . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

4.5 The Tum -OFF Wave form at the Gate ofthe IGB T Under Load Condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

4.6 DC Motor with the Mechanical Load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

4.7 The Current Build up in the DC Motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

4.8 The V oltage Shoot Across the Switche s as a Resul t of Generated Ldildt and Load Inductance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 94

4.9 Current Build up in the DC Motor at Duty Cycle 0.95 . . . . . . . . . . . . . . 98

4. 10 Motor Deve loped Torque at Duty Cycle 0.95 . . . . . . . . . . . . . . . .. . . . . . . . 98

4. 1 1 The Voltage Across the Power Switches at Duty Cycle 0.95 . . . . . . . 99

4. 12 The Current Build up in the DC Motor at Duty Cycle 0.5 . . . . . . . . .. . . 99

4.13 The Motor Developed Torque at Duty Cycle 0.5 . . . . . . .. . ..... . . . . . . . 100

4. 14 The V oltage Across the Power switche s at Duty Cycle 0.5 . . . . . .. ... 100

Vlll

A

BDC

BDCM

BJT

Emf

EV

f

FW D

G

GTO

LIST OF ABBREVIATIONS

Ambient atm osphere

B rush type D C motor

B rushless D C motor

B ipolar jun ction transistor

Motor viscous friction constant N.m.l rad/ s

Load viscous friction constant N.m.lrad/ s

Collector

Oscillator capacitor (Farad)

D uty cycle, or diode general symbol

Emitter

Armature induced Emf. (Volt)

Electromotive force (Volt)

Electric vehicle

Frequency (Hz )

Com er frequency (Hz)

Switching fr equ ency (Hz)

Free wheeling diode

Gate

Gate tum -OFF thyristor

IX

I

IGBT

ICE

J

� I

L

MCT

MOSFET

Current flow in Ampere

Annature current (A)

Collector current (A)

Field current (A)

Gate charging current (A)

Peak current (A)

Peak-to-Peak current (A)

Valley current (A)

Insulated gate bipolar transistor

Internal combustion engine

Junction area

Rotational inertia (Kg.m2)

Dissipated conduction energy (Joules)

Load rotational inertia (Kg.m2)

Motor rotational inertia (Kg.m2)

Generated volts per field ampere

The generated volts per radian/sec or torque per ampere

Conductor length

General inductance symbol (Henry)

MOS controlled thyristor

Metal-oxide silicon field effect transistor.

x

Ni-Cd

Ni-Fe

Ni-MH

Re

S

SDC

SITH

T

Tern

V

Z CS

Nicke l-Cadmium

Nicke l- Iron

Nicke l-Metal Hybrid

Annature generated e le ctric power (W)

Conduction power loss (W)

Shaft mechanical power (W)

Switching power loss (W)

Tot al power dissipation (W)

Printe d circuit board

Charge ( coul omb)

General symbol for the e le ct rical re sist ance (ohms)

Curre nt shunt re sist ance (ohm s)

Thennal re sistance e C/W )

He at sink

Step down converter

St atic- Induction thyrist or

General symbol for the tempe rature (0 C) , t hyristor symbol

Motor electromagnetic t orque (N.m)

Junction tempe rature (0 C)

Load working torque (N.m)

General symbol for t he V olt age measure d in (V olt s)

Zero current switching

xi

ZV S

<I>

Z ero voltage switching

Flux per pole , in webers

Time constant

Mechanical angular rotational velocity radians/sec.

xu

Abstract of Thesis Submitted to the Senate ofUniversiti Putra Mal aysia i n Ful fillment of the R equirements for th e D egr ee of Master of Science.

DESIGN AND CONSTRUCTION OF A DC-TO-DC CONVERTER FOR ELECTRIC VEHICLE APPLICATION

By

EY AD MOH'D RADWAN

October 1998

Chairman: Dr. Ir. Norman Mariun

Faculty: Engineering

A DC-to-DC converter has been designed to control the speed of a DC

motor for el ectric vehicl e appl ication. The power circu it of the converter

consists of transi stori sed power switches (IGB Ts) to step-down the vol tage to

the l evel required by the speed and l oad demand. The seri es shunt resi stor

method i s u sed to control the current and keep i t bel ow the maximum rate of the

power transi stors and the motor especially at the starting point. The transi stor

gate drive circuit was designed to provide the maximum isolation between the

power and the control circuits.

A controll er chip originall y used to control a th ree phase bru shl ess DC

m otor is programmed and m odi fied to control a brushed DC motor. This

xiii

contr oller chip provide s the pulse width modulation (PWM) control signal in

or der to dr ive the power switche s at fixe d frequency and variable duty cycle .

Moreover using thi s chip a control over the curre nt flow through the power

circuit could be achieved, this will prote ct the cir cuit from any faulty condit ions

taking the bene fit of Cyc1e-by-Cyc1e curre nt dete ction.

xiv

Abstrak bagi tesis yang diserahkan kepada Senat Universiti Putra Malaysia bagi memenuhi Syarat Penganugerahan Ij azah Sarj ana Sains.

Pengerusi

Fakulti

REKABENTUK DAN PEMBINAAN PENUKAR ARUS TERUS KE ARUS TERUS

UNTUK APL IKAS I KENDERAAN ELEKTRIK

Oleh

EYAD MOH'D RADWAN

Oktober 1998

Dr. Ir. Norman Mariun

Kejuruteraan

Sebuah penukar arus tern s ke arus tern s telah direka untuk mengawal kelajuan

sebuah motor arus tern s untuk aplikasi kenderaan elektrik. Litar bekalan kuasa

bagi penukar tersebut terdiri daripada beberapa suis kuasa bertransistor

(Transistor Dwikutub Get Tert ebat - IGBT) untuk merendahkan voltan kepada

suatu peringkat yang diperlukan oleh kelajuan dan beban. Kaedah perintang

pirau siri digunakan untuk mengawal arus dan untuk mengekalkannya supaya

berada di bawah kadar maksimum bagi transistor kuasa dan motor terntama

sekali pada peringkat permulaan. Litar pemacu get transistor telah direka untuk

menghasilkan pemencilan yang maksimum antara litar bekalan kuasa dan litar

kawal an.

xv

Pada asalnya, cip pengawal digunakan untuk mengawal satu motor tiga fasa

tanpa bem s tapi kemudiannya diprogramk an dan diubah suai untuk mengawal satu

motor aru s tem s yang mempunyai bem s. Cip pengawal ini menghasilkan isyarat

kawalan lebar denyut pemodulat (PWM) untuk memacu sm s-suis kuasa pada frekue� si

yang tetap dan kitar kerja boleh ubah. Se lain daripada itu, pengawalan arus meneru si

litar bekalan kuasa juga boleh dicapai dengan penggunaan cip tersebut. O leh itu, ia dapat

me lindungi litar daripada sebarang ke adaan kerosakan dangan menggunakan kae dah

penge sanan aru s se cara kitar demi kitar.

xvi

CHAPTER I

INTRODUCTION

There have been growing interests in e lectric vehicles (EV ) in the past

15 years part icularly since 1985. The recent BV deve lopments were mainly

simulate d by the environmental conce rns (Chang, 1993). Because of the up

coming short age of gasoline products, the cost, and supply of them have

encouraged t he pe ople to look at the BV as a possible altern ative mode of

transportation.

As electricity can be generated from many alternate energy res ources

BV s are the ultimate flexible fuel ve hicle, more over the y are generall y

recharged when the power utilities have excess energy available.

Basically an electric vehicle consists of (1) a batte ry pack that provides

the powe r, (2 ) an e lectric motor, and (3) a controlle r unit that regulates the

energy fl ow to the motor per instruction provided by the drive r. The controlle r

and the motor will be the main two parts discussed and analyse d in this

dissert ation.

2

The deman d for control of the electric power for the electric motor drive

system and industrial controls exists for many years, and this led to the early

development of the Ward-Leon ard system to obtain a variable D C voltage for control

of D C motor drives. Power electronics have revolutionised the concept of power

control for power con version and for control of electrical drives.

D C motors have variable speed characteristics and are used extensively in

variable-speed control over a wide ran ge. The methods of speed control are n ormally

simpler and less expen sive than that of AC drives. Both series and separately excited

D C motors are n ormally used in variable-speed drives. However series motors are

traditionally employed for traction application s. Due to the commutator, D C motors

are not suitable for very high-speed application and require more mainten ance than

the AC motors do, however from this point of view D C motors are common for the

EV application s a speed about up to 7000 rpm could be obtain ed from some DC

motor types.

DC drives can be classified in general in to three types,

( 1) Single phase dri ves.

(2) Three phase drives.

(3) Chopper drives.

Sin gle phase and three phase drives are based on con verting (rectifyin g) the AC

voltage into DC voltage usin g either sin gle phase or three phase rectification circuits.

However choppers are used to control unregulated D C input an d supply regulated

D C output.

3

The step-down chopper (convert er) topology would be used to provide a

regulated output voltage to control the speed of the D C motor. The average output

voltage would be controlled using the pulse width modulation (PWM ) techniques; at

a fixed frequency and variable duty cycle.

This dissert ation presents the initial work of providing the required facilities for a

D C-to-D C convert er for commutator series excitation D C motor control. In addition

a scheme of open loop speed control of the series D C motor is presented. The design

of the control circuit using the MC33033p controller produced by Motorola, and the

power circuit using the IGBTs produced by IRF are provided. The dissert ation is

organised in the following m anner.

In chapter Two, a literatu re review of the import ance of the electric vehicle and

the recent developments, the electric vehicle drive train types, and the main

components are discussed in brief. A general study for the D C-to-D C convert er

including, the low power control circuit, and the basic power circuit configuration is

a ls o presented. In chapt er Three, the m aterials and methods us ed in the con trol

circuit design is provided and analysed, including the gate drive technique, the

monitoring and the prot ection circuits. The high power circuit design and analysis is

provided a s well.

4

Chapter Four demonstrates the test results obtained from the output of the D C-to­

D C converter and the control circuit. The discussion of the results is included in the

respective chapter.

Conclusions about the research work associated with this dissertation are

presented in Chapter Five. Suggestions of further research related to this topic are

also included in this chapter.

CHAPTER II

LITRATURE REVIEW

The Electric Vehicle System

The electric vehicle (EV) offers one of the best solutions for improving

air quality while reducing the reliance on fossil fuel to power the vehicles. The

use of EV s remains limited, because of their driving performance has been very

poor and cost has been too high. In order for an EV to be accepted in society,

EV design should take advantage of attributes which could only be incorporated

into EV s, such as lower maintenance, quieter and easier driving.

Until now most of the electric vehicles have been converted from

existing internal combustion engine vehicles. The convert ed EV s have the

characteristics that they are easy to produce, and are less expensive to develop.

However, there was a serious pr oblem that it is difficult to make the vehicle

performance higher, because it is impossible to design by taking the advantage

of the convert ed electric vehicles (Brant, 1994)

5

6

On the other hand some of the gr and-up designed EV s have been produced, the

IZA, and the gener al motors IMP ACT are examples. These EV s achieved remarkably

high per fonnance. For instance, in the IZA the mileage per one charge, on 100 KmIh

r ecor ded 270 Km . It accel erates 0-to-40Om within 18 seconds and its highest speed is

176Km1h (Chan, 1993).

System Technology

The EV system is an integr ation of vehicl e body (chassis, exterior, inter ior),

dr ive train (motor, controll er' s transmission, br akes, sensors), energy storage (batter y),

safety system and auxil iaries. The technologies involved are diversifi ed, which includes

el ectrical and electronic engineering, mechanical and automotive engineering, and

chemical engineering. The phil osophy and architecture of the system are of prime

consideration. System integration and optimisation enabl es perfect matching among

subsystems, bearing in mind that th e components used in the EV are working in mobil e

and sever e temperature conditions. A thorough study on the degree of significant of

interaction among subsystems, components that affect vehicles cost, performance, safety

and other obj ectives shoul d be perfonn ed in order to achieve over all optimisation. The

ener gy management in EV systems is of capital import ance which control s and regul ates

the ener gy flows with in the vehicl e with aims of using the energy from batteries as

economical as possibl e and recharging the batteries mor e convenient and efficient.

7

B ased on the concept of multi-energy system, the batteries can be norm ally

charged up at night or quicker charged up in short period using the dedicated super quick

charger . During deceleration battery charging can be performed through r egenerative

brak ing. They also can be charged by solar ener gy using the solar cells embedded in the

vehicle roof (Chan, 1 993).

B ecause of the energy densities of stor age batteries are so much smaller than that

of the fuel of the internal combustion engine PCE), a larger number of batteries should

be used to assure a certain level of power performance. However, mounting a vehicle

with a larger number of batter ies require various types of tr ade- off. For instance, it

r educes the interior space and luggage space; the reSUlting incre ase in vehicle weight

sacr ifices acceler ation and other areas of per formance; and t he cost of the vehicle also

n se s.

Body Technology

The consistent weight-saving design of EV s is ver y impor tant, which dir ectly

affects the per form ance of EV s. The EV body is of a hybrid design, possibly consisting

of supporting aluminium structure which is light and very r igid, and plastic outer skin.

The EV suspension is purp osely designed to attain simplicity and ver y light we ight.

Low drag coefficient body design can effectively reduce the aerodyn amic re sistance of

the body. In general it is more difficult to reduce the dr ag coeffi cient as the vehicle

length is shortened. However the aerodynamic r esistance can still be r educed through a

good balance among the following features, taper ing of the front and the rear ends, fl at

8

under floor design, adoption of an undercover optimisation of air flow around the front

and rear windows, and slanted front nose design. The drag coefficient of GM IMPACT

reached 0. 19, which is among the lowest figure in present EV (Chan, 1993).

Low rolling resistance tyres are particularly effective in reducing running

resistance at low and medium driving speeds and play an important role in extending the

range of EV s in city driving. This has been achieved through the use of a newly

developed blended tyre polymer, together with an increase in tyre pressure. The rolling

resistance ofGM IMPACT is 0.0048 which is about the half that of conventional tyres.

EV Propulsion Technology

An electric propulsion system is the heart of EV s. Its function is to transfer with

high efficiency the electrical power from the battery to the mechanical power of moving

elements. From functional point of view, an electric propulsion system can be divided

into two parts namely the electrical and mechanical parts. As shown in Figure 2. 1 the

electrical part consists of the following sub-systems:

(1) Electric motor,

(2) Power electronics, and

(3) Electronic control.

On the other hand, the mechanical part includes these sub-systems:

(1) Transmission device, and

(2) Moving elements.