ABSTRACT
This work presented an open loop variable voltage variable frequency (V/F) control of three phase
induction motor for an electric vehicle drive.
The major advantage of v/f is the ease of implementation.
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Simulation and practical implementation of the project was carried out using sequential logic
circuit for the control of the three phase inverter. Also included in the design is a 120V to 600V
boost converter that increases the battery supply voltage to be able to supply the 420V induction
motor. The v/f concept was implemented using NE555 to produce a square wave of 1000Hz,
which was reduced to 100Hz by the help of the decade counter and was further divided by the flipflop
to obtain a maximum frequency of 50Hz.
The results obtained shows that when there is linearity between the voltage and frequency, that
maximum constant torque is always produced, thus agreeing with the concept of v/f control of
induction motor.
TABLE OF CONTENTS
Chapter One
1.1 Energy consumption and Electric drives 1
1.2 Control of induction motor drives 2
1.3 Control of induction motor used in Electric Vehicle 3
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1.4 Statement of research problem 4
1.5 Objective of research 4
1.6 Scope and Limitation of Study 4
1.7 Significance of the study 4
1.8 Study Methodology 5
1.9 Organization of the Thesis 5
Chapter Two
2.1 Literature Review 6
Chapter Three
3.1 Introduction 12
3.2 Concept of rotating Magnetic field 12
3.3 Synchronous speed of a rotating magnetic field 15
3.4 Torque Production 15
3.5 Per-Phase model of an induction motor 16
3.6 Graphical representation of v/f 20
3.7 Problems of scalar Control v/f 21
3.8 Vector Control 21
3.9 Transformation from 3-phase variables to the variable in stationary reference 22
3.10 Transformation from stationary reference frame to synchronous rotating frame 23
3.11 Voltage equation of synchronous rotating reference frame 23
3.12 Torque Developed 26
3.13 Salient features of Vector Control 27
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3.14 Electric Vehicle 28
3.15 How it all started 28
3.16 Where we are now 30
3.17 Electric Vehicle Architecture 32
3.18 Sizing the Electric Motor 34
3.19 Choosing Electric motor 36
3.20 Choosing the Battery 37
3.21 Care of the Battery 37
Chapter Four
4.1 Design and Simulation of open-loop v/f control of 3-phase induction motor 38
4.2 Voltage controlled oscillator (vco) 38
4.3 Boost Circuit 39
4.4 Flip Flop circuit 40
4.5 Inverter Circuit 41
4.6 Three Phase induction motor 42
4.7.1 VCO Calibration and linear characteristics 43
4.7.2 Boost Circuit Simulation result 44
4.7.3 Flip Flop simulation result 45
4.7.4 Inverter output @ 10, 30 and 50Hz 45
4.8 Motor parameter graphs at variable voltage and variable frequency 47
Chapter Five
5.1 Power supply Unit 61
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5.2 12V Power Supply 62
5.3 Voltage Controlled Oscillator (VCO) 62
5.4 Triangular Wave Oscillator 64
5.5 Decade Counter and Buffer 65
5.6 Flip Flop 67
5.7 Karnaugh-Map 70
5.8 Flip Flop Operation 71
5.9 Delay Circuit 72
5.10 Design of the Delay Circuit 74
5.11 Isolation and Driver Circuit 75
5.12 Power Circuit 75
5.12.1 Boost Circuit 76
5.13 Considerations in designing the boost Converter 76
5.14 Design of Inductor 78
5.15 Six step three phase inverter 80
5.16 Principle of operation of a 3-phase six step inverter 80
5.17 Snubber Circuit 81
5.18 Experimental results of the v/f 79
Chapter 6
6.1 Conclusion 85
6.2 Recommendation 86
References 87
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Appendix One 92
Appendix Two 93
Appendix Three 94
Appendix Four 95
Appendix Five 96
CHAPTER ONE
INTRODUCTION
1.1 . Energy consumption and Electric drives.
The need for energy has being on the increase throughout the generation.
The utilization of energy is on the increase for both domestic and industrial sectors of
human existence. This has led to the wider exploration of other forms of energy. The
primary sources of energy are fossil, nuclear, hydro, tidal, wind, geothermal and solar
energy [1]. These sources have different methods of harnessing, making each preferred to
the other in terms of cost. It is estimated that about half the electricity generated in an
industrialized nation is converted to mechanical energy. The major utilization of this
energy is the electric motor; this fuelled the industrial revolution of eighteenth century
following the demonstration carried out by British Scientist, Michael Faraday, on
production of mechanical energy from electrical by the process of electromagnetic
induction. This was however based on the initial work of Andre-Marie Ampere, on the
existence of mechanical force by the interaction of electric current and magnetic field.
These laid the foundation for the emergence of Direct Current (DC) motor by Faraday and
Asynchronous or Alternating Current or induction motor by Tesla.
Electric drives are of many varieties as a result of differences in power, speed and torque
specifications. These find application in small motors used for house hold appliances and
large motors for industrial application [2].
Direct Current motors were initially used in electric drives due to their ease to control, to
analyze and wide range of speed. These advantages were played down by their numerous
disadvantages which include: complicated mechanical structure, high cost, volume, and
weight, limited speed, low efficiency, cannot operate in dirty and explosive environment and
electromagnetic interference (EMI) problem [3,4]. These problems of D.C motor led to the
discovery of control methods of induction motor.
Alternating Current motor particularly the induction motor is the hub of modern industrial
drive systems. It consists principally of a stator and rotor. The stator is also the excitation or
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field winding. The rotor can be a squirrel cage or a wound rotor [5]. The squirrel cage is
commonly used because of its advantages (rugged and efficient control technology).Based on
its principle of operation, the stator is equivalent to the primary winding of a transformer,
while the rotor is equivalent to the secondary winding. Generally, the following are the
merits of induction motor over D.C motor t: simple construction, rugged, reliable, wide range
of power, can operate in hazardous and dirty environment.
1.2. Control of induction motor Drives
The control of induction motor is a vast and complex area of study that is generating a lot of
research interest because of its supreme performance characteristics. Before the days of
power electronics, speed control in A.C motor can be achieved through any of the following
methods: Stator voltage(current) control, Switching the stator voltage connection from star to
delta or vice versa, Rotor control with voltage or current, Pole changing(changing the
number of stator poles) and Slip control[5,6].
These methods of speed control have some demerits which include bulkiness of the control
system, constant maintenance, losses (I2R) and limited speed range. With the advancement in
power electronics, numerous methods of induction motor control have being developed and
research are still on going to either improve existing ones or develop another.
Modern methods of control of induction motor drives are collectively called variable
frequency control (VFC). It can be classified into: scalar control and vector control also called
field oriented control (FOC)[7]. Scalar control, as the name implies is the control of
magnitude of the control variables only. While vector control or FOC is a control method that
controls both the magnitude and phase alignment of the control variables or takes into account
the coupling effect of the motor windings. Figure 1.1 illustrates the full classification methods
of control of induction motor
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1.3. Control of induction motor used in Electric Vehicle.
Figure 1.1 classifications of induction motor control methods [7]
Electric vehicles have been around since late 1800’s [8].The need to reduce global warming,
reduce over dependence in oil and reduce the price of oil has being pushing the development of
electric vehicles popularly called EVs. The quest for environmental friendlier and higher fuel
economy vehicles has led to the development of new technologies such as all electric
vehicle(AEV) battery powered, (HEV)hybrid electric vehicle( internal combustion engine +
battery, ICE + solar energy, ICE+ solar energy+ battery ) and Fuel cell powered electric
vehicle. The battery, Fuel cell and solar powered electric vehicles are also called zero emission
vehicles (ZEV)[9].
At the heart of the electric vehicle is the propulsion system whose efficiency can be evaluated
by the performance of the 3-phase induction motor. The control of the induction motor as we
have mentioned above can be scalar based control or vector based control or field oriented
control (FOC).
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Scalar control as stated earlier controls the magnitude of the control variables. In the
implementation of this research work, the popular Variable-voltage, variable-frequency control
is used. It is a method of controlling the speed of an AC motor by varying the stator voltage
and frequency in a constant ratio thereby controlling the air gap flux, keeping it constant to
provide the maximum torque constantly at any speed to the applied load. This method is good
for low-performance drive such as pump, compressors, fans and grinders.
Vector control is use for high performance drives such as machine tools, Lifts, Elevators, paper
and steel mills [10]. It is also called field oriented control (FOC).
1.4. Statement of research problem
This study is important in our present day economy where the demand for power is exceeds
the supply; hence the need for conservation of any available form of energy and the quest for
energy saving methods of control of an electric machine.
1.5. Objective of this thesis.
The main objective of this research is to determine if the v/f is good for the control of three
phase induction motor, for an electric vehicle application.
1.6. Scope and limitation of Study
The scope of the study is limited to scalar v/f control of three phase induction motor and for
Electric vehicle application.
1.7. Significance of the study
This study is significant because of the benefit to the following:
v Government in building a frame work for developing another way of powering vehicles,
minimizing pollution (air and noise) that is caused by ICE and development of local
manpower.
v Private sector for expanding the energy sector of the economy; through exploring
alternative energy sources.
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1.8. Study Methodology
Two methods were applied in the course of this study; a practical approach which involved
physical construction of all the drive subsystems of the control and a simulation approach which
models the physical system.
1.9. Organization of the Thesis
This thesis is organized as follows: chapter 1 focused on the general introduction, chapter 2
deals with the literature review, chapter 3 is about the modeling of three phase induction motor
and Electric vehicle, in chapter 4, the simulations of variable voltage variable frequency
control was shown. Chapter 5 shows the implementation of the v/f, while chapter 6 presents
conclusions and recommendation
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