A Closed Loop Pulse Width Modulated Vsi-Based Control of Squirrel Cage Induction Motor.

ABSTRACT This project presents a quality model of induction motor showing steady state and dynamic analysis using Volt/Hertz open loop, Volt/Hertz closed loop, Slip differences and constant flux methods. The main objective is to maintain the speed at constant rotor flux and to investigate the control schemes for controlling induction machine, particularly the scalar control method and to evaluate their performance under variable input-output conditions. Analysis of the steady state equivalent circuit model of the induction motor is established showing equations that justify the use of constant Volt/Hertz speed control of both open and closed loop techniques. The induction motor is fed from three phase bridge inverter which is operated with sinusoidal pulse width modulation (SPWM) technique and these are used to evaluate the developed models. With the help of a powerful tool called MATLAB SIMULINK it is observed that the induction motor control performance is improved by adopting the constant flux method, the simulation results have shown the efficiency of the proposed models, the performance of volt/hertz technique and constant flux technique are also compared.

TABLE OF CONTENT

Page

TITLE PAGE…………………………………………………………….….…i

CERTIFICATION………………………………………………………….….ii

DEDICATION…………………………………………………..……….……iii

ACKNOWLEDGEMENT…………………………………….…………..…..iv

ABSTRACT………………………………………………………………….…v

TABLE OF CONTENTS………………………………………….……….…..vi

LIST OF SYMBOLS AND ABBREVIATION…………………………...…...xi

LIST OF FIGURES………………………………………………………...…xiii

LIST OF TABLES………………………………………….….……………...xiv

CHAPTER ONE: INTRODUCTION 1

1. Introduction 1

1.1 Problem description 6

1.2 Research objective 7

1.3 Limitations of work 9

1.4 Scope/outline of work 9

9

CHAPTER TWO: LITERATURE REVIEW 11

2.1 AC INDUCTION MOTOR CONTROL 11

2.2 Types of AC induction motor control. 11

2.3 Field Orientation Control of Induction Machine 12

2.3.1 Indirect Field Orientation Control 13

2.3.2 Direct Field Orientation 14

2.4 Scalar control methods 16

2.4.1 Methods of speed control of induction motor 16

2.4.2 Pole changing method of induction motor 17

2.4.3 Variable terminal voltage control 17

2.4.4 Variable frequency control 18

2.4.5 Variable voltage and variable frequency control 19

2.4.6 Modified volt/hertz method using voltage boost at low frequency

21

2.5 The three phase inverter and Principle of Operation 22

10

2.5.1 Sinusoidal Pulse width modulation (SPWM) 27

2.6 Analysis of Control Strategies. 31

CHAPTER THREE: 32

3.1 Dynamic modeling of squirrel cage induction motor 32

3.1.1 Assumptions for model development. 32

3.1.2 D-Q model of induction motor. 33

3.1.3 Induction motor dynamic equation. 34

3.2 Motor reference frame (synchronous) 38

3.3 Changing stator voltage and frequency in equal proportion 38

3.4. Constant flux control 42

CHAPTER FOUR: SIMULATION RESULTS AND DISCUSSION

4.1 Design of open loop system 48

4.1.1 Volt/Hertz Open loop simulation results and discussion. 49

4.2 Design of closed loop control system. 55

4.2.1 Volt/hertz Open loop simulation results and discussion. 59

11

4.3 Volt/hertz slip speed simulation results and discussion 62

4.4 Constant flux control method simulation and results 65

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION 69

5.0 Conclusion 69

5.1 Recommendation 70

REFERENCES 71

APPENDIX 1 76

APPENDIX 2 77

APPENDIX 3 78

APPENDIX 4 79

APPENDIX 5 81