A Pulse Width Modulated Voltage-Fed Inverter Vector-Controlled Permanent Magnet Synchronous Motor Drive

ABSTRACT 

A Pulsewidth Modulated Voltage-Fed Inverter Vector-Controlled Permanent Magnet Synchronous Motor (PMSM) Drive based on Hysteresis Current Control (HCC) is presented in this work. A detailed conceptual dq modelling of the PMSM was undertaken in the rotor reference 26 frame for open loop studies, thereby setting the pace for the variable speed drive (VSD) of the PMSM which, inherently, is not capable of variable speed operation. Subsequently, vector control by Field Orientation Control (FOC), is used to decouple the flux and torque producing stator current components of the PMSM thereby permitting independent and precise control of flux and torque as obtainable in separately excited dc machines. A complete closed loop control system employing an outer PI speed controller and an inner hysteresis current controller was implemented to realize this speed-controlled drive. Since torque can be made proportional to current either in the stationary or rotor reference frames and effective control of current gives effective control of torque, speed and position, the HCC strategy is aimed at ensuring that the actual motor phase currents track their respective sinusoidal references. The HCC algorithm was developed and employed for the logical firing of the power semiconductor switches of the inverter. The control algorithm was optimised to obtain fast speed response, while maintaining effective current and torque tracking for all practical speed inputs namely Constant, Step and RAMP reference speed inputs. The optimal control variables were identified with emphasis on effective current and torque tracking. Four quadrant operation of the PMSM was also implemented as obtains in numerous applications in industry where controlled starts and stops are required in both forward and reverse directions. Compared to the standard AC6 of MATLAB Simpower systems, the developed model achieved rise time and settling time of 0.0108 seconds and 0.0143 seconds respectively while the corresponding values for AC6 model are 0.1944 seconds and 0.1984 seconds respectively. This, clearly, shows that the developed model has an enhanced speed response.

TABLE OF CONTENT

APPROVAL PAGE i

CERTIFICATION PAGE ii

TITLE PAGE iii

DEDICATION iv

ACKNOWLEDGEMENT v

TABLE OF CONTENTS vi

LIST OF SYMBOLS xi

LIST OF ABBREVIATIONS xiv

LIST OF FIGURES xvi

LIST OF TABLES xxiv

ABSTRACT xxv

CHAPTER ONE: INTRODUCTION 1

1.0 Introduction 1

1.1 PMSM Compared to other AC Machines 2

1.2 Characteristics of Permanent Magnet Materials 4

1.3 Classification of Permanent Magnet Motors 6

1.4 Classification of Permanent Magnet Synchronous Motor (PMSM) 7

1.5 Research Objectives 10

1.6 Thesis Arrangement 11

CHAPTER TWO: LITERATURE REVIEW 14

CHAPTER THREE: THE PERMANENT MAGNET SYNCHRONOUS MACHINE 52

3.1 D-Q Modelling of Permanent Magnet Synchronous Machine using Two Phase Machine 52

3.1.1 Derivation of Inductances as a function of Rotor Position 55

3.1.2 Transformation to Rotor Reference Frame 58

3.2 Three Phase Permanent Magnet Synchronous Motor Model 60

3.3 Development of the PMSM Power and Torque Relationships 63

3.4 Steady State Torque Characteristics 66

3.5 Equivalent Circuit Representation of PMSM 69

3.6 Open Loop Line-Start Permanent Magnet Synchronous Motor 71

3.6.1 Discussion of Results 74

CHAPTER FOUR: FEATURES AND CONTROL OF THE THREE PHASE VOLTAGE-FED INVERTER FOR AC DRIVES 78

4.1 Adjustable Speed Drives (ASD) 78

4.2 The Three Phase Inverter 80

4.2.1 Six-Step Inverter Operation 82

4.2.2 Sinusoidal Pulsewidth Modulation (SPWM) of Three Phase Voltage Source Inverter 90

4.2.3 Space Vector Representation of Voltage Source Inverter Output Voltages 96

4.3 Natural Regular Sampled Pulsewidth Modulation of Three Phase Voltage Source Inverter 102

4.4 Hysteresis Current Control Strategy 106

4.5 Four Quadrant Torque Speed Characteristics 109

CHAPTER FIVE: PERMANENT MAGNET SYNCHRONOUS MOTOR CONTROL 112

5.1 Vector Control in AC Machines versus Control of Separately Excited DC Machines 112

5.2 Vector Control for Permanent Magnet Synchronous Motor 112

5.2.1 Electromagnetic Torque under Vector Control 115

5.3 General Schematic of the Speed-Controlled Drive System 118

5.3.1 Description of the General Schematic of the Speed-Controlled Drive System 119

5.3.1.1 Reference Current Estimation 120

5.3.1.2 Inverter Switch Gating Voltage Signal Estimation 121

5.4 Drive Performance with Sample PMSMs 122

5.4.1 Drive Performance for Motor One (Rated Torque 10Nm) 124

5.4.2 Drive Performance for Motor Two (Rated Torque 26Nm) 126

5.5 Drive Performance under various Speed Reference Inputs for Sample Motor Two 128

5.5.1 Case One: Drive Performance with Constant Reference Speed Input (200 rpm) 129

5.5.1.1 Highlights on Hysteresis Current Control action and the Inverter Switching 132

5.5.2 Case Two: Drive Performance with Step Reference Speed Input (0rpm to 200rpm to 400rpm to -400rpm to -200rpm to 0rpm) 140

5.5.3 Case Three: Drive Performance with RAMP Reference Speed Input (0 rpm to 500 rpm to -500 rpm to 0 rpm) 144

5.6 Drive Performance under Step Speed Transition for Four Quadrant Operation (500 rpm to -500 rpm to 500 rpm) 147

5.7 Drive Speed Response Compared with Response of SIMPOWER AC6 150

CHAPTER SIX: CONCLUSION AND RECOMMENDATIONS FOR FUTURE WORK 156

6.1 Conclusion 156

6.2 Recommendations for Future Work 158

REFERENCES 161

Appendix 1: PMSM Parameters for Open Loop Studies 175

Appendix 2: Codes for Steady State Torque Characteristics 176

Appendix 3: Embedded MATLAB Function Block 177

Appendix 4: Embedded MATLAB Function Codes 178

Appendix 5: Six Step Inverter Model 179

Appendix 6: SPWM Inverter Model 180

Appendix 7: PMSM Ratings 181

Appendix 8: Simulink Model of the Speed-Controlled Drive System 182