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ABSTRACT

This study developedmethods to improve the efficiency and torque production of the single phase induction machine using a sinusoidal pulse width modulation (SPWM) control scheme. This research targets the capacitor-run single phase induction motor(CRSPIM) which is a large consumer of domestic and industrial power supply with the goal of improving its operation at light load conditions.This motor suffers fromlow efficiency when operating under non-rated conditions,leading to wastage of significant amount of electric power since rated voltage is applied fully across its terminals and the flux in the machine operates approximately at rated value regardless of the applied load on the machine. Moreover, during starting time and at steady state, the motor exhibits significant torque pulsations which gives rise to noise and vibration in the machine. In efforts to address these problems, a performance improvement scheme using a pulse width modulated single phase inverter and a PID controller was first developed and implemented in MATLAB/Simulink environment to eliminate steady state torque pulsations in the motor. Although system simulation shows reduction in torque pulsations in the motor under the scheme compared to the performance of the same motor under nominal power supply, this scheme could not eliminate torque pulsations in steady state. Consequently, a pragmatic design modification to the parameters of the auxiliary winding of the existing CRSPIM was proposed. In addition to the design modification, a vector-controlled drive with an efficiency-optimizing function for the modified single phase induction machine was also proposed. This second approachuses a two-phase, two-leg inverter structure. Theproposed scheme was also implemented in the MATLAB/Simulink environment. Simulation results have demonstrated that the proposed strategy eliminates torque pulsations at steady state in comparison to the existing line-operated CRSPIM. It is also shown that the proposed drive control strategy increased machine efficiency over that of the existing CRSPIM significantly at light loads. Specifically, the proposed scheme yielded machine efficiency of 80.8% on all loads whereas the existing CRSPIM gives an efficiency of 79.3%, 47% and 28% for a rated load of 5.1Nm and light loads of 2Nm and 1Nm respectively. Consequently, the proposed drive scheme gives improvements of 1.5%, 33.8% and 52.8% respectively for the 5.1Nm, 2Nm and 1Nm loads over that of the conventionally-driven CRSPIM. The corresponding improvement in power consumption is a decrease of 1.6%, 45.1% and 67.6% for loads of 5.1Nm, 2Nm and 1Nm respectively.These results unveil the capability of the proposed scheme toachieve significant energy saving at light loads. The scheme is potentially able to cancel undesirable noise, reduce energy cost of running the motor, and offer possibility of cumulative savings in electric power resources of electric utilities.

 

 

TABLE OF CONTENTS

TITLE PAGE Error! Bookmark not defined.
DECLARATION ii
CERTIFICATION iii
DEDICATION iv
ACKNOWLEDGEMENT v
ABSTRACT viii
TABLE OF CONTENTS ix
LIST OF FIGURES xvii
LIST OF TABLES xxiiiiii
LIST OF ABBREVIATIONS xxiiiiv
CHAPTER ONE: INTRODUCTION 1
1.1 BACKGROUND 1
1.2 MOTIVATION 2
1.3 SIGNIFICANCE OF RESEARCH 2
1.4 PROBLEM STATEMENT 3
1.5 AIM AND OBJECTIVES 3
1.6 METHODOLOGY 4
1.7 THESIS OUTLINE 5
x
CHAPTER TWO: LITERATURE REVIEW 6
2.1 INTRODUCTION 6
2.2 OVERVIEW OF FUNDAMENTAL CONCEPTS 6
2.2.1 Single Phase Induction Machine 6
2.2.2 The Single Phase Induction Motor Theory 8
2.2.2.1 Main winding of the single phase induction machine 9
2.2.2.2 Main and auxiliary windings of the single phase induction machine 11
2.2.2.3 Torque – slip characteristics of the single phase induction machine 14
2.2.2.4 Modeling of the single phase induction machine 17
2.2.2.5 Voltage and torque equations in machine variables 19
2.2.2.6 Voltage and torque equations in the arbitrary reference frame 22
2.2.2.7 Torque produced by the capacitor-run single phase induction machine 26
2.2.2.8 Condition for zero pulsating torque 28
2.2.2.9 Analysis of auxiliary winding voltage control of the single phase Induction machine 28
2.2.2.10 Generalized condition for balanced stator currents 31
2.2.3 Inverters 34
2.2.3.1 Voltage source inverters 34
2.2.3.2 Single phase inverters 35
2.2.3.3 Pulse width modulation in inverters 38
2.2.3.4 Sinusoidal pulse width modulation (SPWM) technique 39
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2.2.3.5 Pulse width modulated single phase inverter under the unipolar voltage switching 39
2.2.3.6 Inverter topologies for two phase applications 46
2.2.4 Dynamic Modeling of the Single and Two Phase Inverter 52
2.2.5 LC Filter Design 54
2.2.6 Pulse Width Modulated Induction Motor Drive 55
2.2.7 Controller Design 56
2.2.7.1 Frequency response overview 58
2.2.8 Induction Machine Speed and Torque Control 59
2.2.8.1 Control principles of the induction machine 59
2.2.9 Reference Frame Transformation 62
2.2.10 Vector Control Strategy 65
2.2.11 Efficiency Optimization 70
2.2.12 Harmonic Balance Technique (HBT) 69
2.2.13 Fundamental Concepts of AC Machine Windings 73
2.2.13.1 Machine winding terminologies 73
2.2.13.2 Classification of AC windings 75
2.2.13.3 Single phase induction machine winding design 77
2.2.13.4 Poly-phase double-layer winding 81
2.2.13.5 Two phase winding layout 83
2.3 REVIEW OF SIMILAR WORKS 85
xii
CHAPTER THREE: MATERIALS AND METHOD 93
3.1 INTRODUCTION 93
3.2 GENERALIZED MODEL DEVELOPMENT FOR THE CRSPIM 94
3.2.1 Derivation of Winding Inductances 96
3.2.1.1 Stator magnetizing inductances 97
3.2.1.2 Rotor magnetizing inductances 98
3.2.1.3 Stator mutual inductances 98
3.2.1.4 Rotor Mutual Inductances 98
3.2.1.5 Stator – rotor mutual inductances 99
3.2.2 Turn’s Transformation 101
3.2.3 Stationary Reference frame Transformation of Stator Variables 104
3.2.4 Stationary Reference frame Transformation of Rotor Variables 106
3.2.5 Transformation of Flux Linkages 107
3.2.6 Equivalent Circuit of the SPIM with Non-Quadrature Winding 108
3.2.7 Torque Equation 109
3.2.8 Generalized Steady State Model of the CRSPIM Using HBT. 110
3.3 MODEL VALIDATION 114
3.4 INFLUENCE OF SPATIAL ANGLE ON THE TORQUE PRODUCTION 120
3.4.1 Application of Balanced Condition to the 600 and 900 Configurations for Best Torque Performance 121
xiii
3.4.1.1 Steps taken to study the effects of imposing balanced currents in the stator windings of the single phase induction machine. 121
3.5 DEVELOPMENT OF A PWM INVERTER DRIVE FOR STANDARD SPIM TORQUE PERFORMANCE IMPROVEMENTS 123
3.5.1 Model Equations of the Rectifier and its Filter 124
3.5.2 Model Equations of the Inverter and its Filter 124
3.5.3 Model of the Conventional Single Phase Induction Machine 126
3.6 DEVELOPMENT OF A PID CONTROLLER FOR THE INVERTER DRIVE 126
3.6.1 Modeling of the Single Phase PWM Inverter Drive 128
3.6.2 Controller Structure for a Single Phase Inverter Drive 129
3.6.3 Controller Parameters 131
3.6.4 Computation of Reference Voltage 133
3.6.5 Flow Chart 133
3.7 PROBLEM WITH THE METHOD OF USING A PULSE WIDTH MODULATED INVERTER AND A PID CONTROLLER 138
3.8 MODEL OF THE MODIFIED SINGLE PHASE INDUCTION MACHINE 139
3.9 DEVELOPMENT OF A SINUSOIDAL PWM OPEN LOOP INVERTER DRIVE STRATEGY FOR THE MODIFIED SPIM 140
3.9.1 Model Equations of the Inverter and its Filters 142
3.10 DEVELOPMENT OF CLOSED LOOP CONTROL STRATEGY FOR THE MODIFED SPIM 145
3.10.1 Transformation of the Modified SPIM Model Equations from Stationary to Synchronous Reference Frame 146
xiv
3.10.1.1 Transformation of stator voltage equation 146
3.10.1.2 Transformation of rotor voltage equations 147
3.10.1.3 Transformation of flux linkages 147
3.10.1.4Transformation of torque equation 148
3.10.2 Development of the Vector Control Scheme 148
3.10.2.1 Formulation of the rotor flux oriented vector control scheme 149
3.10.2.2 Controller design 152
3.11 DEVELOPMENT OF THE PROPOSED EFFICIENCY OPTIMIZING SCHEME 157
3.11.1 Voltage Equations in Steady State 158
3.11.2 Electrical Power Loss 159
3.12 MODIFIED SPIM WINDING LAYOUT 165
3.12.1 Development of Modified SPIM Winding Layout Design 165
3.12.1.1 Design of modified SPIM winding layout 166
3.12.1.2 Assignment of coils to phases A and B 166
CHAPTER FOUR: RESULTS AND DISCUSSION 168
4.1 DYNAMIC AND STEADY STATE SIMULATION OF THE CRSPIM 168
4.1.1 Simulation Results of the Dynamic Behavior of the CRSPIM 168
4.1.2 Simulation Results of the Steady State Behavior of the CRSPIM 176
4.2 INFLUENCE OF DISPLACEMENT ANGLE ON THE TORQUE PRODUCTION AND EFFICIENCY PROFILE OF THE CRSPIM 179
xv
4.3 EFFECTS OF APPLYING BALANCED CONDITION TO THE 600 AND 900 CONFIGURATIONS FOR BEST TORQUE PERFORMANCE 184
4.4 SIMULATION RESULTS OF PULSE WIDTH MODULATED INVERTER DRIVE USING A PID CONTROLLER 188
4.5 SIMULATION RESULTS FOR OPEN LOOP CONTROL STRATEGY 197
4.5.1 Dynamic Torque Performances of the Modified Single Phase Induction Machine 197
4.6 VARIATION OF ROTOR FLUX WITH ELECTRICAL LOSS AND EFFICIENCY IN THE MODIFIED SPIM 2 202
4.7 SIMULATION RESULTS OFTHE EFFICIENCY OPTIMIZING VECTOR-CONTROLLEDSTRATEGY 212
4.8 MODIFIED SPIM WINDING LAYOUT DESIGN RESULTS 229
4.8.1 Coil Connections 233
4.8.2 Establishing the Direction of Current in Coil Sides 234
CHAPTER FIVE: CONCLUSION AND SUGGESTIONS FOR FURTHER WORK 236
5.1 SUMMARY 236
5.2 CONCLUSION 237
5.3 LIMITATIONS 241
5.4 SIGNIFICANT CONTRIBUTIONS 241
5.5 SUGGESTIONS FOR FURTHER WORK 242
REFERENCES 244

 

 

CHAPTER ONE

INTRODUCTION
1.1 BACKGROUND
Capacitor-run single phase induction motors (CRSPIMs) are designed to operate at a fixed speed and to drive rated loads in a variety of applications such as heating, ventilating and air conditioning systems (HVACs), pumps, compressors, fans, washing machines, hand driers, machine tools, grinding machines, vacuum cleaners, elevators etc. While driving rated loads, the currents in the main and auxiliary windings of the motors are approximately balanced at the rated load and speed (Pei et al,2016). Balanced currents refer to currents whose phase angle difference is equal to 900 and whosemagnitude ratio is equal to the effective winding turns‟ ratio. At any other load and speed, the winding voltages and currents are unbalanced (Muljadi et al., 1993; Krause et al.2002; Chomat and Lipo, 2003; Krischan et al., 2008) and this situation causes low efficiency and increased torque pulsations with associated high noise levels (Blaabjerg et al., 2004; Mademlis et al. 2005; Asghari and Fallah, 2012; Hosseini, 2016). In reality, some industrial, commercial and residential loads driven by SPIMs reduce with time and this load reduction is accompanied by increase in speed (Spirov, 2016). As a result, motor efficiency reduces and torque pulsation levels in the machine increase, leading to undesirable noise and vibrations in the machine (Park, 2001; Zahedi and Vaez-Zadeh, 2009). Furthermore, a lot of energy is wasted at light load operations because conventional SPIMs typically utilize between 60% and 80% of rated input power even when operating at less than half load (Saidur et al., 2012). It is known that electrical losses in alternating current (ac) induction machines can be reduced by reducing the magnitude of currents in the machine windings and by reducing the air-gap flux (Benbouzid et al., 1996; Dong, 2005). Studies have shown that there is an air-gap flux density in
2
an ac induction motor that produces minimum losses for any given load applied to the machine(Naxin et al., 2004; Dong, 2005). By adjusting motor flux to meet load requirements, significant improvements in motor efficiency can be achieved. In addition, significant energy savings can be achieved as well because power losses are reduced with reductions in flux levels in the machine. In this research,the supply of balanced voltages and currents to the windings of the single phase induction machine has been examined and a drive system that regulates the flux and the output torque, while maintaining a constant speed, in a single phase induction machinehas been developedto eliminate torque pulsations at steady state and to increase motor efficiency at light loads.
1.2 MOTIVATION
The problem of high torque pulsations and low efficiency in existing single phase induction machines has been examined by several researchers for more than fifteen years now. Most of these research have been dedicated to improving motor efficiency and reducing torque pulsations at or near rated load operating point. Only very few publications treat performance improvement of these machines at light load (or non-rated) operations and even then these publicationssuch as (Mademlis et al., 2005;Zahedi and Vaez-Zadeh, 2009;Caruso et al, 2012; Jang, 2013)have focused on speed regulation and not optimal flux regulation in single phase induction motors. The motivation for this research, therefore, arises from a desire to fill this gap in the research to improve the performances of single phase induction machines.
1.3 SIGNIFICANCE OF RESEARCH
In Nigeria today, people still experience severe shortage of electric power to meet domestic and industrial needs. To alleviate this shortage situation, there is need for installation of new generating plants and the effective utilization of existing power resources. Unfortunately, very
3
little attention has been focused on efficiency improvement and effective utilization of existing resources. This research starts to look at the single phase induction machine which is a large consumer of domestic power supply with the goal of improving its operation. Efficiency improvement will potentially enable this machine to consume less power and hence reduce running cost thereby making it possible for the limited electric power resources of electric utilities to meet the needs of more customers. With reduced heat loss and noise as consequences of the elimination of torque pulsations, the environment will be safer. It is within this context that this research finds significant national importance and relevance at this time.
1.4 PROBLEM STATEMENT
The Capacitor-run single phase induction motorsuffers from low efficiency when operating under non-rated conditions. This situation leads to wastage of significant amount of electric power since rated voltage is applied fully across its terminals and the flux in the machine operates approximately at rated value regardless of the applied load on the machine. Moreover, during starting and at steady state, the motor exhibits a significant level of torque pulsations which gives rise to noise and vibration in the machine. These conditions of low efficiency at light loads and vibrations lead to electrical, thermal and mechanical stresses on the machine which invariably threatens its useful life. Furthermore, the use of centrifugal switch and capacitors make this motor susceptible to failure should there be a malfunction of any or both of these devices.
1.5AIM AND OBJECTIVES
The aim of this study is to developa scheme to improve the efficiency and torque production in the single phase induction machine using a sinusoidal pulse width modulation (SPWM) control scheme. The objectives of the research are as follows;
4
a) To evaluate the performances of the existing CRSPIM and to change the spatial angular displacement of stator windings in the existing CRSPIM with a view to exploring any gains in terms of torque production and efficiency.
b) To formulate a method to supply balanced currents to existing CRSPIMs with a view to eliminating torque pulsations during steady state operation.
c) Toformulate a method to increase the efficiency and to reduce the level of power consumption in the existing SPIMsignificantly at light loads.
d) To simulate and compare performances of the SPIM under the proposed drive scheme with performances of the line operatedCRSPIM.
e) To develop an improved stator winding layout for torque and efficiency improvement in existing single phase induction machines.
1.6METHODOLOGY
A brief summary of the methodology followed in this research work is outlined as follows;
a) Application of reference frame transformation and harmonic balance techniques to develop a generalized model for the simulation of the dynamic and steady state performances of the existing CRSPIM.
b) Adoption of an appropriate inverter topology for the scheme. Identification and development ofcontrol strategies utilizing sinusoidal pulse width modulation that will enable elimination of torque pulsations at steady state.
c) Engagement of an efficiency-optimizing formulation to be used for investigatingthe performance of the inverter-drive schemeand assessing its contribution to efficiency improvement.
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d) Application of MATLAB/Simulink software to simulate and compare the performances of the proposed motor drive scheme to those of an existing line-operated capacitor-run single phase induction machine.
e) Application of standard winding layout design techniques to develop an improved stator winding layout for the existing machine.
1.7THESIS OUTLINE
Chapter one of this thesis provides the research background information. It also provides information on the aim and objectives of the research. The research motivation, problem, methodology and the significance of research are discussed as well. Chapter two reviews existing literature and fundamental concepts relevant to the research. Chapter three details the materials and methods applied to tackle the research problem while chapter four discusses the results obtained in this work. Chapter five summarizes the research findings. It gives the limitations observed in the work and suggestions for further work. It also outlines the significant contributions made to the body of knowledge and finally concludes the thesis.

 

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