【PDF】Electric Motors and Drives Fundamentals, Types and Applications

Austin Hughes
Senior Fellow, School of Electronic and Electrical Engineering,
University of Leeds


CONTENTS
Preface xvi

1 ELECTRIC MOTORS 1
Introduction 1
Producing Rotation 2
Magnetic field and magnetic flux 3
Magnetic flux density 4
Force on a conductor 6
Magnetic Circuits 7
Magnetomotive force (MMF) 9
Electric circuit analogy 10
The air-gap 11
Reluctance and air-gap flux densities 12
Saturation 14
Magnetic circuits in motors 15
Torque Production 16
Magnitude of torque 18
The beauty of slotting 19
Specific Loadings and Specific Output 21
Specific loadings 21
Torque and motor volume 23
Specific output power – importance of speed 23
Energy Conversion – Motional EMF 25
Elementary motor – stationary conditions 26
Power relationships – conductor moving at
constant speed 28
Equivalent Circuit 30
Motoring condition 32
Behaviour with no mechanical load 32
Behaviour with a mechanical load 35
Relative magnitudes of V and E, and efficiency 37
Analysis of primitive motor – conclusions 38
General Properties of Electric Motors 39
Operating temperature and cooling 39
Torque per unit volume 40
Power per unit volume – importance of speed 41
Size effects – specific torque and efficiency 41
Efficiency and speed 41
Rated voltage 41
Short-term overload 42
Review Questions 42
2 POWER ELECTRONIC CONVERTERS FOR
MOTOR DRIVES 45
Introduction 45
General arrangement of drives 45
Voltage Control – D.C. Output from D.C. Supply 47
Switching control 48
Transistor chopper 49
Chopper with inductive load – overvoltage
protection 52
Features of power electronic converters 54
D.C. from A.C. – Controlled Rectification 55
The thyristor 55
Single-pulse rectifier 56
Single-phase fully controlled converter – output
voltage and control 57
3-phase fully controlled converter 62
Output voltage range 64
Firing circuits 64
A.C. from D.C. SP – SP Inversion 65
Single-phase inverter 65
Output voltage control 67
Sinusoidal PWM 68
3-phase inverter 69
Forced and natural commutation – historical
perspective 69
Matrix converters 70
Inverter Switching Devices 72
Bipolar junction transistor (BJT) 72
Metal oxide semiconductor field effect
transistor (MOSFET) 73
Insulated gate bipolar transistor (IGBT) 74
Gate turn-off thyristor (GTO) 74
Converter Waveforms and Acoustic Noise 75
Cooling of Power Switching Devices 75
Thermal resistance 75
Arrangement of heatsinks and forced air cooling 77
Cooling fans 78
Review Questions 79
3 CONVENTIONAL D.C. MOTORS 82
Introduction 82
Torque Production 84
Function of the commutator 86
Operation of the commutator – interpoles 88
Motional E.M.F. 90
Equivalent circuit 94
D.C. motor – Steady-State Characteristics 95
No-load speed 95
Performance calculation – example 96
Behaviour when loaded 98
Base speed and field weakening 103
Armature reaction 105
Maximum output power 106
Transient Behaviour – Current Surges 107
Dynamic behaviour and time-constants 108
Shunt, Series and Compound Motors 111
Shunt motor – steady-state operating
characteristics 113
Series motor – steady-state operating
characteristics 115
Universal motors 118
Compound motors 119
Four-Quadrant Operation and Regenerative Braking 119
Full speed regenerative reversal 122
Dynamic braking 124
Toy Motors 124
Review Questions 126
4 D.C. MOTOR DRIVES 133
Introduction 133
Thyristor D.C. Drives – General 134
Motor operation with converter supply 136
Motor current waveforms 136
Discontinuous current 139
Converter output impedance: overlap 141
Four-quadrant operation and inversion 143
Single-converter reversing drives 144
Double SP-converter reversing drives 146
Power factor and supply effects 146
Control Arrangements for D.C. Drives 148
Current control 150
Torque control 152
Speed control 152
Overall operating region 154
Armature voltage feedback and IR
compensation 155
Drives without current control 155
Chopper-Fed D.C. Motor Drives 155
Performance of chopper-fed d.c. motor drives 156
Torque–speed characteristics and
control arrangements 159
D.C. Servo Drives 159
Servo motors 160
Position control 162
Digitally Controlled Drives 163
Review Questions 164
5 INDUCTION MOTORS – ROTATING FIELD,
SLIP AND TORQUE 167
Introduction 167
Outline of approach 168
The Rotating Magnetic Field 170
Production of rotating magnetic field 172
Field produced by each phase winding 172
Resultant field 176
Direction of rotation 177
Main (air-gap) flux and leakage flux 177
Magnitude of rotating flux wave 179
Excitation power and VA 182
Summary 183
Torque Production 183
Rotor construction 183
Slip 185
Rotor induced e.m.f., current and torque 185
Rotor currents and torque – small slip 187
Rotor currents and torque – large slip 189
Influence of Rotor Current on Flux 191
Reduction of flux by rotor current 192
Stator Current-Speed Characteristics 193
Review Questions 196
6 OPERATING CHARACTERISTICS OF
INDUCTION MOTORS 198
Methods of Starting Cage Motors 198
Direct Starting – Problems 198
Star/delta (wye/mesh) starter 202
Autotransformer starter 202
Resistance or reactance starter 203
Solid-state soft starting 204
Starting using a variable-frequency
inverter 206
Run-up and Stable Operating Regions 206
Harmonic effects – skewing 208
High inertia loads – overheating 209
Steady-state rotor losses and efficiency 209
Steady-state stability – pullout torque
and stalling 210
Torque–Speed Curves – Influence of Rotor
Parameters 211
Cage rotor 211
Double cage rotors 213
Deep bar rotors 214
Starting and run-up of slipring motors 215
Influence of Supply Voltage on Torque–Speed Curve 217
Generating and Braking 218
Generating region – overhauling loads 219
Plug reversal and plug braking 220
Injection braking 221
Speed Control 221
Pole-changing motors 222
Voltage control of high-resistance cage motors 223
Speed control of wound-rotor motors 224
Power Factor Control and Energy Optimisation 225
Voltage control 225
Slip energy recovery (wound rotor motors) 227
Single-Phase Induction Motors 227
Principle of operation 227
Capacitor-run motors 229
Split-phase motors 230
Shaded-pole motors 231
Size Range 232
Scaling down – the excitation problem 232
Review Questions 233
7 INDUCTION MOTOR EQUIVALENT CIRCUIT 236
Introduction 236
Outline of approach 237
Similarity Between Induction Motor and Transformer 238
The Ideal Transformer 240
Ideal transformer – no-load condition,
flux and magnetising current 240
Ideal transformer – no-load condition,
voltage ratio 245
Ideal transformer on load 246
The Real Transformer 248
Real transformer – no-load condition,
flux and magnetising current 248
Real transformer – leakage reactance 251
Real transformer on load – exact
equivalent circuit 252
Real transformer – approximate
equivalent circuit 254
Measurement of parameters 256
Significance of equivalent circuit parameters 257
Development of the Induction Motor Equivalent Circuit 258
Stationary conditions 258
Modelling the electromechanical
energy conversion process 259
Properties of Induction Motors 261
Power balance 262
Torque 262
Performance Prediction – Example 263
Line current 264
Output power 264
Efficiency 265
Phasor diagram 266
Approximate Equivalent Circuits 267
Starting and full-load relationships 268
Dependence of pull out torque on
motor parameters 269
Analysis 270
Graphical interpretation via phasor diagram 271
Measurement of Parameters 274
Equivalent Circuit Under Variable-Frequency
Conditions 274
Review Questions 277