EBOOK - Magnetic Bearings and Bearingless Drives (Akira Chiba & Các TG)


This book is primarily about bearingless machines, where the magnetic levitation of the rotor is provided from within the main stator bore (in addition to torque production if motoring, or electrical power production if generating). The bearingless type of motor is still, to some extent, in the development stage and therefore still at an early point of evolution.

The basic theory, design and control rules are being researched and investigated and there is still much work to be done. The authors have had many years of experience in the design and operation of bearingless machines and this book represents their combined experience as pioneers in this area. Therefore this book describes the leading edge of the technology as it stands today.

CONTENTS:

1 Introduction 1
1.1 Magnetic bearing and motor drive 1
1.2 Bearingless drives 4
1.3 Definition and related technologies 5
1.4 Early developments 7
1.5 Bearingless structures 9
1.6 Comparisons 11
1.7 Winding structures 13
1.8 Applications 14
References 15
2 Electro-magnetics and mathematical model of magnetic bearings 16
2.1 Electro-mechanical structure and operating principles 16
2.2 Electric equivalent circuit and inductance 17
2.3 Stored magnetic energy and force 20
2.4 Radial magnetic bearing 34
2.5 Unbalance pull force 40
2.6 Block diagram and mechanical system 42
Reference 44
3 Magnetic bearing controllers 45
3.1 Design principles in one-axis magnetic suspension 45
3.2 Adjustment of PID gains 52
3.3 Interference in two perpendicular axes 67
3.4 Unbalance force and elimination 72
vi Contents
3.5 Eccentric displacement 78
3.6 Synchronized displacement suppression 81
4 Mechanical dynamics 85
4.1 Two-axis system 85
4.2 Four-axis and five-axis systems 90
4.3 Thrust magnetic bearing and requirement
of five-axis suspension 94
References 96
5 Power electronic circuits for magnetic bearings 97
5.1 Structure and principles of power electronic circuits 97
5.2 PWM operation 107
5.3 Current feedback 112
5.4 Current driver operating area 119
5.5 Power devices and gate drive circuits 122
6 Primitive model and control strategy of bearingless motors 127
6.1 Principles of radial force generation 127
6.2 Two-pole bearingless motor 131
6.3 MMF and permeance 132
6.4 Magnetic potential and flux distribution 135
6.5 Inductance matrix 138
6.6 Radial force and current 141
6.7 The dc excitation of the primitive bearingless motor 145
6.8 AC excitation and revolving magnetic field 147
6.9 Inductance measurements 149
7 Analysis in rotational coordinates and magnetic suspension
strategy for bearingless drives with 2-pole and 4-pole windings 159
7.1 Vector control theory of electrical motors 160
7.2 Coordinate transformation and torque regulation 166
7.3 Vector control theory in bearingless motors 169
7.4 Coordinate transformation from dc to ac bearingless machines 173
7.5 System block diagrams of bearingless machines 177
References 183
8 Field orientation, VA requirement and magnetic saturation 184
8.1 Misalignment of field orientation 185
8.2 VA requirement 190
8.3 Magnetic saturation 197
References 200
9 Cylindrical permanent magnet synchronous bearingless motors 201
9.1 Structure of surface permanent magnet (SPM) rotor 201
9.2 Radial suspension force and suspension winding current 202
Contents vii
9.3 Equations of voltage and current 204
9.4 Guideline for permanent magnet thickness and airgap length 205
9.5 Irreversible permanent magnet demagnetization
and MMF limitations of stator windings 212
9.6 Control system configuration 216
References 219
10 Inset types of permanent magnet bearingless motor 220
10.1 Structure and features of an inset type of permanent
magnet rotor 220
10.2 Mutual interference between radial suspension forces 221
10.3 Rotor position control strategy 223
10.4 Identification of suspension force parameters 223
References 228
11 Buried permanent magnet bearingless motors 229
11.1 BPM rotor structures 229
11.2 Suspension force for unity current and permanent
magnet demagnetization 231
11.3 Rotor position control strategy 232
References 237
12 Synchronous reluctance bearingless motors 238
12.1 Torque characteristics 238
12.2 Radial force characteristics 241
12.3 Drive systems 244
References 250
13 Bearingless induction motors 251
13.1 Rotor structure and suspension force 251
13.2 Indirect type drives 257
13.3 Direct type drives 264
13.4 Two-pole motor drive 271
References 272
14 Homopolar, hybrid and consequent-pole bearingless motors 274
14.1 Structures and principles 274
14.2 Number of poles 281
14.3 Drive systems 284
References 286
15 Switched reluctance bearingless motors 287
15.1 Configuration of stator windings and principles of suspension
force generation 288
15.2 Derivation of inductances 290
15.3 Assumption and calculation of permeances 291
viii Contents
15.4 Theoretical formulae of suspension force and torque 295
15.5 A drive system 297
15.6 A feed-forward compensator for vibration reduction
considering magnetic attraction force 302
References 307
16 Winding arrangement variations 309
16.1 Modified radial magnetic bearings 309
16.2 Modified motors 311
16.3 p-Pole and (p±2)-pole windings 313
References 316
17 Mechanical structure and position regulation 318
17.1 Mechanical structure 318
17.2 Axial gap bearingless motors 321
References 328
18 Displacement sensors and sensorless operation 329
18.1 Principles of displacement sensor 330
18.2 Improvements in sensitivity 333
18.3 Inductive and eddy current sensors 336
18.4 Sensorless bearingless motor 338
References 342
19 Controllers and power electronics 344
19.1 Structure of digital controllers 344
19.2 Discrete-time systems of PID controllers with thez-transform 347
20 Design procedure and examples 351
20.1 An induction type bearingless motor 351
20.2 A permanent magnet type bearingless motor 356
References 360
21 Applications and test machines 361
21.1 Canned pumps and drives 361
21.2 Compact pumps, bubble bed reactor 365
21.3 Spindle motor and semiconductor processing 370
References 374

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