AXIAL FLUX PERMANENT MAGNET BRUSHLESS MACHINES

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1 AXIAL FLUX PERMANENT MAGNET BRUSHLESS MACHINES Jacek F. Gieras, Rong-Jie Wang and Maarten J. Kamper Kluwer Academic Publishers, Boston-Dordrecht-London, 2004 TABLE OF CONTENETS page Preface v 1. Introduction Scope Features Development of AFPM machines Types of axial flux PM machines Topologies and geometries Axial magnetic field excited by PMs PM eddy-current brake as the simplest AFPM brushless machine AFPM machines versus RFPM machines Power limitation of AFPM machines 19 Numerical examples Principles of AFPM machines Magnetic circuits Single-sided machines Double-sided machines with internal PM disc rotor Double-sided machines with internal ring-shaped core stator Double-sided machines with internal slotted stator Double-sided machines with internal coreless stator Multidisc machines Windings Three-phase windings distributed in slots Drum-type winding Coreless stator winding Salient pole windings Torque production Magnetic flux Electromagnetic torque and EMF Losses and efficiency Stator winding losses Stator core losses Core loss finite element model Losses in permanent magnets Rotor core losses Eddy current losses in stator conductors Rotational losses 50

2 Losses for nonsinusoidal current Efficiency Phasor diagrams Sizing equations Armature reaction AFPM motor Sine-wave motor Square-wave motor AFPM synchronous generator Performance characteristics of a stand alone generator Synchronization with utility grid 68 Numerical examples Materials and fabrication Stator cores Non-oriented electrical steels Amorphous ferromagnetic alloys Soft magnetic powder composites Fabrication of stator cores Fabrication of laminated stator cores Fabrication of soft magnetic powder stator cores Rotor magnetic circuits PM materials Characteristics of PM materials Alnico Ferrites Rare-earth permanent magnets Operating diagram Permeances for main and leakage fluxes Calculation of magnetic circuits with PMs Fabrication of rotor magnetic circuits Halbach array Windings Conductors Fabrication of slotted windings Fabrication of coreless windings 117 Numerical examples AFPM machines with iron cores Geometries Commercial AFPM machines with stator ferromagnetic cores Some features of iron-cored AFPM machines Magnetic flux density distribution in the air gap Calculation of reactances 133 4,5.1. Synchronous and armature reaction reactances Stator leakage reactance Performance characteristics Performance calculation Sine-wave AFPM machine 137

3 Synchronous generator Square-wave AFPM machine Finite element calculations 144 Numerical examples AFPM machines without stator cores Advantages and disadvantages Commercial coreless stator AFPM machines Performance calculation Steady-state performance Dynamic performance Calculation of coreless winding inductances Classical approach FEM approach Performance characteristics Eddy current losses in the stator windings Eddy current loss resistance Reduction of eddy current losses Reduction of circulating current losses Measurement of eddy current losses Armature Reaction Mechanical design features Mechanical strength analysis Attraction force between rotor discs Optimum design of rotor discs Imbalanced axial force on the stator Thermal problems 184 Numerical examples AFPM machines without stator and rotor cores Advantages and disadvantages Topology and construction Air gap magnetic flux density Electromagnetic torque and EMF Commercial coreless AFPM motors Case study: low-speed AFPM coreless brushless motor Performance characteristics Cost analysis Comparison with cylindrical motor with laminated stator and rotor cores Case study: low-speed coreless AFPM brushless generator Characteristics of coreless AFPM machines 208 Numerical examples Control Control of trapezoidal AFPM machine Voltage equations Solid-state converter 222

4 Current control Speed control High speed operation Control of sinusoidal AFPM machine Mathematical model and $dq$ equivalent circuits Current control Speed control Hardware of sinusoidal AFPM machine drive Sensorless position control 243 Numerical examples Cooling and Heat Transfer Importance of thermal analysis Heat transfer modes Conduction Radiation Convection Convection heat transfer in disc systems Cooling of AFPM machines AFPM machines with self-ventilation The ideal radial channel The actual radial channel Characteristics Flow and pressure measurements AFPM machines with external ventilation External fans Heat pipes Direct water cooling Lumped parameter thermal model Thermal equivalent circuit Conservation of energy Machine duties Continuous duty Short-time duty Intermittent duty 280 Numerical examples Applications Power generation High speed generators Low speed generators Electric vehicles Hybrid electric vehicles Battery electric vehicles Ship propulsion Large AFPM motors Propulsion of unmanned submarines Counterrotating rotor marine propulsion system 302

5 9.4. Electromagnetic aircraft launch system Mobile drill rigs Elevators Miniature AFPM brushless motors Vibration motors Computer hard disc drives 315 Numerical examples 316 Symbols and Abbreviations 321 References 331 Index 336

Axial Flux Permanent Magnet Brushless Machines

Jacek F. Gieras Rong-Jie Wang Maarten J. Kamper Axial Flux Permanent Magnet Brushless Machines Second Edition Springer Contents 1 Introduction 1 1.1 Scope 1 1.2 Features 1 1.3 Development of AFPM Machines