Research On Coreless Axial-Flux Permanent-Magnet Synchronous Motor

The axial flux permanent magnet synchronous motor(AFPMSM)with coreless stator has features of both coreless structure and AFPMSM.Due to the small axial dimension,no stator iron loss and no cogging effect,Coreless AFPMSM has the advantages of compact structure,stable operation,high efficiency.It has been widely used in the high speed flywheel energy storage system,Spacecraft Attitude Control and industrial drive system.In this paper,the types,application and research status of AFPMSM and coreless structure are reviewed,and the coreless AFPMSM is studied in the aspects of motor design,analytical modeling,close-loop driving and eddy loss analysis.Firstly,the features and design ideas of coreless AFPMSM is analyzed.According to the technical specifications,the structure of coreless AFPMSM is designed and optimized.The design and optimization method of permanent magnet is emphasized.The installation position of linear Hall and switch Hall is analyzed.Three dimensional finite element method(3D-FEM)is used to study the electromagnetic characteristics of coreless AFPMSM.Then,pointing at the problem that iron core saturation can not be considered by analytical method,an improved 3D no-load magnetic field analytical model of coreless AFPMSM is proposed,which combining the equivalent magnetic circuit method and analytical method.3D-FEM is used to verify the accuracy of the analytical model.According to the distribution of air gap magnetic field,a concise numerical fitting algorithm for air gap magnetic field is proposed.Then,the performance of coreless AFPMSM in the double closed loop control system is studied.The effect of sine wave driving and square wave driving on coreless free AFPMSM is discussed respectively.Aiming at the problem of large speed ripple caused by the small inductance of coreless AFPMSM,a method of connecting a proper inductance with windings in series is adopted to improve the restraining ability of the high order harmonics.The performance of the coreless AFPMSM under the compound drive of sinusoidal / square wave is analyzed and verified.Finally,according to different inverter types and control modes,the rotor eddy loss of coreless AFPMSM with respective to open-loop control with current source inverter,openloop control with voltage source inverter and closed-loop control with voltage source inverter is studied.The relationship between speed,torque and eddy loss is analyzed.The distribution of eddy loss in permanent magnets and rotor iron cores are investigated.The Maxwell is secondary developed to realize closed loop control of the 3D-FEM model of coreless AFPMSM.Under closed-loop control with voltage source,the influence of sine wave driving and square wave driving on the eddy loss is analyzed respectively.