Design And Optimization Of The Permanent Magnets For Disc Coreless In-wheel PMSM

To comply with the national energy conservation and emissions reduction of green development pattern,the paper views the electric car as the breakthrough point and studies its drive motor.As one of the key components of the vehicle,the drive motor is requested to have power density,weight,volume and dynamic performence as well as high efficiency.Through putting the motor and the transmission mechanism in the inner wheel,the in-wheel drive technology can optimize the motor's structure and more importantly reduces the power loss.Besides,it selects disc PMSM with coreless structure as the drive motor and various advantages of the motor make itself very suitable for use as a in-wheel motor,thus making the wheel drive system can play a greater advantage in electric vehicles.Firstly in this paper,according to the relevant data and performance requirements of electric vehicles,basic parameters of the single-disc in-wheel motor are determined.In order to meet the PMSM's requirements of high efficiency and high power density,the waveform of the air-gap magnetic field has to be sinusoidal and the amplitude be high enough.To this end,the above two are regarded as the optimization objectives of the magnetic field analysis of the motor.In order to determine the optimal variables of the magnetic field of the motor,the paper then carries on the qualitative analysis to the magnetic circuit.And the permanent magnet material and structure size are known as the main factors that affect the magnetic field.With excellent and stable magnetic performance,NdFe B is the ideal material.So,magnet size becomes the key to magnetic field optimization.Before that,the magnetic field of the motor is deeply analyzed,and the finite element method is summarized.In order to facilitate the simulation and guarantee the reliability of the calculation results,then the simplification and the solving domain partition of the motor simulation model are studied.The simulation results show that unequal thickness magnets array can effectively improve the quality of magnetic field waveform while 90°Halbach array can significantly improve the flux density amplitude.The design of combining the two structures eventually wins the optimal air-gap magnetic field for single-disc machine.To further improve the output power andtorque of the motor,the multi-disc machine is studied.In order to improve the performance of multi-disc machine,the paper flexibly utilizes the magnet design rules of single-disc type and ultimately realizes the optimization of multi-gap magnetic field.Appling unequal thickness principle to 90°Halbach array can take into account the amplitude and waveform of the air-gap magnetic field and has important significance to improve the power density,reduce the torque ripple,etc.Finally,by using the design principle of the disc motor,the main electromagnetic parameters of the special motor are deduced,which provides a theoretical basis for the subsequent design of axial-flux motors.