Analytical Modeling And Design Of A New Type Of Surface-Mounted Permanent Magnet Motor

Due to their characteristics of high efficiency,high torque density,permanent magnet machines have been widely used in various types of industrial automation.In intelligent robots,spacecraft,medical equipment and mold precision machining industry,they also put forward higher requirements for all of the precise control of the PM motors.In accordance with the drive and control system,permanent magnet motors can be divided into two cataries:brushless DC(BLDC)and permanent magnet(PM)synchronous motors.For BLDC and PM synchronous motors,their main structures are the same in essence.The magnetic field waveforms in two motors are different.In this paper,the electromagnetic performance of the surface-mounted PM motor is analyzed,including the magnetization method,the characteristics of the magnetic field,and the optimal design.It's the significance for theoretical analysis and engineering application.Firstly,the mathematical model of a_BLDC motor is analyzed and the "parallel +radial + parallel" combination magnetization method is proposed.The analytical model of a slotless BLDC motor is established.The air-gap flux density,and no-load back-electromotive force waveforms are obtained,which are almost trapezoidal,for the "parallel + radial + parallel" combination magnetization.In addition,an optimal analytical model is established in terms of the magnet thickness,and the back-EMF flat-top width is analyzed.Secondly,for the PM synchronous motor,based on the combined magnetization for "radial + parallel + radial" and "parallel + parallel + parallel"' the analytical model of the non-magnetic area on the rotor inner surface is established.The back electromotive force and electromagnetism torque are analyzed.Compared with the single parallel magnetization method,the flux density waveform for the combined magnetization is closer to the sine.Meanwhile,it is pointed out that when the nonmagnetic material area exists on the inner surface of the rotor,the main magnetic field of the motor is weakened to a certain extent.Finally,the cogging torque emerges when the stator is grooved.The generation mechanism of the cogging torque is analyzed.In order to reduce the cogging torque,a pole optimization model is proposed.The cogging torque is calculated using a Maxwell's tensor method,and the groove shape and the chamfering size are optimized by an analytical model.Besides,the variation law between the peak torque and the related parameters is obtained.