Influence of magnetization pattern in three-phase permanent magnet synchronous machines

Abstract

This paper investigates the influence of different magnetization patterns in the performance of three-phase permanent magnet synchronous motors (PMSMs). Three magnetization patterns widely used in surface-mounted PMSMs are radial magnetization, parallel magnetization and Halbach magnetization. In this paper, these magnetization patterns are applied to 9-slot/10-pole and 12-slot/10-pole surface-mounted PMSMs. The electromagnetic characteristics and performance of the motors such as air gap flux density distributions, phase back-emf, cogging torque, unbalance magnetic force and output torque are intensively evaluated in 2D finite element method. Important findings indicate that PMSMs with ideal Halbach magnetization exhibit almost zero cogging torque and sinusoidal phase back-emf waveform. Parallel magnetization and radial magnetization yield more trapezoidal phase back-emf waveform which results in higher torque ripples. One way to minimize the torque ripples is by reducing the higher-order harmonic components in the phase back-emf waveform which can be achieved with the best value of magnet pole arc. Additionally, a potential cost saving can be realized since the motor has smaller magnet volume as being demonstrated in the case of 9-slot/10-pole, three-phase surface-mounted PMSM in this paper.