Abstract

For motors with low speeds and loads, torque pulsation by the reluctance torque is an important source of vibration and control difficulty. In this paper, the magnetic field of a motor is calculated by finite element method and the periodic reluctance torque is determined using Maxwell stress method and time stepping method, and then decomposed using Fourier series expansion. The purpose of this paper is to characterize design parameters on the reluctance torque and to design a permanent magnet motor with a reluctance torque less vulnerable to vibration, without sacrificing the motor performance. The design parameters include stator slot width, permanent magnet slot width, airgap length and magnetization direction. A new design with a less populated frequency spectrum of the reluctance torque is proposed after characterizing individual effect of design parameters. Gradual magnetization, by gradually increasing the thickness of the permanent magnets at edges, yields a smooth shape for the reluctance torque with reduced harmonics.

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