Torque Pulsation Minimization in Spoke-type Interior Permanent Magnet Motors with Skewing and Sinusoidal Permanent Magnet Configurations

Abstract

This paper proposes two approaches to minimize torque pulsations, including cogging torque and electromagnetic torque ripple, for spoke-type interior permanent magnet (IPM) motors. The first approach is an improved skewing method, in which the rotor PMs are skewed by being symmetrical in the axial direction within one magnet pole pitch for not only reducing torque pulsations but also maintaining maximum available torque and eliminating unbalanced axial electromagnetic forces. The second one is a sinusoidal PM-shaping method with the aim of achieving the same advantageous effects as the proposed skewing method. Both the proposed methods adopt stepped rotor-PM schemes, and the effects of the rotor-PM step numbers on motor performance are investigated. To highlight the advantages of the proposed approaches, a spoke-type IPM motor with the conventional PM configuration is adopted as the basic model. All the motor characteristics, such as back electromotive force, cogging torque, and electromagnetic torque, are predicted by a 3-D finite-element method with the aid of JMAG-Designer.