Investigation of Torque Ripples in Permanent Magnet Synchronous Machines With Skewing

Abstract

This paper investigates the influence of skewing on torque ripples, including the electromagnetic (EM) torque ripple, and the cogging torque, in permanent magnet (PM) machines. It is found that the effectiveness of skewing largely depends on the axial variation of a torque ripple phase but less on its magnitude under skewing. It is further found that, in both linear and nonlinear cases, the EM and the on-load torque ripple cannot be fully eliminated by skewing one on-load torque ripple period or any other angles, except 360° electrical, which is impractical. This is due to the fact that the EM torque ripple, especially its phase, of each slice is different due to the axial variation of the equivalent current phase advance angle introduced by skewing. In nonlinear cases, the EM torque ripple variation is further aggravated by the axial variation of magnetic saturation. The EM torque ripple as well as the on-load torque ripple may be even increased by skewing, especially when the cogging torque is low and electric loading is high.