Novel Permanent Magnet Pole Shape for Reducing Cogging Torque and Generating Sinusoidal Back EMF in Surface-mounted PM Motors

Abstract

This paper proposes two types of novel permanent magnet (PM) pole shapes for reducing cogging torque and generating sinusoidal back EMF in surface-mounted PM (SPM) motors. Both types of PM pole shapes adopt symmetrical construction for providing balanced axial electromagnetic force. One type is designed to be sinusoidal for obtaining high quality sinusoidal back EMF, and the other is designed to be trapezoidal considering a tradeoff between the cost and performance. Both types show a good availability of cogging torque reduction. The contribution of two types of novel permanent magnet (PM) pole shapes to motor characteristics are confirmed by 3-D finite element method (FEM). And the simulation results are compared with those of a conventional square PM pole shape and a previously reported quasi-sinusoidal PM pole shape, for highlighting the contribution of two proposed PM shapes.