Cost-effective permanent magnet shape for reducing cogging torque and torque ripple in surface-mounted permanent magnet machines

This paper proposes a novel permanent magnet (PM) shape for surface-mounted PM (SPM) machines, with the aim of not only improving the sinusoidal quality of back electromotive force (EMF) and reducing cogging torque as well as torque ripple, but also saving on the magnet material cost. The proposed PM shape is designed to be trapezoidal and symmetrical in the axial direction, and the pieces from breaking the magnets for the trapezoidal shape can be used to create a new pole resulting in a significant reduction of magnet material cost. The design principle of the proposed cost-effective PM shape with two alternatives is illustrated in detail. To highlight the advantages of the proposed PM shape in SPM machines, two conventional rectangular PM shapes and a previously reported sinusoidal PM shape are adopted for performance comparison, based on a 3-D finite element method (FEM) using JMAG-Designer.