An Improved Configuration for Cogging Torque Reduction in Flux-Reversal Permanent Magnet Machines

Abstract

A flux-reversal permanent magnet (FRPM) machine typically suffers from unfavorably large cogging torque due to its special doubly salient structure and high air-gap flux density, resulting in undesired torque and speed ripples, as well as acoustic noise and vibration, especially at low speeds. Therefore, an improved configuration of FRPM machines by introducing a small space-gap between the two adjacent magnets belonging to the same stator tooth is proposed in this paper. The analytical expression of cogging torque taking this small space gap into consideration is derived, and furthermore, the optimal dimensions of the space gap are obtained analytically for cogging torque minimization. In addition, the influences of the space-gap-based configuration on key electromagnetic performances, including cogging torque, back electromotive force, and electromagnetic torque, are investigated by both 2-D finite-element analysis and experimental results. It turns out to be that by employing this configuration, not only the cogging torque, and hence, torque ripples can be suppressed, but also the electromagnetic torque can be improved.