Torque ripple reduction in an axial-flux jigsaw-coil permanent magnet machine

Torque ripple contributes to vibrations and noises, and should be paid attention to during the design of low-speed electrical machines. There have been numerous publications on the possible methods for reducing cogging torque; however, these methods also reduce the machine torque. Furthermore, having low cogging torque does not guarantee low torque ripple at full load and vice versa. The objective of this paper is to investigate the optimal permanent magnet (PM) shape that produces low torque ripples at any load while having excellent torque production. 3D transient finite element method is used to calculate the machine performances under various PM shapes (with constant PM volume). It is found that low torque ripples can be achieved across the whole machine loading by having optimized ratio of PM width to pole pitch and asymmetric skewed PM.