Reducing Torque Ripple Through Innovative Configuration of Permanent Magnet Based on Air Gap Field Modulation Theory in a Novel Axial Flux Reversal Permanent Magnet Machine

Abstract

In this paper, a novel axial flux reversal permanent magnet (PM) (AFRPM) machine, which combines the merits of the axial flux PM (AFPM) machine and flux reversal PM machine, is proposed. Meanwhile, according to the machine characteristics, a method for inhibiting the torque ripple is presented and researched. Firstly, the topology and operation principle of the machine are analyzed. The power-size equation is derived and the design scheme is confirmed to obtain the structure parameters of the machine. Then, the general electromagnetic performances are comprehensively analyzed. Secondly, the model of the magnetomotive force (MMF)-permeance model is eatablished. The air gap flux density is researched from the air gap field modulation perspective. Furthermore, the torque generation mechanism is studied in detail by analyzing the influences of the armature reaction air gap flux density harmonics and no-load air gap flux density harmonics on the electromagnetic torque. Finally, in order to reduce the torque ripple, an optimization method using cos-type PMs, which suppress the harmonic pole pairs that do not contribute to the torque output, is investigated. To simplify the manufacturing process, the segmented sector PMs with different heights and arcs are employed instead of the cos-type PM. The effects of different numbers of the segmented sector PMs on the torque ripple are studied. The results indicate that the proposed machine exhibits large torque capability and high power/torque density. Meanwhile, the torque ripple is significantly reduced by the optimization method.INDEX TERMS axial flux, flux reversal, air gap harmonic analysis, torque ripple, cogging torque.