Pulsating Torque Suppression of Flux Reversal Machines Based on Specific Harmonic Contributions of Rotor Permeance and PM MMF

Abstract

Flux reversal machines (FRMs) exhibit high torque density, but also significant pulsating torque, including cogging torque and torque ripple. Traditional methods fail to separate the harmonics that affect torque density and pulsating torque, leading to a degradation of torque density when reducing pulsating torque. Therefore, to maintain torque density and simultaneously reduce pulsating torque, this paper proposes a novel FRM configuration incorporating shape designs for the rotor and permanent magnets (PMs). First, the key generation mechanisms of cogging torque, average torque, and torque ripple are thoroughly examined, with analytical expressions derived to classify the torque contributions of all air-gap magnetic field harmonics into negative-effect and positive-effect components. Further, the rotor and PM shapes are designed to enhance the positive-effect components and reduce the negative-effect ones of the air-gap permeance and magnetomotive force (MMF). The impacts of geometric parameters are evaluated by using a sensitivity-based hierarchical optimization approach. Then, the proposed FRM is comprehensively compared with a conventional FRM in terms of back-electromotive force (EMF), cogging torque, average torque, torque ripple, efficiency, etc. The results indicate that the proposed machine configuration achieves reductions in cogging torque and torque ripple by 90% and 86.8%, respectively, while maintaining consistent average torque. Finally, a 12-slot/10-pole FRM prototype was built and tested to validate the effectiveness of the proposed machine topology.