Analysis of Air-Gap Field Harmonics and Torque Production Mechanism in Dual-Armature Flux-Switching Permanent Magnet Machines

In this paper, the air-gap field harmonics in dual-armature flux-switching permanent magnet (DA-FSPM) machines with different stator core shapes are investigated from the perspective of flux modulation principle. Firstly, the pole-pair numbers and rotating speed of the air-gap field harmonics in the 12-stator-pole/10-rotor-tooth U-core DA-FSPM machine and its E-core counterpart machine are deduced based on the magnetomotive force model and air-gap permeance model. Then, the production mechanism in DA-FSPM machines is revealed and the contribution of the air-gap field harmonics to the electromagnetic torque are analyzed. It shows that the DA-FSPM machines exhibit abundant air-gap field harmonics including PM field, stator armature reaction field, and rotor armature reaction field harmonics. The stator and rotor saliency function as the modulators of the PM and armature reaction fields to make them have the same pole-pair number and rotating speed so as to produce steady electromagnetic torque. The dominating air-gap field harmonics contributing to the electromagnetic torque are identified and verified by finite element analysis.

I. Introduction

The flux-switching permanent magnet (FSPM) machines are favorable for high speed operation due to its simple and robust rotor structure [1]. However, their torque density are limited by the space conflict between magnets and armature windings which are both accommodated on the stator. With the purpose to improve machine inner space utilization and thus the torque density, novel dual-armature FSPM (DA-FSPM) machines were proposed by adding a set of rotor armature winding to the rotor slots of traditional FSPM machines [2] [3]. It is found that the DA-FSPM machines exhibit many superior performances including high torque density and high fault tolerant capability, which are highly desirable for aerospace applications.