Harmonic Analysis of Airgap Magnetic Fields in Doubly-Fed Flux Reversal Permanent Magnet Machines

Doubly-fed flux reversal permanent magnet (DF-FRPM) machine with two independent armature windings accommodating in stator and rotor slots separately exhibits larger torque density than conventional FRPM due to higher utilization rate of rotor space. In this paper, the investigation is focused on the airgap field modulation and torque contribution of dominating harmonics in DF-FRPM machine. Besides the open-circuit airgap flux density, both stator and rotor armature reaction are qualitatively analyzed by magneto-motive force (MMF)-permeance model considering stator and rotor saliency since the two independently supplied armature windings both make contributions to the torque production. The pole pairs and rotating speed of field harmonics are addressed. Dominating field harmonics that contribute to electromagnetic torque are identified and validated by finite element (FE) analysis.