Analysis of Magnetic Gearing Effect in Partitioned Stator Switched Flux PM Machines

Abstract

The partitioned stator switched-flux permanent magnet (PM) (SFPM) (PS-SFPM) machine is a novel stator-PM machine in which PMs and armature windings are separately placed in two different stators. Compared with the conventional SFPM machine with a single stator in which both PMs and armature windings are located, the PS-SFPM machine can generate higher torque density due to the utilization of the machine's inner space. In this paper, the magnetic gearing effect in the PS-SFPM machine is investigated in terms of air-gap field harmonics based on a simple magnetomotive force (MMF)-permeance model. It is found that the PS-SFPM machine is one type of magnetically-geared machine, in which the modulations of rotor iron pieces to the open-circuit PM and armature reaction fields are similar to those found in the magnetic gear and the conventional magnetically geared machine. The pole-pair numbers and rotating speeds of the air-gap field harmonics obtained by the MMF-permeance model are verified by finite element (FE) analysis. More than 93% of the average electromagnetic torque is contributed by the main air-gap field harmonics having pole-pair numbers $(2i - 1){\boldsymbol p}$ PM and $\rm{| N}_{\rm{r}} \,\pm \, $ (2 i -1) p PM| ( i = 1,2,3) in a PS-SFPM machine with p PM-pole-pair PMs and Nr -rotor-pole. A prototype machine is fabricated and tested to verify the FE analysis.