Novel Hybrid-Pole Rotors for Consequent-Pole PM Machines Without Unipolar Leakage Flux

This paper presents two novel consequent-pole permanent magnet (PM) machines featuring N-iron-N-iron-N-S-iron-S-iron-S and iron-S-iron-S-iron-iron-N-iron-N-iron sequences. In order to provide assistant flux and suppress the subharmonics of the air-gap flux density, the tangential PMs are embedded into the proposed rotors of the consequent-pole PM (CPM) machines to form the novel hybrid-pole PM (HPM) machines. The principle of eliminating unipolar leakage flux and the performance improvement by hybrid pole are analyzed based on the simplified PM magnetic circuit. Then, the proposed rotors of CPM and HPM machines, as well as their conventional counterpart with an N-iron sequence, are optimized by finite-element analyses. Furthermore, the electromagnetic performances of the proposed machines, including the open-circuit air-gap flux density, average torque, torque ripple, loss, efficiency, unbalanced magnetic force, demagnetization withstand capability, and unipolar leakage flux, are compared with that of the conventional surface-mounted PM (SPM) and CPM machines. It is demonstrated that both the conventional CPM and proposed HPM machines have >20% higher PM material utilization ratio than the SPM machine. The proposed HPM machine can obtain almost equivalent torque and efficiency compared to the conventional CPM machine. Moreover, unipolar leakage flux does not exist in the end shaft, and thus the magnetization of the mechanical components can be effectively eliminated. Finally, a 9-slot/10-pole HPM machine is prototyped and measured to validate the analyses.

I. Introduction

Rare-earth magnets are commonly employed as magnetic potential source owing to their high energy density in permanent magnet (PM) machines, making them have high power density and efficiency [1]–[5]. However, due to its shortage and unstable supply around the world, the cost is one of the main drawbacks. Various approaches are proposed to reduce the cost, viz., eliminating rare-earth magnets, replacing the rare-earth magnets with ferrite magnets, or improving the PM utilization.