Elimination of Even-Order Harmonics and Unipolar Leakage Flux in Consequent-Pole PM Machines by Employing N-S-Iron–S-N-Iron Rotor

Abstract

This paper presents a novel consequent-pole permanent magnet (CPM) machine featuring N-S-iron–S-N-iron sequences to eliminate the even-order harmonics of phase back electromotive force (EMF) and the unipolar leakage flux in the end region. The flux barrier is employed to improve the symmetry of the air-gap flux and reduce the saturation of the stator yoke, and hence the output torque can be improved. The proposed CPM machine, as well as its conventional counterpart with N-iron sequences, is optimized by finite-element analyses. Moreover, the electromagnetic performance of the proposed CPM machine, including the open-circuit air-gap flux density, back EMF, average torque, torque ripple, loss, efficiency, and unipolar leakage flux, is compared with the conventional CPM and surface-mounted PM (SPM) machines. Although both the proposed and conventional CPM machines have lower output torque than the SPM machine, the utilization ratio of PM material is increased by >33%. It is demonstrated that the proposed CPM machine has similar output torque and efficiency, but much lower torque ripple compared to the conventional one. Moreover, unipolar leakage flux does not exist in the end shaft of the proposed machine, and thus, the magnetization of the mechanical components can be effectively eliminated. Finally, the 9-slot/6-pole CPM machine is prototyped and measured to validate the analyses.