Design and Analysis of a Radial-Flux Machine with Hybrid-Irregular Pole Pattern for High Power Density

Spoke-type PM machines have strong flux-focusing effect and hence high average torque, however, they generally suffer from high torque ripple because of the abundant high-order magnetic harmonics of the electric machines. In this paper, a hybrid-irregular pole pattern consisting of quasi-spoke-type magnets and surface-mounted magnets is proposed for high-speed machine to reduce torque ripple while maintaining high average torque, simultaneously. The quasi-spoke-type magnets and the surface-mounted PMs with muti-direction magnetization helps to improve average torque greatly. Besides, the surface-mounted magnets with parallel magnetization are conducive to reduce high-order air-gap magnetic harmonics and hence achieving smooth torque output. Firstly, the schematic structure of the high-speed PM machine with hybrid-irregular pole pattern, and its working principle are presented. Secondly, the output performance variation with respect to the major structural parameters of the hybrid pole pattern machine is investigated. Besides, one high-speed electric machine with hybrid pole pattern is deigned. Thirdly, to confirm the merits of the hybrid-irregular pole pattern machine, its electromagnetic characteristics, such as no-load air-gap flux density, back EMF and torque profile are compared with conventional spoke-type PM machine. Finally, a useful conclusion is concluded.