Harmonic Analysis and Optimization of a Spoke-Type Magnetic Geared Permanent-Magnet Machine

Spoke-type (ST) magnetic geared permanentmagnet machine (MGPM) has been reported to exhibit higher torque density than regular surface-mounted (SM) MGPMs. However, this assertion is mainly based on finite element analysis (FEA), and the in-depth mechanism is not clear. This paper provides a new perspective on the torque generation mechanism of the ST-MGPM using the harmonic characteristic analysis. First, the working principles of the ST-MGPM and SM-MGPM are presented, showing that their torque densities are limited by the corresponding coaxial magnetic gear (CMG) part. Then, the radial and tangential harmonic characteristics in the ST-CMG and SM-CMG are analytically derived, identifying the predominant harmonics that contribute to the transmission torque. On this foundation, a harmonic-oriented multi-level optimization method of the ST-MGPM is proposed, which has higher optimization efficiency because only the magnetostatic FEA is needed. Finally, a prototype of the ST-MGPM is built and tested to verify the theoretical analyses.