Design Considerations of Novel Modular-Spoke-Type Permanent Magnet Machines

According to the specific characteristics, including even-order harmonics and unbalanced magnetic force (UMF), etc., special considerations for the design of a novel modular-spoke-type permanent magnet (MSTPM) machine are investigated and implemented in this paper. First, the geometric topology and operating principle of MSTPM machines are briefly introduced. Then, the permanent magnet magneto-motive-force and no-load air-gap flux density in MSTPM machines are compared with those of conventional surface-mounted permanent magnet (SPM) machines to expose the nature of MSTPM machines. Thereafter, the even-order harmonics and UMF in MSTPM machines are elaborately analyzed and the elimination is proposed by designing specific combinations of stator slots and rotor poles. Besides, the electromagnetic torque is optimized to achieve high torque and low torque ripple based on analytical and finite element analysis methods. Then, the performance of an MSTPM machine and a commercial outer-rotor (OR) SPM machine for in-wheel traction application are compared, and the results indicate that the MSTPM machine can produce better flux-weakening performance than the ORSPM machine with the same rated torque and speed. Finally, a prototype MSTPM machine is manufactured and tested, and the measured results have a good agreement with the analytical and predictive results.