Magnets Shifting Design of Dual PM Excited Vernier Machine for High-torque Application

In this study, a novel dual permanent magnet excited vernier machine (DPMEVM) with magnets shifting in stator is proposed. Compared with the conventional permanent magnet synchronous machine (PMSM), the DPMEVM based on the bidirectional field modulation effect can operate in a wider torque range. However, the torque ripple of a conventional DPMEVM is high because of the superposition of the torque generated by the stator-side and rotor-side PMs. Consequently, a novel DPMEVM with magnets shifting is proposed to further reduce the torque ripple. First, the topologies and working principles of the baseline machine and proposed machines are introduced. Second, the torque-contribution harmonics are analyzed and calculated using the Maxwell tensor method. The calculation results reveal that the DPMEVM, benefiting from multiple working harmonics, can offer an enhanced torque capability compared to the PMSM. In addition, the torque ripple characteristics of the proposed machines are analyzed. It is verified that the torque ripple can be significantly reduced through magnets shifting. Third, the performances of the baseline machine and proposed machines are analyzed and compared in terms of flux density, open-circuit back-EMF, and torque characteristics. In addition, the proposed principle can be extended to machines with the same unit motor. Finally, a 120s-110p prototype machine is manufactured for validation.