A New Perspective on High-Torque-Density Mechanism of Permanent Magnet Vernier Machines

This paper presents a new perspective on high-torque-density mechanism of the various emerging permanent magnet (PM) vernier machines (PMVMs) by employing torque quantification of their working harmonics. In order to illustrate the high-torque-density mechanism, some typical PMVMs with integral-slot (IS) and fractional-slot (FS), single modulated teeth (SMT) and multiple modulated teeth (MMT) configurations, consequent-pole PM (CPM) and interior PM (IPM) arrangements are investigated and compared with their corresponding conventional surfaced-mounted PM (SPM) cases. The maxwell stress tensor method is adopted to determine their torque contributions of the working harmonics. The simulation results reveal and confirm a fact that the PMVMs show a high torque density than the regular SPM structures due to its dominant torque contribution of main-order working harmonics, not the field modulation harmonics. That is to say, the main-order working harmonic should be taken into consideration for further improving torque density of the PMVMs, not the field modulated harmonics, which provides a design guideline for PMVM with the pursue of high-torque density. Finally, some tested results on three prototypes with CPM, V-shaped and spoke-type PM configurations are conducted to confirm the theoretical and simulated analyses.