Tradeoff Study of Torque and Losses in Permanent Magnet Vernier and Synchronous Machines for In-Wheel Traction Applications

This article provides a tradeoff study of torque and rotor losses, including the permanent magnet (PM) loss and core loss, in permanent magnet vernier machines (PMVMs), for in-wheel traction. Firstly, the analytical models of PM loss, core loss, and torque are established, and the core loss is calculated by three methods. Besides, the influencing factors on toque and losses are extracted. Secondly, the influence of stator and rotor topologies on torque and losses is studied, and the contribution of flux density harmonic on PM loss, core loss, and torque in various topologies and slot-pole combinations are calculated and compared, where both sub-harmonics and slot harmonics are mostly responsible for core loss and PM loss. Next, the rotor flux barrier in d-axis path is introduced. The influence of flux barrier dimensions on air-gap flux density, core loss, PM loss, and torque is carried out, and it shows that the modulated flux density is reduced with flux barrier, which helps to reduce PM loss. Moreover, the decay rates of losses and torque under the typical conditions are extracted. The PM loss has the dramatic decrease compared with the other ones, but the torque also decreases slightly, which can validate the applicability and correctness of the rotor flux barrier. Finally, a PMVM and a benchmark PMSM are manufactured and tested to validate the theoretical analysis and finite-element analysis (FEA). This article aims to provide the tradeoff design between torque and losses, and introduce a flux barrier solution to alleviate the design conflicts in PMVM for in-wheel traction applications.