Comparative Study of Thermal Characteristic in Permanent Magnet Synchronous Machine and Vernier Machine for In-Wheel Drive

In this paper, the thermal characteristic and loss distribution of permanent magnet vernier machines (PMVMs) and permanent magnet synchronous machines (PMSMs) are investigated for in-wheel direct drive. Firstly, the topologies and heat dissipation design of the outer-rotor in-wheel motors are illustrated. Then, the losses of two selected motors under typical conditions are calculated. Besides, the loss distribution feature is targeted too, where the PM loss is stressed in PMVM and core loss is focused in benchmark PMSM. Secondly, the assembly structure of in-wheel motors is described, where the heat path is through the stator support to motor frame directly without air, so the thermal resistance can be largely reduced and the heat can be transferred easily. In order to verify the analysis, a model is established to calculate the thermal conductivity, and the air-gap thermal conductivity is focused. Besides, the finite-element model is also calculated to identify the temperature difference between PMSM and PMVM. Finally, two prototypes of PMVM and benchmark PMSM are manufactured and tested. Then, the experimental results can match well with finite-element analysis (FEA) and theoretical analysis.