Performance evaluating of rotor arrangement on high torque density in-wheel permanent magnet machines

This article presents a new rotor with fractional slot distribution winding permanent magnet (FSDWPM) machine to improve the torque density of in-wheel motor. In order to achieve the high torque/power density and reduced material weight with constrained rotor inner diameter and stator outer diameter, three traditional rotor topologies, including single-layer V-shaped, double-layer V-shaped, and delta-type, are selected and compared with the proposed FSDWPM machine. Subsequently, the corresponding basic electromagnetic performances, including open-circuit back-EMFs, on-load torque, and efficiency distributions, of the four machines are investigated and compared by finite element (FE) analysis. The simulated results shows that the proposed rotor arrangement exhibits the highest average torque, excellent field-weakening capability, the largest high-efficiency region compared with conventional rotor structures. Finally, a 50 kW FSDWPM machine prototype with double-layer PM arrangement is manufactured, and some experimental results are conducted to confirm the feasibility and effectiveness of the proposed design.