Comparative Study of High Torque Density Spoke-Type PM In-Wheel Motors for Special Vehicle Traction Applications

With the development of the transportation electrification, the demand for high-performance motor is growing rapidly. High torque density and wide constant power operating range are two key requirements of the electric vehicle (EV) traction applications. Considering the limited voltage and current, a successful EV traction machine should realize good linearity of torque–current characteristic and a proper characteristic current. In order to meet these strict demands, an optimized Fractional-Slot Concentrated-Winding(FSCW) permanent magnet (PM) machine with different rotor structures is proposed in this article based on the traditional spoke-type PM machine topology. The machine structures are introduced and optimized in the design procedure, and a magnetic equivalent circuit model is applied to illustrate its principle. The electromagnetic performances, including back electromotive force, output torque, and efficiency map, are compared between the original and optimized design to highlight the performance improvement of the optimized topology. Finally, a prototype machine has been built for the experimental validation. The experimental results, which agree well with the Finite Element (FE)-predicted results, confirm the validity of the analysis method used in predictions and the advantages of the optimized design.