Wound Rotor Synchronous Motor as Promising Solution for Traction Applications

Traction applications, such as electric and hybrid vehicles, require the electrical motor to be operated at low load conditions during most of their driving cycle. Permanent magnet (PM) motors in this case may not be an optimal choice due to their poor efficiency under low load conditions despite the fact that they exhibit the best output characteristics at the rated load. However, the wound rotor synchronous motor (WRSM) demonstrates the best efficiency at low load conditions due to their controllable excitation. This paper presents an interesting comparison of WRSM and the PM motor in terms of their efficiency over the entire drive cycle of traction applications, which demonstrates that WRSMs are more suitable compared to the apparently best performance PM motor. A WRSM with similar dimensions to the 2010 Toyota Prius interior permanent synchronous motor (IPMSM) was designed and optimized in this regard. The performance comparison of the PM motor and the WRSM was presented using 2-D finite element analysis (FEA) for the WRSM and the performance analysis report of the Toyota Prius IPMSM published by the US department of energies. The FEA analysis shows that the WRSM can achieve wide torque speed characteristics. Moreover, the WRSM exhibits better efficiency under low load conditions at the higher speed or field weakening region.