Comparative study of constant power speed range of three permanent magnet brushless machines with different d-axis inductance for electric vehicles

This paper presents a comparative study of constant power speed range of permanent magnet brushless (PMBL) machines with different d-axis inductance for electric vehicles (EVs). According to the flux weakening principle, three typical operation cases, namely, characteristic current is higher, lower than and equals current limitation, are given and analyzed in details. By the finite element analysis (FEA) method, the torque density, permanent magnet utilization ratio, power, losses and efficiency at the rated operating point are investigated and compared. Moreover, considering different d-axis inductance of the three PMBL machines, constant power speed range is researched. Also, performances of losses and efficiency over the whole operating speed range are analyzed and compared. The simulation results show well consistency with the theoretical analysis, hence verifying the validity of adjusting d-axis to improve performances of PMBL machines for EVs.