Comparative Study of PM-Assisted SynRM and IPMSM on Constant Power Speed Range for EV Applications

This paper analyzes and compares the performances of permanent-magnet-assisted synchronous reluctance machines (PMa-SynRMs) and interior permanent magnet synchronous machine (IPMSM) on their constant power speed range (CPSR) capability for electric vehicle (EV) applications. The recent trend of less rare-earth magnet makes the IPMSM unfavorable despite its excellent CPSR. As an alternative, the PMa-SynRM possesses a higher saliency with lower PM quantity. The two different rotor designs would affect the CPSR and these need to be investigated and compared. As a key performance index for EV traction motors, the CPSR calculated by analytical methods often suffers low accuracy due to omission of saturation. Finite-element analysis (FEA) can be used to obtain the CPSR but significant computation time is required. This would be disadvantageous for accurate performance prediction in design stage. To resolve these problems, six 10 kW, 30 Nm/L designs are studied and compared, covering IPMSMs and PMa-SynRMs. An approach associating analytical methods with FEA is developed for accurate and rapid calculation of CPSR for these machines. A discussion on PMa-SynRM rotor designs and suggestion for their PM quantity are provided considering performance, cost, and demagnetization. Two prototypes were tested, one being IPMSM and the other PMa-SynRM to validate the analysis.