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

This work analyzes and compares the performances of permanent-magnet-assisted synchronous reluctance machines (PMa-SynRM) and interior permanent magnet synchronous machine (IPMSM) on their constant power speed range (CPSR) capability for electric vehicle (EV) applications. The CPSR is a key performance index for traction motors to achieve wide speed range where the IPMSM is known to be an excellent candidate. However, a recent trend for traction motor development is to reduce the amount of rare earth magnet used due to its high cost and possible supply uncertainty. As an alternative, the PMa-SynRM possesses a higher saliency (thus higher reluctance torque) and lower PM quantity (thus lower PM torque) compared to IPMSMs. With the same power or torque output, the major distinction between these two types of machines would be the proportions of different torque components (PM and reluctance torques) due to rotor designs. The distinctive rotor designs would significantly affect the CPSR and this needs to be investigated for traction motor designs and various EV applications. Five 10 kW-30 Nm/L designs, with three IPMSMs and two PMa-SynRMs are studied. The analysis results show that the PMa-SynRMs can achieve higher peak speed despite the torque and power are lower at high speed. In contrast, the IPMSM can maintain the power beyond the base speed to achieve superior CPSR but the power drops quickly to zero at high speed. The high efficiency region appears at the mid speed range for the IPMSM but at high speed region for the PMa-SynRM due to their different PM and reluctance torque profiles. Two prototypes were tested, one being IPMSM and the other PMa-SynRM to validate the analysis results.