Five-phase external rotor permanent magnet assisted synchronous reluctance motor for in-wheel applications

This paper presents a five-phase external rotor permanent magnet assisted synchronous reluctance motor (PMa-SynRM) with low torque ripple and cogging torque for in-wheel applications. Multi-phase internal rotor electric motors have been proposed for vehicular applications as they possess low torque ripple and low back-EMF harmonics. However, increase in the power density while maintaining the same size and amount of PMs has been a challenging issue. In comparison to the internal rotor motors, external rotor motors can be optimally designed to produce higher torque density with low torque ripple. In this study, the design technique to develop an optimal five-phase external rotor PMa-SynRM model is discussed in detail. Detailed finite element simulations are conducted on the optimally designed 3.8kW five-phase external rotor PMa-SynRM and the results are compared with five-phase internal rotor PMa-SynRM. With the same size, volume, and lower PM composition, the 3.8kW five-phase external rotor PMa-SynRM is capable of generating higher torque density with lower torque pulsation and almost negligible cogging torque in comparison to the 3kW five-phase internal rotor PMa-SynRM. Experimental results are compared between five-phase internal and external rotor PMa-SynRMs to validate the simulation results.