Design procedure for multi-phase external rotor permanent magnet assisted synchronous reluctance machines

This paper presents the optimal design procedure to develop multi-phase external rotor permanent magnet assisted synchronous reluctance machines (EPMa-SynRMs). With its higher torque density and higher power density compared to the internal rotor PMa-SynRM, external rotor PMa-SynRM is best suitable in applications to electric bikes and aircrafts. Enormous amount of research has been done in optimizing internal rotor PM machines. However, an efficient optimization technique to develop a five-phase EPMa-SynRM is not presented in the literature. The optimization of the EPMa-SynRMs is important to provide better performance characteristics and controllability in terms of lower back-EMF harmonics and cogging torque for critical applications. In this study, a detailed analysis on developing magnetic equivalent circuit for the multi-phase EPMa-SynRM is presented. Differential evolution (DE) optimization algorithm is utilized to develop the optimal models for five-phase EPMa-SynRM. The effects of rotational forces on the rotor in both internal and external rotor PMa-SynRMs are analytically studied. A thermal model for the proposed EPMa-SynRM structure is presented. Initial simulation results for stress and thermal heat flow for the proposed designs are presented. Furthermore, electromagnetic finite element simulation results such as back-EMF, flux linkage, cogging torque, and their harmonics are presented for the developed five-phase EPMa-SynRM model. The best design which has lower back-EMF harmonics and cogging torque is chosen to fabricate and conduct experimental tests.