Recent advances in variable flux memory machines for traction applications: A review

This paper overviews the recent advances in variable flux memory machines (VFMMs) for traction applications with particular reference to newly emerged machine topologies and related control strategies. Due to the use of flux memorable low coercive force (LCF) magnets, the air-gap flux of VFMM can be flexibly varied via a magnetizing current pulse. Thus, the copper loss associated with the flux weakening current and high-speed iron loss can be significantly reduced, and hence high efficiency can be achieved over a wide speed and torque/power operation. These merits make VFMM potentially attractive for electric vehicle (EV) applications. Various novel VFMMs are reviewed with particular reference to their topologies, working principle, characteristics and related control techniques. In order to tackle the drawbacks in the existing VFMMs, some new designs are introduced for performance improvement. Then, the electromagnetic characteristics of an exemplified EV-scaled switched flux memory machine and various benchmark traction machine choices, such as induction machine, synchronous reluctance machines, as well as commercially available Prius 2010 interior permanent magnet (IPM) machine are compared. Finally, the key challenges and development trends of VFMM are highlighted, respectively.