Variable Flux Memory Machines for Electric Vehicles: A Comparative Study

This paper overviews different synchronous machine types and topologies applied to electric vehicles (EV) traction. The very widespread permanent magnet synchronous machine (PMSM) and wound field synchronous machine (WFSM) are first compared in terms of efficiency at equivalent size and power. This comparison raises questions about the ideal properties and features of a synchronous machine to obtain maximum efficiency over the entire torque-speed envelope, which introduces the concept of variable flux memory machines (VFMM). Three hybrid permanent magnet (PM) VFMM configurations are compared for EV use: one with a series configuration of PM, the second with a parallel configuration, and the third with a combined series/parallel configuration. The modeling of the magnetic behavior of non-linear PM and the VFMM analysis methodology are described. The benefits and drawbacks of the three configurations in the context of an EV application are explained and compared. This work aims to highlight the potential of the hybrid PM-VFMM for EV use.