Reluctance synchronous and field intensified-PM motors for variable-gear electric vehicle drives

Reluctance synchronous (RS) and field-intensified permanent magnet (FI-PM) motors are designed and optimised for a variable-gear electric vehicle (EV) drive in this paper. Recent literature shows that EVs with variable-gear drive trains operate at higher drive-cycle efficiencies than fix-gear EV drive trains. The advantages and design challenges of variable-gear EV drives are discussed in the paper. With variable-gear, the operation field-weakening performance of the electric drive is not important, which makes the RS motor drive, amongst others, very suitable. The FI-PM motor with minimum amount of PM material is also attractive from the performance and position-sensorless-control points of view. It is found that both the optimum designed RS and FI-PM motors perform very well considering the volumetric space available and the required torque-speed specifications. In particular, the performance of the FI-PM motor with the same volume as the RS motor is surprising considering the simple FI-PM rotor structure proposed. The variable gear system was tested and the average efficiency was found to above 80%.