Design considerations for induction machines for electric vehicle drives

For an electric vehicle drive motor the properties of high efficiency, high power density and wide speed range are clearly desirable. This paper presents the design of an induction motor for a prototype electric vehicle, namely. a Fiat Cinquecento. It is apparent that the design requires a compromise between achieving low losses on one hand and high power density and wide speed range on the other. The vehicle drivetrain consists of a single motor driving a fixed ratio gearbox and mechanical arrangement of the transmission is simplified by the use of a fixed gear ratio, however this places a demanding specification on the drive motor torque speed requirements. At high speeds, rated current cannot be maintained due to the effect of leakage reactance and the maximum torque is limited by the pull out torque. To achieve a wide speed range it is necessary to minimise the leakage reactance. The authors describe the vehicle model, motor design, and calculate the leakage reactance.