Calculation and identification of a thermal equivalent circuit of a water cooled induction motor for electric vehicle applications

High performance for electric vehicle drives is obtained by allowing the machine to carry a load exceeding its rated values for short periods of time. The limit of such overloading is set by the maximum temperature rise. In this case it is essential to predict the behaviour of the machine for any time varying load. With the help of a thermal equivalent circuit, the dynamic temperature behaviour of the machine can be determined. This paper presents an analytical calculation of the elements of the thermal equivalent circuit of an induction motor and the result of the estimation of these elements using different parameter identification methods. Results are presented for a 17 kW induction motor built for an electric vehicle.