A new thermal model for EV induction machine drives

This paper introduces a new thermal model that can be used for design, protection, efficiency maximization, and speed estimation of an electric vehicle machine drive. The model can predict the winding temperature even in transient conditions. The proposed thermal model of the machine is represented by an equivalent electric circuit. Then the thermal equations are derived and used for temperature estimation. Two techniques for temperature estimation are proposed. The first technique is based on prediction of the winding temperature from the machine frame temperature. In the second method, the winding temperature is estimated from the ambient temperature. In order to investigate transient behavior of the winding temperature, the temperature dependent model of the EV drive has been simulated to calculate the winding temperature when the vehicle is driven under different loads and applied torques. The predicted temperature from the thermal model has also been compared with the actual measurements and found to agree very closely with measured values. It is shown that this thermal model can be used for design and protection of electric vehicles. Another important issue that is addressed in this paper is efficiency optimization by using the predicted temperature from the thermal model. The system efficiency is improved by choosing an appropriate flux level for each speed, torque, and winding temperature.