Research on the speed-dependence of heat convection in high-speed EV motors and its application in the model-based rotor temperature monitoring technology

Abstract

Using the embedded onboard digital thermal model is an economical and effective way to monitor the rotor temperatures of the electric vehicle (EV) propulsion Permanent Magnet Synchronous Motor (PMSM) in real-time. The onboard thermal model is generally in an analytical form with constant thermal resistances. However, in practical situations, the thermal convection intensities on the surfaces of the air gap and the end-cavity vary significantly with the rotational speed, producing a non-negligible influence on the estimation accuracy of the onboard thermal model. Aiming at eliminating this error and improving the accuracy, this paper explores the variation of the airflow's aerodynamics characteristics and the heat convection with the rotational speed through a syncretic study of theoretical, experimental, and numerical methods. It is found that the changing trend of the airflow presents a multi-stage characteristic in the speed range of 0–12,000 rpm. The speed-dependent convective thermal resistances are formulaically parameterised and then used to replace the related constant thermal resistances in the thermal model. The standard vehicle driving cycle test result shows that this optimisation brings a nearly 11% reduction of the overall estimation error.