Bidirectional electromagnetic–thermal coupling analysis for permanent magnet traction motors under complex operating conditions

Abstract

Temperature increase has a significant effect on the performance and service life of permanent magnet in-wheel motors (PMIWMs) in the traction systems of electric vehicles under complex operating conditions. Herein, we propose a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a PMIWM considering the effect of increased temperature on the permanent magnet. The heat dissipation coefficient and electromagnetic–thermal coupling field model of each component of the PMIWM were analyzed. The distributions of electromagnetic loss and thermal loss of the PMIWM were investigated under constant-speed plus constant-torque and variable-speed plus variable-torque conditions. An 8 kW outer rotor PMIWM was used to study the electromagnetic–thermal coupling characteristics. Simulations and experimental results showed that the thermal field of each component of the PMIWM calculated using the proposed bidirectional electromagnetic–thermal coupling method was more accurate than that of the traditional unidirectional electromagnetic–thermal coupling method under complex operating conditions. The effectiveness of the proposed bidirectional electromagnetic–thermal coupling method provides solid support for the cooling design of PMIWMs operating in harsh environments.