Transient Electro-Thermal Analysis for a MOSFET based Traction Inverter

In this paper, an approach to evaluate the instantaneous junction temperature of MOSFET modules used in a high-power three-phase inverter is introduced. A Cauer resistor-capacitor model for the whole system is presented which is based on the MOSFET foster network model. In addition, a thermal impedance matrix of an air-forced cooling heat sink is developed by transient thermal analysis using computational fluid dynamics (CFD). Temperature dependence of power losses has been analyzed and a dynamic electro-thermal simulation considering the thermal coupling effect between different phases under real motor operating conditions is performed. Then, the wide time scale separation of the thermal time constants and transient temperature fluctuation caused by the small heat capacity of the chips are discussed. The thermal performance of the inverter under stall torque condition is also analyzed. The proposed approach is an effective tool for the reliability analysis and thermal management system design in traction inverters.