CFD Model for Thermal Impedance Evaluation of a SiC-Based Traction Inverter Considering Heat Coupling Effects

The aim of this study is to develop a transient thermal analysis by means of Computational Fluid Dynamics (CFD) to assess the thermal impedance of a SiC-based direct-cooled traction inverter from STMicroelectronics. Thermal impedance measurements are performed during a power cycle test. The virtual junction temperature of the switches is determined assuming the body diode voltage drop as a Temperature-Sensitive Electric Parameter (TSEP). In more detail, one switch is heated, and the junction temperature is measured by TSEP for the other switches, accounting for cross-heating between them. Subsequently, a sensitivity analysis of the time step is performed to allow the adoption of a variable time step during the investigated time range. Following this analysis, the computational time required for the simulation is reduced by 60% compared to using a constant time step. Finally, the CFD results are compared with the TSEP results, demonstrating good accuracy.