Thermo-fluid simulation of the advanced IGBT module in a power stack

Insulated gate bipolar transistor (IGBT) modules are essential in power electronic application. Due to the improvement in chips and packaging, the maximum operation junction temperature T_vj,op of the latest IGBT module has been increased up to 175°C, comparing to 150°C of the previous generation. With the enhancement of power density, its application at high temperature gives rise to more concerns of the reliability. Nevertheless, few literatures exist concerning the thermal design of the advanced IGBT module. External cooling system such as forced air cooling and liquid cooling is commonly utilized to make sure that the junction temperature T_j is not larger than 175°C. But the employment of such cooling components consequently increases the variance in T_j among chips within one single module during its usage. The heat dissipated by chips, transferred by packaging and carried by coolant leads to higher T_j of chips in the downstream area and lower T_j in the upstream. Nonetheless, this phenomenon has not been adequately evaluated. The present paper describes a thermo-fluid simulation model of the advanced IGBT modules in a power stack, by employing Computational Fluid Dynamics (CFD) and Finite Volume Method (FVM). Through grid independent study, the numerical error of model in T_j is found less than 1°C. The ambient temperature is set at 55°C for simulating the extreme environment condition in the cabinet. Furthermore, the variance in T_j among chips of IGBT components within one single module is inspected. Its correlations with power loss and air flow velocity are examined.