Two-Branch Coupling Cauer Model in IGBT Module Considering FWD Thermal Coupling Effect

Insulated gate bipolar transistor (IGBT) modules are often operated under high switching frequency and large electromagnetic inertia, and the internal freewheeling diode (FWD) chip generates non-negligible heat due to its freewheeling effect. In the conventional Cauer model, only the heat generated by the IGBT chip itself is considered, and the thermal coupling effect between the IGBT chip and the FWD chip is ignored, which leads to a large calculation error. Therefore, this article focuses on the thermal coupling effect between the IGBT chip and the FWD chip inside the module, and proposes the basis for determining the existence of thermal coupling and the method for determining the position of thermal coupling. Based on the conventional Cauer model, a two-branch coupling Cauer model for calculating the junction temperature of the IGBT chip and the FWD chip is established, and the extraction method of model parameters is given. Finally, a single-phase half-bridge inverter circuit is selected, and it is experimentally verified that the improved Cauer model has higher junction temperature calculation accuracy than the conventional Cauer model.