Decoupling Compact Thermal Model in Multichip IGBT Modules: A Methodology Based on Concepts of Positive and Negative Mutual Thermal Coupling

To accurately characterize the thermal behavior of the multi-chip IGBT modules, the thermal coupling effects in a thermal network model must be considered, which will increase the model complexity significantly. The thermal coupling effects are related to the macro operating condition. In some operating conditions, the thermal coupling effects can be ignored and the coupled thermal model can be simplified or decoupled. However, in the existing literature, the relationship between the thermal coupling and operating conditions has not been comprehensively analyzed. Therefore, in this study, based on the compact thermal model, we propose a general methodology to analyze the thermal coupling and decouple the coupled thermal model in the multi-chip IGBT modules. By studying the "decoupled" form of the simplest compact thermal model with only two chips, the concepts of the positive and the negative mutual thermal coupling are proposed and some important mathematical relations between the Cauer-type and the Foster-type thermal models are found. With these concepts and findings, we deduce the general expression of the decoupling condition. Further, the above-obtained conclusions are extended to the compact thermal model with n chips. Under the given power loss inputs, the decoupling condition for an average compact thermal model with 4 chips is obtained. Finally, both the simulation and experimental results verify the validity of the theoretical analysis and the correctness of the obtained decoupling condition.