A Physics-Based Improved Cauer-Type Thermal Equivalent Circuit for IGBT Modules

A physics-based Cauer-type thermal equivalent circuit (TEC) can be constructed for an insulated-gate bipolar transistor (IGBT) module based on its geometry. In the conventional Cauer-type TEC, each layer of the IGBT module is modeled as a lump with the uniformly distributed temperature. However, this method oversimplified the transient thermal behavior of the IGBT module, leading to unsatisfactory transient junction temperature estimation. Based on a new concept of lumped-capacitance approximation error, this letter proposes a method to determine the number of sublayers that a layer in an IGBT module should be subdivided. For the bulky-baseplate layer, an analytical expression of its thermal impedance is derived and simplified to a first-order transfer function, which can be represented by a thermal resistance and capacitance pair in the TEC. The proposed Cauer-type TEC model is much more accurate than the conventional Cauer-type TEC model for the transient junction temperature estimation of IGBT modules with a slightly increased order only. The improvement of the proposed model over the conventional Cauer-type TEC model is validated by comparing with a finite element analysis model for a commercial IGBT module using simulation studies.