Enhanced online thermal modeling for power electronic temperatures in (hybrid) electric vehicles

In electric and hybrid electric vehicles, the power losses of the semiconductors within power modules lead to strong self-heating. The resulting thermal stresses are major factors regarding critical overload and lifetime reliability. The relevant temperatures and temperature profiles are important design parameters. Additionally, it is necessary to monitor these temperatures during operation of the vehicle. However, if the number of relevant temperatures is larger than the number of sensors or the point of interest is not accessible for sensor placement, it is advantageous to use a model-based method to estimate these temperatures and use the given sensor information to correct the model. A so-called feedback observer can be used to reconstruct the non-measureable temperature. The capability of such an observer is based on the size and structure of the implemented model. In this paper multiple models and model structures are presented, which can be used to meet different requirements: Asymmetrical load distribution within the modules; coolant inlet and outlet estimation and/or the adaption of those models for the situation if the coolant flow rate of the inverter is variable. However, every extension of the model results in an increase of complexity and therefore in an increase of computational effort. Hence, to model as compact as possible is another requirement that has to be met. The result is a systematic approach which allows to combine those modeling methods within a modular construction system for thermal modeling of power converters. The presented models are compared regarding capability and computational effort.