Simplified Estimation of the Junction Temperature Fluctuation at the Output Frequency for IGBT Modules in Modular Multilevel Converters

Thermal modeling of modular multilevel converters (MMCs) are of interest for reliability-oriented component sizing. However, conventional analytical thermal modeling is difficult to consider an inherent thermal unbalance in MMCs, while a time-domain simulation is challenging to process one-year mission profiles in reliability evaluation. This paper proposes a thermal modeling method for IGBT modules in MMCs based on simplified equivalent power loss profiles. It compromises the accuracy and computation time. A derived analytical equation quantifies the modeling error and the level of simplification for periodic power loss profiles related to the ac output frequency of MMCs. The theoretical results have been verified by both simulations and experiments.