Simplified thermal modeling for IGBT modules with periodic power loss profiles in modular multilevel converters

One of the future challenges in modular multilevel converters (MMCs) is how to size key components with compromised costs and design margins, while fulfilling specific reliability targets. It demands better thermal modeling compared to the state-of-the-arts in terms of both accuracy and simplicity. Different from two-level power converters, MMCs have inherent dc-bias in arm currents and the power device conduction time is affected by operational parameters. A time-wise thermal modeling for the power devices in MMCs is, therefore, an iteration process and time-consuming. This paper, thus, proposes a simple analytical thermal modeling method, which adopts equivalent periodic power loss profiles. More importantly, time-domain simulations are not required in the proposed method. Benchmarking of the proposed methods with the prior-art solutions is performed in terms of parameter sensitivity and model accuracy with a case study on a 30-MW MMC system. Experiments are carried out on a specifically designed scaled-down system to verify the electrothermal aspects.