Experimental Investigation on Fatigue Failure Evolution of Press-Pack IGBT Devices Under MMC Operating Conditions

Converter valves based on the modular multilevel converter (MMC) topology are the core of the voltage source converter-based high-voltage direct current transmission system, with press-pack insulated gate bipolar transistor (PP IGBT) modules being the key components. Studying the long-term aging failure mechanism of the PP IGBT under actual MMC operating conditions is of great significance for improving the safe and reliable operation of the transmission system. In this article, an electric–thermal–mechanical coupled multifield model of the PP IGBT device is built to analyze the influence of junction temperature and pressure on stress and strain distribution, identifying the weak points. Then, based on the alternating current (ac) power cycling tested rig, which equivalently reproduces the working conditions of the MMC submodule, the influence of different junction temperatures and pressures on long-term aging failure is studied, revealing the evolution of key characteristic parameters during the aging process. Two main failure modes are identified under ac power cycling tests. One mode is caused by overvoltage short-circuit failure due to the blocking voltage drop, and the other is induced by open-circuit failure due to uncontrolled gate current. Finally, the evolution of microscopic morphology and static characteristic parameters over the entire lifetime during the power cycling test are obtained, emphasizing the differences between ac and direct current (dc) power cycling tests. The results show that there are significant differences in overheating failures between ac and dc power cycling tests, highlighting the critical role of ac conditions in failure analysis and reliability assessment. The study of the long-term failure evolution mechanism of the PP IGBT device under actual MMC working conditions aims to guide operational management, control protection, and device optimization design for the reliability of MMC systems.