Design and testing of the World´s first single-level press-pack IGBT based submodule for MMC VSC HVDC applications

The Modular Multilevel Converter (MMC) based VSC HVDC is an increasingly popular technology worldwide for both engineering installation and academic research purposes over the years. A submodule serves as the basic unit for the MMC, and the typical topology of a submodule is a half bridge configuration. Normally, controllable power devices are used for switches in a submodule, and plastic module IGBT and diodes (PMIs) are common choices. However, PMIs have a relatively short lifetime, since they are prone to bonding wire failure and solder layer fatigue as a result of power and thermal cycling. Another disadvantage of PMIs is their open-circuit failure mode. Thus, it´s challenging for PMI based MMC HVDC to meet lifetime and long-term reliability requirements. On the other hand, press-pack IGBT/IEGT (PPI) can offer a much longer lifetime than PMIs, they have the unique short-circuit failure mode (SCFM), and they can carry higher currents. This is due to their special package design, which features double-side cooling and the removal of bonding wire and solder layer. Hence, PPIs are prefect devices for MMC HVDC, especially when power ratings are very high for future systems. The ±160kV/200MW MMC HVDC station is the largest one in the Nan´ao multi-terminal HVDC system, and it´s also the world´s first MMC HVDC that is based on single-level PPI devices for submodules. It is hoped that this paper provides insight into the design, analysis and testing process of its innovative submodule.