Modular multilevel converters MMC are subdivided into identical submodules. Current high power systems for power transmission (i.e. HVDC) use state of the art industrial power semiconductor modules. Great improvements are possible by optimizing the construction of the power modules for the special boundary conditions in MMCs. A promising concept is to mount the bottom switch directly onto the heat sink, which removes unnecessary thermal and electrical isolation barriers. In this work the thermal resistances of different design concepts were simulated and compared to the state of the art. As a result, an improvement of 70% in the thermal performance is attainable, which was confirmed by measurements. First active reliability tests were performed for a noninsulating test assembly which shows lifetime results comparable to state of the art assemblies.
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