Dimensioning of a novel design concept for MMC submodules

Modular multilevel converters (MMC) comprise of a multitude of identical submodules. Current high power systems für 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 towards the special boundary conditions in MMCs. A promising concept is to mount the top switch directly onto the heat sink. This measure removes unnecessary thermal and electrical isolation barriers. Moreover considering copper heat buffers as semiconductor top-side contacts, module as well as auxiliary safety components can be saved because of an increased intrinsic failure capability. In this work the approach of designing such 6.5 kV submodules for a 1280 MVA system by electrical and thermal simulations is given. Furthermore thermal measurements are carried out to review the thermal simulations and compare different assemblies.