Modeling of cross-circulating currents in a MMC with parallel connected submodules in Solid State Transformers

Solid state transformers based on modular structures have become a suitable alternative to provide high voltage rating, reliability, and fault tolerance at the distribution level. Among them, the SST based on Modular Multilevel Converter with an input-series output-parallel interconnected by Dual Active Bridges configuration appears as a good solution to reach high voltage levels at the input and large currents at the output stage. However, the parallelization of SM generates cross-circulating currents among modules. In this paper, the cross-circulating currents are analyzed and mathematically modeled. Simulation results shown the cross-circulating currents and their dependency under mismatches in both inductance and resistances.