Advanced Control Method for Quasi-Three-Level Operation of a Conventional Converter Extended by a Modular Multilevel Branch

This paper presents an advanced control method for a two-level converter-based topology with the extension of a modular multilevel branch as a third current path to enable the quasi-three-level operation mode. The advanced control method predicts the dynamic current changes during the commutation processes within the phase legs. It is shown via simulation that in comparison to a basic control method based only on fixed thresholds, the commutation periods and the current overshoots can be reduced significantly.