A Novel Approach for Inter-Leg Balancing of a Three-Phase MMC in HDVC Applications

This paper proposes a harmonic balancing based approach to deal with the equalization process of the capacitors stored energies in the six legs of a three-phase Multi Modular Converter (MMC) serving as the active interface between an AC grid and a HVDC link. Indeed, the harmonic balancing control, applied to the converter energies status variables written in a special form by exploiting the Space Vector/Zero Component and Common/Differential Mode decompositions, allows to highlight all the viable controllable interactions able to constrain the MMC stored energies to the desired balanced status. The conceived voltage control strategy is validated by an extensive numerical simulation.