A capacitor voltage balancing algorithm for hybrid modular multilevel converters in HVDC applications

This paper presents a sorting and balancing algorithm for the Hybrid Modular Multilevel Converter (Hybrid-MMC) consisting of half bridge and full bridge cells. The proposed algorithm can be used in combination with a standard control scheme of a common MMC (which consists of only one cell type) and increases the power transmission capability by reducing the switching frequency of the half bridge cells. Furthermore, it presents an analysis on the cell capacitor sizing and a method to adjust the average switching frequency.