A branch energy control method based on optimized neutral-point voltage injection for a hexagonal modular multilevel direct converter (Hexverter)

Hexverter is a recently proposed direct AC/AC modular multilevel converter (MMC). It features significant advantages for low-frequency drives compared to traditional MMC in back-to-back configuration. This paper presents a novel branch energy control method based on the injection of optimized circulating current and neutral-point voltage. It can effectively balance the energy stored in the six branches of the hexverter and simultaneously minimize the module-capacitor voltage fluctuation. The control performance is verified by simulation studies.