A single-phase to three-phase direct AC/AC modular multilevel cascade converter based on double-star bridge-cells (MMCC-DSBC)

A modular multilevel cascade converter based on double-star bridge-cells (MMCC-DSBC) is expected to be one of the next-generation medium-voltage PWM converters intended for grid connections. This converter is formed by six modular arms, each of which consists of a cascaded stack of multiple full-bridge converters. The DSBC is capable of single-phase to three-phase direct ac/ac conversion provided that the input and output frequencies are different. In this operation mode, the conversion efficiency can be improved compared to the ac/dc/ac indirect conversion. Hence, the DSBC is applicable to grid-connected high-power wind turbine generation systems using permanent-magnet synchronous generators. This paper presents experimental results obtained from a 200-V 6-kW downscaled system, which carries out single- to three-phase direct conversion, to verify the validity of the operating principles and control method developed in this paper.