A single-phase five-branch modular multilevel converter for direct AC/AC equal frequency conversion

For medium- to high-voltage, high-power direct AC/AC conversion, modular multilevel converter (MMC) is a potential solution due to its outstanding features. However, MMC suffers from branch energy instability when frequencies of input and output are equal. This paper presents a single-phase five- branch MMC which is capable of direct AC/AC equal frequency conversion without branch energy stability problem. The branch energy stability criterion is described. A branch energy balancing strategy is proposed to achieve stable operation of the single-phase five-branch MMC. The proposed MMC and the control strategy are validated by MATLAB/Simulink simulations.