Variable Capacitor Voltage Threshold Value Based Power Loss-Balancing Control for MMCs Under Grid Voltage Imbalance

The modular multilevel converter (MMC) becomes one type prospective converters for high voltage and high-power applications because of its high modularity and low harmonic distortion step by step. Gird voltage imbalance will lead to arm current imbalance, resulting in power loss imbalance among three phases, which will reduce the lifetime of the MMC. In this manuscript, a variable capacitor voltage threshold value control (VCVTV) is proposed. In the case of grid voltage imbalance, by changing the value of the capacitor voltage threshold of each phase, the switching loss generated by the power devices of each phase of MMC can be changed, and the power loss balance among the three phases of MMC could be effectively realized. The proposed VCVTV control could availably balance the power loss among three-phase arms and enhance the lifetime of MMC operation. Using the professional tool software PSCAD and experimental platform built in the laboratory, the availability of the put forward VCVTV is confirmed.