Coordinated Control Method of MMC-MTDC Based on Power Addition

Maintaining DC voltage stabilization is one of the key technologies to achieve stable operation of a multi-terminal flexible DC power transmission (VSC-MTDC) system. Aiming at the characteristic of slow DC voltage adjustment of VSC-MTDC under single-point voltage control, this paper analyzes the mechanism of DC voltage change due to power change, and design control links to offset the effect of power change, and proposes a voltage outer loop improved coordinated control strategy for multi-terminal converter stations. Compared with the traditional single-point voltage control, this strategy not only reduces the fluctuation of the DC voltage of VSC-MTDC system, but also improves the adjustment speed of the DC voltage and active power. Finally, a multi-terminal high-voltage direct current transmission (MMC-MTDC) system model based on modular multilevel converters was built in PSCAD / EMTDC. The traditional control strategy and improved control strategy were compared under different working conditions. The comparative experimental results show the effectiveness of the proposed control strategy.