Research on Control Strategy of Multi-terminal HVDC Based on MMC

The multi-terminal flexible DC system is more reliable than traditional two-terminal system in power supplying, and the control system is more complicated relatively. To make up the defects of voltage margin control and voltage droop control, a hybrid control strategy is designed in this paper. The multi-terminal system converter station between stations and hybrid control scheme applied in station for configuration are used in this strategy, and the transient overvoltage of DC voltage is suppressed during transient process by introducing droop control at the phase of voltage margin in station, which avoids power synchronous changes in multiple-converter stations when disturbance occurs in system. In the end, a five-terminal MMC-MTDC simulation model is built in PSCAD/EMTDC, and the transient characteristics of three kinds of controls are simulated. The results show that the designed hybrid control system has good transient characteristics, and increases the multi-terminal system flexibility and effectiveness of coordinated control.