A New DC Voltage Control Strategy for Multiterminal Transmission Systems

Research on control strategy of multi-terminal transmission systems has become the focus of recent power system development. After summarizing various system-level DC voltage control strategies, this paper proposes a new DC voltage control strategy named the distributed DC voltage control strategy. The DC voltage of the multi-terminal transmission systems can be controlled by more than one converter station in the new strategy. Also, it can indirectly control the active power by changing the DC current distribution coefficient of the converter station. To further explain the proposed strategy, the overall control structure, steady-state control and fault control are discussed. Two typical fault simulations on PSCAD/EMTDC are carried out to compare the dynamic characteristics among the master-slave control, the dead-band voltage droop control and the distributed DC voltage control. The result shows that the proposed control strategy has smaller DC overvoltage level, smaller DC current fluctuation and less transient process time during typical faults, and the dynamic response characteristics are better.