Research on seamless switching of DC voltage control methods of MTDC system

A seamless switching control strategy for multi-terminal flexible HVDC system, presented in this paper, can maintain DC voltage of system stable and ensure a reasonable power allocation of converter stations. This strategy improves active channels of the outer loop, which enhances flexibility and selectivity of control by setting droop control mode cover fixed DC voltage control mode and constant active power control mode. Only by changing the control mode selection coefficients can realize switching of three kinds of control mode and self-switching of droop control mode, which reduces the fluctuation and shock generated by using the switching hardware and improves the transient stability of the system. Finally, a RT-lab simulation model of the five-terminal flexible HVDC transmission system is built to verify the effectiveness of the proposed control strategy, and the seamless switching among the control modes is realized.