VSG-based adaptive droop control for frequency and active power regulation in the MTDC system

In this paper, a VSG (virtual synchronous generator)-based method with adaptive active power and DC voltage droop is proposed for the control of VSC stations in the multi-terminal DC (MTDC) system. This control strategy can improve the inertial level of the AC networks and attenuate the rate of change of frequency when a disturbance occurs. In addition, the droop control of the active power and DC voltage is implemented to make the AC networks share the unbalanced power in the MTDC. The droop coefficients are adaptively adjusted depending on the frequency margin of every AC network, which makes the allocation of unbalanced power among AC networks more reasonable from the frequency variation perspective. The control strategy is evaluated in the scenarios of sudden load change and wind turbine tripping, and the results are presented to demonstrate its effectiveness.