Adaptive Droop Control for Compromise Between DC Voltage and Frequency in Multi-Terminal HVDC

By connecting many wind farms and grids via multi-terminal high-voltage direct current transmission (MT-HVDC), the reserve power of each grid can be shared to balance the power mismatch. Resulting from a shortage of generated power, the frequency nadir and the lowest DC voltage may violate the constraints of continuous operation. Using a trade-off, this paper proposes a new control strategy based on adaptive droop control to make a compromise between DC voltage and grid frequency. By applying the proposed method, the demands from both sides are efficiently met. The proposed method relies on a decentralized approach, avoiding dependence on the communication link. In addition, wind farms are allowable to operate at the optimal power point without using a de-loading strategy. Time-domain simulations are conducted in PSCAD. The improvement in system reliability is proved by comparing with existing methods.