Coordinated direct current matching control strategy for multi-terminal DC transmission systems with integrated wind farms

A new direct current matching control (DCMC) scheme is proposed in this paper. The scheme is ideally suited for the integration of a large number of wind farms with AC grid systems via a multi-terminal HVDC (MTDC) network incorporating several grid-side converters. The proposed DCMC, which matches, in a near-instantaneous fashion, the cumulative injected DC currents from all wind farms with the total of the output DC currents to the AC grids (via inverters) by communicating real-time data between all terminals, is an improvement upon and potential replacement for conventional DC voltage droop and master-slave control strategies. Through the utilization of a wide-area supervisory control and data acquisition (WA-SCADA) system, the proposed DCMC aims to enhance MTDC network voltage stability and facilitate flexible power dispatch to the supplied AC grids, while maximizing the total amount of generated wind power and offering more flexibility in terms of the ability for wind farms to independently control and maximize their outputs without any requirement for output to be constrained. A six-terminal MTDC system connecting three wind farms to three independent mainland AC grids is used to validate the proposed DCMC and compare its performance with conventional control strategies, three simulation studies are carried out to test and verify the DCMC.