A coordinated control strategy of series multi-terminal VSC-HVDC for offshore wind farm

After the analysis of the characteristics of the direct driven wind turbine with permanent magnet synchronous generator (D-PMSG) and VSC-HVDC, the paper proposed a circuit topology based on the series multi-terminal VSC-HVDC for offshore wind farm integration. The topology simplifies the D-PMSG structure by eliminating the inverter side of full power converter for the D-PMSG, and cascades rectifiers to form a series multi-terminal VSC-HVDC structure. The onshore grid side inverter employs multi-level VSC structure. This topology can decrease the steps for electricity conversions thus it will reduce the system complexity and the system power loss. Control strategies for both sending side and receiving side are proposed for the topology. A system based on the topology is modeled and a large wind farm is simulated. The simulation demonstrates that the control strategy can achieve the wind turbine maximum power point tracking individually and the stable operation of each converter in the system.