Hybrid AC/DC Collection and HVDC Transmission Topology for Large-scale Offshore Wind Farms

Conventional offshore wind integration systems use 33kV or 66kV AC cables to collect wind energy and employ high voltage direct current (HVDC) transmission technology to deliver wind power to onshore grids. This scheme suffers from high costs for collection systems and offshore platforms when the capacity of offshore wind farms increases. This paper proposes a hybrid AC/DC collection and HVDC transmission concept for the large-scale offshore wind integration system. Wind farms near the offshore converter platform are integrated using AC collection cables, while the remaining wind farms are integrated using DC collection cables. The AC and DC collection cables infeed to the offshore converter platform, which features a three-terminal hybrid AC/DC/DC hub. The system layout and operating principle of the hybrid AC/DC collection and HVDC transmission system are introduced in detail. The control strategy and parameter design of the hybrid AC/DC/DC hub are presented. An economic evaluation comparing conventional AC collection and HVDC transmission schemes is conducted. It is indicated that the proposed integration concept can reduce the operating power capacity and power loss of the offshore converter, enhancing the economic efficiency of the overall integration system. Finally, the effectiveness of the proposed integration technology is validated in a 2000MW offshore wind power integration system by PSCAD/EMTDC simulation analysis.