Hybrid-Arm-Based DC Station for Wind Power Collection and HVDC Transmission: Implementation and Operation Supporting Startup

The startup issue has become a major concern of the offshore wind power collection and transmission system (OWPCTS). To tackle with it, a novel design of offshore station is proposed in this paper with an asymmetrical forward-and-reverse power transmission capability. With the modular multilevel cells and diode units integrating in different phases of bridge arm, the detailed topology of the proposed offshore station is implemented by a special hybrid-arm structure which contributes to smaller footprint and saved cost. During the normal operation mode, the proposed offshore station performs the function of voltage boosting and wind power delivering from wind farm (WF) to onshore station. During the system startup mode, the proposed offshore station reversely transfers the startup power from the onshore station to WF. The corresponding control scheme is presented with the capability of supporting startup. Both simulation and hardware-in-loop experiment are carried out, and the working performances of the proposed offshore station are validated for typical scenarios.