An Offshore Wind Farm With DC Collection System Featuring Differential Power Processing

The analysis of wind turbine output power measurements from the offshore wind farm Horns Rev 1 demonstrates a significant likelihood of wind turbine output powers to be very similar at a given time within offshore wind farms. This paper exploits this observation by proposing a new offshore wind farm configuration with DC collection system and series-connected wind turbines based on partial power processing converters (PPPCs) and diode-bridge rectifiers. In the proposed wind farm configuration, PPPCs are only required to process output power differences among wind turbines in a wind farm to achieve maximum power point (MPP) operation, yielding a potential for efficiency and sizing improvements. This paper addresses major design considerations at wind farm, wind turbine, and PPPC levels. System operation of the wind turbine design is derived, alongside with a matching control system and HVDC-link current scheduling algorithm. The proposed wind farm is successfully tested for low voltage ride through, power curtailment, inertia response, and communication system outage scenarios. Time-transient simulations of a 30-turbine series string using measured and artificial wind speed profiles demonstrate that wind turbines can achieve MPP operation while only a fraction of power needs to be processed by the PPPCs.