Grid-Forming Control of Wind Turbines for Diode Rectifier Unit Based Offshore Wind Farm Integration

Offshore wind farms are the main trend of future wind power exploitation. The diode rectifier unit (DRU) shows great potential in offshore wind power integration due to its economy and reliability benefits, and stable AC voltage control of the offshore gird is the key technology of the DRU based scheme. In this paper, the sensitivities of the DRU based system are defined and the sensitivity calculation method is proposed. According to the sensitivity characteristics analysis, the relationship between the wind turbine (WT) active power (or reactive power) and the WT output voltage (or system frequency) is clarified. On this basis, a grid-forming control strategy for WT converters is proposed. The stable operation mechanism of the grid-forming WTs in the DRU based system is demonstrated according to the analysis of steady state operation point existence and small disturbance stability. The time domain simulations of two DRU based offshore wind farm integration systems are carried out in PSCAD/EMTDC, and the feasibility of the proposed grid-forming control is verified.