Black Start Strategy of DRU-Based Low-Frequency AC Transmission System for Offshore Wind Power Integration

The diode rectifier unit (DRU) based low-frequency AC transmission system is an attractive option for integrating offshore wind power due to its low construction cost and high economic efficiency. However, since DRU cannot transmit active power to offshore wind farms, an additional black start power source is required to provide the initial energy required for the wind turbines. In this paper, an auxiliary converter-based black start strategy is proposed for the above transmission system. The position and topology of the auxiliary converter are introduced, and the method for selecting its capacity is analyzed. The black start strategy of the transmission system is then designed, including the black start for the auxiliary converter and the grid-forming wind turbines based on self-synchronizing control. Finally, a simulation model is developed using PSCAD/EMTDC, and the simulation results demonstrate the feasibility and effectiveness of the proposed black start strategy.