Black Start and Fault Crossing Control Method of New Energy Island Connected to Grid by Flexible DC System

To ensure stable grid operation, this study investigates black start and fault ride-through control methods for renewable energy islands connected via Flexible DC (FDC) systems. A comprehensive grid model integrating renewable energy units, FDC systems, and AC grids is established, with detailed explanations of components using wind farms as examples. A three-phase coordinated recovery strategy for wind-storage hybrid systems participating in receiving-side grid black start is proposed, encompassing energy storage self-start, wind turbine support, and low-frequency oscillation suppression. For onshore AC grid faults, the research analyzes power imbalance between sending and receiving ends, implementing low-load reduction for wind turbines and short-term voltage stabilization through energy-absorbing devices. A method for setting energy-absorbing resistor values is provided to enhance economic efficiency under severe faults, thereby achieving fault ride-through control for renewable energy islands connected via FDC systems. Experimental results demonstrate that the proposed method reduces bus voltage fluctuations from ±8% to within ±2.5% during black start scenarios, and improves the minimum voltage point from 0.4p.u. to 0.65p.u. in fault ride-through scenarios. Power fluctuation suppression rates increased by an average of 25.7% across 8 samples, with sample 5 achieving a 28.3% improvement. These findings validate the method′s significant effectiveness in enhancing grid resilience and stability.