Multi-Stage Black-Start Strategy for Pure New Energy Power Grid Based on Grid-Forming Energy Systems

The increasing penetration of renewable energy is driving the use of grid-forming energy storage (GFM-ES) for black start in pure renewable power grids. However, practical implementation is challenged by three coupled problems: transient voltage overshoot during bus energization, imbalance of state of charge (SOC) among distributed storage units during islanded operation, and synchronization shocks during grid reconnection. This paper proposes a coordinated multi-stage black-start strategy that integrates (1) an improved V/f startup control with a two-segment voltage reference to soften bus energization; (2) an SOC-aware adaptive droop law based on a bounded arcsine SOC index to balance the charge/discharge effort among distributed storage units; and (3) a virtual-capacitor-based phase-angle control to accelerate synchronization before grid connection. Compared with existing black-start schemes, the proposed framework provides stronger voltage regulation, better SOC consistency, and shorter synchronization time in a pure renewable scenario. The method is validated through PSCAD/EMTDC simulations and an engineering case study of the Ejina pure renewable grid.