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

The current development trend in the power sector is the utilization of grid-forming energy systems (GF-ESs) in renewable energy black-start. Potential issues when utilizing GF-ESs as power sources for black-start include significant voltage fluctuations, imbalanced state of charge (SOC) among energy storage units, and substantial grid connection impacts. Hence, this study proposes three key solutions: first, an improved V/f control strategy is developed to rapidly smooth drastic voltage variations caused by wind power during the initial black-start phase. Second, an SOC control method for GF-ESs is introduced to modify active power droop coefficients to enable real-time adjustments of power change rates based on current SOC statuses. This adjustment prevents SOC limit violations caused by an unreasonable power distribution among distributed energy storage units. Third, a virtual capacitor-based phase angle control method is proposed to mitigate grid connection impacts. Simulations were performed, and the results demonstrated that the proposed GF-ES strategy effectively suppresses voltage fluctuations, maintains balanced SOC statuses across distributed energy storage units, and improves the success rate of black-start operations in renewable energy grids.