Grid Impedance Estimation with Large SCR Disturbances based on Grid-Forming Converter

Grid-Forming (GFM) converters face significant synchronization challenges when suddenly exposed to ultra-weak grid conditions, primarily due to the lack of prior knowledge about grid impedance. This paper proposes a passive method for estimating grid impedance during large disturbances caused by a substantial reduction in the grid short-circuit ratio (SCR). The proposed method relies solely on local measurements, specifically the point of common coupling (PCC) voltage and output power. By dynamically adjusting the active power reference based on these estimates, GFM converters can maintain synchronization even under extremely low SCR conditions, well below 1. This method has been validated through experimental results.