Comparative study of battery-based STATCOM in grid-following and grid-forming modes for stabilization of offshore wind power plant

This paper presents a comparative analysis of a static synchronous compensator (STATCOM) based on battery energy storage system with grid-following and grid-forming operations utilized for stability enhancement of offshore wind power plants (WPPs). The small-signal model of a typical offshore WPP system is developed first, then compared from two perspectives - oscillation index for stability margin evaluation of a multi-input multi-output system and damping ratio of dominant poles, with respect to the critical control parameters. The theoretical comparative analysis proves that the grid-forming control offers evident stability margin and damping to the WPPs especially in weak grids, superior to the grid-following STATCOM. This conclusion holds true for most conditions with properly designed parameters, including different bandwidths of the alternating voltage control of STATCOM in 1 similar to 10 Hz and phase-locked loop of grid-following STATCOM ranging from 5 to 100 Hz, which is benefited from the sufficient stability margin of GFM mode. The small-signal models and comparative analysis are corroborated by electromagnetic transients (EMT) simulations.