Proportional Allocation Analysis of Grid-Following and Grid-Forming Wind Turbines with Consideration of Grid Strength

Grid-following wind turbines (GFL-WTs) are prone to oscillation problems under weak grid conditions. In contrast, grid-forming wind turbines (GFM-WTs) exhibit active grid-support capabilities. Configuring a certain proportion of GFM-WTs in wind farms can enhance system stability. However, excessive GFM-WTs will lead to grid instability with the increase in grid strength. Therefore, the capacity configuration of GFM-WTs under different grid strengths is a key issue. Consequently, this paper selects typical weak and strong grid scenarios, and investigates the impact of GFM penetration levels on critical system stability under different grid strengths. First, a dynamic mathematical model of grid-connected wind farms is established. Then, the equivalent short-circuit ratio (ESCR) is employed to quantify grid strength. Subsequently, a small-signal stability model of the full system is developed and validated through time-domain simulations. Finally, eigenvalue analysis is applied to determine the critical ESCR (CESCR) thresholds under different GFM-WTs penetration levels. Recommendations on the capacity ratio of GFM-WTs under different grid strengths are obtained.