Stability Analysis of Grid-Following and Grid-Forming Converters Connected to Generators

Abstract

This work presents an examination of the main interactions between grid-following (GFL) and grid-forming (GFM) voltage source converters (VSCs) and synchronous generators (SGs), capturing the dynamics of a real power grid and pointing out the limitations of considering an ideal one for stability studies. Eigenvalue trajectories and participation factors are studied to perform in-depth small-signal analyses. Specifically, the GFL and GFM converters are compared in different grid strength scenarios by varying their rating powers and the grid short circuit ratio. Then, time-domain simulations of the non-linear and the developed linear systems are run to validate the mathematical findings from the stability analysis. The results reveal that the stability of VSCs-dominated grids, either in GFL or GFM mode, is strongly affected by both the grid strength and the VSC power, due to the coupling between the VSC control and the SGs.