Oscillation Analysis in Power Grids Dominated by Grid Forming Converters: A Study of VSM and Droop Control Strategies

In power systems with high penetration of Converter-Based Resources (CBRs), Grid Forming Converters (GFMCs) are a promising technology for renewable integration. Particularly, GFMCs can improve grid voltage support, so they are becoming a potential solution to addressing the weak-grid oscillation issues induced by the grid-following converters. However, recent reports have indicated the low-frequency oscillation issues in GFMC-dominated power grids. The causes of the GFMC-driven oscillations are yet unknown. In this paper, we investigate the impact of different GFMC control strategies, i.e., Virtual Synchronous Machine (VSM) control and droop control, on the GFMC-driven oscillations on a testbed of multi-GFMCs by using electromagnetic transient simulations. The results show that for both of these two control strategies, the GFMC-driven oscillations are associated with network parameters, control parameters, and the rated capacity of GFMCs.