Transient Synchronization Stability of Grid-Following Converters with Integration of Grid-Forming Converters Under Symmetrical Grid Faults

The essence of transient instability of grid-following (GFL) converters is voltage imbalance, while the transient instability of grid-forming (GFM) converters is due to power imbalance. As a result, different transient instability mechanisms would lead to complicated transient synchronization characteristics of hybrid GFL/GFM converter systems due to the coupling between the converters. Previous studies have analyzed the influence of the GFL-controlled converter on the transient process of the GFM-controlled converter. To further complete the research, this paper uses the phase portrait and the equal area criterion (EAC) to analyze the influence of the GFM-controlled converter on the transient synchronization stability of the GFL-controlled converter under symmetrical grid faults. Simulation results are finally provided to verify the effectiveness of the analysis.