Stability Region Analysis of the GFL-GFM System Based on Impedance Method

With the increasing penetration of power electronic converters, maintaining power system stability has become significantly challenging. Nowadays, extensive stability analyses have focused on the interactions between converters and the grid, as well as between multiple converters, which often overlook the impact of different operating points on stability. This paper investigates the stability of a typical system combining a Grid-Following inverter (GFL) with a Grid-Forming inverter (GFM) under various operating conditions. Firstly, impedance-based methods for stability analysis are developed, and the procedure for determining stability regions is outlined. Then, it compares the stability regions across various GFM capacity configurations and assesses the impact of different system operating points on stability. Finally, the proposed methods are employed to delineate the system's stability region, and the accuracy of the analysis and the stability region is validated using a time-domain model implemented in MATLAB/Simulink.