Transient Synchronization Stability of an Islanded AC Microgrid Considering Interactions Between Grid-Forming and Grid-Following Converters

Microgrid has been rapidly developed for the integration of distributed renewable energy, owing to their superiority of flexible operation and high reliability. Without frequency support from the main grid, the microgrid under islanded operating mode is more likely to lose stability in the presence of large-signal disturbances. However, previous studies mainly focus on weak grid conditions and ignore the interaction effects between different-type converters. Therefore, this article investigates the transient synchronization stability of an islanded ac microgrid considering dynamic interactions between grid-forming converter (GFMC) and grid-following converter (GFLC). First, a simplified nonlinear model of the islanded microgrid is established, which reveals the nonlinear interaction and damping impact on system stability. Based on the passivity principle and LaSalle ’ s theorem, an explicit stability criterion is formulated to reveal the instability mechanism. With the proposed stability criterion, the impacts of different system parameters are analyzed, which points out the direction of parameter optimization to enhance stability. To validate the effectiveness of the proposed method, simulations and experiments are carried out.