Transient Synchronization Stability Analysis of Parallel-Connected Grid-Forming Converters and Grid-Following Stations

In novel power systems, complex coupling among stations and devices with diverse synchronization mechanisms profoundly impacts system stability. To enhance the transient synchronization stability of hybrid systems integrating grid-forming (GFM) converters and grid-following (GFL) stations, this study investigates the transient interaction mechanisms during current-limiting operation. Considering the current-limiting characteristic, a dynamic model is developed to evaluate the transient synchronization stability of the hybrid GFM and GFL converter system, and the phase plane method is adopted to theoretically analyze the influence of key parameters on transient synchronization stability. The theoretical analysis show that reducing the current saturation angles of both devices, which entails injecting more reactive current into the grid during fault conditions, improves system stability by reducing the acceleration area and increasing the deceleration area through the voltage-power coupling effect between GFM and GFL units; decreasing the GFM converter’s active power command primarily enhances its own transient stability; shortening the GFM converter’s line distance benefits the transient stability of both units. Time-domain simulations are further carried out to verify the correctness of the above theoretical conclusions. The novelty of this study lies in revealing the dynamic coupling mechanism of the GFM-GFL hybrid system under current-limiting operation and clarifying the influence patterns of critical control parameters on transient synchronization stability.