Modeling and Transient Stability Analysis of Hybrid Power System with Synchronous Generator and Grid-Following/Grid-Forming Generation Units

With the increasing penetration of power electronic converter-based renewable energy plants (e.g., photovoltaic and wind power) and energy storage systems in power grid, gridforming converters are progressively being integrated into renewable energy plants to enhance grid stability, as conventional grid-following converters exhibit insufficient stability in weak grid conditions which exceed the support capacity of local synchronous generators. To investigate the transient stability characteristics of hybrid systems containing grid-forming energy storage, synchronous generators, and grid-following renewable sources in parallel operation, this paper establishes a mathematical model of the hybrid system under purely inductive network conditions. The power coupling characteristics among different power sources are analyzed. Employing machine-like power angle curves for renewable energy converters and phase-plane analysis methodology, this study reveals the nonlinear influence patterns of grid-forming energy storage power output and reactive current injection from grid-following renewable energy stations on the hybrid system's transient stability. The theoretical findings are validated through a Simulink simulation model. The results provide significant references for optimizing grid-forming energy storage configurations and renovating renewable energy stations in power systems with high renewable penetration.