Abstract: With the rapid increase in the penetration of renewable energy generation, the structure of the power system gradually shifts from being dominated by synchronous generators to a hybrid system composed of both grid-connected and standalone renewable energy sources. Due to the complex dynamic interactions between different generation units, which exhibit strong nonlinear coupling characteristics, the new challenges arise for the synchronization stability of the system. To address these issues, a mathematical model for the transient stability analysis of generation units, considering different synchronization control methods, is established to reveal the underlying instability mechanisms. The phase-plane method is then used to analyze the impact of the power command of the grid-connected renewable energy, virtual synchronous control parameters, and the phase-locked loop control parameters of the standalone renewable energy on the system's synchronization stability. Based on these analyses, design principles for controller parameters suitable for the stable operation of hybrid systems are proposed. finally, simulation results under fault scenarios are used to validate the effectiveness of the proposed model and the correctness of the parameter design method, providing a theoretical basis for the stable operation and controller parameter tuning of high-penetration renewable energy power systems.

Key words: grid-following, grid-forming, hybrid system, synchronization stability, synchronization control