Transient stability analysis of grid-forming converters based on trajectory analysis method

With the increasing integration of high-proportion new energy into the power grid, the transient stability assessment of power systems is confronted with significant challenges. This paper proposes a transient stability assessment method for grid-forming (GFM) converters based on the trajectory analysis method. Focusing on GFM converters controlled by virtual synchronous generator (VSG) control, this method obtains the angular speed and accelerating power trajectories of the post-fault system through time-domain simulation. Based on the single-machine energy function theory, the changes in kinetic and potential energy are analyzed, and a stability index Si is constructed to quantitatively characterize the transient stability margin. To validate the effectiveness of the proposed method, a grid-connected system simulation model incorporating both grid-forming and grid-following (GFL) converters is established on the MATLAB/Simulink platform. Fault scenarios of varying severity, including single-phase, double-phase, and three-phase short circuits, are configured for testing. The results indicate that the stability index Si decreases monotonically with the increase in fault severity and can effectively reflect the system's stable state. The research confirms that the trajectory analysis method is applicable to the transient stability assessment of GFM converters, providing a new approach for the stability analysis of power systems with a high proportion of new energy.