Transient Stability Analysis for Paralleled System of Virtual Synchronous Generators Based on Damping Energy Visualization and Approximation

With the increasing penetration of virtual synchronous generator (VSG)-controlled inverters in the renewable power system, the transient stability analysis of the paralleled VSG system with the interactions between inverters is urgently needed. However, the large damping effect brought by VSGs on the relative motion between inverters is still unclear, which impedes the accurate transient stability evaluation of the paralleled system. In this article, the damping effect in the paralleled VSG system is explored with the recognition of the uniform and the nonuniform damping effects, and it is found that the large damping in VSGs may also destabilize the system under some nonuniform damping configurations. To figure out the influential mechanism of the damping terms in the paralleled VSGs, two customized phase portraits are presented to visualize the uniform and the nonuniform damping energies with the respective areas. On top of that, a damping energy approximation method is further proposed to quantitatively depict damping energy, and thus, the critical clearing time can be analytically solved. The effectiveness of the proposed method is validated by both simulation results and control hardware-in-loop experimental results. The results demonstrate that the proposed method can clearly characterize the large damping effects and accurately solve the critical fault clearing point, which may provide some new insights for the transient stability analysis of the paralleled VSG system.