Current-Constrained Power-Angle Characterization Method for Transient Stability Analysis of Grid-Forming Voltage Source Converters

The necessity of limiting the output current of grid-forming (GFM) voltage source converter (VSC) has led to drastic deformation of its power angle characteristic (PAC), posing a great challenge to the transient synchronization stability (TSS) analysis. This current limitation associated TSS issue has been extensively studied in the context of the conventional dual loop controlled GFM VSC, while the analysis for the lately prevailing virtual admittance control (VAC) is less explored. To this end, this paper proposes the current-constrained (CC)-PAC method for TSS analysis of VAC-based GFM VSC. Based on the proposed CC-PAC, first, the TSS mechanism exclusive to VAC-based GFM VSC is revealed, and the impact of resistive and inductive virtual impedance is discussed. Then, the Lyapunov's direct method-based TSS assessment is rigorously achieved and performed by using the obtained CC-PAC, including the region of attraction (ROA) estimation and the critical clearing time (CCT) analysis. Finally, effectiveness of the CC-PAC along with its TSS analysis is thoroughly verified by PSCAD/EMTDC simulations.