A Transient Stability Evaluation Method for DC-Link Synchronization Control Grid-forming Converter Considering Time-Varying Inertia and Internal Voltage

Grid-Forming converters considering the DC-link voltage dynamics have been extensively studied. Among the existing control structures, DC-link voltage synchronization control (DVSC), which directly generates the synchronization frequency through the DC-link voltage control, is widely concerned. However, the transient stability of DVSC-based grid-forming converter is rarely studied due to its time-varying inertia and internal voltage. In this digest, the second-order nonlinear large signal model of DVSC-based grid-forming converter is established considering the impacts of virtual admittance. By applying the equal area criterion (EAC), the transient stability boundary is derived from the perspective of energy conservation law, which is an implicit function set over power angle, frequency and internal voltage. An iterative algorithm is proposed to solve this implicit function set and derive the transient stability boundary. Accuracy of the second-order nonlinear large signal model and the derived stability boundary is verified by simulation and experiment.