Impacts of Terminal Voltage Control on Stability of Power Synchronization Control in Grid-forming Converter Connected to Low-impedance Grid

The grid-forming coupling effect between low-impedance grid and grid-forming converter intensifies the interactions among multi-time scale control loops, leading to instability in power synchronization control (PSC). This paper contributes to giving physical insights into PSC stability affected by terminal voltage control (TVC) in grid-forming converter connected to low-impedance grid. Small-signal model and dynamic model for analysis of the impact of TVC on PSC stability are developed. Modal analysis is employed to quantitatively evaluate the influence of TVC on PSC by studying the changes in PSC modal characteristic roots and participation factors under varied grid-connected impedance and control loop bandwidths. Besides, dynamic analysis characterizes PSC stability through damping and synchronizing power, and further introduces self-stabilizing and en-stabilizing components to assess the impacts of TVC on PSC stability. By analyzing the evolution of en-stabilizing component, the dynamic mechanism of TVC affecting PSC stability is revealed. It is indicated that in the case of low grid-connected impedance, low TVC bandwidth, and high PSC bandwidth, the adverse impact of TVC on PSC stability is exacerbated. Finally, the theoretical analysis is validated through simulations and experiments involving the grid-forming converter connected to low-impedance grid.