Transient stability control method for reducing power angle/frequency fluctuations in grid-forming converters during fault ride-through

• A nonlinear perturbation method is used to analyze post-fault power angle trajectories, offering high accuracy under large disturbances and aiding control design. • A simple angular frequency dynamic PI compensation method reduces power angle and frequency fluctuations without real-time tuning. • An in-depth comparison shows the proposed method greatly reduces frequency and power angle fluctuations and works even without a stable equilibrium. Grid-forming converters controlled by virtual synchronous generator control (GFM-VSG) are gradually becoming integral components of modern power systems. During fault ride-through, the power angle and frequency of the GFM-VSG often exhibit significant fluctuations. Excessive power angle fluctuations can cause transient instability in the GFM-VSG, while excessive frequency fluctuations compromise the safe operation of grid-connected systems. To address this issue, this paper first analyzes the transient stability of the GFM-VSG based on the distribution pattern of its power angle equilibrium points during fault ride-through. Subsequently, a transient stability enhancement method based on angular frequency dynamic PI feedback compensation (AFDPI) is introduced into the active power control loop. Compared to conventional methods, this method features a simpler control structure. The introduced compensation coefficients k m and k n require no real-time adjustment, significantly reducing the GFM-VSG’s output frequency and power angle fluctuations during grid faults. Furthermore, this paper mathematically demonstrates that the output power angle of the GFM-VSG converges to a stable equilibrium point (SEP) after implementing the AFDPI control method. Then, based on nonlinear perturbation theory, the dynamic influence mechanism of compensation coefficients on transient power angle trajectories is analyzed. A systematic design criterion for compensation coefficients is derived with the control objectives of minimizing transient power angle and frequency fluctuations. Finally, simulations demonstrate the superiority of this method over others in suppressing frequency and power angle fluctuations, and experiments validate its effectiveness in practical engineering control.