Impact of Vector Control on Small-signal Synchronization Stability for Virtual SG

The virtual synchronous generator (VSG) are designed to be voltage-source external characteristics that behave with positive damping in weak grids but deteriorate low-frequency oscillation in strong grids. Using the damping torque method for low-frequency oscillation analysis of SG, this paper analyzes the effect of convertor vector control on the small-signal synchronization stability for VSGs. Firstly, comparing the damping torque of the synchro with armature reactance only and the grid-forming converter with current inner loop only, the influence of the inner loops on the small-signal synchronization stability is analyzed. Secondly, considering the voltage outer loop, the damping torque of the converter with complete vector control loops is derived, and the influence of outer loop bandwidth on the small-signal synchronization stability is analyzed. The results show that the current inner loop provides a little negative damping in the low-frequency band and has less influence on the small-signal synchronization stability. The voltage outer loop provides significant positive damping in the low-frequency band, and the damping increases with the increase of bandwidth, so it has a greater influence on the small-signal synchronization stability.