Interaction Between Grid-Forming Converters With AC Grids and Damping Improvement Based on Loop Shaping

Grid-forming converters (GFC) are promising technology for improving the grid inertia and frequency stability via voltage source converters (VSC). However, GFCs could make the ac-side oscillations more complicated since it mimics the dynamics of synchronous generators (SG), and the ac-side oscillations could spread to the dc systems. This paper investigates the mechanism of the interactions between GFCs and ac grids, and proposes an enhanced GFC to improve the damping performance on oscillations. By separating the system model into GFC-related transfer functions (TF) and the ac grid-related TFs, the interaction and stability margin can be investigated by the phase difference of these TFs at the cross-gain frequency (CGF). A lead compensator is designed to reshape the phase characteristic of GFC-related TF for enhancing the damping performance of the GFC. The effectiveness of the enhanced GFC is tested according to the simulations on DIgSILENT/PowerFactory.