Active Damping of Low-Frequency Oscillations in VSG-Based Grid-Forming E-STATCOMs

Abstract

The rapid proliferation of inverter-based resources (IBRs) in modern power systems has intensified the need for enhanced reactive power support and voltage regulation, making the static synchronous compensator (STATCOM) an essential grid-supporting asset. Particularly, energy-storage-assisted grid-forming (GFM) STATCOMs, termed E-STATCOMs, based on virtual synchronous generator (VSG) control have emerged as a preferred solution for weak and low-inertia grids. Nevertheless, VSG-based E-STATCOMs are inherently susceptible to low-frequency oscillations, which become particularly pronounced under weak-grid conditions where the reduced short-circuit ratio (SCR) limits the system stability margin. Although increasing the VSG damping coefficient can partially mitigate oscillations, it is intrinsically coupled with the primary frequency-regulation loop, resulting in a contradiction between transient stability and steady-state accuracy. To address this trade-off, this paper proposes an active damping regulator (ADR) embedded in parallel with the VSG swing equation. The ADR provides targeted, frequencyselective damping of the dominant low-frequency mode using a single tunable gain, without compromising steady-state behavior or modifying the inner control structure. A detailed MATLAB/Simulink model of the 10 kVA E-STATCOM is developed, and simulation results under a 50% voltage sag confirm significant suppression of power and voltage oscillations compared with the conventional VSG. Sensitivity studies with respect to the ADR gain and robustness evaluation across varying grid-strength conditions further validate the practical applicability of the proposed method.