Low-Frequency Oscillation Suppression Strategy Based on NPOD-SVC-VSG Grid-Connected System

Abstract

The power control loop in a virtual synchronous generator (VSG) exhibits inherently insufficient damping, making it prone to low-frequency oscillation (LFO) under disturbances. Moreover, the dynamic coupling between active and reactive power can induce unnecessary reactive power fluctuations during active power transfer. This not only affects voltage stability but may also further exacerbate LFO. Leveraging the static VAR compensator (SVC)'s capability for fast reactive power support and supplementary damping, this study proposes an LFO suppression strategy based on the NPOD-SVC-VSG grid-connected system. First, this study develops a small-signal model and state-space representation of the SVC-VSG grid-connected system. Eigenvalue analysis is then employed to investigate the stability influence mechanisms in the SVC-VSG grid-connected system under weak interactions. Furthermore, a Phillips–Heffron model of the SVC-VSG system is developed for the mechanism analysis of LFO. To enhance system damping, nonlinear power oscillation damping (NPOD) is proposed that adaptively adjusts gain based on oscillation amplitude while considering the impact of communication delay between the SVC and VSG. NPOD is incorporated into the voltage control loop of the SVC, and its parameters are designed using the phase compensation method that accounts for communication delay. Finally, MATLAB/Simulink simulations demonstrate that the proposed NPOD-SVC-VSG strategy effectively suppresses LFO, increasing the system damping ratio by 10.93% compared to the VSG strategy. The strategy also rapidly compensates for reactive power deficits during transients, thereby enhancing system voltage stability.