Virtual Synchronous Generator Stability Enhancement and Power Oscillation Suppression With Adaptive Virtual Impedance Control

Abstract

With the rapid growth of renewable power generation (RPG), grid inertia gradually decreases. Therefore, the virtual synchronous generator (VSG) is proposed to enhance the inertia and damping of the power system. High-penetration RPG, characterized by intermittency, stochasticity, and output volatility, could cause grid impedance variations, thereby leading to short-circuit ratio (SCR) fluctuations that are detrimental to system stability. When the grid reactance is much larger than its resistance, VSG is stable under weak grids while less stable under strong grids, so it is challenging for VSG to meet the stability criteria under a wide range of SCRs. Furthermore, power oscillation may occur during SCR fluctuations. Therefore, this article proposes an adaptive virtual impedance (AVI) control strategy which fully retains the characteristics of the grid-forming (GFM) mode, mitigates power oscillation during SCR fluctuations, and improves the stability of VSG under strong grids. First, a state-space model of the VSG is developed to analyze the control parameters. Then, an open-loop small-signal transfer function of the active power loop (APL) is derived to analyze the proposed strategy. Finally, an appropriate feedback coefficient is determined based on the developed model. Experimental results verify the effectiveness of the proposed strategy.