Transient synchronization stability enhancement for virtual synchronous generators in renewable energy grid integration under voltage sags

Abstract

With increasing renewable penetration, virtual synchronous generators (VSGs) have become an important solution for stabilizing converter-interfaced renewable generation because of their inertia support and grid-forming capability. However, under weak-grid voltage sag conditions, the transient synchronizing stability of VSGs deteriorates significantly. In particular, virtual resistance, although effective in improving small-signal damping and suppressing synchronous resonance, may further weaken the synchronism-preserving capability under large disturbances. To address this issue, this paper investigates the effect of virtual resistance on transient synchronizing performance and proposes an additional transient damping control method. A power transfer model and a transient dynamic model are established for the VSG with virtual resistance. The results show that virtual resistance reduces the active-power transfer capability and narrows the power-angle margin, thereby weakening transient synchronizing stability. An additional damping branch is then introduced into the active power control channel, and a third-order nonlinear model is developed to analyze the stability enhancement mechanism and parameter effects. Simulation and hardware-in-the-loop results demonstrate that, with proper parameter settings, the proposed method can effectively suppress the initial post-fault acceleration process, reduce power-angle oscillations and frequency deviations, and enhance the synchronism-preserving capability during voltage sags.