Dynamic Analysis of Grid-Forming Control Strategies under High RoCoF Conditions

Abstract

The increasing penetration of inverter-based resources reduces system inertia, increasing the sensitivity of system frequency to power imbalances and potentially leading to higher rates of change of frequency (RoCoF) during disturbances. Nowadays, grid-forming (GFM) converter control strategies are being required to provide inertial support in low-inertia networks. Very often these strategies imitate the behaviour of a synchronous machine (virtual synchronous machines, or VSMs). This paper compares the dynamic behaviour of three approaches to a VSM using electromagnetic transient simulations of a converter connected to an infinite bus: (a) a virtual synchronous machine with a phase-locked loop (VSM-PLL), (b) an integral–proportional (IP) control, and (c) a virtual synchronous machine with a washout filter (VSM-washout). The inertial active-power response of these strategies is evaluated under severe frequency ramp conditions within the operational capability limits of the generation unit. The results show that IP and VSM-PLL provide effective inertial support without compromising stability, whereas VSM-washout exhibits higher sensitivity to parameter tuning, leading to a less favorable trade-off between inertial power injection and damping.