Seamless Switching Strategy for Grid-Following and Grid-Forming Control of Grid-Connected Energy Storage Systems

To supply indispensable transient inertia and damping support for power systems, particularly weak grid scenarios, grid-forming (GFM) generation exhibits superior performance compared with traditional grid-following (GFL) interfaces. Nevertheless, conventional GFL/GFM mode transition schemes suffer from abrupt switching behaviors or slow dynamic responses, which easily induce relay maloperation and even large-scale system instability. To tackle these drawbacks, this paper presents a seamless operating mode switching strategy for inverter-based power generation units. By coordinately optimizing the output states of phase-locked loop (PLL) and multi-loop current controllers, severe transient voltage and current surges during mode transition are effectively suppressed. A 2 MW grid-connected energy storage system is developed to validate the proposed control algorithm. The results demonstrate the feasibility and effectiveness of the proposed seamless switching strategy under grid-connected energy storage system scenarios.