A Flexible Dual-Mode Switching Strategy for Grid-Connected Energy Storage Considering Fault Ride Through Capability and Support for AC Microgrid Stability

The substantial integration of renewable energy sources, specifically photovoltaic (PV) power into the power grid, has gradually weakened its strength. A novel switching control for a PV storage system with a GFL/GFM control structure was proposed in response to this challenge. By leveraging integrators and the state follower method, a smooth switching control strategy between these two control modes was facilitated, ensuring stable operation across varying grid strengths. Through employing the Kuramoto model and basin stability method, the parameter stability domain of the microgrid under GFM control was delineated, and the switching boundary was established based on the short-circuit ratio. Additionally, recognizing the requirements of stable operation for PV storage systems under grid faults, a fault ride through control method with a negative sequence current suppression strategy was proposed. This method effectively suppressed negative sequence current under GFM control. Subsequently, simulation-based validation confirmed the effectiveness of the proposed control strategies. It ensured the smooth operation of the PV storage system under a gamut of conditions, including symmetric and asymmetric faults, as well as islanding scenarios. The proposed control strategies ensure that the DC bus remains stable and that the current distortion rate does not exceed 5% during faults.