Adaptive Seamless Switching Strategy Considering Current Limiting for Renewable Energy Converters Based on PCC Condition Awareness

Abstract

With the high penetration of renewable energy into power grids, grid-connected converters face severe challenges in adapting to wide-range variations of grid strength and suppressing fault overcurrents. A single grid-following (GFL) or grid-forming (GFM) control mode cannot ensure system stability across weak, moderately weak, and strong grid conditions, while the lack of current limiting measures may lead to damage to power electronic devices. To address these issues, an adaptive seamless switching strategy (ASSS) considering current limiting is proposed in this paper. The ASSS integrates three core modules: harmonic injection-based impedance identification for short-circuit ratio (SCR) calculation, a state variable reset method for seamless mode switching, and a hysteresis switching criterion to avoid frequent mode transitions. Besides ASSS, an adaptive virtual impedance is employed for fault current suppression. Based on MATLAB/Simulink, simulation verifications are conducted under typical working conditions including grid voltage sags and large-scale SCR variations. The results show that the proposed strategy can limit the maximum fault current efficiently, realize seamless switching between GFL and GFM modes with waveform distortion rate less than 5%, and ensure stable system operation across the entire range of grid strength variations. This strategy effectively improves the fault ride-through capability, grid adaptability, and switching dynamic stability of grid-connected converters, providing a reliable control solution for high-penetration renewable energy integration.