An Improved RFR Method for Enhancing Large-Signal Stability of Grid-Following Inverter Under Weak and Faulty Grid Conditions

The classical phase-locked loop based vector current control scheme has been widely used in grid-following (GFL) inverter systems. However, GFL inverters with this classical control scheme suffer from synchronization instability issues under weak and faulty grid conditions, which has become a major stability challenge for GFL inverters. To address this challenge, a reference frame rematching (RFR) method has been proposed recently, which enables the GFL inverter to ride through severe low-voltage faults (e.g., zero-voltage ride-through) stably under nominal grid frequency conditions. However, when the grid frequency varies, the existing RFR method becomes less effective. To solve this problem, this letter proposes an improved RFR method, which can stabilize the GFL inverter in either grid voltage sag or grid frequency drop case. So, the large-signal stability and robustness of the GFL inverter can be improved. Simulations and experimental results verify the effectiveness of the proposed method.