Leakage Current Suppression Strategy of Non-isolated Low-voltage Flexible Interconnection Devices Based on Three-phase Four-leg Converter

Abstract With the increasing penetration of distributed renewable energy, non-isolated flexible interconnection devices (FID) are widely applied in low-voltage distribution networks. However, the absence of isolation transformers easily causes severe leakage current issues. Existing solutions for leakage current suppression often depend on additional hardware, leading to higher cost and complexity. To overcome these limitations, this paper proposes an improved FID topology combined with a hybrid control strategy, which integrates a notch filter in the current control loop with a closed-loop control in the leakage current loop. With the method, both high-and low-frequency leakage currents can be suppressed simultaneously without additional hardware. Experimental results demonstrate that under grid voltage imbalance and phase difference conditions, the leakage current is reduced from 50 A to 1 A, while the three-phase currents remain sinusoidal and balanced. This work provides an effective and low-cost approach for enhancing power quality of the non-isolated FID, which is of great significance for promoting the secure integration of renewable energy.