Direct Mitigation of Common Mode Current in Transformerless Flexible Interconnection Devices

The use of flexible interconnection device (FID) in low-voltage distribution networks results in significant common-mode current (CMC). To overcome these drawbacks, a CMC direct mitigation strategy based on specific average common mode voltage space vector modulation (specific average-CMV SVM) for low-voltage distribution networks in transformerless FID is proposed. First, a common-mode equivalent circuit is established to derive the relationship between the CMC and CMV. Second, a closed-loop CMC mitigation method is proposed. Third, based on the average-CMV during switching cycles, an improved SVM strategy with direct regulation of the average-CMV is proposed by adjusting the duration of zero vector. Furthermore, to overcome the limitations of the average-CMV regulation capability of single converter, a coordinated control method of the average-CMV for both the rectifier and inverter is proposed, which expands the CMC mitigation capability for the FID system. Finally, simulations and experimental results demonstrate the effectiveness of the proposed method.