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With more and more distributed energy resources (DERs) being installed, the utility requires these generation systems and their interface converters to remain grid connected during voltage sags to ensure the operating stability of the ac power system. These low-voltage ride-through (LVRT) requirements also suggest that the DER generation system injects real power and reactive power to support grid voltages. In this paper, a positive- and negative-sequence current injection method is proposed to meet the LVRT requirement. The proposed method imposes a predefined ampere constraint in its current injection to reduce the risk of overcurrent during the LVRT operation. Its operation principle and control method are explained and analyzed. Experimental results are presented to validate the effectiveness of the proposed method. Comparisons of the proposed method and other LVRT techniques are also presented.
Date of Publication: July-Aug. 2011