Mitigation of inrush current in dynamic voltage restorer injection transformers

The dynamic voltage restorer (DVR) is among the most cost-effective solution against voltage sags. By using the transformer coupled topology, DVR could take the advantage of electrical isolation and voltage boost. However, at the start of compensation, the injection transformer may experience a flux linkage that is up to twice its steady-state value. The flux linkage will be driven to the level of magnetic saturation and severe inrush current occurs. Oversizing the transformer is a common approach to avoid the inrush current, but this would dramatically increase the cost, size and weight. This paper proposes a new technique for mitigating the inrush current. By taking use of the relationship between injection voltage and flux linkage, this method is characterized by interrupt compensation around the peak or trough of injection voltage to make the interruption time shortest. Detailed explanations of this technique are presented, and the effectiveness of this scheme is verified by laboratory test results.