Load Transformer Inrush Current Mitigation Technique for Series Voltage Sag Compensator

Manufacturing companies are located in industrial park. Based on survey it is observed that 90% of interruption in industrial system is voltage sag related. An inrush current mitigation technique is proposed for sag compensator controller. The voltage sag compensator is based on three phase voltage source inverter and a coupling transformer for serial connection. In various companies voltage sag may affect many manufactures and may reduce the efficiency of the system which results sufficient losses in the power system. It is the most cost effective solution against voltage sags. When voltage sag happen, the transformers, which are often installed in front of critical loads for electrical isolation, are exposed to the disfigured voltages and a DC offset will occur in its flux linkage. A transformer inrush may occur at the start of sag compensator. This over current may damage the inrush protection of the series connected inverter and the transformer output voltage is greatly reduced due the magnetic saturation. When the compensator restores the load voltage, the flux linkage will be driven to the level of magnetic saturation and severe inrush current occurs. The compensator is likely to be interrupted because of its own over current protection. This paper proposes an inrush current mitigation technique together with a state-feedback controller for the Voltage sag compensator.