A control method of 3-phase transformer-less dynamic voltage restorer

This paper represents a control method of 3-phase Transformer-less Dynamic Voltage Restorer (DVR). The merit of transformer-less inverter is well recognized. But such a DVR consists of three single-phase inverters with mutually insulated DC power supplies. When the DVR is applied to asymmetrical voltage sag or unbalanced load, the output power from each inverter is not usually equal. Therefore the total energy of the DC power supply cannot be used equally, and the DVR has disadvantage of the DC energy storage size. To this problem, the method proposed here provides the technique for controlling the power from each inverter and DC power supply by controlling zero sequence of the DVR output voltage, and realizes the effective use of DC energy. © 2008 The Institute of Electrical Engineers of Japan.