Energy control of dynamic voltage restorer for voltage sag mitigation

Voltage sag is one of the very severe power quality (PQ) problems encountered by the customers and utilities. Dynamic voltage restorer (DVR) is one of the devices that compensate PQ problems of the loads against sags. The energy storage in the DVR is limited and cannot inject large amount of active power to the system during the sag. The objective of this paper is to control the exact amount of active power from the DVR and to avoid the increase in the injected voltage amplitude so that the voltage magnitude of the load is kept at 1p.u. It can be achieved by controlling the angle between the injected voltage and the load voltage. In this paper a new controller is proposed to control the energy source of the DVR. The proportional integration (PI) and phase locked loop (PLL) controller are used to track the signal and regulate the load voltage. The Photovoltaic (PV) source is also incorporated to charge the energy source and maintain dc voltage at the nominal value. The results show that the proposed controller can control the exact power injection during the sag. The dc magnitude is obtained by connecting the external source directly to the DVR with the energy source capacitor (ESC).