Phase Advanced Dynamic Voltage Restorer Control System Design

The increment of voltage-sensitive load equipment has made industrial processes much more susceptible to degradation in the quality of power supply. Voltage deviations, often in the form of voltage sags, can cause severe process disruptions and result in substantial economic loss. Among the several novel custom power devices, the dynamic voltage restorer (DVR) for application in distribution systems is a recent invention.The compensation capability of a DVR depends primarily on the maximum voltage injection ability and the amount of stored energy available within the restorer. In this paper a new phase advance compensation (PAC) strategy for the DVR is proposed in order to enhance the voltage restoration property of the device. Also a method of determining the exact amount of voltage injection required to systematically correct a specific voltage drop is proposed with minimum active power injection. Using the proposed method it can be shown that a particular disturbance can be corrected with less amount of storage energy compared to that of existing in-phase boosting method. Analytical expressions for both the magnitude and angle of the injected voltage are also derived. A closed-loop controller that consists of an inner current loop and an outer voltage loop is also incorporated into the DVR system. Theoretical analysis shows that the capacitor current feedback scheme is superior over the inductor current feedback scheme in terms of steady state error and disturbance rejection.