A novel dynamic series compensator with closed-loop voltage and current mode control for voltage sag mitigation

The increased use of voltage-sensitive equipment in the industrial sector has made industrial processes more susceptible to supply voltage quality problems in the form of voltage sags. Series-connected voltage source converter (VSC)-based devices have been gaining popularity in protecting sensitive loads against voltage sags. This paper presents a novel transformerless dynamic series compensator (DSC) to mitigate long-duration voltage sags effectively. A line-side controllable rectifier connected to the proposed DSC maintains the dc-link voltage at a specific value while the DSC compensates voltage sags. The DSC is controlled by a closed-loop voltage and current mode controller which provides better damping and dynamic performance than that of in open-loop controller. The closed-loop controller consists of an outer voltage loop and an inner current loop derived from filter capacitor current. Performance of the proposed DSC is tested under varied voltage sag conditions, and simulated and experimental results are presented to show the effectiveness of the proposed DSC in mitigating long-duration voltage sags.