Controller design for dynamic voltage restorer with harmonics compensation function

This paper describes the design of the control loop of a enhanced dynamic voltage restorer (DVR) controller which can handle power quality problems from not only voltage sag/swell but also harmonics. A novel controller, which has a feed-forward loop and two feed-back loops, is proposed. A feed-back loop is used to actively increase the damping component of LC filter system to keep the output voltage overshoot within allowable range, while a feed-forward loop is used to compensate the voltage drop due to the feedback loop. Another feed-back loop based on the digital repetitive control algorithm is implemented to compensate the periodic harmonics of load voltage, which may come from the source, power converter, and nonlinear load. The feasibility of the proposed DVR controller has been verified by the computer simulation results and also by experimental results on 5 kVA DVR system under the various source and load conditions. The both results reveal satisfactory performance not only against sag/swell but also against harmonics.