Control Strategy for Dynamic Voltage Restorer Under Distorted and Unbalanced Voltage Conditions

Under the condition where power grid voltage is unbalanced and distorted, dynamic voltage restorer (DVR) is used to compensate the negative sequence voltage and harmonic voltage. In this paper, a novel double closed-loop control strategy is presented. The outer voltage loop of the controller is based on proportional multi-resonant (PMR) controller, while the inner current loop is based on proportional controller. Parameter tuning of inner current loop is investigated and the optimal gain is obtained through root locus curve. This method can maximize the stability of current loop and effectively suppress LC resonance at the same time. Simulation and experimental tests show that the proposed control strategy significantly improves the output voltage quality of DVR.