Mitigation of voltage sags by grid-connected distributed generation system in series and shunt configurations

Voltage sags are considered as the most serious problem of power quality. At the same time, distributed generations from renewable resources are more and more widely used owing to the growing concern on environmental protection. In general, these generation units are connected to the utility grid by a power electronic interface, which has large potential to be utilized to incorporate the function of voltage sag mitigation. In this paper, two configurations of interconnect distributed generator systems to mitigate voltage sags are analyzed. The discrete vector control algorithm which incorporates both inner loop current controller and outer loop voltage controller is derived to control the compensation for both balanced and unbalanced dips. Simulation results show that controller possesses good dynamic and static performances and the load voltage can be compensated to the reference level.