A novel flexible fault eliminator with active disturbance rejection and soft grid-connection in distribution networks

Abstract

Among the possible fault types in the distribution networks, single-line-to-ground (SLG) fault has the highest probability. The SLG fault current and arc can easily cause personal injury and death. This study proposed a flexible fault eliminator (FFE) based on a cascaded H-bridge topology to limit the SLG fault current and extinguish fault arc in the medium voltage distribution networks. An active disturbance rejection controller for the FFE was designed to improve the current limiting performance of FFE in the presence of insulation parameter measurement errors and sampling errors from potential/current transformers. The controller with good robustness adapts to different ground fault resistances. In addition, a soft grid-connection control scheme based on bistable smooth switching was proposed to avoid the injected current impulse of FFE at the moment of grid connection. Simulation and experimental results showed that the fault current was limited to a small enough value and the fault arc was extinguished effectively. The output current and voltage of FFE at the time of grid connection were in a smooth transition, avoiding the impulse on the power grid system. The FFE can eliminate the SLG fault flexibly and stably.