Abstract
When voltage sag occur, the sensitive equipment with unexpected shut-downs often result in substantial economic losses, so series compensator are usually used to restore voltage during sag for improving power quality and riding through voltage sag. However, voltage restorer cannot protect sensitive loads when short circuit fault occurs at load side. A fault current mitigation strategy based on the structure of series compensator has been proposed. When the compensator is activated, it acts like a virtual inductor in the system. Not only the fault current can be mitigated effectively, but also the voltage sag problem will not occur at other feeders. In this thesis, a fault current mitigation technique is proposed based on the concept of virtual inductor, whereas both positive and negative sequence inductor are used to mitigate fault current. When grounding fault is detected, positive and negative fault current can be mitigated by virtual inductors which is put in the system by series compensator. The selection on the value of positive and negative sequence inductors are based on the rating of converter. Additionally, the value of optimal virtual inductor are designed respectively under one phase and two phase fault. And using the value of inductor to effectively limit fault current with finite rating of converter. In this thesis, first of all the principles of operation of the proposed that fault current mitigation technique is presented in detail, and the influence of virtual inductor on fault current is derived. Finally, the proposed fault current mitigation algorithm has been tested in simulation and is validated by experiments in laboratory.