DC Bus Differential Protection Based on Fault Component Current in Flexible DC Grid

With the significant increase in DC loads, DC buses play an increasingly important role in enhancing the reliability of flexible DC grids. However, the traditional differential protection for DC buses will lack sensitivity to respond to the faults with high transition resistances. Hence, this paper studies a novel differential protection for DC buses that achieves higher sensitivity by using fault component current. Moreover, a branch equivalence method, which equates multiple branches into two branches based on the branch with the maximum current, is presented to make the criteria of differential protection simpler. And an appropriate restraint method is also selected to further improve the protection sensitivity by obtaining a smaller restraint current during internal faults. Then a protection scheme based on the proposed method is designed. Finally, the proposed method is compared to traditional full current differential protection through a large number of comparative simulations. The simulation results demonstrate that the proposed method can improve the protection sensitivity effectively and avoid refusing trips to a certain extent during high resistances faults.