Selectivity and security of DC microgrid under line-to-ground fault

Over the recent years, low-voltage dc (LVDC) distribution systems have become increasingly interesting. One of the main problems in their diffusion is the realization of reliable protection systems ensuring selectivity and security to the loads. Several solutions to this problem are studied in the current literature and are mainly focused on the design and integration of new protection devices. Nevertheless, for some faults, it is possible to use traditional protection devices if proper control strategies are used on the power converters. In this paper, the ground fault of one of the dc poles is considered for grids operated with the neutral ground connected on the ac side and isolated on the dc side. In these conditions, if, as usual, a voltage source converter (VSC) is used as an interface between ac and dc grids, the IGBTs of the VSC are capable neither of limiting nor of blocking the fault current. In this paper, the integration of a proper control strategy implemented on the VSC with the protection devices is proposed to allow the system to interrupt, clearing the fault, saving the power converter. The proposed strategy ensures selectivity and security to the loads because it implies the interruption only of the faulty feeder of the dc microgrid. In this paper, the proposed strategy is tested by means of numerical simulations and experimental results, thus proving its good performances.