Extending protection selectivity in low voltage DC microgrids using compensation gain and artificial line inductance

Abstract

Vulnerability of power electronic converters in DC microgrids in case of fault occurrence in DC cables necessitates using a fast fault detection and isolation scheme. In this paper, a modified, fast and selective protection scheme has been presented, which provides the required tripping of low voltage DC (LVDC) microgrids. This protection scheme has been developed based on the natural characteristics of the fault current, in which the first and second derivatives of the fault current have been employed to define thresholds for discriminating between faulted and non-faulted situations. To enhance fault detection capability of the protection scheme, definition of thresholds have been improved by introducing compensation gains, which makes the thresholds adaptive to amplitude of line current. Furthermore, in order to extend time validity of the thresholds which are calculated by approximated equations, artificial line inductance (ALI) technique has been proposed. Since no communication link is involved and all measurements are local, any types of fault can be detected without time delay. As a result, fault detection is achieved within 250 μs. To show the superiority of the proposed protection scheme, different case studies are investigated and results are compared with the earlier study.