High-Impedance Fault Detection Method for DC Microgrids

High-Impedance Faults (HIFs) in DC systems are challenging to detect as they might not trip the over-current protections, instead being perceived as load increments. These HIFs are produced by low-conductivity elements, such as tree branches, touching the live conductors. Active loads, common in DC systems, have a characteristic negative incremental behavior that can be detrimental to stability but can give insight to differentiate faults from load increments. In this paper, an active fault detection method for HIFs in DC systems is presented. The proposed method is built into the source power converter using a digital Lock-In Amplifier (LIA). It identifies a qualitative difference between faults and load increments, and does so with a minimal signal injection in the system due to the high sensitivity of the LIA. Simulations of the proposed method for challenging scenarios are presented. Validation of the proposed technique is extended by implementing the algorithm using a standard microcontroller.