Method and system for fault location and protection of inverter-dominated islanded ungrounded microgrids

Abstract

Disclosed a method and system for fault location and protection of Microgrids which are operated under islanded mode by being disconnected from distribution systems under large disturbance or disaster scenarios. The disclosed method is invented to meet the protection needs for disconnected ungrounded microgrids without appropriate protection systems that are usually installed only at distribution substations. Moreover, the disclosed protection method or scheme is targeted at inverter-dominated microgrids in which fault current limiters are installed to protect inverters introduced by the increasing penetration of inverter-based distributed generators (IBDGs). Based on transient analysis and dynamic simulation of islanded ungrounded microgrids during different types of faults, it is realized that of the first terminal and second terminal sensors of the branch different types of faults can be effectively detected based on sequent components of currents flowed through terminals at faulted branches or sections, even with multiple IBGDs deployed in the Microgrids under different control strategies. The phase angle differences of zero sequence currents, and magnitude differences of negative sequence currents, and sign changes of phase currents are used to locate and protect against unsymmetrical and symmetrical faults within the islanded microgrids with lower fault currents, respectively.