A Unified Directional Protection Element for Converter-Based Islanded Hybrid Microgrid

This paper proposes a unified directional element (UDE) for protecting converter-dominated islanded hybrid microgrids (IHMGs) relying on phase current samples. For the AC sub-network, the fault diagnosis component (FDC) is constructed by averaging the first-order derivative (FOD) of the phase currents at each line end over one power cycle. On the DC side, the FDC is obtained directly by computing the FOD of the pole current. The current direction of each phase/pole can be identified based on the first peak sign of the FDC. Once a disturbance occurs, the UDE is activated utilizing a startup unit, and the first peak sign of the FDC of each phase/pole is shared between both terminals of the line to differentiate internal faults from other disturbances or external faults. A phase/pole is being faulted if both values of the FDC at both sides of the line have the same sign. The developed UDE is verified by simulating the modified IEEE 33-bus IHMG on PSCAD/EMTDC. Several scenarios are carried out including load switching as well as external and internal faults. Additionally, the effect of different factors is examined, encompassing measurement inaccuracies and high resistance faults.