Microgrid relay protection scheme based on harmonic footprint of short-circuit fault

Due to the low overcurrent capacity of the inverter-based microgrid, traditional overcurrent protect is not suitable for the entire power system including microgrid. A fast detecting method and a whole protection scheme is needed to identify the fault and keep the system stable. This paper proposes a microgrid relay protection scheme combining a fast fault detection algorithm and low voltage ride through(LVRT) strategy. The detection algorithm combines a new harmonic analysis method and impedance delay which can complete fault detection within several milliseconds. Under a fault condition, the LVRT strategy utilizes an enhanced phase-locked loop(EPLL) to allow the microgrid to operate under unbalanced conditions for a period of time. In addition, for the dispatch requirements of power system, it also has communication based power compensation functionality. The scheme given in this paper is verified by simulation, verifying feasibility of its application in practice.