Two-Stage Load Shedding for Secondary Control in Hierarchical Operation of Islanded Microgrids

A two-stage load shedding scheme is presented to cope with potential power deficits caused by microgrid islanding. Coordinated with the fast response of inverter-based grid-forming distributed energy resources, the proposed approach estimates the load shedding at each stage and the resulting power flow redistribution. The first stage of load shedding will cease any rapid frequency decline in which the locally measured frequency deviation is employed to guide the load shedding level and process. Once a new steady state is reached at the end of first stage, the second stage is activated, which performs load shedding according to load priorities. The effectiveness of the proposed scheme is verified through time-domain simulations in PSCAD/EMTDC based on a scaled-down microgrid system.