I. Introduction
With a successive growth of power generation using renewable energy sources, i.e., photovoltaics (PVs) and wind turbines, the penetration rate of IIDGs in the power system is increasing at a rapid pace. Unlike conventional centralized generation using SGs, inverters do not have a rotating mass to provide inertia support for the grid. Therefore, since SGs are gradually replaced by inverters, operators of the power grid are faced with the issue of lack of inertia, which intrinsically leads to a large ROCOF in the grid. As a result, the power system is prone to frequency fluctuation, and the design of ROCOF-based relays should be reconfigured [1].