Optimal Linear Protection Scheme of Inverter‐Based Distributed Energy Resources: Meeting Fault‐Ride‐Through Requirement

This paper presents a new two‐stage protection strategy for active distribution networks that not only addresses selectivity constraints along protected lines but also incorporates fault‐ride‐through (FRT) requirements of inverter‐based distributed energy resources (IBDERs). The proposed coordination strategy (PCS), which distinguishes it from previous work, employs piecewise linear curves for directional overcurrent relays (DOCRs) that are optimally defined through a linear optimization model where plug settings are also optimally assigned. In the first stage, the slopes and endpoints of the piecewise linear segments, along with consideration of the problem constraints, are included in the optimization process where relay operation times are minimized. In this process, to ensure selectivity for all faults along the protected lines, a simple but effective technique is employed in which the starting point of the backup relay’s operating segment is positioned above the endpoint of the main relay’s segment, taking into account the coordination time interval (CTI). At this stage, it is also imperative to establish the constraints that delineate the inverse fashion of the final curve. In the second stage of PCS, a mathematical expression is derived that deploys the optimized piecewise linear segments to prepare a continuous final curve for numerical implementation on relays. Results are discussed in depth.