Optimal Over-Current Protection Coordination in AC Microgrid via Novel Pickup Scaling Coefficient

AC microgrid protection schemes are often compromised by dynamic changes introduced by diverse Distributed Generators (DGs). These dynamic variations, resulting from different DG types and sizes in Grid-Connected Mode (GCM), Islanded Mode (IM), and network topologies emerging from line and DG outages, significantly alter the fault current levels and lead to miscoordination of conventional Directional Over-Current Relays (DOCRs). Hence, this paper introduces an adaptive protection strategy utilizing a novel pickup scaling coefficient, which adjusts relay settings based on local voltage and current measurements. Further, the proposed method is the first AC microgrid protection strategy capable of maintaining consistent relay operating times and Coordination Time Intervals (CTIs) across different topologies, including GCM, IM, line, and DG outages and varying DGs' injections, by determining a single optimal set of DOCR settings. Extensive simulations for various faults, including high resistance faults, in different scenarios of modified IEEE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$13-$</tex-math></inline-formula>bus distribution network with synchronous and inverter-interfaced and comparison with previous works validate the proposed adaptive pickup, ensuring improved sensitivity, selectivity and reliability of the proposed method under diverse operating conditions. Further, Controller-Hardware-Loop (CHIL) simulations using TI-LAUNCHXL-F28379D DSP board and Real-Time Digital Simulator (RTDS) validate the real-time feasibility of the proposed method for varying scenarios.