Adaptive Droop-Based Differential Current Protection Scheme for Inverter-Based Islanded Microgrids

The fault current limitation embedded in the current controller of inverter-based distributed generators (IBDGs) in islanded microgrids poses a significant challenge for microgrid protection. This paper presents a novel adaptive droop-based protection scheme for islanded microgrids supplied by IBDGs. During fault conditions, one or more IBDGs can adaptively adjust their droop settings by modifying the no-load frequency limit (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NL</inf>), resulting in different frequencies across the distributed generators. To achieve this adjustment, the droop-based controller of the selected IBDGs is enhanced with a unique positive sequence voltage versus no-load frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(V_{I \ BDG}^{+}-f_{NL})$</tex> droop. These modifications result in different frequency current components at both terminals of the faulted line that aid in fault detection. The effectiveness of the proposed scheme is evaluated using a modified IEEE 33-bus islanded microgrid modeled in PSCAD/EMTDC, demonstrating its ability to detect and isolate faults in the inverter-based islanded microgrid. The simulation results show that the proposed adaptive droop-based protection scheme can accurately distinguish between normal and faulty conditions.