Design of Zone-Based Hierarchical Protection System for 100% Renewable Microgrids

Design of a reliable and secure protection system for a 100 % renewable microgrid with only inverter-based resources (IBRs) is quite challenging. Most existing protection schemes reflecting the current state of the art are suitable for microgrids with mixed types of distributed energy resources (DERs), including both rotating machine-based DERs as well as IBR-based DERs, where the fault current level is moderately high. Due to the drastic reduction in the fault current level of IBRs, the existing protection schemes face critical challenges in a 100 % renewable microgrid. To address these fundamental challenges, this article proposes a zone-based hierarchical protection scheme that partitions a microgrid into various zones of protection and assigns speed-based hierarchical protection schemes. The performance of the proposed scheme is evaluated using a time-domain simulation study on a microgrid test system. The results corroborate that the proposed hierarchical zone-based protection scheme exhibits good reliability, security, and dependability when tested with various fault cases (fault types, locations, and impedances) and non-fault cases during both grid-tied and islanded mode.