Optimal directional overcurrent relay settings for stable microgrids with synchronous and inverter-based resources

Microgrid (MG) is a small-scale system that offers on-site energy production and storage capabilities, allowing for the seamless integration of different technology-driven distributed energy resources (DERs), including inverter-based and synchronous-based DERs. Nonetheless, due to the changes caused by DERs in fault currents, providing protection for MGs is more challenging than traditional systems. The article examines the deployment of directional overcurrent relays (DOCRs) in MGs, considering the stability of DERs. Given the impact of inverter-based DERs’ integration and the limited inertia of synchronous-based DERs, extending the operating times of DOCRs may compromise MG stability after fault clearance. Therefore, a novel dual inverse settings for DOCRs to ensure relay coordination and MGs stability is proposed. Critical clearing times for DERs, accounting for inverter-based DER participation, are determined and integrated with coordination constraints to obtain DOCR settings using genetic algorithm. The proposed scheme is evaluated on an IEEE 33-bus test system with synchronous and inverter-based DERs.