Under-frequency Load Shedding for Power Reserve Management in Islanded Microgrids

TL;DR

This paper develops under-frequency load shedding schemes tailored for islanded microgrids with a single grid-forming resource, enhancing power reserve management and load balancing through innovative device control and delay strategies.

Contribution

It introduces novel UFLS schemes utilizing sectionalizers, smart meters, and controllable appliances, with delay analysis to prevent unnecessary shedding in islanded microgrids.

Findings

UFLS schemes effectively restore power reserves and balance phase power.

Smart meters and controllable loads enable more precise, progressive load shedding.

Simulation confirms improved voltage balance and load management.

Abstract

This paper introduces under-frequency load shedding (UFLS) schemes specially designed to fulfill the power reserve requirements in islanded microgrids (MGs), where only one grid-forming resource is available for frequency regulation. When the power consumption of the MG exceeds a pre-defined threshold, the MG frequency will be lowered to various setpoints, thereby triggering UFLS for different levels of load reduction. Three types of controllable devices are considered for executing UFLS: sectionalizers, smart meters, and controllable appliances. To avoid unnecessary UFLS activation, various time delay settings are analyzed, allowing short-lived power spikes caused by events like motor startups or cold-load pickups to be disregarded. We tested the proposed UFLS schemes on a modified IEEE 123-bus system on the OPAL-RT eMEGASIM platform. Simulation results verify the efficacy of the proposed approaches in restoring power reserves, maintaining phase power balance, and effectively handling short-lived power fluctuations. Furthermore, in comparison to sectionalizer-based UFLS, using smart meters or controllable loads for UFLS allows for a more accurate per-phase load shedding in a progressive manner. As a result, it leads to better balanced three-phase voltage and serves more loads.