Microgrids (MGs) are revolutionizing modern power systems by enabling decentralized energy production, renewable energy integration, and enhanced grid resilience. However, the increasing complexity of MGs, particularly with the integration of Distributed Energy Resources (DERs), poses significant challenges for traditional protection schemes. This study addresses the coordination of Directional Overcurrent Relays (DOCRs) in MGs through a Mixed-Integer Linear Programming (MILP) model. The main contribution is a MILP model that optimizes relay settings, including Time Multiplier Settings (TMS) and standard characteristic curves, to minimize tripping times, while ensuring selectivity. Another key contribution of this work is the integration of both IEC and IEEE standard curves, which enhances coordination performance compared to using a single standard. The model was tested on the IEC benchmark microgrid, and the results demonstrated significant improvements in fault-clearing times across various operational modes. By leveraging advanced optimization techniques and diverse characteristic curves, this study contributes to the development of resilient and efficient protection systems for modern microgrids, ensuring reliable operation under varying fault conditions and DER penetration.

Protecting AC microgrids (MGs) is a challenging task due to their dual operating modes—grid-connected and islanded—which cause sudden variations in fault currents. Traditional protection methods may no longer ensure network security. This paper presents a novel approach to protection coordination in AC MGs using non-standard features of directional over-current relays (DOCRs). Three key optimization variables are considered: Time Multiplier Setting (TMS), the plug setting multiplier’s (PSM) maximum limit, and the standard characteristic curve (SCC). The proposed model is formulated as a mixed-integer nonlinear programming problem and solved using four metaheuristic techniques: the genetic algorithm (GA), Imperialist Competitive Algorithm (ICA), Harmonic Search (HS), and Firefly Algorithm (FA). Tests on a benchmark IEC MG with distributed generation and various operating modes demonstrate that this approach reduces coordination times compared to existing methods. This paper’s main contributions are threefold: (1) introducing a methodology for assessing the optimal performance of different standard curves in MG protection; (2) utilizing non-standard characteristics for optimal coordination of DOCRs; and (3) enabling the selection of curves from both North American and European standards. This approach improves trip time performance across multiple operating modes and topologies, enhancing the reliability and efficiency of MG protection systems.

Guaranteeing the effective coordination of directional overcurrent relays (DOCRs) within microgrids (MGs) is a complex nonlinear problem due to bidirectional power flows, varying fault current levels, and the need for adaptive operation across multiple grid configurations. To address this challenge, this paper proposes a hybrid matheuristic approach combining a Biased Random-Key Genetic Algorithm (BRKGA) with Mixed-Integer Linear Programming (MILP). This formulation treats the selection of relay characteristic curves as a decision variable, allowing for simultaneous optimization of time multiplier settings (TMS), plug setting multipliers (PSM), and curve types. The BRKGA handles the global search, while the embedded MILP decoder performs exact optimization under fixed conditions. The proposed BRKGA–MILP method was tested on the IEC benchmark microgrid under multiple operating modes. Compared with conventional MILP-based coordination, it achieved up to 18.31% reduction in total relay operating times (11.81% on average) while maintaining proper coordination time intervals (CTI). Relative to previous heuristic and hybrid approaches, the method improved protection speed by up to 14.87%. These results indicate that the proposed framework effectively enhances coordination performance in adaptive microgrid protection, particularly under bidirectional power flows and varying fault current levels.

This paper presents the implementation of an AC three-phase programmable electronic load (PEL) that emulates load profiles and can be used for testing equipment in microgrids (MGs). The implemented PEL topology is built with a voltage source inverter (VSI) which works as a current controlled source and a Buck converter which permits the dissipation of active power excess. The PEL operation modes according to the interchange of active and reactive power and its operation in four quadrants were determined. The power and current limits which establish the control limitations were also obtained. Three control loops were implemented to independently regulate active and reactive power and ensure energy balance in the system. The main contribution of this paper is the presentation a detailed analysis regarding hardware limitations and the operation of the VSI and Buck converter working together. The PEL was implemented for a power of 1.8 kVA. Several experimental results were carried out with inductive, capacitive, and resistive scenarios to validate the proper operation of the PEL. Experimental tests showed the correct behavior of the AC three-phase currents, VSI input voltage, and Buck converter output voltage of the PEL for profile changes, including transient response.

This paper proposes a Python tool for the analysis of balanced, unbalanced, sinusoidal and nonsinusoidal three-phase systems based on the IEEE Std. 1459. The proposed tool was developed to be used by electrical engineers and professionals of related careers providing a free access for electrical power calculations that allows validation and power analysis in power systems. The proposed tool is available for use on a GitHub link and only requires voltage and current signals as inputs, making it possible to dispense expensive commercial network analyzers. The tool is made of two interfaces, one for making power calculations of sinusoidal three-phase systems and the other one for making calculations of nonsinusoidal three-phase systems; both interfaces can be accessed through a main menu. The proposed tool facilitates decision-making in electrical system issues, which helps improving the efficiency and power quality of electrical systems.

Este estudio presenta el diseño de una estrategia de control para cargas electrónicas programables (PEL, en inglés) en corriente alterna (AC, en inglés), aplicado a escenarios de pruebas en microrredes de energía. La estrategia de control se basa en control de corriente por histéresis (HCC, en inglés) para la operación de un inversor trifásico con el objetivo de emular perfiles de carga. El diseño de la PEL es dividido en etapas de control y potencia para identificar los principios operativos. La topología empleada es una PEL trifásica en AC con conexión en estrella de cuatro conductores y conexión del bus DC partido. La PEL es diseñada para operar en los modos de potencia, impedancia y corriente constante. Se concluye que la simulación de la PEL funciona de manera adecuada, representando las formas de onda de la etapa de potencia y las señales de control de acuerdo con la teoría.