This paper addresses the protection coordination problem of microgrids combining unsupervised learning techniques, metaheuristic optimization and non-standard characteristics of directional over-current relays (DOCRs). Microgrids may operate under different topologies or operative scenarios. In this case, clustering techniques such as K-means, balanced iterative reducing and clustering using hierarchies (BIRCH), Gaussian mixture, and hierarchical clustering were implemented to classify the operational scenarios of the microgrid. Such scenarios were previously defined according to the type of generation in operation and the topology of the network. Then, four metaheuristic techniques, namely, Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Invasive Weed Optimization (IWO), and Artificial Bee Colony (ABC) were used to solve the coordination problem of every cluster of operative scenarios. Furthermore, non-standard characteristics of DOCRs were also used. The number of clusters was limited to the maximum number of setting setting groups within commercial DOCRs. In the optimization model, each relay is evaluated based on three optimization variables, namely: time multiplier setting (TMS), the upper limit of the plug setting multiplier (PSM), and the standard characteristic curve (SCC). The effectiveness of the proposed approach is demonstrated through various tests conducted on a benchmark test microgrid.

This paper proposes a comprehensive 26-bus microgrid (MG) test system designed to validate or propose new protection coordination schemes. The proposed MG test system comprises various components facilitating the simulation of diverse configurations and operating modes. It also presents a predefined overcurrent protection scheme which is validated with and without Distributed Generation (DG), offering detailed specifications and settings for the test network. The MG test system outlined in this paper incorporates multiple DG sources in different buses, multiple voltage levels, and two operating modes (with and without DG). Additionally, the overcurrent protection scheme considers multiple functions and devices simultaneously. The detailed features of the proposed protection coordination scheme enable the simulation of various fault types and contingencies. The paper also presents specific details of the MG test system under different single-phase and three-phase faults, reporting bus voltages in nodes, transformer and line loadability, short-circuit currents, and operating times. The MG test system is meant to serve as a valuable tool for researchers to conduct comparative studies and develop new strategies regarding the operation and planning of MGs.