Contents lists available at ScienceDirect Electric Power Systems Research journal homepage: www.elsevier.com/locate/epsr Optimal protection coordination in the micro-grid including inverter-based distributed generations and energy storage system with considering grid- connected and islanded modes Saeed Abrisham Foroushan Asl, Majid Gandomkar ⁎ , Javad Nikoukar Department of Electrical Engineering, Saveh Branch, Islamic Azad University, Saveh, Iran ARTICLE INFO Keywords: Dual setting overcurrent relay Energy storage system Fault current limiters Optimal protection coordination Renewable energy source Grid-connected and islanded micro-grid ABSTRACT This paper presents the optimal protection coordination (OPC) to grid-connected and islanded micro-grid (MG) consisting renewable energy sources (RESs), and energy storage system (ESS). The proposed approach considers objective function as minimizing the total operation time of the dual setting overcurrent relays (DSORs) in primary and backup protection mode. Problem constraints are the regulation parameters limits of the DSROs, sizing limit of FCLs and also the coordination time interval (CTI) inequality. MG includes generally RESs and ESS, hence, this problem needs to the daily optimal operation results of MG in both grid-connected and islanded modes to obtain the network variables before the fault occurrence. Therefore, it is minimized the MG operation and load shedding costs of islanded MG while it is constrained to MG optimal power flow equation in the presence of RESs and ESS. The proposed OPC includes non-linear model, hence, this paper uses the crow search algorithm (CSA) to obtain a reliable and optimal solution for this formulation. Finally, this strategy is im- plemented on the 9-bus and 32-bus MGs, thus, it can obtain the high quick protective solution for these MGs by selecting optimal regulation parameters and sizing to DSORs and FCLs, respectively, according to numerical results. 1. Introduction Network protection in the fault condition is a fundamental re- quirement in the power system especially in the distribution network that is included more than 80% of the occurred outage in the power grid [1,2]. The suitable protection formwork must be able to disconnect part of the network that has faulted at the shortest possible time by coordinating between protective devices such as relays and fault cur- rent limiters (FCLs) [3]. Moreover, noted that the distribution network is recently included several micro-grids (MG) due to the presence of the new technologies such as renewable energy sources (RESs), energy storage system (ESS), etc. In this network, where each MG is a multi- direction supply network that is operated in the grid-connected and islanded modes [4]. Hence, the dual setting overcurrent relay (DSOR) plays a significant role in the fault condition for the MGs, where it is able to operate in both forward and reverse directions with different setting, and with a low bandwidth communication to maintain proper protection coordination [5]. Also, the traditional optimal protection coordination (OPC) is not suitable in this condition because it is de- signed for single-direction supply network [6]. Therefore, this paper presents the OPC for multi-direction supply MG that is considered in the grid-connected and islanded modes and containing RESs and ESS to obtain optimal value for DSRO regulation parameters and FCL sizing. There are many researches about the OPC in the distribution net- work and MG, so that the authors of [7] have expressed this strategy for MG to optimally set the dual setting directional overcurrent relays. Also, the cuckoo-linear optimization algorithm is used for the OPC in the [8] to obtain optimal value for the setting parameters of the DSORs and FCL capacity, and it has coordinated all the double-inverse over- current relays in the distribution network based on the proposed strategy in [9] to achieve the quick protective solution at the fault condition. Moreover, the stability index is investigated in [10] for this method and N – 1 contingency-based security index is considered for the OPC problem in [11]. Generally, this strategy is modeled as non- linear programming (NLP), hence, the authors of [12–15] have solved this problem with the genetic algorithm, fuzzy-based genetic algorithm, multi-objective particle swarm optimization (MOPSO) according to fuzzy decision-making tool (FDMT), adaptive modified firefly algorithm (AMFA), respectively. In addition, noted that the OPC formwork in the network that is included distributed generations (DGs) is different from https://doi.org/10.1016/j.epsr.2020.106317 Received 21 December 2019; Accepted 6 March 2020 ⁎ Corresponding author. E-mail addresses: saeed.abrisham@stu.iau-saveh.ac.ir (S.A.F. Asl), gandomkar@iau-saveh.ac.ir (M. Gandomkar), j.nikoukar@iau-saveh.ac.ir (J. Nikoukar). Electric Power Systems Research 184 (2020) 106317 Available online 30 March 2020 0378-7796/ © 2020 Elsevier B.V. All rights reserved. T