Citation: Shirzadi, N.; Rasoulian, H.; Nasiri, F.; Eicker, U. Resilience Enhancement of an Urban Microgrid during Off-Grid Mode Operation Using Critical Load Indicators. Energies 2022, 15, 7669. https:// doi.org/10.3390/en15207669 Academic Editor: Abu-Siada Ahmed Received: 15 September 2022 Accepted: 16 October 2022 Published: 18 October 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Resilience Enhancement of an Urban Microgrid during Off-Grid Mode Operation Using Critical Load Indicators Navid Shirzadi , Hadise Rasoulian, Fuzhan Nasiri and Ursula Eicker * Gina Cody School of Engineering and Computer Science, Concordia University, 1455 Boulevard de Maisonneuve, Montréal, QC H3G 1M8, Canada * Correspondence: ursula.eicker@concordia.ca Abstract: Microgrids (MGs) can be used as a solution to ensure resilience against power supply failures in electricity grids caused by extreme weather conditions, unavailability of generation capacities, and problems with transmission components. The literature is rich in research focusing on strengthening the planning of microgrids based on overall load demand. In this study, a critical load demand indicator will be calculated and used to identify optimum operation strategies of microgrids in a power failure mode. An urban microgrid with a large educational building is selected for the case study. Operation dispatch scenarios are developed to reinforce the system’s resiliency in severe conditions. A mixed-integer linear programming (MILP) approach is employed to identify global optimum dispatch solutions based on a next 48 h plan for different seasons to formulate a whole-year operational model. The results show that the loss of power supply probability (LPSP), as an indicator of resiliency, could be lowered to near zero while minimizing operational cost. Keywords: microgrids; resilience; renewable energy systems; operation management 1. Introduction Grid power failures are common, especially in urban areas that rely on a conventional mono-grid. The most common causes of electrical disturbances in the power grid could be severe weather conditions such as storms or flooding [1] or natural hazards such as earthquakes. Beyond environmental hazards, there are other causes, such as equipment failure, transmission line damage, or cyberattacks. These may impact the operational resilience of the energy system based on their severity. Therefore, the designed energy system requires not only reliability but also resiliency, which is the ability of the system to quickly recover from events that cause outages [2]. A microgrid is a small-scale energy system including distributed generators, energy storage, load, and control units, which could work in a grid-connected or off-grid mode, ensuring the power supply for a defined region [3]. Microgrids can play a significant role in supplying resilience at the neighborhood, or even community, level [4]. Although micro- grids could work in an isolated mode and are a reliable solution, operation management is necessary to mitigate the unbalanced power supply and increase its quality in the case of disconnection from the grid. The control-based strategy that helps the microgrid mend and alleviates the consequences of major contingencies could be considered operationally resilient [5]. To increase the system’s operational resiliency, the probability of loss should be lowered as much as it is possible while considering the economic aspect of the system. During the last decade, several types of research have been accomplished on optimally controlling a microgrid’s operation. In [6], the authors studied the different optimal dis- patching procedures of a grid-connected microgrid. They compared the ability of different optimization methods to minimize the operation cost. In [7,8], scheduling problems were solved considering several uncertainties to bring the operating cost to the minimum level. Augustine et al. [9] investigated the dispatch rate of power for a standalone microgrid consisting of wind turbines and solar panels as main generators using the reduced gradient Energies 2022, 15, 7669. https://doi.org/10.3390/en15207669 https://www.mdpi.com/journal/energies