## 2 Background of Microgrids
### Definition and Classification of MGs  
An MG can be defined as a network consisting of various power generation sources and loads that operate either in isolation (island mode) or in interconnection with the utility grid (grid-connected mode) through integration of these sources. The connection and disconnection of the microgrid to the utility grid are determined based on technical and financial considerations. DERs form a crucial part of MGs, encompassing independently regulated power generation sources that work together to establish an efficient and flexible grid infrastructure. Even if some sources are temporarily disconnected from the generation cycle, the operational perspective of an MG ensures its sustainability. ESSs and power converters connected to the utility grid play a role in managing excess generation within the microgrid. MGs can have installed power capacities ranging from a few kilowatts to multiple megawatts (MW). The primary objective of microgrid installations is to provide power to consumers in remote areas and critical industrial and military facilities. Factors such as the scarcity of fossil fuels, power quality issues, resiliency and flexibility challenges in existing grid infrastructure, and network architecture degradation have stimulated advancements in grid technology and spurred research in MGs. Properly implementedMGs serve as critical infrastructures that enhance the reliability and resilience of the utility grid by providing a backup system against grid disturbances. Key components of MGs include isolation and protection devices at the point of common coupling (PCC), DERs encompassing various power generation technologies, and RESs such as wind power, solar photovoltaics, fuel cells, biomass, and CHP plants [59; 60; 61]. The MGs are categorized into five types: industrial, community, campus, the military, and remote MGs. Industrial MGs are specifically designed to meet the energy needs of industrial facilities, such as manufacturing plants, refineries, mining sites, and data centers. These MGs often operate in conjunction with the main grid but have the capability to disconnect and operate independently during grid outages. Industrial MGs prioritize reliability, cost-effectiveness, and power quality to ensure uninterrupted operations. They may incorporate a combination of onsite generation, energy storage, and advanced control systems to optimize energy usage and minimize disruptions. The community MGs serve a specific community or neighborhood, providing localized power generation, distribution, and resilience. They are typically designed to integrate RESs, such as solar and wind, and may include energy storage systems. Community MGs prioritize energy resilience, allowing them to operate independently during grid outages and provide critical services, such as emergency shelters, medical facilities, and community centers, with electricity. These MGs often promote energy efficiency, local energy production, and community engagement in energy management. The campus MGs are designed to serve large institutions or campuses, such as universities, military bases, industrial complexes, and business parks. They provide reliable and efficient energy supply to multiple buildings and facilities within a localized area. Campus MGs often incorporate diverse energy sources, including renewable energy, CHP systems, and energy storage. They can optimize energy usage, reduce carbon emissions, and enable better control and management of energy resources. Campus MGs may also act as living laboratories for research and development of advanced energy technologies and systems. Military MGs are deployed in military bases and installations to ensure secure and reliable energy supply for critical operations. These MGs enhance the energy resilience and independence of military facilities, reducing reliance on vulnerable and extended transmission and distribution lines.