## 2 Background of Microgrids
### Historical Development of Microgrids
By becoming self-sufficient, these communities could enhance their energy security and reduce vulnerability to disruptions in the centralized grid. Isolated MGs often provided a cost-effective solution for meeting the energy needs of remote areas. Building a smaller-scale generation and distribution system tailored to the local demand was more economical than extending long transmission lines. Additionally, isolated MGs offered increased reliability compared to the centralized grid. Since the distribution network was shorter, the risk of widespread outages due to faults or failures in the main grid was minimized. This aspect was particularly important in areas prone to natural disasters or with challenging terrain, where restoring power from a distant grid could be time-consuming and costly. In some cases, the motivation behind isolated MGs stemmed from environmental concerns. Remote communities or environmentally conscious industries aimed to reduce their carbon footprint and minimize reliance on fossil fuels. By establishing MGs with RESs, such as solar, wind, or small-scale hydroelectric systems, these entities could generate clean energy locally and contribute to sustainability goals. Isolated MGs provided a platform for integrating and maximizing the utilization of renewable resources in areas where centralized grid expansion was not feasible. In summary, the motivations behind the creation of isolated MG systems included overcoming geographical limitations, achieving energy self-sufficiency,addressing cost and reliability considerations, and embracing environmental sustainability. These motivations drove the early development of microgrid technology and paved the way for subsequent advancements and the interconnected microgrid networks that are seen today [49; 50; 51; 52; 53; 54; 55; 56; 57; 58]. MGs offer a potential solution to the challenges mentioned earlier by enabling localized and decentralized electricity generation and distribution. They can operate independently or in conjunction with the main grid and can incorporate various RESs such as solar, wind, and biomass. This enhances their resilience to disruptions and improves overall power supply efficiency and reliability. The Consortium for Electric Reliability Technology Solutions (CERTS) initiative in the United States and the MGS project in Europe were pioneering efforts in studying and implementing microgrid systems. CERTS, established in 1999, is widely recognized as the originator of the modern grid-connected microgrid concept. Its proposal focused on developing MGs that could integrate multiple distributed energy resources (DERs) while presenting themselves as typical consumers or small generators to the existing network. The emphasis was on seamless and automatic islanding and grid reconnection, utilizing passive control schemes such as reactive power, voltage, and active power-frequency relationships. The goal was to minimize reliance on centralized controllers and high-speed communications, creating a flexible \"plug-and-play\" system that could accommodate the addition or removal of DERs without extensive redesign. This approach aimed to reduce initial system costs and provide cogeneration facilities with the flexibility to be located near thermal loads. The CERTS microgrid concept has been successfully tested and implemented in real-world microgrid applications. While initially focused on improving reliability rather than directly lowering greenhouse gas emissions, CERTS MGs can incorporate renewable microgeneration sources. Similarly, the MGS project in the European Union addressed technical challenges such as safe islanding and reconnection procedures, energy management, control techniques for both islanded and interconnected modes, protection devices, and communication protocols. Ongoing research and development continue to explore and refine these issues in the field of MGs [8]. MGs have the ability to provide new economic and social benefits in addition to their technical advantages.