## 2 Remarks on the Topology of Microgrid
### Integration of Renewable Energy Sources  
Given the increasing focus on RES to achieve sustainability goals, their integration into microgrids should be emphasized. Understanding the challenges and benefits of different types of RES provides the basis for design strategies and optimization methods. This section explores the role of RES in microgrid systems, and the following sections discuss their impact on energy management. RES have been increasingly integrated worldwide in recent years due to their outstanding potential to mitigate climate change, improve energy security, promote economic development, create employment, and offer sustainable access to energy, especially in regions with limited access [30]. Leading RES institutions such as the Renewable Energy Policy Network for the 21 st Century (REN21) [30], the International Energy Agency (IEA) [31], and the International Renewable Energy Agency (IRENA) [32] agree with the following definition: renewable energies are those obtained from natural sources that are continuously replenished and could be considered inexhaustible in the human time scale. Their environmental impact is considerably reduced compared to traditional fossil fuels. The following are examples of renewable energy which are detailed in the 2024 REN21 report [30]:  
* Solar energy comes from solar radiation that can be converted into electricity or heat. It is one of the most abundant and accessible sources of renewable energy. * Wind energy generated from the wind moves the blades of wind turbines to produce electricity. It is incredibly efficient in regions with strong and constant winds. * Hydroelectric power harnesses water movement, generally in rivers or dams, to generate electricity. It is one of the most traditional forms of renewable energy. * Geothermal energy originates from the natural heat of the Earth's interior. It can be used to generate electricity or for direct heating in geothermal areas. * Biomass from organic materials such as wood, agricultural residues, and organic waste can generate energy through combustion or conversion into biofuels. RES have been successfully integrated into microgrids for power generation through various approaches. Their integration is crucial in microgrid planning due to the increasing need for sustainability and carbon emission reduction. They offer significant advantages, such as availability and low environmental impact [33]. However, there are several challenges associated with these sources' intermittent and variable nature. Addressing these challenges requires optimizing the size and combination of these resources, balancing generation and demand, minimizing costs, and maximizing efficiency [34]. It could also involving generating the hybridization of AC and DC operation modes, involving several stages of power conversion, and making an indispensable EMS that guarantees the control of energy sources and the supply to the demand. Figure 4 shows an approach to the connection diagram of a microgrid integrating RES and power conversion stages. This diagram shows that microgrids with RES could also include controllable power sources, such as a diesel generator, to help ensure the reliability of the power system. This figure