## 2 Concept of Micro-Grid Systems  
A typical microgrid refers to a set of distributed generation (DG) systems based on renewable and/or nonrenewable sources, incorporating an energy storage system (ESS) and local controllable loads, generally connected to the distribution system [10]. It may operate in both grid connection as well as isolated mode depending on the load condition. Microgrids can be grouped into diverse categories depending on the location (such as campus, military, residential, commercial, and industrial), size (such as small, medium, and large scale), and application (such as premium power, resilience-oriented, and loss mitigation) [11].  
A microgrid involves the integration of several distributed energy sources; the power from these sources is collected, converted, and distributed according to the load requirements. A control system is needed to ensure the proper operation of the microgrid when the power electronics interface with it to form a single unit. The control system is essential; besides providing flexibility, it also preserves the specific energy production and the power quality [12]. Each of these three sorts of microgrid presents advantages and disadvantages. The following Figure 1 presents the different types of microgrids.  
DC microgrids have recently received much attention, especially for commercial and residential small-scale applications, as they provide increased efficiency and controllability with additional power conversion stages being eliminated, and the synchronization and compensation of reactive power is no longer needed [13]. In a typical microgrid, the common bus is DC; hence, AC generators are connected to the DC bus via rectifiers, while inverters are used to supply AC loads (see Figure 2).  
The DC microgrid can operate connected to the grid or isolated from it. It gives various operational advantages [14]. Many of the devices which are connected to a DC microgrid are generally electronic devices. As they are directly connected to a DC microgrid, no power systems like AC-to-DC, DC-to- AC, or AC-to-DC-to-DC are needed, which could be needed for an AC microgrid. No transformer is used in a DC microgrid; this characteristic makes it more efficient, reduces its size, and makes it more reliable in a DC power system [15]. However, a DC microgrid still presents various problems that must be surmounted. There are no good practices implemented to manage fault situations and a basic protective element such as circuit breakers, fuses, and protection relays is lacking, as in the case of AC microgrids [16].  
The hybrid microgrids result from the combination of AC and DC microgrids; they include both AC and DC types of buses [17]. The type of connection to each bus depends on the proximity of the distributed generation unit and the load on the bus. The following steps in the electricity improvement distribution system are the AC microgrid systems.  
Figure 1: Classification of the microgrids based on power type [9].  
Figure 2: Islanded DC microgrid structure [14].  
They can operate in a grid-connected or island mode. Based on the tasks that they have been designed to accomplish, their grid-connected or island modes can possess many suboperational states and or topological configurations [18]. DC-AC converters are used to connect DC generators and energy storage systems to AC buses, while rectifiers are used to supply DC loads.  
To optimize the components of a microgrid system, an energy management system is used, which resolves decision-making strategies. These strategies consider increased system energy efficiency, increased reliability, reduced power consumption, the reduced operating cost of distributed energy resources, reduced system losses, and mitigated greenhouse gas emissions for sustainable improvement [9].