## 2 Concept of Micro-Grid Systems
### Distributed Generation Sources  
A distributed generation system is composed of different sources, both renewable and nonrenewable. Renewable sources are generators that utilize renewable energy technologies such as photovoltaic, solar thermal power, wind power, biomass, tidal power, and geothermal power as the primary energy to generate power [19], whereas nonrenewable sources utilize natural resources that are not naturally replenished to produce power [20]. 1. Solar Power: Solar power can produce power through two different forms, which include solar thermal generation and photovoltaic conversion. The first method, which is the solar thermal process, is a process of converting solar power into heat, and that heat runs a steam turbine which produces power, and photovoltaic conversion converts sunlight into electricity using photoelectric phenomena [21]. A solar cell is a basic component of a PV system. Solar cells can be grouped in series and parallel to constitute modules, which are also connected in series to form strings, and the strings are finally connected in parallel to form arrays. Different from the photovoltaic system, solar thermal generation utilizes solar collectors to collect heat, and the most widely used include parabolic, concentrated solar collectors, etc. [22]. 2. Wind Power: The wind turbine operating mode is focused on two methods. Firstly, the kinetic energy of the moving air is converted into mechanical energy. This conversion is obtained by using aerodynamic rotor blades and a mechanical power controller. Secondly, the electromechanical energy is converted into electric power via a generator [23]. According to the wind turbine topology, they can be classified into two categories (horizontal axis and vertical axis); however, the most used topology is the horizontal axis wind turbine [24; 25]. Various generator topologies are utilized to convert the electro-mechanical energy into electricity. 3. Geothermal Power: A geothermal power system converts the energy contained in the hot rock into electricity by injecting water into the rock to absorb heat from the rock and transport that heat to the surface of the Earth, where it can be converted into electrical power through a turbine generator. High-temperature water (>240 \({}^{\circ}\)C) is vaporized into steam, and that heat is transferred to a low-pressure steam turbine, which converts the steam into mechanical energy [26]. Usually, exploitable geothermal reservoirs are mostly located close to young volcanic rock areas [27]. 4. Hydropower: Hydropower is a process that produces electricity from water flowing in the river or the oceans. The purpose of hydropower production is to generate clean energy [28]. A hydropower plant is generally composed of a generator, a turbine, a penstock, and a wicket gate. Mainly, two types of turbines are utilized, which include a pulse turbine (a Pelton Wheel turbine) and a reaction turbine like [PERSON] and Kaplan turbines. Generally, the generator and turbine are directly linked to the same vertical shaft [29]. 5. Biomass Power: A biomass power system utilizes biomass to produce biogas, which is utilized as fuel for a biomass generator [30]. The utilized biomass includes both energy crops and wastes, such as forest residues and a range of other agricultural and industrial compounds. Actually, the use of biomass is a fundamental part of global renewable energy and contributes to an ever-increasing share of global electricity capacity [31]. * Micro-Turbines: Micro-turbines are energy generators, which have a range of capacity between 15 and 500 kW. They operate under the open cycle gas turbine principle, and they have shown many different characteristics and operate easily and at high speed. Some of their benefits include having variable speeds, being easy to install, having compact sizes, being low maintenance, having air bearings, having low NOx emissions, and being mostly recuperators [32]. Micro-turbine generators have demonstrated strong improvements in distributed small-scale power production.