# Comparative Study of Different Approaches for Islanding Detection of Distributed Generation Systems
## 2 Literature Review  
### Distributed Generation  
Distributed generation (DG) is the system that indicates the energy sources that provide reliable electricity to the end users. These technologies are site-specific and referred to small renewable energy sources such as solar, wind, micro-hydro. It can be at a local level or end-user level. The local level DG is the renewable energy systems that electrify a community, whereas the end-user level includes the technologies adopted by the single consumer with similar characteristics of the system. The energy storage system plays a vital complementary role in DG. Although being the decentralization and the smaller size, DG and the energy storage system are highly preferred for low energy costs with high reliability, and a more efficient, cost-effective and eco-friendly nature [33; 34; 35; 36; 37; 38; 39; 40]. Figure 1 presents an example of a DGS containing micro-hydro power plant, solar PV, wind turbine, diesel generator as the energy-producing units, the battery bank as a storage device, load, and finally grid as an optional choice. The voltage level of AC and DC bus bars may be the same or different, but in general the DC level is low and controlled through the converter. A circuit breaker (CB) is placed between the grid and the AC bus system. Here, if the CB is open, the energy system, excluding the grid system, can be considered as IES, and, if the status of CB is closed, the system will be grid-connected. In Figure 1, the system can be operated in either an isolated or grid-connected mode. The flow of the current in the CB section may be unidirectional or bidirectional, depending on the nature of the connection and the local policy of energy trading. Conventionally, the energy systems are of two types; isolated and grid connected system. The isolated energy system (IES) is a collection of energy generator, load and the controlling components that are designed to fulfill the energy demand of a community or a system in isolated form. There is no connection of the national grid line to get power from any reliable service. Generally, IES seems to be a promising option for electriying remote locations where grid extension is not feasible or economical. The integration of battery banks as a means of energy storage with different renewable energy systems can enhance the system reliability and its overall performance. Therefore, appropriate choices of generator sizes and the battery bank capacity are critical to the success of such renewable-based, isolated power systems. However, there are numerous challenges in renewable energy based IES such as high-cost, poor reliability and power quality, low load factor, periodic nature of renewable sources, problems in maintenance and monitoring activities [41]. Because of the periodic nature and dependency on weather factors, the characteristics of the energy generated from renewable energy sources (RES) like solar and wind are unreliable, which can be improved by using sufficient storage devices or by interconnecting multiple energy resources type, called optimal hybridization [42; 43]. An optimized hybrid energy system (HES) is quite a promising technique on behalf of cost, power quality and reliability able to provide the electricity to the area where expansion of the national utility's grid system is quite difficult and expensive [44; 45; 46]. It can be made more efficient and cost-effective by reducing the disadvantages associated with these technologies [41; 47]. However, there are other problems as well, such as: low load factor, low diversity factor, low reliability, protection, etc. in the isolated energy system. To resolve these problems, the mini-grid concept may be a good option. It is proven that the mini-grid concept contributes to the enhancement of social impact by improving the local governance structure via direct participation of the local community, since it is the best option to electrify the isolated rural communities [45; 48].