Distribution network is expanded in radial form

Distribution network is expanded in radial form, and the generation can’t reach the existing load so that, additional power must feed the electric network in the loading part, this power is taken from distributed generation units (DG). DGs will affect the distribution system by changing the power flow of the distribution feeders, 1.
Distributed generation (DG) can be defined as small electric power source with the capacity of less than 100MW connected directly to distribution system in the load part 2, 3, and 4. There are four type of DG. The first type of DG injects only Real power such as PV, MT and FC with PE interface. The second type of DG injects only reactive power only such as synchronous compensator and capacitor bank. The third type of DG injects both real power and reactive power such as Synchronous generator. The fourth type of DG injects real power and consumed reactive power such as wind turbines 5.
Some advantages of DG are listed by Hernandez, Velasco, and Trujillo (2011) 6 includes: (a) Minimization of total network power losses. (b) Improves the reliability and voltage profile of the system. (c) Reduces the total emission of the system. (d) More flexible energy solution due to the small size. (e) Mitigates environmental concerns.
The problem of finding the best placement and size of DG units is important. If selecting DG sources in a load part is selected randomly, it will adversely affect network performance such as; increasing power loss, reducing reliability level and growing cost in the system. Therefore, it is important to allocate of DG to maximize and improving the system performance 7, 8.
Optimization techniques have become the most common use in recent years, and extend to include a different type of study. Different optimization methods have been applied to solve the DG and capacitor allocation problem while improving network performance.
In order to obtain the best location and size of DG, the previous researchers have been used several methods that are classified as:
Effect of DG only; The effects of DG on the stability of the power system, angle, frequency and voltage stability have been presented by Dang Jiqing Yu Tong Dang Bo HanK., Chengdu A (2011) 9; Donnelly, Dagle, Trudnowski, ; Rogers (1996) 10; Reza, Slootweg, Schavemaker, Kling, ; Van der Sluis (2003) 11. Prakash DB, Lakshminarayana C (2016) 12 is presented the effect of type and number of DG on the voltage profile and losses. Nguyen TP, VO DN (2018) 13 is presented the impact of DG on the network power losses. The effect of DG was formulated with multi-objective functions explained by clonal selection based artificial immune system (AIS) 7, the four objectives are to minimize the real and reactive power loss, improve the voltage regulation and voltage stability. Evolutionary particle swarm optimization (EPSO) 14 is used to calculate the DG capacity, taking into account reducing energy loss and improving voltage profile. A multi-objective harmony search algorithm 15 is presented to evaluate the effect of DG location for optimal planning, improving network performance.