**2. Case Study**

In this paper, four transformer centers have been considered at the start/end points, which are supplied by A point and finally used by D point. Each point has been analyzed by their maintenance history and current peak load point. Transformer maintenance history and current peak load point can illustrate most of their qualities. This research attempts to create a defined glance to recognize points, which are necessary for determining the location of EV charging stations, that can help to build a connection with the grid plan. In the next sections, the proposed solution for determining the coordination of EV charging stations will be elaborated with examples. Ankara metropolitan electricity grid is one of the real cases to study, indicating important parameters, when the grid should be ready to supply electric vehicle and storages.

As demonstrated in the literature, the categories of charging stations distance can change quality of power, service, cost and EVs technology acceptance ratio between members of society. The range of charging stations were determined by various items, such as the grid infrastructure and existing EVs going around. Additionally if the grid does not use charging stations, some locations should be determined by other specifications. These can be different in each grid and depends on the grid's condition. According to the previously mentioned information and Ankara metropolitan electricity infrastructure, the distance of grid terminals and power capacity are critical points in the coordination of electric vehicle charge station topic. A city's transportation routes are different from the route of the power transmission grid and each location has specific power capacity details. In the first step, designers must select locations like points or places, which have the lowest distance to electricity terminals and are suitable for transportation systems. The goal is to measure energy, and responsibility for supply and demand. For example, two different points in Ankara have been assessed - the A and B transformer centers. Both of them are on main and crowded streets, but the A transformer center's condition makes it more operational than the B transformer center. This is, because the A transformer center is close to downtown where the main transportation terminals, such as buses and trains are localized. Whereas 1~2 km from downtown, metro, terminals and location of transformer A and B have many free spaces, parking, schools, hospitals and ministries. It seems that in this area, a large amount of vehicles are stationary and this can be potentially beneficial. In contrast, the B transformer center does not have those options, and because of this, the B transformer center loses its priority to build a charging station. Figure 1 has given the locations of both transformer centers and a map of Ankara for clarity.

Location EV charge station points should be categorized by reasonable distances such as 30, 35, 40, 45, and 50 km, depending on area and infrastructure condition. In the mentioned case, the grid conditions were analyzed, based on the transformer status, even though there was no pre-defined storage center or organized charge station. This indicates that transformer specifications could provide prospective information to evaluate the likelihood of charging stations.

**Figure 1.** Map of Ankara, and area maps of the A and the B Transformer Centers [16].

### **3. Grid Conditions in Ankara**

One of the important factors in grid stability is its dependency on the grid size and infrastructure revises, but efficiency and responsibility are negotiable. The electricity grid of the provinces of Ankara, Bartın, Çankırı, Karabük, Kastamonu, Kırıkkale, and Zonguldak are controlled by the ENERJISA Company (Hanımeli Avenue No:1 Sıhhiye/ANKARA) [17]. At first, the stability of grid should be examined with respect to power and size. This area has special specifics, which help to stabilize the grid. As the area is located in the middle of Turkey and neighbors the five other grid control areas, Ankara can receive energy from five different electricity areas, which means that this area has enough reserve power from the Turkish National Grid. This area is formed from provinces, which have an energy generation rate more than their consumption rate. Some information about those provinces are shown in Table 1.


**Table 1.** Some energy consume and generate details of province which are under the control of ankara province [18].

The grid has been shown to be stable at high penetration rate. The energy terminals are in special places, where they can provide high performance in particular aspects such as energy responsibility. However, they cannot exceed an appropriate amount, which are key points in the energy transfer between grids and storage, thus, both of their accessibilities observe different purposes. Figure 2 illustrates this point clearly. Generally, bi-directional energy transfer has been operated between medium voltage and low voltage range. Bi-directional operation procedures develop in parallel with grid infrastructure and customers.

**Figure 2.** Energy injection side and areas can be operational by storages.
