# PV-Powered Electric Vehicle Charging Stations: Preliminary Requirements and Feasibility Conditions
## 4 PV-Powered EV Charging Stations Power Flow Management  
The EV charging station considered in this paper is PV-powered including stationary storage and public grid connection, modeled using MATLAB/Simulink R2015b as illustrated in Figure 3.  
Where \(p_{PV\ MMPT}\) is the PV power in maximum power point tracking (MPPT) mode, \(p_{PV}\) is the PV power, \(p_{G}\) is the public grid power, \(p_{S}\) is the stationary storage power, \(p_{EVs\ D}\) the EVs total demand power, and \(p_{EVs}\) is the total EVs power. The public grid can absorb or supply power. The capacitor C represents a common DC bus, where the components of the charging station are coupled through their dedicated converters. PV sources are connected to the DC bus through the DC/DC converter to extract the MPPT power. The stationary storage is needed to construct the DC microgrid and it is connected through a reversible DC/DC converter. The DC load, represented by the EVs' batteries, is connected through the DC/DC converter. The public grid connection is required to ensure power at all times and mitigate the power difference between the power production and the load demand; it is connected through a three-phase bidirectional AC/DC converter. The stationary storage is charged by PV sources only and can discharge power to the DC common bus. The energy management strategy, as shown in Figure 4, follows the priorities: PV is the first energy  
Figure 3: Photovoltaic (PV)-powered EV charging station scheme. Figure 2: Required time for EV charging based on demand charge and delivered/accepted power. source to charge EVs, then stationary storage is the second energy source, and the public grid is the last energy source to charge EVs. Stationary storage is charged with excess energy produced by PV sources and the public grid by excessive energy from PV sources when the stationary storage reaches its maximum limits (power or state of charge). The design of the PV-powered charging station is based on a DC microgrid, as shown in Figure 3. Therefore, it is required to keep the power balance [35] given by (1):  
\[p_{PV}(t_{i})=p_{EVs}(t_{i})+p_{S}(t_{i})+p_{G}(t_{i}),\text{ {with} }t_{i}=\{t_{0},t_{0}+\Delta t,t_{0}+2\Delta t,\dots,t_{F}\}, \tag{1}\]  
where \(t_{i}\), \(t_{0}\), \(\Delta t\), and \(t_{F}\) are continuous time, initial time instant, time interval between two samples, and time instant at the end of time operation respectively. The PV power is calculated in MPPT mode, \(p_{PV\text{ }MPPT}\), [36] as given by (2) and (3):  
\[p_{PV\text{ }MPPT}(t_{i})=P_{PV\text{-}STC}.\frac{g(t_{i})}{1000}\cdot[1+\gamma \cdot(T_{PV}(t_{i})-25)]\cdot N_{PV}, \tag{2}\]  
\[T_{PV}(t_{i})=T_{amb}(t_{i})+g(t_{i}).\frac{NOCT-T_{air-test}}{G_{test}}, \tag{3}\]  
where \(P_{PV\text{-}STC}\) is the PV power under standard test conditions (STC), \(g\) is the solar irradiation, \(\gamma=-0.29\%/^{\circ}\)C is the power temperature coefficient, \(T_{PV}\) is the PV cell temperature, \(N_{PV}\) is the number of PV panels, \(T_{amb}\) is the ambient temperature, \(NOCT=41.5\)\({}^{\circ}\)C is the nominal operating cell temperature, \(T_{air-test}=20\)\({}^{\circ}\)C is the fixed air temperature, and \(G_{test}=800\)\(W/\text{m}^{2}\) is the fixed solar irradiation for testing. A simplified state of charge of the stationary storage [37], \(soc_{S}\), is used as in (4) for its simplicity, where self-discharge and temperature are not taken into account, and the over-charging/discharging protections [35] are expressed by (5) and (6):  
\[soc_{S}(t_{i})=SOC_{S_{0}}+\frac{1}{3600.E_{S}}\int\limits_{t_{0}}^{t}p_{S}(t _{i})dt, \tag{4}\]  
\[SOC_{S\_min}\leq soc_{S}(t_{i})\leq SOC_{S\_max}, \tag{5}\]  
\[-P_{S\_max}\leq p_{S}(t_{i})\leq P_{S\_max}, \tag{6}\]  
Figure 3:0 Flowchart for the power flow management of the PV-powered EV charging station.