# PV-Powered Charging Station for Electric Vehicles: Power Management with Integrated V2G
## 4 Simulation Results and Analyses
### Simulation Results under ICDA  
The first simulation case works under ICDA and the EV can directly be charged/discharge within the EV power limit. As shown in Figure 8, the steady DC bus voltage is 400 V within the simulation period, which proves that the power management strategy works well to balance the powers under ICDA. Figure 9 shows the storage _soc_ and distribution coefficient \(k\) under ICDA. The _soc_ of storage is limited between 20% and 80% to extend storage life [33]. \(k=1\) means only the storage is working and \(k=0\) means only the public grid is working. \(0<k<1\) means the storage and the public grid are working simultaneously. Storage current evolution under ICDA is shown in Figure 10. The storage current is between \(-115\) A and \(115\) A to reduce the damage of the storage. The value \(-115\) A is the maximum discharge current of batteries, while the value \(115\) A is the maximum current for batteries to be charged. The simulation result shows that the current is successfully limited. The power flow of the DC microgrid under ICDA is shown in Figure 11. PV source can switch freely between PV-constrained production control and PV - maximum power point tracking control [34]. Figure 8: DC bus voltage evolution under ICDA. Figure 10: Storage current evolution under ICDA. Figure 9: Storage _soc_ and distribution coefficient \(K\) under ICDA. The power \(p_{EVs}<0\) means that EVs show a total tendency to discharge, \(p_{EVs}>0\) means that EVs show a total tendency to be charged. During the \"peak\" periods of the public grid: 11:00-13:00 and 18:00-20:00, the injection power limit is 100 kW, and the supply power limit is \(-10\) kW to prevent the public grid from overloading. During the \"valley\" periods of the public grid, the injection power limit is 50 kW, and the supply power limit is \(-50\) W. Setting different power limits according to the \"peak\" periods and \"valley\" periods of the public grid is beneficial to improve the stability of the public grid, which also respects the power flow given in Figure 2.  
Figure 12 shows the parking periods of EVs. The parking periods of EVs are different according to the willingness of users. From EV_charger_1 to EV_charger_5 represent EVs connected to chargers one to five, respectively, e.g., EV_charger_1 represents the ordinal number and parking periods of the EVs connected to the charger one. The power evolutions of EVs under ICDA are shown in Figure 13. If the power is positive, it means that the EV is being charged; if it is negative, it means that the EV discharges. Figure 14 shows the \(soc_{EV}\) evolutions under ICDA. Figure 11: Power flow of DC microgrid under ICDA. Figure 12: Parking periods of EVs at each charger. Figure 13: Power evolutions under ICDA. The operating time of EVs connected to charger 1 is shown in Figure 11.0 \(t_{EV\_charger\_1}\) represents parking periods of EVs connected to charger 1. \(t_{EV\_operate}\) represents the start operating time of EVs. \(t_{EV\_arrive}\) represents the arrival time of EVs. \(t_{EV\_depart}\) represents the departure time of EVs. As shown in Figure 15, EVs connected to the charger 1 in chronological order are the 1 st, 3 rd, 5 th, 6 th, 12 th, 14 th. After an EV arrives at the charging station, when the power is met, the charging/discharging operation begins. EVs that immediately start charging/discharging operations after arriving at the charging station are the 5 th, 6 th, 12 th, while the 3 rd EV enters the waiting state after arriving at the charging station, then discharges when power is met. Moreover, the 1 st and 14 th did not discharge until they left because of unsatisfactory power. The operating time of EVs connected to charger 2 is shown in Figure 11.1 As shown in Figure 16, EVs connected to the charger 2 in chronological order are 2 nd, 4 th, 7 th, 13 th, 15 th.