Seite - 77 - in Hybrid Electric Vehicles

winter, in the conventional charging system, the first connected vehicle enjoys a higher charg- ing rate, while the second vehicle must contend with significantly lower charging rate because of limited contracted power capacity. The first and second vehicles reach battery SOC of 80% after charging of about 20 and 30 min, respectively. When charging with BAC, similar to the case in winter, both vehicles could be charged almost at the same charging rate while maintaining the contracted power capacity. Both vehicles could be charged in a relatively short time of about 20 min. The stationary battery discharges its electricity until the total charging rate of two vehicles is equal or lower than the contracted power capacity. It is clear that BAC improves the charging quality, especially during simultaneous charging of multiple vehicles. In addition, from the point of view of the electricity grid, application and deployment of BAC can reduce the stress on the grid because of the high demand for vehicle charging. 5. Simultaneous charging with developed BAC system Figure 6 shows the demonstration test results during winter and summer under the con- tracted power capacity of 30 kW. Simultaneous charging of eight vehicles during summer can be conducted quicker than one during winter because of higher charging rate. However, the SOC of the stationary battery decreases considerably. It is because of the high discharging rate of the stationary battery to assist the quick chargers as well as cover the electricity demand due to limit of the contracted power capacity. In addition, the stationary battery cannot be charged because of no available marginal electricity from the electrical grid. On the other hand, the discharging rate of the stationary battery is significantly lower during winter due to slower charging rate to the vehicles. Hence, the total charging rate of two quick chargers can be maintained to be lower than the contracted power capacity. It results in the marginal electricity that can be utilized to charge the stationary battery. Therefore, the SOC of the stationary battery in winter does not largely decrease compared to one during summer. Figure 7 shows the simultaneous charging of eight vehicles during summer under a con- tracted power capacity of 15 kW. Compared to Figure 6, there is almost no significant change in the charging rate of vehicles, except that of the last connected vehicle. However, the dis- charging rate of the stationary battery is very high, resulting in significant decrease in its SOC. The SOC of stationary battery drops rapidly and reaches 10% during charging of the last two vehicles. As the result, the last connected vehicle is charged only using the electricity received from the electrical grid, with no assistance from the stationary battery. As the contracted power capacity is very low, the very last connected vehicle is not charged until the vehicle before it is charged completely. The stationary battery cannot be charged during simultane- ous charging because of the lack of marginal electricity and the high charging rate of vehicles. Based on the results of the demonstration test, the application of BAC is potential to improve significantly the charging performance of quick chargers, especially during the simultaneous charging of multiple vehicles. The balance among vehicle charging rate, contracted power capacity and stationary battery SOC seems to be very important. Therefore, PHEVs and BEVs charging demand must be forecast initially. Advanced Charging System for Plug-in Hybrid Electric Vehicles and Battery Electric Vehicles http://dx.doi.org/10.5772/intechopen.68287 77