Page - 71 - in Hybrid Electric Vehicles

batteries are generally charged with a constant current (CC)–constant voltage (CV) method [22]. Charging under lower temperature leads to a gradual decrease in the charging current with charging time or increase in battery SOC. In contrast, charging under relatively warmer conditions resulted in a higher charging current, especially at low battery SOCs. Higher CC of about 105 A is obtained at the initial charging of 5–10 min (battery SOC of up to about 50%). With regard to charging voltage, although there is no significant difference between charging in both conditions, charging in a relatively higher temperature (summer) results in a higher initial charging voltage before it is settling down to a certain constant value. Therefore, the CV condition can be reached faster. It is clear that the ambient temperature affects significantly the charging behaviour of PHEVs and BEVs. Charging under relatively high ambient temperature (such as summer) facilitates a higher charging rate, especially because of higher charging current and faster increase in the charging voltage. Hence, a shorter charging time can be achieved. When the vehicles are near to empty, the electricity can flow at a high rate and it starts to pace down when the battery SOC is higher than 50%. In addition, it gets really slower when SOC is higher than 80%. This phenomenon is generally called as tapering. 4. Advanced charging system The widespread deployment of PHEV and BEV charging, especially fast charging, has some critical impacts on the electrical grid including the quality deterioration of the grid and grid overload. Therefore, it is very crucial to schedule and control the charging of PHEVs and BEVs. One strategic method to charge the vehicles with minimum impact on the electric grid is to adopt a battery to assist the charging. Aziz et al. [14] have proposed and studied the battery-assisted charger (BAC) for PHEV and BEV. The battery is embedded inside the char- ger with the aims of improving the quick-charging performance and minimizing the concen- trated load to the grid. The developed BAC is able to limit the received power from electrical grid, as well as control the charging rate to the vehicles. It is important to manage the received power from the grid in order to avoid the electricity demand larger than the contracted capacity and also optimize the electricity demand following the grid conditions. In future, as the share of renewable energy increases, the electrical grid also faces some problems including intermittency. This leads to the requirements of energy storage and demand control. BAC manages the electricity distribution inside the system, such as electricity received from the grid, battery and chargers, to realize the optimum performance. Therefore, BAC is able to satisfy both supply side (minimizing the grid load through load shifting and reduction of electricity cost) and demand side (fascinating the vehicle owners through quick charging, although during peak hours). The purposes of BAC covers: (1) reducing the contracted power capacity from the electrical grid, (2) avoiding the high electricity demand during peak hours due to PHEV and BEV charg- ing, (3) shortening the charging time, as well as the waiting/queueing time, (4) facilitating a Advanced Charging System for Plug-in Hybrid Electric Vehicles and Battery Electric Vehicles http://dx.doi.org/10.5772/intechopen.68287 71