Page - 74 - in Hybrid Electric Vehicles

certain threshold value due to high and continuous charging of vehicles (stationary battery is not able to supply the electricity unless being recharged). In the latter, BAC manages the charging rate of each charger to corresponding vehicle; hence, the contracted power capac- ity can be maintained avoiding any penalty. Electricity flow in the battery idling mode can be represented as follows: P grid = P QC1 + P QC2 + P loss . (3) BAC always maintains that the value of Pgrid must be lower than or maximally equal to the contracted power capacity. Furthermore, Ploss is the total power loss in the system due to some factors, such as AC/DC and DC/DC conversions and internally consumed electricity the sys- tem. Therefore, the value of Ploss in each quick-charging mode might be different. Table 2 shows the specification of the developed BAC system and the used vehicles during experiments. Nissan Leaf having battery capacity of 24 kWh is used as the vehicle. Figure 4 shows the results of simultaneous quick charging of two vehicles during winter conducted using conventional quick charger and BAC under contracted power capacity of 50 kW. The electricity received from the grid is kept at 50 kW or below. In case of charging using the conventional charging system, the first connected vehicle is charged with higher charging rate than the vehicles connected later. This is due to the limit on contracted power capacity as well as the available power for charging. The charging rate of the second connected vehi- cle increases gradually as the charging rate of the first connected vehicle starts to decrease; therefore, the total electricity can be maintained to be lower or equal to the contracted power Component Property Value Installed battery in the charger Battery type Total capacity Nominal voltage Maximum charging voltage Cut-off voltage during discharge Maximum current during discharge SOC threshold during charge SOC threshold during discharge Li-ion 64.2 kWh 364.8 V 393.6 V 336.0 V 176 A 90% 10% Quick charger Number Standard Output voltage Output current Rated output power 2 units CHAdeMO DC 50–500 V 0–125 A 50 kW Vehicle Vehicle type Battery type Total battery capacity Maximum voltage Nominal voltage Cell rated capacity Cell average voltage Cell maximum voltage Nissan Leaf Laminated li-ion 24 kWh 403.2 V 360 V 33.1 Ah (0.3 C) 3.8 V 4.2 V Table 2. Specifications of the developed BACS. Hybrid Electric Vehicles74