Analysis of BMW I3 Battery Charging Process

Recently, battery electric cars are rapidly gaining popularity. These cars have many advantages compared to traditional fuel-powered cars, and one of the biggest advantages is less pollution. Electric cars use a rechargeable HV battery pack as a power source, which is charged from the mains. There are several ways of charging, but in all cases, there are some energy losses during charging, and when evaluating the pollution and energy costs of electric cars, these losses should also be evaluated. The purpose of this research is to evaluate the energy losses during the charging of electric car batteries. The BMW i3, a popular battery electric car on the market, was used in the research. It can be charged in two ways - with the help of a Type 2 connector using alternating current (AC) and with the help of a Combined Charging System connector (hereinafter - CCS connector) using direct current (DC). In the course of the research, natural experiments were carried out, during which the actual electricity consumption of the BMW i3 electric car from the high-voltage battery pack was evaluated. After experimental driving, the battery of the electric car was charged to the initial charge level and, during charging, the actual consumption of electricity from the mains or charging device was evaluated. By comparing the actual electricity consumption evaluated during the experiments from the power grid and the high-voltage battery of the electric car, the charging losses were calculated, and they are set from about 3 to 11% depending on the charging method. Experimentally evaluated energy consumption was compared with theoretically calculated results. The experiments performed and the results obtained show that the electric power losses experienced when charging the high-voltage battery of an electric car with direct current electricity (DC) were lower than when charging with alternating electricity current (AC). The battery charging intensity of the BMW i3 electric car is determined, which is controlled by the car’s BMS unit and depends on the battery charge level, battery temperature and other factors. Charging the battery from a DC fast charging station resulted in an average charging intensity of 23.46 kWh/h or 141 km/h. By comparing the characteristics declared by the battery manufacturer of electric car high-voltage batteries with the results obtained during the experiments, the battery state-of-health (SOH) index was calculated and result was given about 75%, which was similar to the one that was obtained with the diagnostic device BOSCH KTS.