Comparison of the efficiency of AC/DC charging for different charging power for an Electric Vehicle (EV) and determination of the energy loss between the charging station and the battery of the vehicle

Abstract

The increase in the number of electric vehicles (EVs) has led to questions regarding the efficiency of their charging methods. In addition to this, there exists a difference between the energy (kWh) supplied by the electric vehicle supply equipment (EVSE) and the EV. This difference corresponds to the energy lost during charging, for example energy consumed by the electronic control units (ECUs) of the EV. There exist two conductive charging methods notably direct current (DC), and alternating current (AC) charging. This thesis provides an overview of these charging methods and their differences. The thesis is also meant to give an insight into which charging method is better in terms of the overall charging efficiency for a specific investigated vehicle. Charging a Nissan Leaf EV at different set powers helps to appreciate and understand the difference in charging efficiencies as well as the difference in charging time. It is expected that at high set charging power values, the efficiency of the charging process is higher compared to lower set charging power values. The experiments are conducted at the „Deutsches Zentrum für Luft und Raumfahrt (DLR) “in Oldenburg. The results obtained from the measurement of energy during charging show that as the charging power increases for the DC charging experiments the energy difference between the supplied energy by the EVSE and the energy charged into the vehicle’s battery increases. The charging efficiency decreases when the charging power is decreased. For AC charging, 2 experiments are carried out and the energy difference during charging is lower at low set charging AC power and higher at a higher set power. The experiments show, that DC charging is generally more efficient than AC charging for the investigated EV. For 4.5 kW DC charging, an efficiency of 95.67 % was recorded and an efficiency of 94.84 % was recorded for 6 kW charging. A third experiment wasIII done for 10 kW charging and an efficiency of 95.8 % was recorded. During AC charging, an efficiency of 85.49 % was recorded for 6.6kW charging and 86.78 % was recorded for 4.4 kW charging.