Grid-Oriented Charging of Electric Vehicles as Approach for Increasing Penetration in Residential Areas

Abstract:
The Mobilitätswende in Germany is a politically desired change from vehicles with conventional engines to electric vehicles. The number of electric vehicles and charging stations has risen during the last years. Especially in suburban residential areas, an increase in electric mobility and private charging infrastructure can be assumed. Battery capacities and charging powers will continue to increase in the future. Charging powers will be possible up to 22 kW (AC). If many electric vehicles charge at the same time, this can endanger grid stability. For this reason, grid-oriented charging approaches are necessary in order to be able to guarantee secure grid-operation even with an increasing penetration of electric mobility. Against this background, simulations were first carried out. An extreme grid was used for these simulations and an extreme scenario was defined in order to obtain the greatest possible impact from electric vehicles. With the help of reactive power supplies and voltage-dependent charge power reduction, safe operation at high penetrations can be guaranteed even in the worst-case scenario selected. Subsequently, a laboratory setup was built to demonstrate grid-oriented functions with an off-board battery charger in real charging processes. The grid-oriented functions implement decentralized active and reactive power control to stabilize the mains voltage. With regard to reactive power supply, several options are tested and then compared on the basis of the test results. The presented results show that a voltage-rated characteristic Q(V), which is used separately per phase, is recommended due to the low energy consumption and the possibility to contribute to voltage symmetry.