On the Integration of Electric Vehicles into German Distribution Grids through Smart Charging

Efforts to decarbonise the transport sector lead to an increasing share of electric vehicles (EVs), which can impose significant stress on future distribution grids. The level of stress is thereby not only dependent on the number of integrated EVs but also the existing topology of the grid and present shares of supply and demand units. These factors are also likely to influence strategies to help the integration of EVs, such as utilising EV flexibility through smart charging. We therefore examine the influence of different charging strategies on distinct distribution grid types, namely PV-, wind- and load-dominated grids. With the help of a quadratic problem formulation including linearised AC power flow constraints, we deduce optimised charging profiles to minimise the additional stress on the grids. In reality, a central optimisation of all EVs might be challenging to implement. We therefore compare the results to rule-based charging strategies to extract suggestions for the effective integration of EVs. Our analysis shows that the potential of the examined charging strategies to decrease curtailment that is necessary to solve arising grid issues is limited. However, the additional grid expansion costs caused by EV integration, which mainly occur in the low voltage (LV), can be reduced significantly compared to the reference charging, where EV charging is mostly uncontrolled. Our results also show that the charging strategies prove to be differently useful in the different types of grids. This stresses the importance of considering various grid topologies when investigating the influence of smart charging on distribution grids.