Analysis of the influence of grid-serving charging strategies on distribution grids due to the increasing grid integration of electric vehicles (Helfenbein 2021)

Master’s Thesis

Electric vehicles will play a key role in decarbonizing the transport sector due to theirhigher efficiency compared to alternative technologies. With an increasing market ramp-upof electric vehicles, the energy demand increases and especially in the case of uncoordinatedcharging, this will put additional stress on the distribution grids.

For this reason, this thesisinvestigates whether grid-friendly charging strategies can support the grid integration ofelectric vehicles and in addition fluctuating renewables. Therefore, two preventive and oneactive charging strategies are evaluated. WithSimBEV, a tool is co-developed for the creation of driving profiles and the determination of the charging demand of electric vehicles. Thedemand is allocated locally and transferred in the form of load time series to the spatially and temporally high-resolution grid models of five typical medium voltage grids includingunderlying low voltage grids. Subsequently, a load flow analysis is used to highlight any gridissues. Finally, the curtailment of load and generation necessary to solve any arising gridissues is determined.

Based on these values, investigations are made about the extent to whichthe charging strategies are able to avoid or reduce critical grid stresses. A preventive charging strategy with reduced charging power can successfully reduce grid issues arising from highload. In contrast, a preventive charging strategy with alternating charge time windows canreduce the load-induced stresses only to a small extent. Furthermore, the preventive charging strategies also lead to an increase in the curtailment of fluctuating renewables, as the chargingdemand is reduced during periods of high feed-in. With the active charging strategy, which isdependent on the residual load in the grid, the curtailment of load is reduced more stronglyin some cases, but less strongly in most cases than with the preventive charging strategywith reduced charging capacities. On the other hand, especially in photovoltaic-dominatedgrids, only the active charging strategy offers the potential to reduce the curtailment ofgeneration and thus supports the grid integration of fluctuating renewables.

The success ofthe active charging strategy depends strongly on the extent to which the global residual loadin the medium voltage grid reflects the situations in the individual grid sections. Primarilyin wind-dominated grids, the global residual load proves to be an insufficient optimizationparameter, which leads to negative effects on the curtailment of load and generation.

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