Grid Impact studies of electric vehicles

With Deliverable D4.3 very interesting studies from Green eMotion regarding the influence of EVs on distribution networks are now available. The three areas under investigation cover the most pressing issues for a scalable ramp up for the number of EVs charged from the low-voltage network:

 A1: EVs’ impact on power quality related to harmonics

Harmonic load flow simulations in Power Factory have been performed for three different charging strategies: User dependent, Timer Based and Load dependent. A “base-case” simulation (30 specific low-voltage grids from Italy, Spain and Denmark) was evaluated and 6 specific grids have been selected for a more comprehensive assessment.

From the analysis, harmonic emissions from EVs are not expected to create a need for reinforcement of the grid in nearest future, but could be considered as a severe issue for correct operation of electronic devices and communication like e.g. Power Line Communication. Furthermore, the results show that the total level of harmonics is highly dependent on other types of equipment connected to the grid also.

 B1: Parameters for assessment of EVs’ impact on low voltage grids

Here the parameters relevant for performing a comprehensive assessment of EV’s impact on the electricity grid are described. The study is based on the work of previous funded project as well as on DSO surveys. The charging profiles are subject to some degree of uncertainty, especially when assessing EVs’ impact on local low voltage grids, e.g. at a residential level. Thus a stochastic method has been used to derive charging profiles to assess EV’s impact on local low voltage grids, which includes the uncertainties.

 B2: Reinforcement costs in low voltage grids

The evaluation is focused on how different EV and grid parameters affect the reinforcement costs. The evaluation has been done by developing and analyzing a set of scenarios that vary the parameters under study.

Load flow simulations have been performed on each scenario using ITRES. ITRES is a tool developed within Green eMotion that can evaluate reinforcement costs over a number of years with a user-specified load increase. The reinforcement schedule and reinforcement cost results have been analyzed and comparisons have been made for different charging profiles, different charging powers and different rates of penetration as well as the location of the EVs along the feeders.

The results have shown that with an advanced charge management strategy, considering the overall load of the low voltage grid, it is possible to avoid most reinforcements and their associated costs, reducing the significance of all the other parameters. Furthermore the results have shown that simple charge management strategies, such as timer based charging strategies are challenged by high penetration levels.   

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