EV Penetration Impact on a Distribution Grid

Abstract

Although the idea of electric vehicles fell out of favour in the 1930s, it seems this phenomenon is now reversing and that many companies are willing to invest again on this technology. The advantages are clear: no emissions and the possibility to power vehicles by means of sustainable sources. On the other hand, a high number of simultaneously active charging stations would likely lead to severe problems in the electrical network, e.g. grid congestions and voltage issues. One of the main goals of this work is to estimate the impact that a higher EV penetration has on the power loading of the lines and transformers in a distribution grid. Once these effects are clear, the focus can move towards the investigation of possible strategies to limit it. Excluding an equipment reinforcement, the only possible way to keep a grid operating when the general working conditions approach the technical limits, is to improve the power management. In this regard, five control strategies were tested in different combinations. Among these, three were implemented on a single charging station level to control the charging operations of the single vehicles. These are the uncontrolled charging (the most commonly used strategy worldwide), the average power charging, where a constant low power is provided during the whole parking time, and the local optimisation charging, where a completely local optimisation analysis is carried out to calculate the cheapest operation possible. The other two strategies instead were implemented at central level, to curtail power in case of necessity. These are the Equal Curtailment Method, that prioritises an equal division of the curtailment among the chargers, and the Flexible Curtailment Method, that optimises the curtailment considering the flexibility of the charging stations. Several tests were run by means of simulations on real Dutch distribution grid models and they showed that simple charging strategies - such as the average power charging – can lead to both low charging prices and low loading percentages. It seemed hardly possible, though, to make the charging stations take greater advantage of the low prices at night, without causing overloading issues. However, this could be achieved if a curtailment scheme was also included by means of a central coordination unit. Therefore, it is clear that different levels of complexity may bring benefits to the network, but they may also present drawbacks. The purpose of this work is to shed some light on the different possibilities and to provide hints on how to choose the most appropriate strategy for each situation.