The impact of EV’s recharging on the planning of a typical Italian urban area The challenge of recharging Plug-in Electric Vehicles on distribution grids

摘要

The paper addresses the assessment and planning of low voltage distribution grids in the urban area ofa major Italian city considering the introduction of electric mobility. Two scenarios are analyzed: thefirst scenario, at 2020, considers that 10% of the total circulating vehicles in Italian major cities will beEV and that they will be mostly recharged on low voltage distribution networks. The second scenario,at 2030, considers that 20% of the total circulating vehicles in the same urban area will be EV,recharged on LV distribution networks while the remaining (in addition to the 20%) will use fastcharging stations connected to MV grids.Data collected by the smart metering system allowed the construction of load curves for all LV users,all lateral feeders, all main feeders and all transformers (cyan in Figure 1). Knowledge of topology ofLV networks and technical data for all components (transformers, main feeders and laterals feeders)allowed the evaluation of the hosting capacity both in term of “maximum power” available forrecharging of electric vehicles (dark blue line), and in term of the “maximum additional energy” thatmay flow on the LV network in a week within network technical constraints (the dark blue areas).That information was used to evaluate the maximum number of cars that can be recharged in parallelboth for slow mono phase charging (3.3 kW or 6.6 kW) and for fast three phases charging (10kW and20 kW) and the “maximum theoretical” number of cars that may be recharged in the LV using a“smart charge” system. The systematic analyze of load diagrams for all trunks of LV networksallowed to identify at the same time, both the maximum “hosting capacity” and to set thresholds afterwhich cable upgrading is needed. In addition to the analysis of all LV trunks, the study did consideralso the effect that uncontrolled charging may have on the daily load diagram of LV transformersplaced in residential or tertiary urban areas. The charging load diagram was, than, added to eachcharacteristic load diagrams both residential and tertiary grids.Cumulative curves show that quite a number of cars can be recharged in parallel with slow 3.3 kWcharging, without reinforcing the network and without any remote charging control. However for fastcharging remote charging control is necessary. The study highlighted that in the scenario 2020, theexpected penetration of cars in residential areas will require substitution of transformers in a verysmall number of substations, which will be even smaller in case of tertiary networks. The scenario2030 will differ a little, requesting an additional little percentage transformers’ upgrading. Additionally, the paper will present a methodology that allows to identify, weak trunks of LVnetworks (e.g. main feeders, lateral feeders ecc.) which substitution shall be planned to avoid failuresdue to the recharging of EV.