Charging of plug-in electric vehicle fleets in urban environment

Juuso Lindgren

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

This thesis studies the performance and charging of electric vehicle fleets in an urban environment,using three research questions that focused on: 1) allocation of limited total charging power; 2) effect of different charging infrastructure parameters on the total distance driven in electric-only mode, and; 3) effect of cold and warm ambient temperature on the performance and charging of the fleet, respectively. An agent-based computer simulation was employed, with parameters tuned such that the resulting vehicle travel patterns would resemble the observed behaviour of conventional cars in the city of Helsinki, Finland. Two different simulators were used: in the first one, the vehicles travel in a node network according to a stochastic trip-generation algorithm. In the second one, the vehicles' status changes according to the results of a Finnish travel survey. Two different vehicle battery models were also used: a simple linear "kilowatt-hour counter" and a more advanced battery model with temperature dependency. It was found that smart charging power allocation can improve the total distance driven in electric-only mode compared to a "dumb" equal allocation strategy, but the gain is heavily dependent on the battery capacity. If no predictions about the future are made, the gain is small (1%), but with full knowledge on future travel patterns, it increases to over 5%. In general, more power should be allocated to vehicles that depart earlier and travel longer distances before their next charging session. Among plug-in hybrid electric vehicles, those with small battery capacity gain the most benefit from improved charging infrastructure, in terms of total distance driven in electric-only mode. Battery capacity holds the highest potential out of all parameters tested. The second and third most important infrastructure parameters are the number of parking slots around a single charging station and the number of these charging stations. A charging station should be placed in a central location with several parking slots around it, to allow sequential charging of multiple vehicles by switching the charging cable from one vehicle to the next. Low battery temperature has a negative impact on fully electric vehicle charging. This manifests as slightly reduced median state of charge (3–6%-units) for the vehicle fleet and significantly lower median charging rate (15% in terms of self-weighted mean charging power). Battery heating can be used to achieve higher state of charge, as well as increased charging rate for certain vehicles. Deviation from the close-to-optimal +20°C temperature for the cabin and the battery results in reduced efficiency (km/kWh) and eventually reduced number of planned trips that can be realized. Cabin preconditioning and active battery thermal management improve the median efficiency of the fleet around 8-9% at −10°C and +40°C.
Translated title of the contributionPlug-in-sähköajoneuvolaivueiden lataaminen kaupunkiympäristössä
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Lund, Peter, Supervising Professor
  • Lund, Peter, Thesis Advisor
Publisher
Print ISBNs978-952-60-7739-0
Electronic ISBNs978-952-60-7740-6
Publication statusPublished - 2017
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • electric vehicle
  • charging infrastructure
  • charging power
  • battery
  • temperature

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