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Current harmonic modeling of aggregated electric vehicle loads in the low voltage grid
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-8720-748x
2021 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The proliferation of Electric Vehicles (EVs) poses new challenges for the Distribution System Operator (DSO). For example, the rectifiers that are used for charging EV batteries could significantly influence Power Quality (PQ), in terms of harmonic distortion. The emissions from individual EV, are well regulated by current harmonic emission standards. But what the aggregation of multiple EV loads will look like is still uncertain and the research being made in this area is still in its early stage. 

The DSO responsibilities include ensuring grid code compliance confirmed by PQ metering.  In general, 10 minute RMS values are sufficient. However, the large scale integration of non-linear loads, like EVs, could lead to new dynamic phenomena, possibly lost in the process of time aggregation.

In this thesis PQ and, in more detail, the concept of harmonics, and how this is related to EVs, is presented. A current-harmonic load model using power exponential functions and built from actual measurement data during the individual charging of four different fully electric vehicles was constructed. The model was based on individual emitted current harmonics as a function of state of charge (SOC), and was used to deterministically simulate the simultaneous charging of six vehicles fed from the same bus. The aggregation of current harmonics up to the 11th was simulated while randomizing battery SOC, the start of charging, and the kind of vehicle. Additionally, an investigation of the impact on aggregation in time was conducted.

The analysis clearly shows the importance of phase angle information, its correlation to SOC, and how the aggregation of EV loads is influenced by these factors. The analysis also shows that 10 minute RMS aggregation could lead to significant deviations from the “actual” (200ms) data.  This indicates that 10 minute value monitoring could lead to information losses.

Place, publisher, year, edition, pages
Västerås: Mälardalen University , 2021. , p. 59
Series
Mälardalen University Press Licentiate Theses, ISSN 1651-9256 ; 302
Keywords [en]
Electric Vehicles, current harmonics, modeling, aggregation, power-exponential functions
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-53169ISBN: 978-91-7485-494-7 (print)OAI: oai:DiVA.org:mdh-53169DiVA, id: diva2:1521978
Presentation
2021-03-05, Delta + digitalt via Zoom, Högskoleplan 1, Västerås, 09:00 (English)
Opponent
Supervisors
Funder
Knowledge FoundationAvailable from: 2021-01-25 Created: 2021-01-25 Last updated: 2021-03-03Bibliographically approved
List of papers
1. The impact of aggregation interval on current harmonic simulation of aggregated electric vehicle loads
Open this publication in new window or tab >>The impact of aggregation interval on current harmonic simulation of aggregated electric vehicle loads
2020 (English)In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, IEEE Computer Society , 2020, article id 9177899Conference paper, Published paper (Refereed)
Abstract [en]

Electric vehicles (EVs) poses new challenges for the Distribution System Operator (DSO). For example, EVs uses power electronic-based rectifiers for charging their batteries, an operation that could significantly impact Power Quality (PQ) in terms of harmonic distortion. The DSO responsibilities include ensuring grid code compliance confirmed by PQ metering. In general, 10 min rms values are sufficient. However, the large scale integration of non-linear loads, like EVs, could lead to new dynamic phenomena, possibly lost in the process of time aggregation.This paper presents an analysis of the impact on time aggregation (3 s-, 1min-and 10 min rms), when modelling current harmonics of aggregated EV loads, using power exponential functions. The results indicate that, while3 s rms and 1 min rms marginally affect the outcome, 10 min rms aggregation will lead to a significant deviation (>30%) in terms of maximum current harmonic magnitude. 

Place, publisher, year, edition, pages
IEEE Computer Society, 2020
Keywords
Aggregation interval, current harmonics, electric vehicles, power-exponential functions, simulations
National Category
Energy Systems
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-50209 (URN)10.1109/ICHQP46026.2020.9177899 (DOI)000589426600028 ()2-s2.0-85090469982 (Scopus ID)9781728136974 (ISBN)
Conference
19th International Conference on Harmonics and Quality of Power, ICHQP 2020; Dubai; United Arab Emirates; 6 July 2020 through 7 July 2020
Available from: 2020-09-17 Created: 2020-09-17 Last updated: 2021-01-25Bibliographically approved
2. Measurement-based current-harmonics modeling of aggregated electric-vehicle loads using power-exponential functions
Open this publication in new window or tab >>Measurement-based current-harmonics modeling of aggregated electric-vehicle loads using power-exponential functions
2020 (English)In: World Electric Vehicle Journal, E-ISSN 2032-6653, Vol. 11, no 3, article id 51Article in journal (Refereed) Published
Abstract [en]

This paper presents an aggregate current-harmonic load model using power exponential functions and built from actual measurement data during the individual charging of four dierent fully electric vehicles. The model is based on individual emitted current harmonics as a function of state of charge (SOC), and was used to deterministically simulate the simultaneous charging of six vehicles fed from the same bus. The aggregation of current harmonics up to the 11th was simulated in order to find the circumstances when maximal current-harmonic magnitude occurs, and the phase-angle location. The number of possible identical vehicles was set to four, while battery SOC, the start of charging, and the kind of vehicle were randomized. The results are presented in tables, graphs, and polar plots. Even though simulations did not consider the surrounding harmonics, supply-voltage variation, or network impedance, this paper presents an innovative modeling approach that gives valuable information on the individual current-harmonic contribution of aggregated electric-vehicle loads. With the future implementation of vehicle-to-grid technology, this way of modeling presents new opportunities to predict the harmonic outcome of multiple electric vehicles charging. 

Place, publisher, year, edition, pages
MDPI AG, 2020
Keywords
Aggregated loads, Current-harmonic summation, Electric vehicles, Modeling, Power exponential functions, Charging (batteries), Exponential functions, Harmonic analysis, Harmonic functions, Actual measurements, Current harmonics, Innovative models, Maximal current, Measurement-based, Phase angles, State of charge, Supply voltage variation, Vehicle-to-grid
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Vehicle Engineering
Identifiers
urn:nbn:se:mdh:diva-49806 (URN)10.3390/WEVJ11030051 (DOI)000937475300005 ()2-s2.0-85089491136 (Scopus ID)
Available from: 2020-10-08 Created: 2020-10-08 Last updated: 2024-04-29Bibliographically approved

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Foskolos, Georgios

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