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Aggregation and control of electric vehicles (EVs) via vehicle-to-grid (V2G) technologies is seen as a valid option for providing ancillary power system services. This work presents results from V2G-ready equipment tests and modelling. The technical capabilities of an EV connected to a commercial V2G charger are investigated when controlled either locally or remotely. The charger is characterized in terms of efficiency characteristics, activation time, response granularity, ramping-up/down time, accuracy and precision. Test results show the performance for different operating conditions, highlighting the importance of a good calibration and knowledge of the employed hardware when providing standard-compliant grid regulation services via V2G technology. Ultimately, a set of simulations demonstrates that the designed EV charger model replicates accurately the operating conditions of the real hardware.
The paper characterizes dynamics and modelling of a Lithium-ion battery. Theoretical formulation and literature review are combined to derive the necessary battery characterization. The three main dynamics for modeling the battery are: direct-current electrical equivalent circuit, state-ofcharge (SOC) and thermal dynamic. Furthermore, the capacity fade caused by degradation is considered as a fourth dynamic. Degradation is considered as the sum of calendar aging and cycling loss dynamics. The modeling procedure has general validity and can be used for different battery chemistries by changing specific parameters. The model is tailored for a 40 kWh Lithium Nickel Manganese Cobalt (NMC) Oxide battery, which is currently used in the Nissan LEAF 2018. Considering a user driving 45 km/day and the temperature of the years 2017 and 2018 in Denmark, the battery capacity fade is found to be between 2 and 5% of the battery capacity after two years of use. Degradation is highly dependent on the average level of SOC during the years.
Abstract-The purpose of this paper is to quantify the effect of biased system frequency deviations and charger losses in order for an aggregation of electric vehicles (EVs) to provide reliable primary frequency control (PFC). A data set consisting of one year of frequency measurements of the Nordic synchronous zone is used for the analysis. The average system frequency can be biased over the hour, which can lead storage units, performing PFC, to become fully charged or depleted. This paper presents statistical bounds on how variable the average system frequency can be on different time scales. Additionally, a method for calculating the expected energy loss caused by continuous charging and discharging is presented together with efficiency measurements of a commercial bidirectional EV charger. It is found that during a year, the energy balance of the service provider, relative to the grid, is within the calculated bounds. The efficiency losses are calculated and validated to have a linear relationship with the reserve capacity and the provision time.
Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
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