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Abstract
Electrification is a key solution to an emissions-free transport sector, but it also poses a number of technical challenges to the power system. On the one side, a proper description of charging behaviour is a cornerstone for electric vehicle (EV) integration in the power system. This is increasingly relevant when considering controllable charging, which makes the assessment of charging behaviour even more challenging. On the other side, controlled EV charging can offer substantial benefits to the power system, but the role of user needs is often neglected. This thesis investigates the technical and economic benefits of EV integration in the power system, taking into account user needs and battery considerations. The initial focus of the thesis is on available data to derive EV charging profiles. Main sources of data are classified into three groups - surveys, car trials, and charger trials - and valuable information for the modelling of charging profiles is identified per each source. To understand how these sources can be used in EV studies, a minimum level of data for deriving EV charging profiles is defined: battery capacity, charging power, plug-in state of charge (SOC), plug-in/out time and charged energy. Since these data are often not directly available, guidelines and limitations to using available information and avoiding assumptions are provided. An additional complication arises when considering controlled charging profiles because their derivation depends on users’ willingness to participate in controlled charging, whose knowledge is still limited on a large scale. This leads to the second direction of this thesis, where techno-economic benefits of controllable charging are investigated by assessing how they can be used to generate value for end-users. First, unidirectional EV smart charging is compared with the introduction of a battery energy storage system (BESS) to facilitate and promote grid integration of residential photovoltaic production. The two solutions show similar results in terms of self-sufficiency and economic savings. However, with the current BESS prices, smart chargers are substantially more attractive economically. Second, the provision of primary frequency regulation with EVs and vehicle-to-grid (V2G) chargers is investigated. The profitability of the service is found to be largely dependent on costs associated with charger conversion losses. Indeed, the additional wear of the battery due to service provision seems to be limited compared to energy conversion losses, representing only a few percentage points of total costs. However, battery lifetime remains a major concern for EV users and reliable estimations of the capacity are of great importance. This thesis addresses how battery capacity can be estimated by reducing the usage of resources and time. EV battery capacity can be estimated by measuring the energy flowing into the battery pack during a full charge cycle. For safety reasons the battery pack is not directly accessible, thus existing practice relies on the usage of DC chargers and expensive measurement equipment. This thesis shows that accurate estimations can be carried out by relying on AC chargers and battery management system (BMS) measurements, significantly simplifying existing methods. Extensive experimental activities are carried out on six different EV batteries, where data from BMS and expensive experimental equipment are collected and compared. BMS data are shown to provide accurate measurements for battery capacity estimation, with errors limited to a few percentage points for the newest vehicles. However, lengthy battery capacity measurements are often inconvenient for power system application studies, where simple-to-realize models are necessary to simulate battery behaviour over long time periods. This thesis takes the first steps in developing and validating a Li-ion EV battery pack model without the need for disassembling the battery from the vehicle. The model describes battery behaviour with errors limited to a few percentage points for all considered electrothermal-aging dynamics and shows the importance of considering the interactions between them. Finally, working with EV batteries gives additional complications both during measurements and model implementation. This is discussed in the thesis, while insights from an implementation and field testing perspective are provided as a relevant starting point for future investigations.
Original language | English |
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Publisher | DTU Wind and Energy Systems |
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Number of pages | 202 |
DOIs | |
Publication status | Published - 2022 |
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Dive into the research topics of 'Grid integration of electric vehicles: battery degradation and user needs'. Together they form a unique fingerprint.Projects
- 1 Finished
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Large-scale integration of distributed energy resources in islanded power systems considering user needs
Calearo, L. (PhD Student), Grillo, S. (Examiner), Marinelli, M. (Main Supervisor), Ziras, H. (Supervisor), Turri, R. (Supervisor) & Korpås, M. (Examiner)
01/08/2019 → 02/11/2022
Project: PhD