Sandschulte, Arne 
ORCID: 0000-0002-3041-2271
(2022)
Scale and Bandwidth Extension of Power Converter–Based Impedance Spectroscopy.
PhD thesis, University of Liverpool.
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Abstract
The ongoing energy transition from fossil fuels to renewable energy sources has led to a substantial rise in the use of electrochemical energy storage devices. For example, electric vehicles and energy storage for distributed generation are two applications in which batteries are being widely adopted as energy storage solutions. This research project is concerned with the development of diagnostic monitoring techniques for electrochemical energy storage devices, with a particular focus on lithium-ion batteries. Diagnostic monitoring is a critical part of systems employing such energy storage devices, as it ensures their safe, reliable, and efficient operation. This makes accurate diagnostic monitoring techniques essential for the successful adoption of the aforementioned technologies. Electrochemical Impedance Spectroscopy (EIS) is an established technique that is used widely in the characterisation of electrochemical systems, including batteries. Recent work has focused on a novel power converter-based EIS implementation, which has the potential of making EIS accessible outside of research laboratories. The aim of this work is to contribute to the development of the power converter–based EIS technique, focusing primarily on extending its scale and bandwidth. A method is presented to compensate for variations in the state of charge, allowing the measurement bandwidth to be extended to frequencies in the millihertz range. Further, a strategy is developed to extend the upper end of the measurement bandwidth when the available sampling rate is limited. An experimental setup involving signal acquisition and real-time control capabilities is built. Experimental results allow the correct operation of the system to be validated, thus permitting for the first time a battery pack consisting of 16 series-connected lithium iron phosphate cells to be monitored using the power converter-based EIS method. With the batteries discharging at a dc current of 20 A, the controller is able to introduce the ac current perturbations in the range from 10 mHz up to 100 Hz. The measurement precision is shown to be high enough to allow meaningful impedance variations to be detected: both due to small differences between cells in a battery pack, and also due to changes in the state of charge.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering > School of Electrical Engineering, Electronics and Computer Science |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 16 Aug 2023 15:40 |
| Last Modified: | 16 Aug 2023 15:41 |
| DOI: | 10.17638/03170312 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3170312 |
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