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Energy storage system of the converted discharge energy under VLF testing conditions

  • Power cables play an important role in power grids. Insulation faults in cables can have adverse effects on the operating behaviour. These effects can be assessed through an AC withstand test by using a very-low frequency high voltage generator. This generator produces a sinusoidal voltage waveform at 0.1Hz with high voltage levels up to 65kV peak. During the quality assessment, the power cable is repeatedly charged and discharged. The discharging process is done by a discharging circuit where the energy is dissipated thermally. But to reuse the dissipated energy a novel extension in form of an energy storage system is presented. This thesis, therefore, describes the design process of an energy storage system that allows the temporary storage of the discharge energy. The developed system is composed of a bidirectional DC/DC converter and an aluminium electrolytic capacitor as storage type. Based on the maximum VLF system ratings the energy storage unit is dimensioned and sized. The effective power flow control between the storage system and the available discharge energy is done by a synchronous buck-boost converter. This bidirectional converter works in continuous conduction mode over the complete charging phase. Together with a theoretical analysis of the underlying problem and the use of converter analysis methods the selected synchronous buck-boost converter is dimensioned and sized. In addition, a state space AC modeling of the converter with its electrical uncertainties is conducted. With the converters AC model, the controller is designed. A closed-loop input converter current control scheme based on a proportional-integral controller is implemented. The system assessment is done by a model-based hardware implementation in Matlab Simulink and Plecs Blockset. The system is rated to store discharge energies up to 4.3kJ in a short charging period of 2.5s. The maximum peak power during the charging phase is 2.7kW. The digital proportional-integral controller is implemented through an emulation process of the designed analog controller. Based on a C-code implementation of the digital controller the gap between the real hardware is reduced. During the design process theoretical calculations are made and reveal that designing a capacitor storage unit has a direct impact on the peak system currents and also impose also limitations on permissible DC voltage ranges on electrical components. The developed energy storage system and its power flow control strategy were investigated through simulation studies. The results show proper charging of the energy storage medium. In addition, also a statement of the final technical feasibility is made. In total, this work summarizes a detailed design process of the energy storage system. This proof of concept is intended to further advance the system integration.

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Metadaten
Author:Maximilian Preiss
DOI:https://doi.org/10.25924/opus-4615
Advisor:André Mitterbacher
Document Type:Master's Thesis
Language:English
Year of publication:2022
Publishing Institution:FH Vorarlberg (Fachhochschule Vorarlberg)
Granting Institution:FH Vorarlberg (Fachhochschule Vorarlberg)
Release Date:2022/10/17
Tag:DC/DC power converter; aluminium electrolytic capacitor; buck-boost converter; digital control strategy; energy storage system
Number of pages:XVII, 113
DDC classes:600 Technik, Medizin, angewandte Wissenschaften
Open Access?:ja
Course of Studies:Mechatronics
Licence (German):License LogoUrhG - The Austrian Copyright Act applies - Es gilt das österr. Urheberrechtsgesetz