Research on islanding detection method and grid-connected stability of DC microgrid based on adaptive frequency disturbance

Shi, Tianling

Research on islanding detection method and grid-connected stability of DC microgrid based on adaptive frequency disturbance

Shi, Tianling

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Publication Type:: Thesis
Issue Date:: 2024

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Field	Value	Language
dc.contributor.author	Shi, Tianling
dc.date.accessioned	2025-03-28T01:41:56Z
dc.date.available	2025-03-28T01:41:56Z
dc.date.issued	2024
dc.identifier.uri	http://hdl.handle.net/10453/186262
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	In recent years, distributed generators (DGs) have been developing rapidly to achieve a low-carbon energy transition. Owing to the high conversion efficiency and simple control structure of the DC microgrid, it is regarded as a promising technology for integrating a high proportion of DGs. During the operation of the DC microgrid, affected by unexpected line faults and severe weather, the microgrid will disconnect from the utility grid and operate in the islanding mode. When the DG power exactly neutralizes the load power, the occurrence of islanding events will not cause any variation in the voltage at the point of common coupling (PCC), namely unconscious islanding. Failure detection of unconscious islanding will seriously threaten the security of DGs and maintenance personnel. Therefore, the rapid and accurate islanding detection is the essential basis for the safety and protection of DC microgrids. Selected frequency islanding detection is gaining widespread acceptance in DC microgrids due to its good power quality. However, the selected static disturbance frequency at a specific operating state causes the expansion of the non-detection zone (NDZ) and the decrease of the detection speed under different system power conditions. In this thesis, the sensitivity model from PCC voltage to current perturbation is developed first to intuitively reveal the mechanism of the occurrence of the NDZ. On this basis, an islanding detection method (IDM) based on adaptive frequency disturbance is developed for DC microgrids. In this manner, the detection speed is improved while the zero NDZ is also achieved. Secondly, an equivalent high-order model of the DG equipped with the proposed IDM is established to reveal the limitation of the frequency domain-based design method. On this basis, the dynamics model of the PCC voltage is investigated and simplified, which lays a good foundation for the derivation of the time domain model. More importantly, an islanding detection time calculation method based on voltage envelope is proposed, and it provides detection time constraints on the islanding detection parameters. Finally, the DC output impedance model of the voltage source converter and DGs are developed to reveal the instability mechanism caused by the IDM. Then, a communication-less active damping method based on a notch filter is proposed. In this manner, the stability of the grid-connected system can be improved while the islanding detecting speed is enhanced.	en_US.UTF-8
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/186262/1/thesis.pdf
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	© 2024 Tianling Shi
dc.rights	au.edu.uts.lib/cph
dc.title	Research on islanding detection method and grid-connected stability of DC microgrid based on adaptive frequency disturbance	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

In recent years, distributed generators (DGs) have been developing rapidly to achieve a low-carbon energy transition. Owing to the high conversion efficiency and simple control structure of the DC microgrid, it is regarded as a promising technology for integrating a high proportion of DGs. During the operation of the DC microgrid, affected by unexpected line faults and severe weather, the microgrid will disconnect from the utility grid and operate in the islanding mode. When the DG power exactly neutralizes the load power, the occurrence of islanding events will not cause any variation in the voltage at the point of common coupling (PCC), namely unconscious islanding. Failure detection of unconscious islanding will seriously threaten the security of DGs and maintenance personnel. Therefore, the rapid and accurate islanding detection is the essential basis for the safety and protection of DC microgrids. Selected frequency islanding detection is gaining widespread acceptance in DC microgrids due to its good power quality. However, the selected static disturbance frequency at a specific operating state causes the expansion of the non-detection zone (NDZ) and the decrease of the detection speed under different system power conditions. In this thesis, the sensitivity model from PCC voltage to current perturbation is developed first to intuitively reveal the mechanism of the occurrence of the NDZ. On this basis, an islanding detection method (IDM) based on adaptive frequency disturbance is developed for DC microgrids. In this manner, the detection speed is improved while the zero NDZ is also achieved. Secondly, an equivalent high-order model of the DG equipped with the proposed IDM is established to reveal the limitation of the frequency domain-based design method. On this basis, the dynamics model of the PCC voltage is investigated and simplified, which lays a good foundation for the derivation of the time domain model. More importantly, an islanding detection time calculation method based on voltage envelope is proposed, and it provides detection time constraints on the islanding detection parameters. Finally, the DC output impedance model of the voltage source converter and DGs are developed to reveal the instability mechanism caused by the IDM. Then, a communication-less active damping method based on a notch filter is proposed. In this manner, the stability of the grid-connected system can be improved while the islanding detecting speed is enhanced.

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