Transformer-less Grid-Tied AC Module Systems Suitable for Single-Phase Renewable Energy-Based Applications

Barzegarkho, Reza

Transformer-less Grid-Tied AC Module Systems Suitable for Single-Phase Renewable Energy-Based Applications

Barzegarkho, Reza

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Publication Type:: Thesis
Issue Date:: 2023

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Field	Value	Language
dc.contributor.author	Barzegarkho, Reza
dc.date.accessioned	2023-07-14T01:18:20Z
dc.date.available	2023-07-14T01:18:20Z
dc.date.issued	2023
dc.identifier.uri	http://hdl.handle.net/10453/171495
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	Grid-tied converters/inverters with a transformerless (TL) circuit configuration are an efficient power electronics interface between the power grid and renewable energy resources. Such a tremendous inclination to use the TL converters originates from their appropriate power density and higher overall efficiency with a lower manufacturing cost in comparison to their transformer-based counterparts. However, detaching the galvanic isolated transformer from the converter and the grid and using the commercially available two or three-level voltage source inverters lead the following challenges: 1) Variable common mode voltage (CMV) and the ground leakage current problem, 2) the need for another power processing stage to meet the minimum requirement of the grid voltage amplitude while utilizing a relatively low value of the dc input voltage, and 3) power quality enhancement issue. The aim of this thesis is to investigate the above-mentioned constrains/challenges among various developed versions of the existing TL inverters, and accordingly propose several new circuit configurations to address such issues. All the proposed converters/inverters are able to generate a multilevel staircase output voltage waveform using a single dc source leading to improve the injected power quality and reduce the need for large bulky interfaced filters. To alleviate the effect of high frequency CMV in grid-connected PV systems and to nullify the concern of leakage current, the design configuration of all the proposed topologies is either based on a common-ground circuit architecture or a mid-point-clamping technique. Through the incorporation of switched-capacitor and/or switched-boost technique, all the proposed structures possess either a static or dynamic voltage conversion gain, which make them an attractive choice when the input dc source is variable and low. Extending the operating range of the grid-connected TL converters for a wide range of the input dc voltage, reduction on voltage/current stress profile of the switches, circuit extension capability to generate larger number of output voltage levels, and reduced number of required power electronics elements, i.e., switches, gate drivers, inductors, and capacitors are some other important characteristics of the proposed topologies. Since the major goal of each of the proposed TL-based grid-tied inverters/converters is to inject a tightly controlled current to the grid, the performance of all the proposed structures is governed within a closed-loop control platform. Comparative study and the design guidance of the proposed converters are developed. And finally, several simulation and experimental results are presented to prove the feasibility and correct operation of each of the proposed converters.	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/10453/171495/1/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	© 2023 Reza Barzegarkho
dc.rights	au.edu.uts.lib/cph
dc.title	Transformer-less Grid-Tied AC Module Systems Suitable for Single-Phase Renewable Energy-Based Applications	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

Grid-tied converters/inverters with a transformerless (TL) circuit configuration are an efficient power electronics interface between the power grid and renewable energy resources. Such a tremendous inclination to use the TL converters originates from their appropriate power density and higher overall efficiency with a lower manufacturing cost in comparison to their transformer-based counterparts. However, detaching the galvanic isolated transformer from the converter and the grid and using the commercially available two or three-level voltage source inverters lead the following challenges: 1) Variable common mode voltage (CMV) and the ground leakage current problem, 2) the need for another power processing stage to meet the minimum requirement of the grid voltage amplitude while utilizing a relatively low value of the dc input voltage, and 3) power quality enhancement issue. The aim of this thesis is to investigate the above-mentioned constrains/challenges among various developed versions of the existing TL inverters, and accordingly propose several new circuit configurations to address such issues. All the proposed converters/inverters are able to generate a multilevel staircase output voltage waveform using a single dc source leading to improve the injected power quality and reduce the need for large bulky interfaced filters. To alleviate the effect of high frequency CMV in grid-connected PV systems and to nullify the concern of leakage current, the design configuration of all the proposed topologies is either based on a common-ground circuit architecture or a mid-point-clamping technique. Through the incorporation of switched-capacitor and/or switched-boost technique, all the proposed structures possess either a static or dynamic voltage conversion gain, which make them an attractive choice when the input dc source is variable and low. Extending the operating range of the grid-connected TL converters for a wide range of the input dc voltage, reduction on voltage/current stress profile of the switches, circuit extension capability to generate larger number of output voltage levels, and reduced number of required power electronics elements, i.e., switches, gate drivers, inductors, and capacitors are some other important characteristics of the proposed topologies. Since the major goal of each of the proposed TL-based grid-tied inverters/converters is to inject a tightly controlled current to the grid, the performance of all the proposed structures is governed within a closed-loop control platform. Comparative study and the design guidance of the proposed converters are developed. And finally, several simulation and experimental results are presented to prove the feasibility and correct operation of each of the proposed converters.

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