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Analysis of DC Breaking Phenomenon in DC Microgrids

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Thesis(3.53 MB)

Date

2024

Authors

Supervisor

Lie, Tek Tjing
Gunawardane, Kosala

Item type

Thesis

Degree name

Doctor of Philosophy

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Publisher

Auckland University of Technology

Abstract

This PhD thesis explores the pivotal role of the switching phenomenon in the operational dynamics of DC microgrids (DC MGs), emphasizing the design and optimization of Solid-State DC Circuit Breakers (DCCBs) to manage switching surges. Predominantly switching surges pose significant challenges in DC systems, necessitating innovative solutions for effective mitigation. This research bridges the existing knowledge gap by introducing and evaluating advanced surge absorption techniques, aiming to enhance the reliability and protection of DC MG systems. The study's central focus lies in the design, modeling, and experimental validation of 48VDC solid-state circuit breakers, with a threshold interruption current ranging between 10A and 20A. This selection corresponds to the voltage level specified in the Future Architecture of Network (FAN) Project and the capabilities of the laboratory's experimental facilities, providing a practical basis for testing. Various solid-state switches, including Insulated Gate Bipolar Transistors (IGBTs), Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), and Thyristors, along with their gate drivers, are utilized to investigate their performance under worst-case scenarios and real-world conditions. To address the challenges of surge absorption, three novel techniques are proposed and extensively analyzed: 1. Bidirectional Thyristor-Capacitor (BiTriCap) Technique This technique introduces a bypassed path with a snubber subcircuit comprising two antiparallel thyristors. These thyristors absorb the current surge during fault conditions and discharge a capacitor during normal operation. The BiTriCap technique effectively bypasses the surge through the capacitor, leveraging its charge-discharge dynamics. Its scalability across a wide voltage and current range makes it a versatile solution. Experimental validation considers worst-case scenarios with inductances in the millihenry range to simulate high-surge conditions. 2. Divided Surge Absorption Technique (DSAT) The DSAT employs surge division principles, redirecting the load-side surge through a load-side diode and the line-side surge into a bypassed thyristor-RC subcircuit. This technique demonstrates high reliability and rapid surge absorption, significantly reducing voltage stress across the main switch. 3. Bidirectional Passive Technique (BPT) Designed for bidirectional DC applications, the BPT uses a passive RCD subcircuit to filter and absorb surges. This method minimizes surge voltage across the main switch while simplifying circuit complexity by relying on fewer active components, making it a cost-effective and efficient solution for complex systems. The thesis includes comparative analyses of these proposed techniques against conventional models, highlighting their efficacy in surge absorption, operational reliability, and scalability. Experimental results confirm the superiority of the proposed methods, offering significant improvements in performance and resilience. This research contributes a comprehensive framework for the design and implementation of advanced DCCBs, paving the way for more robust and efficient DC MG systems. The proposed techniques demonstrate potential applicability across various voltage and current ranges, establishing a foundation for further exploration and commercialization in DC power systems.

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http://hdl.handle.net/10292/19263

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Doctoral Theses