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Protection Strategy Impact on the Interaction Between Converters
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- Author / Creator
- Zaidi, Syeda Narjis F.
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The availability of the renewable energy sources in remote onshore and offshore locations and the advancements of power electronics have given rise to the use of high voltage direct current (HVDC) transmission for bulk power transmission. HVDC technology is more economical than high voltage alternating current (HVAC) technology for power transmission over distances longer than 500 km. Moreover, HVDC systems can connect unsynchronized AC networks and provide a controlled transfer of active power.
HVDC systems utilizing voltage source converter (VSC) technology are widely used for constructing multiterminal DC (MTDC) systems for connection of renewable energy sources to the grid and are a promising technology for future realization of large HVDC grids. VSCs based on the modular multilevel converter (MMC) technology provide higher power quality, reliability, and efficiency as compared to other multilevel converter topologies. Therefore, MMCs are prominent candidates for various HVDC applications such as MTDC grids, offshore wind farm systems, and static synchronous compensators (STATCOMs).
In HVDC systems with more than one point-to-point DC link, faults occurring on one DC link affect all healthy converters, which are in close proximity to the faulted converter. The degree of the impact of this fault on healthy converters depends on the type of protection strategy used for DC fault clearance. The literature proposes several protection strategies based on AC circuit breakers (ACCBs), DC circuit breakers (DCCBs), fault blocking converters, and half-bridge MMCs (HB-MMCs) augmented with various configurations of thyristors to clear the DC fault. In this thesis, firstly, the impact of different protection strategies on the point of common coupling (PCC) and the operation of healthy converters in a test system comprising of HB-MMCs is evaluated. Secondly, the faulted converter is operated in the STATCOM mode under different protection strategies, and its impacts on the PCC and the healthy converter are analyzed and compared. In this study, three protection strategies comprising of ACCBs, DCCBs, and HB-MMCs augmented with three-phase full-wave thyristor bridges (Graetz bridges) are considered.
Study results show that (i) the protection strategy using DCCBs enables the PCC voltage and active power of the healthy converter to reach their steady-state values faster than the other two protection strategies, (ii) the protection strategy using HB-MMCs augmented with Graetz bridges allows the PCC voltage and active power of the healthy converter to reach their steady-state values faster than the protection strategy using ACCBs, (iii) the protection strategy using DCCBs has the shortest fault clearance time than the other two protection strategies, (iv) the protection strategy using HB-MMCs augmented with Graetz bridges eliminates the fault current faster than the protection strategy using ACCBs, (v) the STATCOM mode of operation of the faulted converter restores the PCC voltage to its pre-fault value, whereas without the STATCOM mode, the steady-state value of the PCC voltage is higher than its pre-fault value, and (vi) the STATCOM mode of operation of the faulted converter allows active power of the healthy converter to reach its steady-state value faster than without the STATCOM mode, thereby increasing the reliability and security of the healthy link. -
- Graduation date
- Fall 2020
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.