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Advanced Control Techniques for Grid-Interactive Smart Inverters under Asymmetrical Conditions
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- Author / Creator
- Masoud Mohammadalizadeh Shabestary
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Grid-interactive smart inverters (GSIs) are becoming the main interface for integrating modern power units, such as renewable energies, energy storage systems, electric vehicles, distributed generation (DG) units, microgrids, and high-voltage direct-current transmission systems into smart power grids. Their expected high integration in future smart grids brings certain reliability and complexity challenges. Tackling these challenges with advanced control techniques can provide more efficient and optimal operation in future highly interconnected power grids. Riding through abnormalities while supporting host grids by smart inverters is one of these challenges which has attracted a lot of attention among system operators, regulatory organizations, manufacturing companies, and academia. This research project thus aims to present novel techniques in four stages for optimal and more reliable operation of GSIs, utilized in different configurations, under asymmetric grid conditions. In the first stage, a comprehensive control scheme, with multiple objectives, is proposed for the optimal operation of a single GSI under unbalanced grid conditions. These optimal behaviors bring significant advantages to the emerging GSIs, empowering them to be more fault resilient and smartly responsive to abnormal grid conditions. They also provide noteworthy benefits to the host grid such as improving its stability, delivering maximum ancillary services, avoiding unnecessary outages, better complying with the grid interconnection codes, and increasing overall efficiency, reliability, and profitability. In the second stage, this research proposes a regulation guideline for riding through asymmetric faults as well as dynamic flexible support of the grid. To date, most of the available grid codes only focus on the regulation of the DG operation under balanced faults due to the complexity, lacking the proper remedies for more common unbalanced conditions. Implementing in different test cases and using comparative analyses, the proposed regulation guideline and its unique control technique are proven to be very effective and superior to the state-of-the-art methods. They can thus be adopted by the updated versions of grid codes for more efficient integration of large GSIs and DG units. In the third stage, a novel voltage support scheme is proposed with improved accuracy in regulating the phase voltages within the pre-set safety limits, by (1) considering the zero-sequence voltage compensation, (2) considering the output active power and being adaptive to complex grid impedance, (3) augmenting the adjustable limited active power oscillation and the maximum active power delivery strategies. This empowers large DG units to provide their maximum asymmetric support to the grid without a negative impact on their performance. In the last stage of the thesis, the proposed techniques are extended for multiple GSIs structures: (1) parallel-operated grid-interactive inverters (e.g., in hybrid energy sources) and (2) multiple distributed inverters (e.g., in multi-DG active distribution networks). The effectiveness of the proposed techniques is validated using simulation and experimental results. The proposed techniques facilitate the effective integration of renewable energy resources, via reliable GSIs, into smart power grids.
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- Graduation date
- Spring 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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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.