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Analysis, design and control of LCC resonant power converters

Gilbert, Adam John (2007) Analysis, design and control of LCC resonant power converters. PhD thesis, University of Sheffield.

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Through the judicious and efficient use of energy in both domestic and commercial products, the rate at which the world's fossil fuels and mineral resources are depleted, can be minimised, thereby securing energy reserves for the future. This thesis considers a number energy saving roles the power systems engineer can contribute, with specific emphasis on the impact of improving DC-DC power converters for providing significant energy savings. It is shown that by increasing the efficiency of such converters, through the greater use of switched-mode supplies, huge reductions in the production of green house gases can be obtained. Moreover, resonant converters, a specific subset of switched-mode supply, are identified as a candidate technology for future widespread use. Since the behavioural dynamics of resonant converters are inherently non-linear, the analysis and design of such systems is extremely complex when compared to other families of converter, and has been a critical factor in impeding their widespread adoption. This thesis therefore aims to provide new tools to aid the designer in overcoming such reservations. Novel analysis and design procedures are developed in Chapters 3 and 4, for the series-parallel inductively-smoothed and capacitively smoothed resonant converters, respectively, which, unlike previously reported techniques, allows a designer with little knowledge of resonant converter systems to readily select preferred components for the resonant tank based on design specifications. Specifically, the analysis in Chapter 3 develops a new methodology that extends 'Fundamental Mode Analysis' (FMA) techniques, and provides a first-order estimate of component values to meet a given specification. Chapter 4 then considers the steady state behaviour of the converter, from a state-plane perspective, and provides exact component values and electrical stress analyses based on ideal converter characteristics. The presented methodology normalises the converter behaviour, such that the gain of the resonant tank (at the resonant frequency and minimum load resistance), and the ratio between the two tank capacitances, fully characterises the behaviour of the converter as the load is varied and the output voltage regulated. To further aid the designer, various new design curves are presented that makes the use of traditional, and complicated, iterative calculation procedures, redundant. Chapter 5 further develops a high speed 1 transient analysis technique for resonant converters that is shown to provide a IOOx reduction in simulation times compared to integration-based methods, by considering only signal envelopes. The technique is shown to significantly aid in the design of variable frequency controllers. Chapters 6 and 7 further consider the control of resonant converters. Specifically, Chapter 6 derives a novel self-oscillating control methodology, which, unlike previously published techniques, approximately linearises the large-signal dynamics of the converter, and thereby readily enables the robust design of an outer loop controller for output-voltage/-current regulation purposes. Additionally, in contrast to other methods for the robust control of resonant converters, little knowledge of the converter state-variables is required, thereby minimising the number of high-bandwidth sensors necessary. The technique simply requires the real-time polarity of current-flow through the series-inductor, and output-voltage/-current, to be known. Through additional (optional) measurement of supply-voltage and a feed-forward control component, the effects of supply-voltage disturbance are shown to be greatly attenuated, thereby requiring reduced outer-loop control action and improving overall regulation performance. Finally, Chapter 7 considers the control of resonant converters when the cost of isolated feedback sensors is prohibitive. Unlike traditional techniques, where the output-voltage is estimated under fixed load conditions, through use of an Extended Kalman Filter observer scheme, non-isolated measurements are used to estimate both the output-voltage and the load-resistance. The load resistance estimation is then used to aid in fault-detection and for improving transient dynamic behaviour via the provision of feed-forward action, resulting in safer converter operation and enhanced regulation performance, and, ultimately, reduced cost.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Electronic and Electrical Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.633052
Depositing User: EThOS Import Sheffield
Date Deposited: 26 Oct 2016 14:44
Last Modified: 26 Oct 2016 14:44
URI: http://etheses.whiterose.ac.uk/id/eprint/15028

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