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
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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.