Modelling, analysis and design of LCLC resonant power converters.

The thesis investigates the modelling, analysis, design and control of 4th -order LCLC resonant power converters. Both voltage-output and current-output variants, are considered. Key research outcomes are the derivation of new frequency- and time-domain models of the converters, based on normalised component ratios, and including the effects that parasitic elements have on circuit behaviour, and a detailed account of multi-resonant characteristics; extensions to the use of cyclicmode modelling methods for application to LCLC converters, to provide rapid steady-state analysis, thereby facilitating the use of the derived methodologies as part of an interactive design tool; the formulation of analytical methods to predict the electrical stresses on tank components-an important consideration when designing resonant converters, as they are often higher than for hard-switched converter counterparts; the characterisation of both continuous and discontinuous modes of operation and the boundary conditions that separate them; and a substantial treatment of the modelling, analysis and design of LCLC converters that can provide multiple regulated outputs by the integrated control of both excitation frequency and pulse-width-modulation. The proposed methodologies are employed, for validation purposes, in the realisation of two proof-of concept demonstrator converters. The first, to satisfy the requirements for delivering 65V (rms) to an electrode-less, SW, fluorescent lamp, to improve energy efficiency and lifetime, and operating at a nominal frequency of 2.65 MHz, is used to demonstrate capacitively-coupled operation through the lamp tube, thereby mitigating the normally detrimental effects of excitation via the electrodes. The second prototype considers the realization of an LCLC resonant power supply that can provide multiple regulated outputs without the need for post-regulation circuitry. The two outputs of the supply are independently, closed-loop regulated, to provide asymmetrical output voltage distributions, using a combination of frequency- and duty-control. Although, an analysis of the supply shows that the behaviour is extremely complex, due, in particular, to the highly non-linear interaction between the mUltiple outputs and parasitic inductances, and rectifier, an analysis to provide optimum performance characteristics, is proposed. Moreover, a PICIFPGA-based digital controller is developed that allows control of the transient performance of both outputs under start-up and steady-state conditions.