The thesis describes theoretical and experimental studies on the chaotic behaviour of a peak current-mode controlled boost converter, a parallel two-module peak current-mode controlled DC-DC boost converter, and a peak current-mode controlled power factor correction (PFC) boost converter. The research concentrates on converters which do not have voltage control loops, since the main interest is in the intrinsic mechanism of chaotic behaviour. These converters produce sub-harmonics of the clock frequency at certain values of the reference current I[ref] and input voltage V[in], and may behave in a chaotic manner, whereby the frequency spectrum of the inductor becomes continuous. Non-linear maps for each of the converters are derived using discrete time modelling and numerical iteration of the maps produce bifurcation diagrams which indicate the presence of subharmonics and chaotic operation. In order to check the validity of the analysis, MATLAB/SIMULINK models for the converters are developed. A comparison is made between waveforms obtained from experimental converters, with those produced by the MATLAB/SIMULINK models of the converters. The experimental and theoretical results are also compared with the bifurcation points predicted by the bifurcation diagrams. The simulated waveforms show excellent agreement, with both the experimental waveforms and the transitions predicted by the bifurcation diagrams. The thesis presents the first application of a delayed feedback control scheme for eliminating chaotic behaviour in both the DC-DC boost converter and the PFC boost converter. Experimental results and FORTRAN simulations show the effectiveness and robustness of the scheme. FORTRAN simulations are found to be in close agreement with experimental results and the bifurcation diagrams. A theoretical comparison is made between the above converters controlled using delayed feedback control and the popular slope compensation method. It is shown that delayed feedback control is a simpler scheme and has a better performance than that for slope compensation.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Master Thesis presents the study and proposes a digital control system applied to the PFC boost converter operating in mixed conduction mode. The motivation to this subject, a bibliographic review of the existing current control techniques and the objectives of this work are presented in the first chapter. The control system is composed of a current loop, which has the objectives to provide low harmonic content to the input current and high power factor to the converter, and a voltage loop, which has the goal to regulate the output voltage of the converter. Initially, the study of the conduction modes of the PFC boost converter, highlighting their operation conditions, and details of the mixed conduction mode operation are showed. Next, two predictive digital current controllers with feedforward action are approached in details, including the equations deduction, block diagram, operation process, design, simulation results and parametric variation analysis. A comparative analysis between both controllers is also accomplished. The proportional-integral voltage controller is presented following, comprising its structure, design and simulation results. After, issues related to the practical implementation of the converter and control system, as the converter design and the control device programming, are shown. Finally, the experimental results obtained through the implementation of the proposed system, including the waveforms acquired using a prototype constructed in laboratory and the quality indexes as the power factor and the total harmonic distortion, are presented with the purpose to validate and prove the content of this work. / Esta Dissertação de Mestrado apresenta o estudo e propõe um sistema de controle digital para o conversor boost PFC operando no modo de condução mista. A motivação para este assunto, uma revisão bibliográfica das técnicas de controle de corrente existentes e os objetivos do trabalho são apresentados no capítulo introdutório. O sistema de controle é composto de uma malha de corrente, que tem por objetivo proporcionar baixo conteúdo harmônico para a corrente de entrada e alto fator de potência para o conversor, e uma malha de tensão, que tem por objetivo regular a tensão de saída do conversor. Inicialmente, o estudo dos modos de condução do conversor boost PFC, destacando as suas condições de operação, e detalhes da operação no modo de condução mista são mostrados. Em seguida, dois controladores digitais preditivos de corrente com ação feedforward são abordados em detalhes, incluindo o equacionamento, diagrama de blocos, funcionamento, projeto, resultados de simulação e análise da variação paramétrica. Uma análise comparativa entre ambos também é realizada. O controlador proporcional-integral de tensão é abordado na seqüência, compreendendo sua estrutura, projeto e resultados de simulação. Posteriormente, questões relativas à implementação prática do conversor e do sistema de controle, como o projeto do conversor e a programação do dispositivo de controle, são mostradas. Por fim, os resultados experimentais obtidos com a implementação do sistema proposto, incluindo as formas de onda adquiridas em um protótipo construído em laboratório e os índices de qualidade como o fator de potência e a distorção harmônica total, são apresentados com o intuito de validar e comprovar o conteúdo deste trabalho.