Estabilidade e controle de sistemas lineares variantes no tempo e de sistemas chaveados lineares

Orientador: Pedro Luis Dias PeresTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de ComputaçãoResumo: Esta tese apresenta contribui»coes para a solucao de problemas de anaalise de estabilidade e de sintese de controladores para sistemas lineares com parametros variantes no tempo pertencentes a um politopo e para sistemas chaveados lineares com funcoes de chaveamento arbitrarias atraves de condicoes na forma de desigualdades matriciais lineares baseadas em funcoes de Lyapunov. Para sistemas lineares variantes no tempo (caso continuo), sao fornecidas condicoes de verificacao de estabilidade e de computo de custos garantidos H1 quando os parametros pertencentes a um politopo sao supostos incertos e com taxas de variacao limitadas. Para o problema de sintese, supondo que os parametros sao conhecidos em tempo real, sao fornecidas condicoes de projeto de ganhos de realimentacao de estados que variam de forma nao-linear com os parametros e que asseguram a estabilidade com um certo custo garantido H1 para o sistema em malha fechada sujeito a taxas de variacoes parametricas limitadas. No caso de taxas de variacoes parametricas arbitrarias, sao fornecidas condicoes de c^omputo de ganhos que variam de forma linear (caso continuo) ou de forma nao-linear (caso discreto) com os par^ametros, assegurando a estabilidade com requisitos de desempenho H1 para o sistema em malha fechada. Para sistemas chaveados lineares (casos continuo e discreto), sao fornecidas condicoes para computar ganhos chaveados de realimentacao de estados que resolvem os problemas de estabiliza cao e de controle H1, incluindo especi¯cacoes de alocacao de piolos, permitindo melhorar o desempenho do sistema em malha fechada sujeito a funcoes de chaveamento arbitrarias disponiveis em tempo real. Exemplos numericos incluindo problemas de controle com restri»cao de estrutura, de controle sob falhas de atuadores e uma aplicacao em circuitos eletricos chaveados ilustram como as condi»coes propostas reduzem o conservadorismo nos problemas de analise e de sintese das classes de sistemas dinamicos sob investigacaoAbstract: This thesis presents contributions to the solution of problems of stability analysis and control synthesis applied to linear systems with time-varying parameters belonging to a polytope and to switched linear systems subject to arbitrary switching functions using linear matrix inequality conditions based on Lyapunov functions. Concerning linear time-varying systems (continuous-time case), the proposed conditions assess the problems of stability analysis and computation of H1 guaranteed costs when the parameters belonging to a polytope are supposed to be uncertain with bounded rates of variation. For the problem of synthesis, assuming that the parameters are available in real time, the thesis provides conditions to design state feedback gains which depend nonlinearly on the parameters and assure stability with a given H1 guaranteed cost to the closed-loop system for the case of bounded rates of parametric variations. When the rates of parametric variations are assumed to be arbitrary, the given conditions can determine gains that depend linearly (continuous-time case) or nonlinearly (discrete-time case) on the parameters, assuring stability with H1 performance to the closed-loop system. In the context of switched linear systems (continuous and discrete-time cases), the proposed conditions are suitable to determine switched state feedback gains that solve the problems of stabilization and H1 control including pole location speci¯cations, allowing to improve the performance of the closed-loop system subject to arbitrary switching functions available in real time. Numerical examples including problems of structurally constrained control, robustness against actuator failures and an application on switched electrical circuits illustrate how the proposed conditions reduce the conservatism of the problems of analysis and synthesis for the classes of dynamic systems under investigationDoutoradoAutomaçãoDoutor em Engenharia Elétric

Effective removal of non-steroidal anti-inflammatory drug from wastewater by adsorption process using acid-treated Fagopyrum esculentum husk

In this work, buckwheat husks (Fagopyrum esculentum) were modified by acid treatment and posteriorly employed to remove the ketoprofen in batch adsorption. The characterization results indicated that a more irregular surface with new empty spaces was generated after acid treatment. The adsorptive process was favored at acidic pH = 3. The dosage of 0.85 g L−1 was fixed for the kinetic and isothermal tests, obtaining good removal and capacity indications. The kinetic studies were better represented by pseudo-second-order, obtaining an experimental capacity of 74.3 mg g−1 for 200 mg L−1 of ketoprofen. An increase in temperature negatively affected the adsorption isotherm curves, resulting in a maximum capacity of 194.1 mg g−1. Thermodynamic results confirmed the exothermic nature of the process with physical forces acting. The adsorbent presented high efficiency in treating a synthetic effluent containing different drugs and salts, 71.2%. Therefore, adsorbent development from buckwheat husks treated with a strong acid is an excellent alternative, given the good removal results and the low cost for its preparation

Robust stability analysis of grid-connected converters based on parameter-dependent Lyapunov functions.

This paper deals with the problem of robust stability analysis of grid-connected converters with LCL filters controlled through a digital signal processor and subject to uncertain grid inductance. To model the uncertain continuous-time plant and the digital control gain, a discretization procedure, described in terms of a Taylor series expansion, is employed to determine an accurate discrete-timemodel. Then, a linear matrix inequality-based condition is proposed to assess the robust stability of the polynomial discrete-time augmented system that includes the filter state variables, the states of resonant controllers and the delay from the digital control implementation. By means of a parameterdependent Lyapunov function, the proposed strategy has as main advantage to provide theoretical certification of stability of the uncertain continuous-time closed-loop system, circumventing the main disadvantages of previous approaches that employ approximate discretized models, neglecting the errors. Numerical simulations illustrate the benefits of the discretization technique and experimental results validate the proposed approach