This dissertation proposes a power management and control strategy for islanded microgrids, which consist of multiple electronically-interfaced distributed energy resource (DER) units, to achieve a prescribed load sharing scheme. This strategy provides i) a power management system to specify voltage set points based on a classical power flow analysis; 2) DER local controllers, designed based on a robust, decentralized, servomechanism approach, to track the set points; and 3) a frequency control and synchronization scheme. This strategy is then generalized to incorporate both power-controlled and voltage-controlled DER units. Since the voltage-controlled DER units do not use inner current control loops, they are vulnerable to overcurrent/overload transients subsequent to system severe disturbances, e.g., faults and overloading conditions. To prevent DER unit trip-out or damage under these conditions, an overcurrent/overload protection scheme is proposed that detects microgrid abnormal conditions, modifies the terminal voltage of the corresponding VSC to limit DER unit output current/power within the permissible range, and restores voltage controllers subsequently. Under certain circumstances, e.g., microgrid islanding and communication failure, there is a need to switch from an active to a latent microgrid controller. To minimize the resultant transients, control transition should be performed smoothly. For the aforementioned two circumstances, two smooth control transition techniques, based on 1) an observer and 2) an auxiliary tracking controller, are proposed to achieve a smooth control transition. A typical microgrid system that adopts the proposed strategy is investigated. The microgrid dynamics are investigated based on eigenvalue sensitivity and robust analysis studies to evaluate the performance of the closed-loop linearized microgrid. Extensive case studies, based on time-domain simulations in the PSCAD/EMTDC platform, are performed to evaluate performance of the proposed controllers when the microgrid is subject to various disturbances, e.g., load change, DER abrupt outage, configuration change, faults, and overloading conditions. Real-time hardware-in-the-loop case studies, using an RTDS system and NI-cRIO industrial controllers, are also conducted to demonstrate ease of hardware implementation, validate controller performance, and demonstrate its insensitivity to hardware implementation issues, e.g., noise, PWM nonidealities, A/D and D/A conversion errors and delays.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: David A. Kendrick. Vita. Includes bibliographical references.

Thesis (M. Sc.)(Electronic Engineering)--University of Pretoria, 2006. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Made available in DSpace on 2014-06-11T19:30:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-08-30Bitstream added on 2014-06-13T20:21:16Z : No. of bitstreams: 1 souza_wa_dr_ilha.pdf: 2047760 bytes, checksum: 8e0dca06c80251e6c3a1e6e46925aa1a (MD5) / Esta tese propõe novos métodos de projeto de controle chaveado para algumas classes de sistemas: lineares com incertezas politópicas e não lineares incertos descritos por modelos fuzzy Takagi-Sugeno. Inicialmente são propostos métodos que utilizam uma função quadrática de Lyapunov e a estabilidade quadrática é utilizada para projetar vários ganhos do controlador, baseado em desigualdades matriciais lineares (do inglês Linear Matrix Inequalities - LMIs). Os controladores propostos são compostos por um único ganho que é escolhido por uma lei de chaveamento que retorna o menor valor da derivada temporal da função quadrática de Lyapunov. Para o caso linear, os controladores concebidos apresentam um melhor desempenho quando comparados com o controlador que emprega um único ganho de realimentação do estado normalmente implementado, e as LMIs utilizadas para encontrar os ganhos são mais relaxadas. Para o caso não linear, os controladores propostos também apresentaram um bom desempenho e eliminam a necessidade de encontrar as expressões explícitas das funções de pertinência que muitas vezes podem ter expressões longas e/ou complexas, ou serem desconhecidas devido às incertezas na planta. Em seguida foram propostos novos métodos de projeto de controle chaveado e um novo critério de estabilidade para sistemas não lineares incertos descritos por modelos fuzzy Takagi-Sugeno. O projeto do controlador chaveado é baseado na função de Lyapunov quadrática por partes do tipo mínimo e na minimização da derivada temporal desta função de Lyapunov. As condições do novo critério de estabilidade são representadas por um tipo de desigualdades matriciais bilineares (do inglês Bilinear Matrix Inequalities - BMIs) que podem ser resolvidas de forma eficiente pelo método... / This thesis proposes new switched control design methods for some classes of linear systems with polytopic uncertainties and uncertain nonlinear systems described by Takagi-Sugeno fuzzy models. Initially, are proposed methods that use a quadratic Lyapunov function and quadratic stability to design, based on Linear Matrix Inequalities (LMIs), the feedback gains. The controller gain is chosen by a switching law that returns the smallest value of the time derivative of the quadratic Lyapunov function. For the linear case, the proposed methodology presents a better performance when compared with the controller usually implemented which uses only one state feedback gain and the LMIs for finding the switched gains are more relaxed. For nonlinear plants described by Takagi-Sugeno fuzzy models, the proposed controller also presented good performance and eliminates the need to obtain the explicit expressions of the membership functions of the Takagi-Sugeno fuzzy controllers, which can often have long and/or complex expressions, or may not be known, for instance due to the plant uncertainties. The design of the switched controllers is based on a minimum-type piecewise quadratic Lyapunov function and the minimization of the time derivative of this Lyapunov function. The conditions of the new stability criterion are represented by a kind of Bilinear Matrix Inequalities (BMIs) that can be efficiently solved by the path-following method. Furthermore, the proposed switched controller can also operate even with an uncertain reference control signal. To verify the efficacy of the proposed methodology are presented numerical simulations, including robust nonlinear control designs of a ball-and-beam system and of a magnetic levitator, and finally a robust... (Complete abstract click electronic access below)

Orientador: José Paulo Fernandes Garcia / Banca: Jean Marcos de Souza Ribeiro / Banca: Cristiano Quevedo Andrea / Resumo: O principal objetivo do trabalho é explorar a técnica de controle robusto com Modos Deslizantes para a acomodação e atenuação de uma falha no sinal de controle de um helicóptero. Foram projetados dois controladores, o Controle com Estrutura Variável e Modos Deslizantes contínuo no tempo (CEV/MD), e o segundo é o Controle Discreto com Modos Deslizantes (CDMD). Foi usado um modelo matemático não linear que representa um simulador de voo (Helicóptero 3-DOF da Quanser R ), que é um equipamento útil para o ensino, aplicação e desenvolvimento de técnicas de controle robusto. Os resultados experimentais obtidos, fazem uma comparação entre o controle contínuo e o controle discreto. Para que essa comparação seja feita foi inserida uma falha no sinal de controle. Mesmo diante das diferenças na resposta do sinal de controle, entre os controladores, o sistema teve um bom desempenho quando controlado pelo CEV/MD e CDMD, mostrando assim a eficiência da técnica de controle com Modos Deslizantes / Abstract: The main objective of this work is the exploration of the robust control technique with Sliding Mode (VSC-SM) for fault accommodation and attenuation in an aircraft's propulsion system. Two controllers were designed, Variable Structure Control with Sliding Mode (VSCSM) and Discrete Control with Sliding Modes (DCSM). For that, it was used a mathematical model of a flight Simulator of a Quanser's helicopter, named as 3-DOF Helicopter, which is an excellent module for teaching, application and development of robust control techniques. The results obtained in digital simulations show great performance of the system in fault when controlled by VSC-SM and DCSM / Mestre

COSTA, M. V. S. Controle MPC robusto aplicado ao conversor Boost CCTE otimizado por inequações matriciais lineares. 2017. 178 f. Tese (Doutorado em Engenharia Elétrica)–Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017. / Submitted by Marlene Sousa (mmarlene@ufc.br) on 2017-09-06T17:10:36Z No. of bitstreams: 1 2017_tese_mvscosta.pdf: 5929867 bytes, checksum: 81ddf2f8352a8740c1bfba2216f43bfa (MD5) / Approved for entry into archive by Marlene Sousa (mmarlene@ufc.br) on 2017-09-06T17:11:16Z (GMT) No. of bitstreams: 1 2017_tese_mvscosta.pdf: 5929867 bytes, checksum: 81ddf2f8352a8740c1bfba2216f43bfa (MD5) / Made available in DSpace on 2017-09-06T17:11:16Z (GMT). No. of bitstreams: 1 2017_tese_mvscosta.pdf: 5929867 bytes, checksum: 81ddf2f8352a8740c1bfba2216f43bfa (MD5) Previous issue date: 2017-07-21 / This work proposes a MPC predictive control strategy applied to a three-state switching cell boost (3SSC) converter that gives more simplicity and systematization to the control design steps and analysis. The integral gain controller can adjusted, eliminating the re-design the weighting matrices. Besides, the stability elipsoid theory are used to simplify the stability analysis of converter. The proposed MPC begins using the linear time varying (LTV) model plant. The parameters variations are considered polytopic uncertainties using linear matrix inequalities approach (LMIs) with relaxations. Theoretical and experimental aspects are applied and analyzed to a 1 kW 3SSC boost converter with voltage input and load uncertainties. To 500 W experimental test, it is considered load and voltage input steps variations. To 1000 W experimental test, it is only considered load steps variation. Also, the proposed MPC-LMI is compared with a classical LQI known in the literature. Theoretical-experimental aspects are applied and analyzed in a 1 kW converter with uncertainties in the input voltage and load. For the experiments, the voltage and load step tests for the 500 W project and a load step test for the 1000 W one were considered. In addition, to establish a performance reference, the proposed MPC is compared with the classic LQR controller known in the literature. The proposed control strategy presents advantages considering the variations of the model due to load tests in DC-DC 3SSC boost applications, being a feasible proposal in solving problems for high-performance converters. / Este trabalho propõe uma estratégia de controle preditivo MPC aplicado a um conversor boost com célula de comutação em 3 estados (CCTE) que confere mais simplicidade e sistematização nas fases de projeto e análise do controlador. O ganho integral do controlador pode ser ajustável, dispensando o reprojeto nas matrizes de ponderação. Para simplificar a análise de estabilidade do controlador, utiliza-se o conceito de elipsóides de estabilidade. O controle MPC proposto parte da modelagem da planta no espaço de estados médio linear e variante no tempo (LTV). As variações paramétricas, no contexto deste trabalho, são tratadas como incertezas politópicas expressas por meio de desigualdades matriciais lineares (LMIs) com relaxações. Aspectos teórico-experimentais são aplicados e analisados em um conversor boost CCTE de 1 kW com incertezas na tensão de entrada e na carga. Para os ensaios, são considerados os testes de degrau de tensão e de carga para o projeto em 500 W e para o degrau de carga com operação em 1000 W . Além disso, para estabelecer uma base de desempenho, o MPC proposto é comparado com o controlador LQI clássico conhecido na literatura. A estratégia de controle proposta apresenta vantagens considerando as variações do modelo decorrente dos testes de cargas em aplicações boost CC-CC do tipo CCTE, sendo uma proposta viável na solução de problemas em conversores de alto rendimento.

This work describes the modeling, control design, and experimental verification of an electromagnetic suspension system with position feedback using infrared sensors. A nonlinear model is obtained by fitting a first principle analytical model of the system to experimental data. A sliding control strategy is designed using a sliding surface derived from the model to achieve robust stabilization for the closed-loop system. The control is then implemented on an embedded commercial DSP system for experimental verification of the designed control on a laboratory scale electromagnetic suspension system. To compensate for the steady-state tracking error, two modifications are considered. In the first method, a small magnitude integral term is added to the error feedback, equivalently adjusting the reference signal and eliminating the constant bias. In the second method, an integral sliding control is considered, using a higher-order sliding surface, which also eliminates the constant bias. The experimental results show the efficacy of all designed control techniques. The modified techniques, unlike the original design, effectively eliminate the constant position error.

Made available in DSpace on 2014-11-10T11:09:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-04-25Bitstream added on 2014-11-10T11:58:01Z : No. of bitstreams: 1 000794484.pdf: 4606369 bytes, checksum: 3b03f3088fb54f098f7565bc5b9ad8da (MD5) / Nesta tese apresentam-se resultados para a estabilidade robusta de sistemas lineares sujeitos a incertezas paramétricas do tipo politópicas, variantes no tempo (do inglês Linear Parameter Varying - LPV). De início, expõe-se um método aprimorado para o projeto com otimização da norma de controladores robustos via desigualdades matriciais lineares (do inglês Linear Matrix Inequalitites - LMIs), com base na teoria de estabilidade segundo Lyapunov. Esta nova formulação foi manipulada utilizando o lema de Finsler, e permitiu encontrar melhores resultados de factibilidade com o acréscimo de matrizes extras e redução do número de LMIs. Neste novo equacionamento houve a inclusão do índice de desempenho da taxa de decaimento, responsável por diminuir o tempo de duração do período transitório, e também da otimização da norma dos controladores, responsável por menores ganhos mantendo a mesma eficiência dos requisitos de projeto. Devido a importantes resultados da literatura para o projeto de controladores robustos com incertezas variantes no tempo, optou-se por explorar o projeto de controladores dinâmicos chaveados, inovando-se no tocante ao acréscimo da taxa de decaimento e à otimização da norma dos controladores chaveados, o que possibilitou encontrar melhores resultados de implementação. Por fim, foram propostos critérios menos conservadores para a análise de estabilidade e projeto de controladores chaveados, utilizando funções de Lyapunov quadráticas por partes do tipo mínimo. A vantagem desse procedimento está no aumento dos parâmetros de relaxação porém, concebido através de formulações baseadas em desigualdades matriciais bilineares (do inglês Bilinear Matrix Inequalitites - BMIs), nos quais os termos e se encontram no produto entre variáveis escalares de otimização e matrizes, que também são variáveis do procedimento de otimização. Apresentam-se, no corpo do texto, exemplos numéricos e ... / This thesis presents results for robust stability of linear systems subject to polytopic timevarying parametric uncertainties (LPV). To start with, an improved method for the optimal gain design of robust controllers via Linear Matrix Inequalities (LMI), based on Lyapunov stability theory is presented. This new formulation was manipulated using the Finsler lemma, which enabled finding better feasibility results with the addition of extra matrices and reducing the number of LMIs. In this new equation it was included the decay rate performance index, responsible for reducing the transitional period time, as well as the controllers norm optimization, responsible for lower gains while maintaining the same project requirements efficiency. Then, due to important results in literature regarding the design of robust controllers with time-varying uncertainties, the design of switched dynamic controllers was explored by including the decay rate index and the optimization of the switched controllers norm in the equation, which allowed finding better implementation results. Finally, less conservative criteria were proposed for stability analysis and design of switched controllers using minimum-type piecewise quadratic Lyapunov functions. The advantage of this procedure lies in the increase of relaxation parameters, however, designed through formulations based on Bilinear Matrix Inequalities (BMIs), where the bilinear terms are in the product between optimization scalar variables and matrices, which are also variables on the optimization procedure. Numerical examples are presented and simulated to illustrate the efficiency of the proposed methodologies in relation to other existing throughout the text. The designed controllers were implemented using these new proposals in a Three Degrees Of Freedom (3-DOF) helicopter or in the Shake Table II (STII) + Active Mass Dumper - One Floor (AMD-1) system, in order to validate in practice the proposed theories