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This paper provides a procedure to design robust controllers based on observed states applied to three-phase inverters with LCL filters connected to a grid with uncertain and possibly time-varying impedances, which can arise in renewable energy systems and microgrid applications. Linear matrix inequalities are used to rapidly compute, off-line, based only on the choice of two scalar parameters for pole location, sets of gains for the controller and the observer, and also to provide a theoretical certificate of the closed-loop stability, including a limit for the rate of variations of the grid impedances. The proposed design procedure allows the easy implementation of robust state feedback controllers with a reduced number of sensors, ensuring good performance for different sets of grid impedances. Additionally, larger regions of guaranteed stability are provided by the proposed procedure, when compared with a similar condition from the literature. The control law using the observed states can ensure grid currents with low harmonic content, complying with the IEEE 1547 Standard requirements, with negligible loss of performance concerning the feedback of the measured state variables. Three optimal state feedback controllers from the literature are reproduced here and successfully implemented using the observed state variables based on the proposed procedure. In all cases, the viability of the proposal was confirmed by simulations and experimental results.

Este trabalho propõe um procedimento para obter ganhos robustos de realimentação parcial de estados para controle das correntes de conversores conectados à rede com incertezas paramétricas. Controladores por realimentação parcial de estados permitem diminuir o número de sensores, produzindo respostas de boa qualidade com menor custo de implementação. Neste cenário, condições de projeto baseadas em LMIs podem fornecer resultados conservadores devido a restrições de estrutura (e.g., diagonal) que devem ser impostas nas variáveis de otimização. Em contrapartida, LMIs de análise são menos conservadoras e podem prover um certificado de estabilidade robusta do sistema em malha fechada de forma eficiente para um dado controlador. Como contribuição, é proposto aqui um procedimento de projeto para encontrar ganhos de realimentação parcial de estados otimizados, combinando uma meta-heurística com uma LMI de análise, para prover uma garantia teórica de estabilidade. Um estudo de caso mostra a vantagem da proposta em relação a LMIs de síntese para obter ganhos de realimentação parcial de estados. Resultados em tempo real mostram a superioridade do controlador proposto quando comparado a um controlador proporcional-integral da literatura. Resultados experimentais em protótipo de padrão industrial confirmam a viabilidade prática da proposta, com respostas em conformidade com a norma IEEE 1547.

This paper investigates the problem of control design for dc–dc converters, where the solution is especially suitable to address variations in the input voltage, a frequent situation in photovoltaic systems, and the problem of constant power load, where a nonlinear load is connected to the output of the converter. The proposed approach models the converters in terms of Linear Parameter-Varying (LPV) models, which are used to compute gain-scheduled robust gains. The synthesis conditions provide stabilizing controllers with an attenuation level of disturbances in terms of the H∞ norm. Moreover, the design conditions can also overcome pole locations to comply with physical application restrictions when ensuring transient performance. The validation of the controllers is made via simulation of the classical converters (buck, boost and buck-boost), showing that the proposed method is a viable and generalized control solution that works for all three converters, with guarantees of closed-loop stability and good performance.

Este artigo trata do projeto e da validação experimental de controladores robustos aplicados à regulação de velocidade de motores síncronos de ímãs permanentes. O motor é descrito por um modelo politópico, considerando que os parâmetros elétricos e mecânicos podem variar dentro de intervalos limitados. As equações dinâmicas do motor para as correntes id, iq e para a velocidade wm são discretizadas incluindo o atraso de implementação digital e uma ação integral sobre o erro de rastreamento da referência. Desigualdades matriciais lineares são utilizadas para obter rapidamente, de forma offline, ganhos de controle por realimentação de estados para as duas malhas de controle de corrente e para a malha de velocidade, em uma estratégia de projeto que só demanda do projetista a escolha de dois parâmetros, limitados entre zero e um, que estabelecem uma região para alocação dos polos de malha fechada. Resultados experimentais para um motor comercial de 11 kW ilustram um bom rastreamento de correntes e uma boa regulação de velocidade. Estudos comparativos mostram desempenho dinâmico superior ao de controladores PIs da literatura, sem demandar aumento no número de sensores, permitindo também a redução do acoplamento cruzado entre os eixos direto e em quadratura.

This paper proposes a new theoretical stochastic model based on an abstraction of the opportunistic model for opportunistic networks. The model is capable of systematically computing the network parameters, such as the number of possible routes, the probability of successful transmission, the expected number of broadcast transmissions, and the expected number of receptions. The usual theoretical stochastic model explored in the methodologies available in the literature is based on Markov chains, and the main novelty of this paper is the employment of a percolation stochastic model, whose main benefit is to obtain the network parameters directly. Additionally, the proposed approach is capable to deal with values of probability specified by bounded intervals or by a density function. The model is validated via Monte Carlo simulations, and a computational toolbox (R-packet) is provided to make the reproduction of the results presented in the paper easier. The technique is illustrated through a numerical example where the proposed model is applied to compute the energy consumption when transmitting a packet via an opportunistic network.

Este artigo propõe um novo procedimento de projeto para controladores por realimentação de estados com aplicação prática em inversores conectados à rede, levando a resultados em conformidade com a norma IEEE 1547, inclusive para o caso de implementação utilizando um número reduzido de sensores. O procedimento baseia-se na otimização de objetivos considerando estabilidade, erro de rastreamento e atenuação de distúrbios. Um algoritmo genético é utilizado para buscar, orientado por modelos simples, os ganhos de controle, levando a um conjunto de soluções viáveis (fronteira de Pareto). O ganho de controle escolhido possui estabilidade robusta contra incertezas e variações paramétricas, certificada por meio de análise baseada em desigualdades matriciais lineares. Restrições no espaço de busca permitem encontrar, de forma automática, ganhos por realimentação total ou parcial de estados, superando limitações de desigualdades matriciais de sínteses e levando a resultados experimentais de boa qualidade, o que torna este procedimento uma alternativa útil no projeto de controladores robustos para conversores de potência.

This paper addresses the design of robust PI controllers for permanent magnet synchronous motors in terms of a linear matrix inequality based problem. A polytopic model of the plant is obtained and validated for the motor uncertain parameters belonging to intervals. The design procedure proposed here encompasses: i. suitable plant uncertainties inclusion and the use of practical design control constraints; ii. robust PI computation based on linear matrix inequalities with a very fast solution; iii. simulation analyses; and iv. experimental evaluations. The robust PI controller can produce superior speed regulation than a PI controller designed only for the nominal parameters, including better disturbance rejection and H-infinity performance. Experimental results confirm the viability of the proposal, which can be seen as an efficient alternative to trade off performance and robustness for PI controllers in this application.

This paper proposes a new communication protocol for output-feedback control through multi-hop Wireless Sensor Network (WSN). The protocol is based on a Hop-by-Hop transport scheme and is especially devised to simultaneously fulfill two conflicting criteria: the network energy consumption and the stability/performance (in terms of H∞ norm) of the closed-loop system. The proposed protocol can be implemented by means of three heuristics, basically using distinct rules to control the maximum number of retransmissions allowed in terms of the voltage level of the batteries of the network nodes. As another contribution, a Markov jump based representation is proposed to model the packet loss in the communication channel, giving rise to a systematic procedure to determine the transition probability matrix and the Markov chain operation modes of a network with multiple information sources. The synthesis of the output-feedback controller is made in two steps (observer filter plus a state-feedback controller) for the Markov model assuming partial availability of the operation modes. The efficiency and applicability of the communication protocol is illustrated by means of a numerical experiment, based on a physical model of a coupled tanks plant. The features of each heuristic of implementation of the proposed protocol are presented in the numerical comparisons.

This paper proposes the design and the experimental validation of a robust H2 control technique applied to boost converters. Differently from conventional techniques, the proposed controller has a certificate of stability and performance under arbitrary parameter variations. The design procedure adopts a linearized model with a polytopic structure for the converter affected by time-varying parameters. An optimal H2 state feedback controller (under quadratic stability) is synthesized using convex optimization based on linear matrix inequalities. This framework allows the determination of the control gains in a very fast way, using a finite set of inequalities to obtain a controller that ensures robust stability and performance for the entire set of uncertain parameters. An experimental setup of a boost converter is used to validate the controller designed here. The input voltage, the operating point duty cycle and the load are considered as arbitrarily time-varying uncertain parameters. The synthesized control gains produce good simulated and experimental results when compared to those obtained with a classical strategy based on PI controllers, without introducing additional implementation cost. The experimental validation proves the viability of practical application of this important robust control technique for boost converters.