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Walter Barra

Bio: Walter Barra is an academic researcher from Federal University of Pará. The author has contributed to research in topics: Control theory & Electric power system. The author has an hindex of 8, co-authored 31 publications receiving 207 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors investigated the use of self-tuning Linear Quadratic Gaussian control with Loop Transfer Recovery (LQG/LTR) applied in Thyristor Controlled Series Capacitors (TCSC) installed in interconnected power systems.

39 citations

Journal ArticleDOI
TL;DR: An interval robust controller, by linear programming based on Kharitonov rectangle, is proposed to regulate the output of source converter, which shows the effectiveness of the proposed controller when the multi-converter buck–buck system is subjected to a variation of power reference.
Abstract: Multi-converter electronic systems are becoming widely used in many industrial applications; therefore, the stability of the whole system is a big concern to the real-world power supplies applications. A multi-converter system comprised of cascaded converters has a basic configuration that consists of two or more converters in series connection, where the first is a source converter that maintains a regulated dc voltage on the intermediate bus while remaining are load converters that convert the intermediate bus voltage to the tightly regulated outputs for the next system stage or load. Instability in cascaded systems may occur due to the constant power load (CPL), which is a behavior of the tightly regulated converters. CPLs exhibit incremental negative resistance behavior causing a high risk of instability in interconnected converters. In addition, there are other problems apart from the CPL, e.g., non-linearities due to the inductive element and uncertainties due to the imprecision of a mathematical model of dc-dc converters. Aiming to effectively mitigate oscillations effects in the output of source converter loaded with a CPL, in this paper, an interval robust controller, by linear programming based on Kharitonov rectangle, is proposed to regulate the output of source converter. Several tests were developed by using an experimental plant and simulation models when the multi-converter buck-buck system is subjected to a variation of power reference. Both simulation and experimental results show the effectiveness of the proposed controller. Furthermore, the performance indices computed from the experimental data show that the proposed controller outperforms a classical control technique.

37 citations

Journal ArticleDOI
TL;DR: A novel robust controller is presented, based on linear programming based on the Chebyshev theorem as a robust control technique considering the Kharitonov's theorem that ensures the minimization of the total deviation from the desired performance in a closed-loop system, specified by a family of characteristic polynomials.
Abstract: In recent years, dc microgrid (MG) is increasing rapidly in electric power grids and other isolated systems, integrating more efficiency and suite better some of the renewable energy sources, storage units, and dc loads. However, dc MG stability analysis becomes a challenge when constant power loads (CPLs) are applied to dc bus, which introduces destabilizing effects in the system due to its negative impedance characteristics. This paper presents a novel robust controller, based on linear programming based on the Chebyshev theorem as a robust control technique considering the Kharitonov’s theorem that ensures the minimization of the total deviation from the desired performance in a closed-loop system, specified by a family of characteristic polynomials. The purpose of the proposed controller is to tightly regulate the dc bus voltage, ensuring MG stability due to the effects of power variation on CPLs. The simulation and experimental tests are performed by using a MATLAB/Simulink simulator and a developed prototype of the DC MG system, respectively, to ratify the robustness and effectiveness of the proposed method of robust controller design.

34 citations

Journal ArticleDOI
TL;DR: In this article, a Power System Stabilizer synthesized by a static Artificial Neural Network (ANN) is presented. But the proposed neural network is not suitable for the case of reactive power, as it suffers great variations when absorbing reactive power.

29 citations

Journal ArticleDOI
TL;DR: The experimental results show that the proposed methodology can maintain a desirable performance even in the presence of parametric uncertainties, and the performance indexes calculated from experimental data show that it outperforms classical MIMO control techniques.
Abstract: This paper describes a novel robust decentralized control design methodology for a single inductor multiple output (SIMO) DC-DC converter. Based on a nominal multiple input multiple output (MIMO) plant model and performance requirements, a pairing input-output analysis is performed to select the suitable input to control each output aiming to attenuate the loop coupling. Thus, the plant uncertainty limits are selected and expressed in interval form with parameter values of the plant model. A single inductor dual output (SIDO) DC-DC buck converter board is developed for experimental tests. The experimental results show that the proposed methodology can maintain a desirable performance even in the presence of parametric uncertainties. Furthermore, the performance indexes calculated from experimental data show that the proposed methodology outperforms classical MIMO control techniques.

12 citations


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Journal Article
TL;DR: In this paper, two major figures in adaptive control provide a wealth of material for researchers, practitioners, and students to enhance their work through the information on many new theoretical developments, and can be used by mathematical control theory specialists to adapt their research to practical needs.
Abstract: This book, written by two major figures in adaptive control, provides a wealth of material for researchers, practitioners, and students. While some researchers in adaptive control may note the absence of a particular topic, the book‘s scope represents a high-gain instrument. It can be used by designers of control systems to enhance their work through the information on many new theoretical developments, and can be used by mathematical control theory specialists to adapt their research to practical needs. The book is strongly recommended to anyone interested in adaptive control.

1,814 citations

Journal ArticleDOI
01 May 1986

232 citations

Journal ArticleDOI
TL;DR: In this paper, a supplementary VSC-HVDC Power Oscillation Damping (POD) controller based on wide area measurement signals (WAMS) is presented.
Abstract: The paper presents a supplementary VSC-HVDC Power Oscillation Damping (POD) controller based on wide area measurement signals (WAMS). The controller is designed as Multi Input Single Output (MISO) using a Modal Linear Quadratic Gaussian (MLQG) methodology in order to target critical inter-area electromechanical modes. The approach has been tested on a large (16 machine, 68 bus) test network incorporating parallel HVDC/AC transmission and has shown improved damping compared to a traditional Power System Stabilizer (PSS) based controller structure utilizing local signals. The design process has incorporated the effects of wide area signal transmission delays. Variation in these signal delays and the complete loss of signals has been also investigated to establish the robustness of the WAMS based controller and its sensitivity to loss of signals. Extension of the controller to incorporate reactive power modulation has been investigated, as has variation in available active power modulation capacity. The proposed controller performance has been assessed through small and large disturbance analysis.

150 citations

Journal ArticleDOI
TL;DR: In this paper, Dill'erenzl et al. stellen wir in einfacher Form einige nichttriviale Probleme aus dem Alltag vor, wie sie im Unterricht an der Temple University behandelt wurden.
Abstract: Finite Dill'erenzlOsung von elektrodynamiscben Problemen Die Einfiihrung der finiten Differenzmethode in Studentenkursen war bisher auf einfache ProbIerne beschriinkt, die so gut wie nichts mit der Welt, in der Studenten leben, zu tun hatten. In diesem Artikel stellen wir in einfacher Form einige nichttriviale Probleme aus dem Alltag vor, wie sie im Unterricht an der Temple University behandelt wurden.

140 citations

Journal ArticleDOI
TL;DR: Various control approaches have been reviewed to match the impedance, such as the nonlinear disturbance observer (NDO) feedforward compensation method, linear programming algorithm, hybrid potential theory and linear system analysis of polyhedral uncertainty.
Abstract: In order to overcome the problem of power generation in distributed energy, microgrid(MG) emerges as an alternative scheme. Compared with the ac microgrids, the dc microgrids have the advantages of high system efficiency, good power quality, low cost, and simple control. However, due to the complexity of the distributed generation system, the conventional droop control shows the drawbacks of low current sharing accuracy. Therefore, the improved primary control methods to enhance current sharing accuracy are systematically reviewed, such as particle swarm optimization programming, probabilistic algorithm and voltage correction factor scheme. However, it is difficult to achieve stable and coordinated operation of the dc microgrids by relying on the primary control. Hence, the various secondary control approaches, such as dynamic current sharing scheme, muti-agent system (MAS) control and virtual voltage control methods have been summarized for voltage regulation. Furthermore, the energy management system (EMS), modular-based energy router (MBER) and other coordinated control methods are reviewed to achieve power management. Besides, various control methods to compensate the effect of communication delay are summarized. Moreover, linear matrix inequality (LMI), Lyapunov-Krasovskii functional stability and Takagi-Sugeno model prediction scheme can be adopted to eliminate the influence of communication delay. In addition, due to the constant power loads (CPL) exhibit negative impedance characteristics, which may result in the output oscillation of filter. Thus, various control approaches have been reviewed to match the impedance, such as the nonlinear disturbance observer (NDO) feedforward compensation method, linear programming algorithm, hybrid potential theory and linear system analysis of polyhedral uncertainty. The merits and drawbacks of those control strategies are compared in this paper. Finally, the future research trends of hierarchical control and stability in dc microgrids and dc microgrid clusters are also presented.

122 citations