Teses em Engenharia Elétrica (Doutorado) - PPGEE/ITEC

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2317

O Doutorado Acadêmico inicio-se em 1998 e pertence ao Programa de Pós-Graduação em Engenharia Elétrica (PPGEE) do Instituto de Tecnologia (ITEC) da Universidade Federal do Pará (UFPA).

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Agora exibindo 1 - 7 de 7

Acesso aberto (Open Access)
Desenvolvimento de framework para análise e simulação dinâmica de sistemas elétricos de potência
(Universidade Federal do Pará, 2013-01-18) SENA, José Adolfo da Silva; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
This thesis presents a flexible Object Oriented (OO) methodology for the design and implementation of simulation software system used to perform dynamic studies of large electrical power systems. The proposed OO methodology aims at make easier the development, upgrade and maintenance of complex software systems. The user's requirements are mapped to set base classes which are atomic classes to perform the modeling of the dynamic devices such as electrical generators. In order to evaluate the methodology, a simulation software system was developed using the OO modeling. In order to evaluate the Framework performance, two study cases were carried out. The first one apply the Framework on the modeling and simulation of generation units at Tucuruí Power Plant. The simulation results were comparated to data measurements from field tests and shown the good performance of the Framework on reproducing electromechanical phenomena of this large Power Plant. In the second study, by its turn, the Framework was applied to the modeling of a Photovoltaic (PV) generation system, along with its Maximum Power Tracking (MPPT). The MPPT control was implemented using digital techniques. The simulation results show the good performance of the Framework on modeling the current as well as MPPT control of PV generations systems.
Acesso aberto (Open Access)
Estudos de geradores distribuídos de grande porte conectados ao sistema elétrico via conversores cc-ca aplicados ao projeto de estabilizadores de sistemas de potência
(Universidade Federal do Pará, 2015-12-16) FONSECA, Maria da Conceição Pereira; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
This thesis presents a study to develop linear models suitable for conducting stability studies in interconnected electrical power systems that include large utility-scale inverterconnected power stations. To that end, an extended Heffron-Phillips-type model was developed for a study power system consisting of a utility-scale inverter-connected power source and a synchronous generator, both of which having similar power ratings and being interconnected to a larger power system (infinite bus bar). Due to the presence of the distributed generator and associated current regulating control subsystem, the extended model presents a set of signal channels originating at the current regulation subsystem of the distributed generator and arriving at the torque summing point of the synchronous generator. By performing a large set of computational tests, for a wide range of operating conditions, the relative importance of these new channel gains were assessed. It was found that the gains associated with the direct paths have a predominant influence on the contribution of the distributed generator for both synchronizing as well as damping torques actuating on the synchronous generator shaft. Furthermore, the values of these path gains prove to be negligible when the generation level of the distributed generator is rather reduced. This observation allowed for performing further model simplifications in order to obtain a more suitable model for Power System Stabilizers (PSS) design for such class of power systems. In addition, new formulae are proposed hereby which allow for estimating the values of the synchronizing and damping torque coefficients as a function of the active power generation level of the distributed generator. For the test power system, a PSS damping controller was designed by using the developed simplified model. Subsequent ly, the PSS performance degradation has been investigated for a large set of operating conditions, The results showed considerable PSS performance detuning for those operating conditions corresponding to increased generating level at the distributed generator in comparison to synchronous active power generating level. Supplementary computational tests were performed to evaluate potential adverse interacting effects between the PSS and the proportional and integral (PI) control of a TCSC FACTS device in the area. It was found that moderate values must be chosen in order not to substantially reduce the system stability.
Acesso aberto (Open Access)
Identificação em malha fechada para controle tolerante a falta passivo aplicado a um sistema industrial de bombeamento hidráulico
(Universidade Federal do Pará, 2019-08-30) ROCHA, Erick Melo; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
Fluid pumping systems are part of many industrial applications. From the traditional water supply, to the cooling systems of thermonuclear power plants and the complex aircraft maneuvering system, using pneumatic actuators, we find examples of application of these systems. As any physical system, fluid pumping systems may also be subject to anomalous behaviors or failures that can lead to malfunction or even loss of stability of an entire process. Such faults may cause permanent damage due to the effect of undesirable phenomena such as cavitation and water hammer, for example. Thereby, this work proposes the development of a Fault Tolerant Control System (FTCS) aiming at to mitigate the undesirable effects of pressure oscillation and speed variation that may affect this type of system. This research assumes that, for economic and safety reasons, industrial systems operate by default in closed-loop to ensure stability and desired performance. Therefore, a methodology is introduced to identify the open-loop transfer function of industrial plants, based on data obtained by signal measurement, of the industrial process operating in closed-loop, denominated Two-Stage Method. The identified model is used to design a controller that meets the performance criteria defined by the FTCS instead of the traditional control system, designed for a specific operating point regardless of the fault acting in the system. For experimental evaluation, an industrial fluid pumping bench was used, developed at the Automation and Control Laboratory of Federal University of Pará (UFPA). A passive FTCS was designed using robust control technique based on parametric uncertainties. For that end, it was used a set of uncertain models, obtained by parametric identification, considering a desired operating range for the test plant, with the system operating under both normal and fault conditions. Performance indices were calculated in order to quantitatively evaluate the performance of the FTCS monitored system, with the results obtained for the system operating without the FTCS (using classical controller). The results show the good performance of the proposed methodology.
Acesso aberto (Open Access)
Investigação de estratégias de controle robusto multivariável descentralizado aplicadas à melhoria do desempenho de um conversor de potência CC/CC do tipo buck com estrutura single inductor multiple output
(Universidade Federal do Pará, 2018-02-05) MEDEIROS, Renan Landau Paiva de; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
The DC/DC power converter systems are important devices to use in several applications in many sectors of the society. For this reason, several DC/DC converter topologies are developed to improve the performance of devices, aiming at reducing losses and improving the converter energy quality. However, such improvements should assess the control strategies that enable the correct functioning of the power converters. This works covers experimental assessment of the design of robust decentralized multivariable controller applied to a specific topology of the multivariable step-down power converter, where a single inductor element is shared by multiples outputs. Furthermore, it is important to ensure the system stability, as well as the multiple outputs regulations, however some difficulties remains, e.g., hard coupling between system’s outputs, non-linearities due to the inductive element and uncertainties due to imprecision of mathematical models and/or variation of nominal values of the discrete elements that compose the DC/DC converter. Aiming to assess the performance of the proposed design methodology for a multivariable robust controller, to perform experiments of parametric variations on the DC/DC power converter, it is developed several experimental tests and simulations using the Matlab. The results show the improved performance of the proposed methodology.
Acesso aberto (Open Access)
Investigação e desenvolvimento de um framework para testes de estratégias de controle automático visando melhoria de desempenho em servidores web apache
(Universidade Federal do Pará, 2019-08-29) BARRETO, Marcos Vinicius Sadala; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
In this work, a study is carried out for the computational development of automatic control tests in computer response systems to “HTTP” “Apache” request. In particular, the implementation details and results in an environment for digital performance control of the HTTP response system are discussed. Thus, it was necessary to design and develop an environment for performing data collection in the computational system that provides the response service to “HTTP” requests and makes interventions in the values of the available parameters in order to control the system automatically in closed loop. The parameter to be obtained as endogenous variable of the computational system is MaxRequestWorks, and the exogenous one will be the amount of memory consumed. The tool developed modifies neither the source code of the response software to the clients’ “HTTP” requests nor the operating system code of the host computer, being non-intrusive regarding original system configuration. A proportional-integral (PI) controller was designed in order to keep the average perceived time response of “HTTP” messages regulated. Experimental tests carried out on an Apache server show the improvement obtained on the system's time response.
Acesso aberto (Open Access)
Investigação experimental de estratégias de controle robusto aplicadas à melhoria de desempenho de um conversor de potência CC/CC do tipo buck com estrutura Single Inductor Multiple Output
(Universidade Federal do Pará, 2024-08-05) MONTAÑO SAAVEDRA, Alvaro Christian; MEDEIROS, Renan Landau Paiva de; http://lattes.cnpq.br/8081923559538095; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
Recently, DC/DC power converters have gained wide attention, especially in industry,telecommunications, and the control of renewable energy sources. The increase in the use of this technology can be explained by the growing demand for high-quality DC voltage regulation in various applications. Additionally, recent advances in power electronics along with control engineering have accelerated the development of DC/DC power converters. Therefore, they looked to optimize these converters in several ways, such as improving conversion efficiency and reducing their weight and cost. In the proposed work, control strategies for voltage regulation in a single-inductor, dualoutput Buck DC-DC converter system (SIDO) are investigated. Based on a nominal multiple-input, multiple-output plant model and performance requirements, both a Linear Quadratic Regulator (LQR) and a Decoupled PI control strategy are designed to control the power converter system under parametric uncertainties such as variation of the voltage source, variations of constant power loads (CPLs) and variations of load resistances. A prototype of a single inductor dual output DC-DC Buck converter was developed for experimental testing. The results indicate that the proposed LQR strategy approach is reasonable and provides adequate performance improvements in SIDO converter controllers under conditions of varying voltage source and varying load resistances, offering robust performance and system stability; however, more research is needed to address variations in constant power loads and in the design of a PI controller for its application in this kind of system.
Acesso aberto (Open Access)
Investigação experimental de estratégias de identificação e controle LPV aplicadas ao amortecimento de oscilações eletromecânicas em sistemas elétricos de potência
(Universidade Federal do Pará, 2012-06-29) NOGUEIRA, Fabrício Gonzalez; BARREIROS, José Augusto Lima; http://lattes.cnpq.br/1246564618922453; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
In this thesis is performed an experimental investigation of the performance of a LPV (linear parameter varying) control strategy applied to damp electromechanical oscillations in electric power systems. The study was performed in a 10kVA electric power system, which is configured as a single machine connected to an infinite bus. Furthermore, were also performed field tests on a generating unit of Tucurui Hydroelectric Power Plant. Firstly, a set of routines for the analysis and synthesis of LPV damping controllers were developed and tested computationally, along with routines for the identification of LPV models of the plant. The coefficients of the LPV damping controller, in this case a power system stabilizer (PSS), depends on the value of a variable representative of the system operating condition (scheduling parameter), which in this study, were the terminal active power (P) and reactive power (Q) of the generating unit. For control ends, the dynamics of the plant was represented by an ARX LPV model, which was estimated from experimental data collected in the plant for a wide range of operating conditions. From the LPV model of the plant, the values of the parameters of the LPV controller were determined via an optimization problem, in the form of a parameterized LMI (PLMI). The solution of PLMI is obtained from a relaxation via sum-of-squares decomposition. The LPV PSS was designed to ensure stability and performance for a wide range of operating conditions of the plant, which is generally not possible to obtain with conventional fixed parameter controllers. The LPV PSS control law was implemented in an embedded system based on a digital signal controller. The experimental results showed an excellent performance of the LPV PSS on the damping of the electromechanical oscillations both in the 10kVA electric microgenerator system, and in the Tucurui generating unit.

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