LuÍs Alberto | Universidade de São Paulo (original) (raw)
Papers by LuÍs Alberto
Proceeding Series of the Brazilian Society of Computational and Applied Mathematics, 2014
The stability analysis of nonlinear systems may involve the analysis of attracting sets, like lim... more The stability analysis of nonlinear systems may involve the analysis of attracting sets, like limit cycles, strange attractors, etc. Methods based on Lyapunov's Theorem provide an estimate of the region of attraction of isolated equilibrium points, but usually, they are not very systematic and do not apply to attracting sets. This work presents a systematic procedure that allows estimating attracting sets of certain nonlinear systems as well as their region of attraction, using Lyapunov Functions with generic forms. The analyzed systems must be written like Lure Problem, but they are allowed to have nonlinear functions with less restrictive characteristics. Keywords Nonlinear systems, attracting sets, region of attraction, Lyapunov function, Lure problem, LMI. Resumo A análise da estabilidade de sistemas não-lineares pode envolver a análise de conjuntos atratores, como ciclos limites, atratores estranhos, etc. Métodos baseados no Teorema de Lyapunov fornecem estimativas das áreas de atração de pontos de equilíbrio isolados mas, em geral, são pouco sistemáticos e não se aplicam a conjuntos atratores. Este trabalho apresenta um procedimento sistemático que permite estimar conjuntos atratores de uma determinada classe de sistemas não-lineares, assim como sua área de atração, utilizando formas genéricas para as Funções de Lyapunov. Os sistemas considerados são os que podem ser escritos na forma do Problema de Lure, mas com uma característica menos restritiva para a não-linearidade. Palavras-chave Sistemas não-lineares, conjuntos atratores, área de atração, função de Lyapunov, problema de Lure, LMI.
IEEE Conference on Decision and Control and European Control Conference, 2011
In this paper, we propose an extension of the invariance principle for switched systems under dwe... more In this paper, we propose an extension of the invariance principle for switched systems under dwell-time switched solutions. Our approach allows the derivative of an auxiliary function V along the solutions of the switched system to be positive on some bounded sets. The auxiliary function V , which plays the role of a Lyapunov function, is called a Lyapunov-like function in this paper. Our results are useful to estimate attractors of switched systems and basins of attraction. Results for a common Lyapunov-like function and multiple Lyapunov-like functions are given. Illustrative examples show the potential of the theoretical results in providing concrete information on the asymptotic behavior of nonlinear dynamical switched systems.
International Journal of Bifurcation and Chaos, 2013
A complete characterization of the boundary of the stability region (or area of attraction) of no... more A complete characterization of the boundary of the stability region (or area of attraction) of nonlinear autonomous dynamical systems is developed admitting the existence of a particular type of nonhyperbolic equilibrium point on the stability boundary, the supercritical Hopf equilibrium point. Under a condition of transversality, it is shown that the stability boundary is comprised of all stable manifolds of the hyperbolic equilibrium points lying on the stability boundary union with the center-stable and\or center manifolds of the type-k, k ≥ 1, supercritical Hopf equilibrium points on the stability boundary.
Sba: Controle & Automação Sociedade Brasileira de Automatica, 2002
The purpose of this work is to obtain uniform estimates, with respect to parameters, of the attra... more The purpose of this work is to obtain uniform estimates, with respect to parameters, of the attractor and of the basin of attraction of a dynamical system as well as to apply these results to analyze the robustness of the synchronization of two coupled subsystems. These estimates are obtained through an uniform version of the Invariance Principle of LaSalle which is stated and proved in this work.
2014 IEEE PES General Meeting | Conference & Exposition, 2014
The two-time scale (TTS) CUEP/BCU method provides the correct calculus of the (uniform) controlli... more The two-time scale (TTS) CUEP/BCU method provides the correct calculus of the (uniform) controlling unstable equilibrium point (CUEP) for TTS power system models in transient stability problems. The energy of CUEP can be used to locally approximate the stability boundary and to provide a conservative critical clearing time (CCT) estimate, however the TTS-CUEP/BCU method also provides a CCT estimate for the fast subsystem, associated with the original TTS power system model, which potentially can be used as a better (less conservative) estimate of the CCT for the TTS model. Despite this fact, the TTS-CUEP/BCU method does not take advantage of this fast CCT estimate in the assessment of the CCT estimate of the TTS system. This paper propose a energy-guided timedomain simulation to accomplish this task.
Advances in Difference Equations, 2010
An extension of the uniform invariance principle for ordinary differential equations with finite ... more An extension of the uniform invariance principle for ordinary differential equations with finite delay is developed. The uniform invariance principle allows the derivative of the auxiliary scalar function V to be positive in some bounded sets of the state space while the classical invariance principle assumes thatV ≤ 0. As a consequence, the uniform invariance principle can deal with a larger class of problems. The main difficulty to prove an invariance principle for functional differential equations is the fact that flows are defined on an infinite dimensional space and, in such spaces, bounded solutions may not be precompact. This difficulty is overcome by imposing the vector field taking bounded sets into bounded sets.
In this paper, a less conservative sufficient condition that ensure the ultimate boundedness of t... more In this paper, a less conservative sufficient condition that ensure the ultimate boundedness of the solutions of switched TS fuzzy systems is proposed. The main result is given in terms of linear matrix inequalities (LMIs), which were formulated by calculating the derivative of the auxiliary function V along the solution of the system formed by a convex combination of the switching subsystems. The LMI conditions were relaxed using the S-procedure. A numerical example illustrates the efficiency of the proposed result.
2009 IEEE Power & Energy Society General Meeting, 2009
This paper proposes a new indirect approach to estimate the power angle of synchronous generators... more This paper proposes a new indirect approach to estimate the power angle of synchronous generators from three-phase currents and voltages, and field voltage measurements. An auxiliary algebraic equation, which relates the power angle with generator parameters and measurements, is included in the generator model. Therefore, the generator is modeled by a set of differential-algebraic equations (DAEs). The procedure is split
2005 IEEE Russia Power Tech, 2005
In this paper, a methodology to estimate parameters of synchronous generator and its excitation s... more In this paper, a methodology to estimate parameters of synchronous generator and its excitation system, based on the trajectory sensitivity technique, is proposed. Some alternatives are proposed for this technique regarding a future 'on-line' application. The parameters of classical and "two-axis"models of generator are estimated. An alternative is also proposed to overcome problems related to differential equations with variables that can not be measurable in the real system. The methodology developed is also used to estimate the parameters of the excitation system (STR1 and DC1 type) in a successful way.
POWERCON '98. 1998 International Conference on Power System Technology. Proceedings (Cat. No.98EX151), 1998
ABSTRACT The main concern of this paper is to create a methodology that, if incorporated to the B... more ABSTRACT The main concern of this paper is to create a methodology that, if incorporated to the BCU method of transient stability analysis, one can assure, for the one-machine-infinite-bus system (OMIB), the stability of the system and not the existence of the first swing only. The methodology constitutes in determining, in an iterative way, a critical damping coefficient that should be associated to the system, so that it is assured that the saddle points used as the controlling equilibrium point are on the boundary of the corresponding attraction area. That is, with that damping coefficient in the system, it can be assured that the one-parameter transversality condition will be satisfied. The methodology, as developed, is an iterative monotonically convergent process very easy to implement and does not require knowledge of fault trajectory at all. An example showing how the methodology works is also incorporated in the paper. The proposed methodology was also applied to a simple multimachine system. In that case however, the proposed methodology needs further studies and adaptation in order to be applied
IEEE Power Engineering Society General Meeting, 2005, 2005
The main concern of this paper is the proposal of an Extended Lyapunov Function (ELF) for a power... more The main concern of this paper is the proposal of an Extended Lyapunov Function (ELF) for a power system model that does not have Lyapunov Function in the usual sense. More precisely, an ELF is proposed for a network preserving model where both, the active and reactive load powers depend on voltage. Then the proposed ELF is used for short term stability analysis including voltage and angle instability phenomenon. The results show that the proposed function can be used to obtain good estimates of the critical clearing time.
PowerCon 2000. 2000 International Conference on Power System Technology. Proceedings (Cat. No.00EX409), 2000
ABSTRACT This paper presents a new topological method for critical measurements identification in... more ABSTRACT This paper presents a new topological method for critical measurements identification in observable networks. A measurement is said to be critical, in observability sense, if its removal from the measurement set leads the associated system to lose observability. The proposed method is based on the properties of both, observable islands (OI) and redundant branch sets (RBS). To reduce the combinatorial bluster, the proposed method divides the measurements in two groups and classifies then in two phases. Indeed, it is simple and fast. In order to clarify the proposed method and to show its simplicity, two examples are provided. The proposed method is successfully tested in the IEEE-14 bus system and in two realistic systems of the Brazilian utilities. The first one is a 121-bus system from ELETROSUL, and the other is a 383-bus system from CHESF (Companhia Hidroeletrica do Sao Francisco)
International Transactions on Electrical Energy Systems, 2013
ABSTRACT SUMMARY This paper proposes an index, called Undetectability Index (UI), to classify the... more ABSTRACT SUMMARY This paper proposes an index, called Undetectability Index (UI), to classify the measurements according to their characteristics of not reflecting their errors into the residuals of the weighted least squares state estimator (WLS) from a geometric analysis of this estimator. Gross errors in measurements with high UIs are very difficult to be detected by methods based on residual analysis, because the errors in those measurements are “masked”, i.e. they are not reflected in their residuals. The paper also presents a very simple algorithm to compute the UI of all available measurements in a metering system. This algorithm is very simple and uses routines already available in the existing WLS Estimator software. Two UI applications are investigated (i) to design more reliable metering systems for bad data processing, i.e. metering systems formed by measurements with UI lower than a pre-specified value and (ii) to estimate the measurement errors. Several simulation results (with IEEE-14 and 30 bus systems) have validated the propositions. Copyright © 2013 John Wiley & Sons, Ltd.
PowerCon 2000. 2000 International Conference on Power System Technology. Proceedings (Cat. No.00EX409), 2000
ABSTRACT This paper proposes a new methodology to study coherency in power systems. The methodolo... more ABSTRACT This paper proposes a new methodology to study coherency in power systems. The methodology is supported by a theoretical background and does not require the solution of the differential equations. The concept of weak coherency is defined as the coherency between a reduced gradient system associated to the power system equations. Much information can be derived from the weak coherency concept. One that is straightforward is the location of the unstable equilibrium points in the state space which can be very useful to improve transient stability analysis through direct methods
2003 IEEE Bologna Power Tech Conference Proceedings,, 2003
The main proposition of this work is the development of an Extended Lyapunov Function for multima... more The main proposition of this work is the development of an Extended Lyapunov Function for multimachine systems taking transfer conductance parameters in consideration. This function is obtained by applying smooth perturbations on the approximated energy-like function as proposed by Athay et al. [2]. This perturbed function is used to estimate critical clearing times (CCT) based on the Extension of Invariance Principle [14]. These estimates are based on a solid theoretical background and also the differences between the proposed Extended Lyapunov Function and the energy-like function is of the order of the smooth perturbation. Examples are given in a multimachine system case to validate the proposed Extended Lyapunov Function.
The main concern of this paper is the ap- plication of the Melnikov's method for computing h... more The main concern of this paper is the ap- plication of the Melnikov's method for computing heteroclinic orbits in a classical SMIB power system model and testing the one-parameter transversality condition required in the BCU method for transient stability analysis. First of all, the Melnikov's method is used to give a first approximation for the minimum damping coefficient, or alternatively for the maximum input mechanical power, that should be associated to the system, so that the transversality condition is satisfied. This first appro- ximation is obtained without solving any differential equation. After that, this approximation is used as an initial condition for a monotonically convergent process which is very easy to im- plement and does not require knowledge of fault trajectory at all.
Sba: Controle & Automação Sociedade Brasileira de Automatica, 2012
Este artigo propõe uma nova metodologia prática e robusta para estimar parâmetros de geradores sí... more Este artigo propõe uma nova metodologia prática e robusta para estimar parâmetros de geradores síncronos. A metodologia proposta utiliza a análise de sensibilidade de trajetória combinada com uma nova abordagem, denominada 'abordagem de minimização' para estimação de parâmetros de sistemas dinâmicos não-lineares modelados por conjuntos de equações algébricos diferenciais. Uma escolha adequada de entradas e saídas permite a divisão da estimação de parâmetros do gerador na estimação independente dos parâmetros elétricos e mecânicos. A metodologia é robusta com relação às condições iniciais dos parâmetros, não requer execução de testes especiais e utiliza apenas medidas de perturbações de fácil obtenção (correntes e tensões trifásicas, tensão de campo e velocidade do rotor) coletadas do sistema de energia elétrica sem desconectar o gerador da rede.
RESUMO -Neste artigo propõe-se um novo método para a identificação das medidas críticas e também ... more RESUMO -Neste artigo propõe-se um novo método para a identificação das medidas críticas e também dos conjuntos de medidas que, se perdidas simultaneamente, fazem um sistema de potência observável tornar-se não observável. Conhecendo-se essas medidas e esses conjuntos de medidas, o método permite a identificação do nível de redundância de cada uma das medidas, associadas a um sistema de potência observável. O método proposto baseia-se nas relações de dependência linear das linhas da matriz Jacobiana. Para determinar essas relações, uma conveniente mudança de base no espaço dos estados é realizada. A característica esparsa da matriz Jacobiana proporciona ao método uma boa velocidade de execução. Para comprovar a sua eficiência, vários testes foram realizados, utilizando para isso o sistema de 14 barras do IEEE, o sistema de 121 barras da ELETROSUL e um sistema de 384 barras da CHESF (Companhia Hidroelétrica do São Francisco).
Proceeding Series of the Brazilian Society of Computational and Applied Mathematics, 2014
The stability analysis of nonlinear systems may involve the analysis of attracting sets, like lim... more The stability analysis of nonlinear systems may involve the analysis of attracting sets, like limit cycles, strange attractors, etc. Methods based on Lyapunov's Theorem provide an estimate of the region of attraction of isolated equilibrium points, but usually, they are not very systematic and do not apply to attracting sets. This work presents a systematic procedure that allows estimating attracting sets of certain nonlinear systems as well as their region of attraction, using Lyapunov Functions with generic forms. The analyzed systems must be written like Lure Problem, but they are allowed to have nonlinear functions with less restrictive characteristics. Keywords Nonlinear systems, attracting sets, region of attraction, Lyapunov function, Lure problem, LMI. Resumo A análise da estabilidade de sistemas não-lineares pode envolver a análise de conjuntos atratores, como ciclos limites, atratores estranhos, etc. Métodos baseados no Teorema de Lyapunov fornecem estimativas das áreas de atração de pontos de equilíbrio isolados mas, em geral, são pouco sistemáticos e não se aplicam a conjuntos atratores. Este trabalho apresenta um procedimento sistemático que permite estimar conjuntos atratores de uma determinada classe de sistemas não-lineares, assim como sua área de atração, utilizando formas genéricas para as Funções de Lyapunov. Os sistemas considerados são os que podem ser escritos na forma do Problema de Lure, mas com uma característica menos restritiva para a não-linearidade. Palavras-chave Sistemas não-lineares, conjuntos atratores, área de atração, função de Lyapunov, problema de Lure, LMI.
IEEE Conference on Decision and Control and European Control Conference, 2011
In this paper, we propose an extension of the invariance principle for switched systems under dwe... more In this paper, we propose an extension of the invariance principle for switched systems under dwell-time switched solutions. Our approach allows the derivative of an auxiliary function V along the solutions of the switched system to be positive on some bounded sets. The auxiliary function V , which plays the role of a Lyapunov function, is called a Lyapunov-like function in this paper. Our results are useful to estimate attractors of switched systems and basins of attraction. Results for a common Lyapunov-like function and multiple Lyapunov-like functions are given. Illustrative examples show the potential of the theoretical results in providing concrete information on the asymptotic behavior of nonlinear dynamical switched systems.
International Journal of Bifurcation and Chaos, 2013
A complete characterization of the boundary of the stability region (or area of attraction) of no... more A complete characterization of the boundary of the stability region (or area of attraction) of nonlinear autonomous dynamical systems is developed admitting the existence of a particular type of nonhyperbolic equilibrium point on the stability boundary, the supercritical Hopf equilibrium point. Under a condition of transversality, it is shown that the stability boundary is comprised of all stable manifolds of the hyperbolic equilibrium points lying on the stability boundary union with the center-stable and\or center manifolds of the type-k, k ≥ 1, supercritical Hopf equilibrium points on the stability boundary.
Sba: Controle & Automação Sociedade Brasileira de Automatica, 2002
The purpose of this work is to obtain uniform estimates, with respect to parameters, of the attra... more The purpose of this work is to obtain uniform estimates, with respect to parameters, of the attractor and of the basin of attraction of a dynamical system as well as to apply these results to analyze the robustness of the synchronization of two coupled subsystems. These estimates are obtained through an uniform version of the Invariance Principle of LaSalle which is stated and proved in this work.
2014 IEEE PES General Meeting | Conference & Exposition, 2014
The two-time scale (TTS) CUEP/BCU method provides the correct calculus of the (uniform) controlli... more The two-time scale (TTS) CUEP/BCU method provides the correct calculus of the (uniform) controlling unstable equilibrium point (CUEP) for TTS power system models in transient stability problems. The energy of CUEP can be used to locally approximate the stability boundary and to provide a conservative critical clearing time (CCT) estimate, however the TTS-CUEP/BCU method also provides a CCT estimate for the fast subsystem, associated with the original TTS power system model, which potentially can be used as a better (less conservative) estimate of the CCT for the TTS model. Despite this fact, the TTS-CUEP/BCU method does not take advantage of this fast CCT estimate in the assessment of the CCT estimate of the TTS system. This paper propose a energy-guided timedomain simulation to accomplish this task.
Advances in Difference Equations, 2010
An extension of the uniform invariance principle for ordinary differential equations with finite ... more An extension of the uniform invariance principle for ordinary differential equations with finite delay is developed. The uniform invariance principle allows the derivative of the auxiliary scalar function V to be positive in some bounded sets of the state space while the classical invariance principle assumes thatV ≤ 0. As a consequence, the uniform invariance principle can deal with a larger class of problems. The main difficulty to prove an invariance principle for functional differential equations is the fact that flows are defined on an infinite dimensional space and, in such spaces, bounded solutions may not be precompact. This difficulty is overcome by imposing the vector field taking bounded sets into bounded sets.
In this paper, a less conservative sufficient condition that ensure the ultimate boundedness of t... more In this paper, a less conservative sufficient condition that ensure the ultimate boundedness of the solutions of switched TS fuzzy systems is proposed. The main result is given in terms of linear matrix inequalities (LMIs), which were formulated by calculating the derivative of the auxiliary function V along the solution of the system formed by a convex combination of the switching subsystems. The LMI conditions were relaxed using the S-procedure. A numerical example illustrates the efficiency of the proposed result.
2009 IEEE Power & Energy Society General Meeting, 2009
This paper proposes a new indirect approach to estimate the power angle of synchronous generators... more This paper proposes a new indirect approach to estimate the power angle of synchronous generators from three-phase currents and voltages, and field voltage measurements. An auxiliary algebraic equation, which relates the power angle with generator parameters and measurements, is included in the generator model. Therefore, the generator is modeled by a set of differential-algebraic equations (DAEs). The procedure is split
2005 IEEE Russia Power Tech, 2005
In this paper, a methodology to estimate parameters of synchronous generator and its excitation s... more In this paper, a methodology to estimate parameters of synchronous generator and its excitation system, based on the trajectory sensitivity technique, is proposed. Some alternatives are proposed for this technique regarding a future 'on-line' application. The parameters of classical and "two-axis"models of generator are estimated. An alternative is also proposed to overcome problems related to differential equations with variables that can not be measurable in the real system. The methodology developed is also used to estimate the parameters of the excitation system (STR1 and DC1 type) in a successful way.
POWERCON '98. 1998 International Conference on Power System Technology. Proceedings (Cat. No.98EX151), 1998
ABSTRACT The main concern of this paper is to create a methodology that, if incorporated to the B... more ABSTRACT The main concern of this paper is to create a methodology that, if incorporated to the BCU method of transient stability analysis, one can assure, for the one-machine-infinite-bus system (OMIB), the stability of the system and not the existence of the first swing only. The methodology constitutes in determining, in an iterative way, a critical damping coefficient that should be associated to the system, so that it is assured that the saddle points used as the controlling equilibrium point are on the boundary of the corresponding attraction area. That is, with that damping coefficient in the system, it can be assured that the one-parameter transversality condition will be satisfied. The methodology, as developed, is an iterative monotonically convergent process very easy to implement and does not require knowledge of fault trajectory at all. An example showing how the methodology works is also incorporated in the paper. The proposed methodology was also applied to a simple multimachine system. In that case however, the proposed methodology needs further studies and adaptation in order to be applied
IEEE Power Engineering Society General Meeting, 2005, 2005
The main concern of this paper is the proposal of an Extended Lyapunov Function (ELF) for a power... more The main concern of this paper is the proposal of an Extended Lyapunov Function (ELF) for a power system model that does not have Lyapunov Function in the usual sense. More precisely, an ELF is proposed for a network preserving model where both, the active and reactive load powers depend on voltage. Then the proposed ELF is used for short term stability analysis including voltage and angle instability phenomenon. The results show that the proposed function can be used to obtain good estimates of the critical clearing time.
PowerCon 2000. 2000 International Conference on Power System Technology. Proceedings (Cat. No.00EX409), 2000
ABSTRACT This paper presents a new topological method for critical measurements identification in... more ABSTRACT This paper presents a new topological method for critical measurements identification in observable networks. A measurement is said to be critical, in observability sense, if its removal from the measurement set leads the associated system to lose observability. The proposed method is based on the properties of both, observable islands (OI) and redundant branch sets (RBS). To reduce the combinatorial bluster, the proposed method divides the measurements in two groups and classifies then in two phases. Indeed, it is simple and fast. In order to clarify the proposed method and to show its simplicity, two examples are provided. The proposed method is successfully tested in the IEEE-14 bus system and in two realistic systems of the Brazilian utilities. The first one is a 121-bus system from ELETROSUL, and the other is a 383-bus system from CHESF (Companhia Hidroeletrica do Sao Francisco)
International Transactions on Electrical Energy Systems, 2013
ABSTRACT SUMMARY This paper proposes an index, called Undetectability Index (UI), to classify the... more ABSTRACT SUMMARY This paper proposes an index, called Undetectability Index (UI), to classify the measurements according to their characteristics of not reflecting their errors into the residuals of the weighted least squares state estimator (WLS) from a geometric analysis of this estimator. Gross errors in measurements with high UIs are very difficult to be detected by methods based on residual analysis, because the errors in those measurements are “masked”, i.e. they are not reflected in their residuals. The paper also presents a very simple algorithm to compute the UI of all available measurements in a metering system. This algorithm is very simple and uses routines already available in the existing WLS Estimator software. Two UI applications are investigated (i) to design more reliable metering systems for bad data processing, i.e. metering systems formed by measurements with UI lower than a pre-specified value and (ii) to estimate the measurement errors. Several simulation results (with IEEE-14 and 30 bus systems) have validated the propositions. Copyright © 2013 John Wiley & Sons, Ltd.
PowerCon 2000. 2000 International Conference on Power System Technology. Proceedings (Cat. No.00EX409), 2000
ABSTRACT This paper proposes a new methodology to study coherency in power systems. The methodolo... more ABSTRACT This paper proposes a new methodology to study coherency in power systems. The methodology is supported by a theoretical background and does not require the solution of the differential equations. The concept of weak coherency is defined as the coherency between a reduced gradient system associated to the power system equations. Much information can be derived from the weak coherency concept. One that is straightforward is the location of the unstable equilibrium points in the state space which can be very useful to improve transient stability analysis through direct methods
2003 IEEE Bologna Power Tech Conference Proceedings,, 2003
The main proposition of this work is the development of an Extended Lyapunov Function for multima... more The main proposition of this work is the development of an Extended Lyapunov Function for multimachine systems taking transfer conductance parameters in consideration. This function is obtained by applying smooth perturbations on the approximated energy-like function as proposed by Athay et al. [2]. This perturbed function is used to estimate critical clearing times (CCT) based on the Extension of Invariance Principle [14]. These estimates are based on a solid theoretical background and also the differences between the proposed Extended Lyapunov Function and the energy-like function is of the order of the smooth perturbation. Examples are given in a multimachine system case to validate the proposed Extended Lyapunov Function.
The main concern of this paper is the ap- plication of the Melnikov's method for computing h... more The main concern of this paper is the ap- plication of the Melnikov's method for computing heteroclinic orbits in a classical SMIB power system model and testing the one-parameter transversality condition required in the BCU method for transient stability analysis. First of all, the Melnikov's method is used to give a first approximation for the minimum damping coefficient, or alternatively for the maximum input mechanical power, that should be associated to the system, so that the transversality condition is satisfied. This first appro- ximation is obtained without solving any differential equation. After that, this approximation is used as an initial condition for a monotonically convergent process which is very easy to im- plement and does not require knowledge of fault trajectory at all.
Sba: Controle & Automação Sociedade Brasileira de Automatica, 2012
Este artigo propõe uma nova metodologia prática e robusta para estimar parâmetros de geradores sí... more Este artigo propõe uma nova metodologia prática e robusta para estimar parâmetros de geradores síncronos. A metodologia proposta utiliza a análise de sensibilidade de trajetória combinada com uma nova abordagem, denominada 'abordagem de minimização' para estimação de parâmetros de sistemas dinâmicos não-lineares modelados por conjuntos de equações algébricos diferenciais. Uma escolha adequada de entradas e saídas permite a divisão da estimação de parâmetros do gerador na estimação independente dos parâmetros elétricos e mecânicos. A metodologia é robusta com relação às condições iniciais dos parâmetros, não requer execução de testes especiais e utiliza apenas medidas de perturbações de fácil obtenção (correntes e tensões trifásicas, tensão de campo e velocidade do rotor) coletadas do sistema de energia elétrica sem desconectar o gerador da rede.
RESUMO -Neste artigo propõe-se um novo método para a identificação das medidas críticas e também ... more RESUMO -Neste artigo propõe-se um novo método para a identificação das medidas críticas e também dos conjuntos de medidas que, se perdidas simultaneamente, fazem um sistema de potência observável tornar-se não observável. Conhecendo-se essas medidas e esses conjuntos de medidas, o método permite a identificação do nível de redundância de cada uma das medidas, associadas a um sistema de potência observável. O método proposto baseia-se nas relações de dependência linear das linhas da matriz Jacobiana. Para determinar essas relações, uma conveniente mudança de base no espaço dos estados é realizada. A característica esparsa da matriz Jacobiana proporciona ao método uma boa velocidade de execução. Para comprovar a sua eficiência, vários testes foram realizados, utilizando para isso o sistema de 14 barras do IEEE, o sistema de 121 barras da ELETROSUL e um sistema de 384 barras da CHESF (Companhia Hidroelétrica do São Francisco).