F. D. Freitas

• PhD
• Professor (Full) at University of Brasília

Some nonlinear real-valued equations have no solution in the real number field, and only roots of this nature are of practical interest. However, complex roots associated with the solution may introduce an interpretation of the physical problem analysis. This paper investigates the solution of nonlinear equations exploiting fractional order derivat...

This paper presents a dynamic homotopy technique that can be used to calculate a preliminary result for a power flow problem (PFP). This result can then be used as an initial estimate to efficiently solve the PFP using either the classical Newton-Raphson (NR) method or its fast decoupled version (FDXB) while still maintaining high accuracy. The pre...

This paper presents a dynamic homotopy technique that can be used to calculate a preliminary result for a power flow problem (PFP). This result can then be used as an initial estimate to efficiently solve the PFP using either the classical Newton-Raphson (NR) method or its fast decoupled version (FDXB) while still maintaining high accuracy. The pre...

This paper presents an approach to calculating the solution to the Power Flow Problem (PFP) in ill-conditioned large-scale system models. The proposed procedure is based on the introduction of a conditioning step applied to the initial estimate attributed to the PFC. This procedure is performed by adding a low-norm diagonal matrix (small disturbanc...

This paper presents a technique based on homotopy to determine the solution to the the ill-conditioned large-scale power flow problem (PFP). The homotopy-based method is used to determine the PFP solution, starting from an initial estimate of the voltage type flat start, which also coincides with the solution of the initial point of the homotopy tr...

This paper proposes a strategy to identify the parameter data for representing an 11- bus system for execution as a case in the MATPOWER software and discusses the ill-conditioned problem associated with it. The referred power system model is largely studied for evaluating iterative nonlinear method performances considering ill-conditioned systems....

This paper presents a contribution to the solution of the power flow problem with HVDC by using a free access tool to its code. For this purpose, it was proposed to use the wellknown MATPOWER tool to incorporate HVDC. The original program only allows AC networks implementations. To include HVDC, the Newton-Raphson Fast Decoupled (NRFD) method was u...

Based on a modal approach, this letter identifies the primary cause for the ill-conditioning of a Power Flow Problem (PFP) and proposes a method to circumvent this numerical weakness. The technique consists in modifying the ill-conditioned PFP Jacobian matrix for the standard Newton method initial iterate by moving away just its smallest magnitude...

This paper proposes a hybrid technique to solve the ill-posed Power Flow Problem (PFP), considering a homotopy approach. The primary proposal is to solve large-scale problems where the traditional Newton– Raphson (NR) fails to converge, as in the case of ill-posed systems. The method explores a dynamical homotopy transient-based technique to improv...

This paper proposes a homotopy-based approach to solve the power flow problem (PFP) in islanded microgrid networks with droop-controlled distributed generation (DG) units. The technique is based on modifying an “easy” problem solution that evolves with the computation of intermediate results to the PFP solution of interest. These intermediate resul...

This short communication describes a conditioning step applied to the initial estimate used in the numerical iterative method to resolve the ill-conditioned power flow problem (PFP). The conditioning step consists of modifying the iterative method’s initial estimate through a process involving the Jacobian matrix and the mismatch of the balance equ...

This paper presents a hybrid method to calculate the power flow problem (PFP) solution for ill-conditioned and large-scale power system models. The hybrid approach is composed of two steps. The first consists of calculating a partial solution of the PFP from a flat start estimate, which is characterized by low precision mismatches and a small compu...

This paper presents an approach for solving the Economic Dispatch Problem (EDP) in power systems considering transmission losses in a recursive manner via a Holomorphic Embedding Method (HEM) applied to the IEEE 14 Bus system and tested for different loading scenarios. The HEM methodology has been proposed recently in power system to solve the powe...

LINK for free downloading before July 13, 2022: https://authors.elsevier.com/a/1f7gKWJH6ZYLn This paper presents a homotopy-based method to calculate the solution of a power flow problem (PFP) starting from a flat initial guess. This Guided Solution by Homotopy-Newton–Raphson (GSH-NR) method uses only the standard NR technique to compute the PFP f...

In this report we present a study on the computation of dominant spectral-zeros (DSZ) of a full order model (FOM) and its application to determining a passivity-preserving reduced order model (ROM). The study demonstrates that introducing a properly scaled transmission term into a Hamiltonian system allows one to more effectively compute the DSZs b...

Este artigo apresenta abordagens para o cálculo da solução do Problema de Fluxo de Carga (PFC) via método de adaptação holomórfica (Holomorphic Embedding Method - HEM). Duas abordagens para o cálculo de aproximações de Padé com fração racional tendo denominador comum são propostas. A partir destas aproximações, são calculados equivalentes modais ob...

Este artigo apresenta resultados da investigação de métodos numéricos para a solução do clássico Problema de Despacho Econômico (PDE) em sistemas de potência, estendido para redes com múltiplas barras e considerando as perdas de transmissão. O PDE é concebido na sua forma tradicional, com formulação baseada em um problema de otimização com restriçõ...

Security and quality of supply continue to be major concern of power system operators. Thus, the expansion of transmission grids is certainly one of the major drivers to achieve this goal. In this scope, this paper presents a three-stage approach to solve the multi-year Transmission Expansion Planning (TEP) problem. This approach uses heuristic alg...

The holomorphic embedding load-flow model (HELM) is a noniterative method based on the computation of a Taylor power series that is a function of an embedded parameter. In this method, a continuous function based on a Padé approximant is used to replace this series, extending the radius of convergence. However, depending on the problem and how it i...

This paper proposes a method for the Model Order Reduction (MOR) of large scale power system models that produces Reduced Order Models (ROM) which preserve the access to selected parameters exactly like the original Full Order Model (FOM). The preserved parameters are related to decentralized power system devices, including, but not limited to, pow...

This paper proposes an approach to solve the load balance (LB) problem which is typical at the low voltage side of a three-phase electrical installation. The approach is based on the application of the metaheuristic optimization algorithm named as Harmony Search (HS) to deal with the combinatorial and integer programming related to LB. A practical...

This work presents a hybrid method based on Harmony Search (HS) and Branch & Bound (B&B) to solve the problem of Static (PEEST) and Dynamic (PDEST) Transmission Network Expansion Planning in electrical power systems. The result of this formulation is mixed-integer nonlinear programming, where the difficulties are intensified in the PDEST by the tem...

RESUMO: Antes da revolução computacional ocorrida nas últimas décadas, a maioria dos algoritmos de otimização em engenharia era baseada em métodos de programação linear, e ou não linear. Tais métodos normalmente requerem informação do gradiente e usualmente necessitam de serem bem inicializados, ou seja, terem a solução inicial próxima do ótimo glo...

This work presents a method based on metaheuristics to solve the problem of Static (STNEP) and Dynamic (DTNEP) Transmission Network Expansion Planning in electrical power systems. The result of this formulation is mixed-integer nonlinear programming (MINLP), where the difficulties are intensified in the DTNEP by the temporal coupling. Therefore, a...

RESUMO: Este trabalho apresenta uma abordagem que utiliza uma associação dos métodos de barreira modificada e de pontos interiores primal-dual para a resolução do problema de Fluxo de Potência Ótimo (FPO) reativo a fim de determinar as tensões nos barramentos para 10 valores aleatórios de susceptância da linha 2-3. Na abordagem proposta foi utiliza...

This paper aims to study the surface gradient potential (SGP) of overhead line conductors in ultra-high voltage (UHV) transmission lines. The SGP is crucial for the performance due to the corona effect. The purpose is to assess the calculation of the gradient of bundle conductors and the main factors that influence this calculation. It is accomplis...

A fast and accurate model order reduction procedure is presented that can successfully be applied to spectral methods for uncertainty quantification problems. The main novelties include (1) the application of model order reduction to uncertainty quantification problems; (2) the improvement of existing model order reduction methods in order to meet...

The combined use of modal and balanced truncations methods is proposed for model order reductions. To efficiently combine these methods, a stopping criterion based on spectral energy concepts is also proposed. This criterion was implemented into the code of the widely known subspace accelerated dominant pole algorithm (SADPA), designed to compute a...

This paper describes the first reliable Newton algorithm for the sequential computation of the set of dominant poles of scalar and multivariable transfer functions of infinite systems. This dominant pole algorithm incorporates a deflation procedure, which is derived from the partial fraction expansion concept of analytical functions of the complex...

This paper proposes three indices which should be best used in combination for the automatic determination of reduced order models (ROMs) for large dynamic linear systems. The first index determines the range in the frequency response of the complete model which contains most of the signal energy, say 95%, and which the ROM should attempt to reprod...

This paper proposes an alternative option to model a dynamical power system process. The model is based on a matrix polynomial form. The model can be obtained naturally writing the high order differential equations of some components (e.g. transmission line models modeled by sequences of RLC PI circuits in power systems) or some subsystems which co...

Esta contribuição técnica (CT) apresenta modelagens para representação dinâmica utilizada em sistemas elétricos de potência. É proposta uma representação por polinômio matricial, cujo desempenho é comparado com o de uma representação de estado tradicional. O modelo por polinômio matricial é obtido excluindo-se linhas e colunas de uma matriz aumenta...

Neste trabalho são propostos dois índices relacionados à determinação automática de Modelos de Ordem Reduzida (MORs) para sistemas dinâmicos lineares de grande porte. O primeiro informa o limite superior da faixa de frequências que o MOR deverá reproduzir, com determinada exatidão, o comportamento do modelo completo. O segundo informa o número de p...

Neste trabalho é proposto um novo método para a obtenção de equivalentes dinâmicos de redes elétricas multi-conectadas (quando existem mais de uma barra de conexão entre as áreas de estudo e externa). Neste método, as impedâncias primitivas são escritas como somatórios de frações parciais em função dos seus pólos dominantes e resíduos associados. U...

This paper compares the computational performances of four model order reduction methods applied to large-scale electric power RLC networks transfer functions with many resonant peaks. Two of these methods require the state-space or descriptor model of the system, while the third requires only its frequency response data. The fourth method is propo...

This paper presents an efficient linear system reduction method that computes approximations to the controllability and observability Gramians of large sparse power system descriptor models. The method exploits the fact that a Lyapunov equation solution can be decomposed into low-rank Choleski factors, which are determined by the Alternating Direct...

This paper presents a method for the delimitation of areas of power systems, through the determination of coherent groups of generators. In the decomposition model presented the structure of the system is explored through an analysis and quantification of the robustness of the connection between the generating units through appropriate coupling fac...

Knowledge of the rightmost eigenvalues of system matrices is essential in power system small-signal stability analysis. Accurate and efficient computation of the rightmost eigenvalues, however, is a challenge, especially for large-scale descriptor systems. In this paper we present an algorithm, based on subspace accelerated Rayleigh quotient iterat...

Objetivo: Apresentar uma metodologia para a determinação de um equivalente dinâmico, com estruturas definidas de geradores e controladores, capaz de substituir uma parcela de um SEP delimitado por uma área externa.

Este trabalho apresenta um método para a obtenção de equivalente dinâmico projetado com a finalidade de substituir parcela de um Sistema Elétrico de Potência (SEP) de grande porte. Para essa finalidade, o sistema original é dividido em uma área interna (as suas barras, equipamentos e ligações são preservados) e uma área externa (sistema elétrico fi...

Este trabalho apresenta uma metodologia para a obtenção de equivalentes dinâmicos capazes de substituir parcelas de um SEP de pequeno ou grande porte, por uma ou mais barras, geradores e seus respectivos controles equivalentes. Para isso, separou-se o sistema em uma área externa (a ser substituída pelo equivalente) e uma área interna (a ser preserv...

This paper presents an efficient linear system reduction method that computes approximations to the controllability and observability gramians of large sparse power system descriptor models. The method exploits the fact that a Lyapunov equation solution can be decomposed into low-rank Choleski factors, which are determined by the alternating direct...

This paper presents a technique to identify a single-input multiple-output (SIMO) model and extract from it the approximate dominant poles and associated system mode-shapes. The technique simultaneously identifies all rotor speed deviations, when a mechanical power disturbance is applied to the input of a single generator. The SIMO model has an inh...

This paper presents a technique to determine the optimal H_infin state-feedback control gain. This gain leads to a closed loop system with the best level of disturbance attenuation. The proposed method uses convergence characteristics of the bisection method and iterative solutions of algebraic Riccati equations (AREs). The numerical inst...

Este artigo descreve o uso de métodos de redução da ordem de modelos dinâmicos aplicados aos sistemas elétricos de potência. Aproximações baseadas na solução numérica das equações de Lyapunov são utilizadas como ferramentas no método da raiz quadrada de posto incompleto para redução de sistemas dinâmicos. Um sistema-teste baseado em um equivalente...

Este trabalho apresenta um método para cálculo da solução de uma equação de Lyapunov de baixo posto (rank). O resultado é utilizado para determinação de uma representação dinâmica reduzida para sistemas de potência modelados para estudo de pequenas perturbações. A redução de sistema utiliza também a técnica de truncamento balanceado, caracterizada...

This paper describes the use of reduction order methods applied to dynamic power system models. Approaches based on the classical Lanczos, implicitly restarted Lanczos methods and Balanced truncation algorithm are presented. Two test-systems are used in order to perform numerical simulation and evaluate the performance of the techniques. Results co...

This paper considers the design of continuous-time state-feedback H_infin control for large scale systems. The optimal H_infin state feedback gain is deduced using Chandrasekhar-type equations. This deduction allows to compute the control gain matrix and attenuation level through numerical integration techniques. This leads to g...

This paper presents a study related to the design of supplementary controllers for stabilizing and damping electromechanical oscillations on a long radial power system. Power system stabilizers (PSSs) in generators and a supplementary controller in a static Var compensator (SVC) are tuned. The power system is based on a new interconnected Brazilian...

The restructuring of the Brazilian Electric Sector (SEB) which occurred in the last years introduced the competition in the generation of electric energy. Such opening process gives opportunity for several independent power producers (IPPs) to have freely access to the transmission network and to offer electric energy to large customers or to distr...

This paper presents an approach for investigating the statistical behavior of voltage harmonic distortions on a commercial load. Stochastic process tools are proposed for analyzing the problem of total harmonic distortion (THD). Voltage signals are used to perform the study. Indices such as probability and time means are employed for verifying cond...

Attention is focused on the efficient application of optimal control methods with structural constraints to large power systems. A novel framework for linear-quadratic regulator problems is proposed which allows the use of matrix and vector sparsity techniques in the solution process. Results concerning the proposed method's computational performan...

Attention is focused on the efficient application of optimal control methods with structural constraints to large power systems. A novel framework for linear-quadratic regulator problems is proposed which allows the use of matrix and vector sparsity techniques in the solution process. Results concerning the proposed method's computational performan...

This paper proposes a method for the design of power system controllers aimed at damping out electromechanical oscillations. It can be applied to the design of both power system stabilizers (PSSs) for synchronous generators and supplementary signals associated with other damping sources. Some attractive features of the method are: the parameters of...

This paper presents a computationally efficient method for calculating the optimal feedback gain applicable to large scale systems. The plant is represented by using descriptor systems and the gain is calculated directly through the numerical integration of the Chandrasekhar equations. This allows the application of modern sparsity techniques, thus...

This paper proposes an integrated method for power system stabilizer design applicable to multimachine systems. The parameters of all stabilizers are jointly determined, so that the dynamic interactions among the system machines are properly taken into account during the design procedure. By imposing output feedback and decentralization as structur...

SUMMARY This paper presents simulation results related to the Brazilian interconnected network dynamic studies. The main purpose is to verify the effectiveness of probing signals used to excite dominant modes of the system and allow their sufficiently accurate measurement. The problem consists in computing modal characteristics from time response s...