Rodrigo A. Ramos

A new methodology for the coordinated design of robust decentralized power system damping controllers

This paper presents the fundamentals and the algorithm of a new methodology for the design of robust power system damping controllers. The methodology provides controllers capable of fulfilling various practical requirements of the oscillations damping problem, which could not be simultaneously satisfied by the majority of the proposed robust approaches until now. The design procedure is based on a special formulation of the dynamic output feedback control problem, which is very well suited for damping controller design. With this formulation, the design problem (which is originally stated as a set of bilinear matrix inequalities) can be expressed directly in the form of linear matrix inequalities. Furthermore, the formulation allows the incorporation of decentralization constraints on the controller matrices, which are one of the practical requirements for power system damping controllers. Another practical requirement is satisfied with the use of the polytopic model (to ensure the robustness of the closed-loop system with respect to the variation of operating conditions). Moreover, the inclusion of a regional pole placement criterion, as the design objective, allows the specification of a minimum damping factor for all modes of the controlled system. The results show the controller is able to provide adequate damping for the oscillation modes of interest.

An improved methodology for the design of power system damping controllers

This paper presents a set of significant improvements made over a previously developed methodology for the design of controllers to damp electromechanical oscillations in power systems. This previous methodology was able to fulfil several practical requirements of the oscillation damping problem, related to robustness, decentralization, and output feedback structure. However, problems related to an adequate controller gain (to avoid interactions with unmodeled dynamics) and disturbance rejection (allowing the use of noisy input signals, such as the rotor speed measurements) were not treated in this previously reported methodology, and are now addressed in this work. Moreover, the requirement of zero gain in steady-state conditions is now met in a more efficient way. The results of the nonlinear simulations show the satisfactory performance of the designed controllers with respect to the mentioned practical requirements.

Robust Design of a TCSC Supplementary Controller to Damp Inter-Area Oscillations

This paper presents a systematic method for the robust design of a supplementary controller for a TCSC device to damp inter-area oscillations in electric power systems. The method is based on a robust control technique structured in the form of linear matrix inequalities (LMIs). The polytopic model is used to guarantee the robustness of the controller with respect to the variations in the operating points of the system. The minimum damping ratio is used in the design stage as performance index for the closed loop system. The proposed controller is based on dynamic output feedback and uses only a local measurement of the active power flow as input signal for the controller, so communications links are avoided. The feasp solver, available in Matlab LMI Control Toolbox, is used to solve the set of LMIs formulated for the control problem. Performance analyses of the closed loop system were carried out by means of modal analysis and nonlinear simulations, showing that the controller is effective in improving the damping of inter-area oscillations of a two-area four-machine test system for several different operating points.

Modeling and evaluation of the protection of distributed synchronous generators connected to unbalanced systems

The study of the imbalance effect on the behavior of protection functions used in synchronous generators, which are directly connected in the distribution and sub transmission systems, is the subject of this work. Very few studies are available for this type of generation, commonly known as Distributed Synchronous Generation (DSG), in spite of its great potential in countries like Brazil, for instance. Within this context, this work presents a detailed modeling for DSG protection and its corresponding evaluation with a full representation of the three-phase system. The results from simulations show the effect of imbalance on the performance and behavior of the types of protection present in distribution systems with DSGs. It was verified that there are cases where the representation of the unbalanced system is necessary for the correct analysis of the protection system performance and its adjustments.

CONTROLADOR ROBUSTO MULTIOBJETIVO PARA O AMORTECIMENTO DE OSCILAÇÕES ELETROMECÂNICAS EM SISTEMAS ELÉTRICOS DE POTÊNCIA

The present paper proposes the application of robust control techniques for the development of a systematic design methodology of multiobjective controllers to damp low-frequency electromechanical oscillations in electric power systems. The control technique adopted considers the uncertainties regarding to the variations of the electric power system operating conditions. The imposition of an upper bound for the output energy of the closed loop system and the regional pole placement are used as design objectives in the proposed methodology. The upper bound for the output energy is proposed as a performance index in the design of damping controllers for power systems. The design methodology is structured to provide controllers that fulfill various practical requirements of the electromechanical oscillations problem in electric power systems. The presented results demonstrate the effectiveness of the designed controllers.

Development and application of a comprehensive small signal stability package embedded in an automatic disturbance analysis multi-agent system

This work presents a case of integration of a small signal stability simulation algorithm in an Automatic Disturbance Analysis software. The small signal stability simulation algorithm is presented in a step by step solution of a chosen case. The algorithm is available for free download1, in order to allow others engineers to reproduce the results and to discuss the developed code. The algorithm was validated using benchmark software, integrated to a multi-agent system for automatic disturbance analysis. The algorithm performance was tested using disturbance cases, which presented satisfying results.

Guidelines resulting from modeling, evaluation and coordination enhancement of Itaipu hydro power plant protection

Generator protection misoperations may intensify a disturbance or even lead the power system to a major outage, especially when it occurs in a large power plant. Additionally, the power system expansion changes the short circuit currents and, thus, from time to time the system requires a re-evaluation of protection coordination. In this paper, Itaipu power plants modeling, analysis and coordination evaluation of the protection functions performed due to scheduled technological update are presented. Lessons learned and undesirable situations concerning operation of large generators connected to large transmission systems observed during this process were used to propose a set of guidelines for overexcitation protection coordination evaluation for generators with the same type of configuration.

Integrating Hierarchical Clustering and Pareto-Efficiency to Preventive Controls Selection in Voltage Stability Assessment

Many methods to estimate the cut-off value in order to determine the actual groups from a dendrogram given via hierarchical clustering methods have been proposed in the litetarure. However, in most of the cases, the determination of this value is critical and based on heuristics. In this context, a new method based on Pareto-optimality and on the hierarchical clustering method called Data Mine of Code Repositories (DAMICORE) to determine the most promising groups in a given dendrogram is proposed. This method is called Pareto-Efficient Set Algorithm (PESA). In order to validate the proposed method, PESA was applied find the most promising groups for the preventive control selection problem in the context of voltage stability assessment in electrical power systems. PESA was able to design a set of controllers to eliminate all critical contingencies and was successfully tested in a reduced south-southeast Brazilian system composed of 107 buses.

Calculation of parameter ranges for robust gain tuning of power system controllers

O presente trabalho propoe uma ferramenta computacional para auxiliar engenheiros de sistemas de potencia no ajuste em campo de controladores de amortecimento e reguladores automaticos de tensao. A abordagem proposta gera faixas de valores de parâmetros para o ajuste em campo dos controladores do sistema. As faixas de valores geradas teoricamente garantem a estabilidade para o sistema em malha fechada. Estas faixas de valores sao dadas na forma de valores limites para os ganhos estaticos dos controladores de interesse, de maneira que o engenheiro responsavel pelo ajuste em campo dos controladores tenha garantia da estabilidade do sistema durante o ajuste do ganho do controlador. Esta caracteristica da abordagem proposta e altamente desejavel do ponto de vista pratico, pois a etapa de comissionamento de controladores de amortecimento e reguladores automaticos de tensao sempre envolve algum reajuste dos ganhos dos controlares, devido as diferencas entre o modelo nominal e o comportamento real do sistema. Considerando essas diferencas como incertezas no modelo, a ferramenta proposta e capaz de garantir estabilidade para o modelo incerto usando uma abordagem baseada em desigualdades matriciais lineares. A metodologia proposta pode ser tambem aplicada para o ajuste de outros tipos de parâmetros de controladores de amortecimento, assim como para o ajuste de outros tipos de controladores (por exemplo, reguladores de velocidade). Dois modelos de sistemas de potencia tipicamente utilizados em estudos de estabilidade sao considerados para a aplicacao e avaliacao da ferramenta proposta.

A mixed procedure based on classical and modern control to design robust damping controllers

Summary form only given. A systematic mixed procedure based on classical and robust control techniques is proposed in this work for the design of robust low-order damping controllers. The procedure formally guarantees a robust performance index for the system in closed loop by employing a minimum performance index associated with a robust control technique. The mixed approach aims at providing an acceptable and easy-to-use robust design procedure as well as controllers with a simple and typical structure. Besides, a great variety of mathematical tools for the analyses and design of control systems may be employed in the overall procedure. The tests and results have shown that the overall procedure is suitable for the oscillation problem in power systems and that the resulting controllers are robust and effective in the damping of low-frequency electromechanical oscillations.