No description available.

Electrical Power System is one of the most complex real time operating systems. It is probably one of the best examples of a large interconnected nonlinear system of varying nature. The system needs to be operated and controlled with component or system problems, often with combinatorial complexity. In addition, time scales of operation and control can vary from milliseconds to minutes to hours. It is difficult to maintain such a system at constant operating condition due to both small and large disturbances such as sudden change in loads, change in network configuration, fluctuations in turbine output, and various types of faults etc. The system is therefore affected by a variety of instability problems. Among all these instability problems one of the important modes of instability is related to dynamic instability or more precisely the small perturbation oscillatory instability. Oscillations of small magnitude and low frequency (in the range of 0.1Hz to 2.5Hz) could persist for long periods, limiting the power transfer capability of the transmission lines. Power System Stabilizers (PSS) were developed as auxiliary controllers on the excitation system to improve the system damping performance by modulating the generator excitation voltage. However, the synthesis of an effective PSS for all operating conditions still remains a difficult and challenging task. The design and tuning of PSS for robust operation is a laborious process. The existing PSS design techniques require considerable expertise, the complete system information and extensive eigenvalue calculations which increases the computational burden as the system size increases. Conventional automatic voltage regulator (AVR) and PSS designs are based on linearized models of power systems which fail to stabilize the system over a wide range of operating conditions. In the last decade or so, a variety of nonlinear control techniques have become available. In this thesis, an attempt is made to explore the suitability of some of these design techniques for designing excitation controllers to enhance small perturbation stability of power systems over a wide range of operating and system conditions. This thesis first proposes a method of designing power system stabilizers based on local measurements alone, in multi-machine systems. Next, a method has been developed to analyze and quantify the small signal performance benefits of replacing the existing AVR+PSS structure with nonlinear voltage regulators. A number of new nonlinear controller designs have been proposed subsequently. These include, (a) a new decentralized nonlinear voltage regulator for multi machine power systems with a single tunable parameter that can achieve effective trade of between both the voltage regulation and small signal objectives, (b) a decentralized Interconnection and Damping Assignment Passivity Based Controller in addition to a proportional controller that can achieve all the requirements of an excitation system and (c) a Nonlinear Quadratic Regulator PSS using Single Network Adaptive Critic architecture in the frame work of approximate dynamic programming. Performance of all the proposed controllers has been analyzed using a number of multi machine test systems over a range of operating conditions.

Orientador: Percival Bueno de Araujo / Resumo: As perturbações ou variações de carga produzem oscilações eletromecânicas que devem ser amortecidas o mais rápido possível para garantir confiabilidade e estabilidade da rede. Neste trabalho apresenta-se uma análise do dispositivo FACTS Interline Power Flow Controller (IPFC) e o controlador Proporcional Integral (PI) no gerenciamento dos fluxos de potência e a influência dos Estabilizadores do Sistema de Potência (ESP) e do IPFC Power Oscillation Damping (POD) sobre a estabilidade do sistema elétrico de potência. Neste trabalho enfoca-se nos estudos de estabilidade a pequenas perturbações usando um Algoritmo Genético Adaptativo com Hiper-mutação (AGAH) para ajustar os parâmetros dos controladores suplementares de amortecimento, o Estabilizador de sistema de potência (ESPs) e o Power Oscillation Damping (POD) em forma coordenada. O AGAH tem como objetivo encontrar os parâmetros ótimos do controlador para melhorar o amortecimento fraco das oscilações de baixa frequência locais e inter-área. Neste trabalho representa-se o sistema de elétrico de potência com a inclusão do dispositivo Interline Power Flow Controller com o modelo de sensibilidade de corrente (MSC). Considera-se como sistema teste o sistema Simétrico de Duas Áreas e o sistema New England como o intuito de avaliar o algoritmo proposto. As simulações são feitas no ambiente do MatLab. Por fim, apresenta-se a comparação do algoritmo genético com o desempenho do algoritmo proposto. / Abstract: Small-magnitude disturbances happen to produce electro-mechanical oscillations which should be damped as quickly as possible to ensure reliability and stability of the network. This work presents an analysis of Interline Power Flow Controller (IPFC) FACTS device and PI controller to control and manage power flow and also how Power System Stabilizers and IPFC Power Oscillations Damping (POD) controller influence over an electric power system stability. This work focuses on small-signal stability studies using an Adaptive Genetic Algorithm with Hyper-mutation (AGAH) in order to tune controller parameters in a coordinated way ensuring proper damping. AGAH aims to find optimal controller parameters to enhance the poor damping of local and inter-area low frequency oscillations. This works represents the electric power system and Interline Power Flow Controller device by a current sensitivity model (CSM). This paper considers two areas 14 bus symmetrical power system and New England power system in order to assess proposed algorithm. Coding and Simulations take place in MatLab platform. AGAH and GA get compared by time convergence and performance. This paper shows AGAH is an interesting optimization technique which outweighs GA. / Mestre

Neste trabalho é apresentada uma abordagem fuzzy para a estabilização de uma classe de sistemas não-lineares com parâmetros descritos por saltos Markovianos. Uma nova modelagem fuzzy de sistemas é formulada para representar esta classe de sistemas na vizinhança de pontos de operação escolhidos. A estrutura deste sistema fuzzy é composta de dois níveis, um para descrição dos saltos Markovianos e outro para descrição das não-linearidades no estado do sistema. Condições suficientes para a estabilização estocástica do sistema fuzzy considerado são derivadas usando uma função de Lyapunov acoplada. O projeto de controle fuzzy é então formulado a partir de um conjunto de desigualdades matriciais lineares. Em adição, um exemplo de aplicação, envolvendo a representação da operação de um sistema elétrico de potência em esquema de co-geração por um sistema com saltos Markovianos, é construído para validação dos resultados. / This work deals with the fuzzy-model-based control design for a class of Markovian jump nonlinear systems. A new fuzzy system modeling is proposed to approximate the dynamics of this class of systems. The structure of the new fuzzy system is composed of two levels, a crisp level which describes the Markovian jumps and a fuzzy level which describes the system nonlinearities. A sufficient condition on the existence of a stochastically stabilizing controller using a Lyapunov function approach is presented. The fuzzy-model-based control design is formulated in terms of a set of linear matrix inequalities. In addition, simulation results for a single-machine infinite-bus power system in cogeneration scheme, whose operation is modeled as an Markovian jump nonlinear system, are presented to illustrate the applicability of the technique.

Small signal oscillation has been always a major concern in the operation of power systems. In a generator, the electromechanical coupling between the rotor and the rest of the system causes it to behave in a manner similar to a spring mass damper system. Following any disturbance, such as sudden change in loads, actuations in the output of turbine and faults etc. it exhibits an oscillatory behaviour around the equilibrium state. The use of fast acting high gain AVRs and evolution of large interconnected power systems with transfer of bulk power across weak transmission links have further aggravated the problem of these low frequency oscillations. Small oscillations in the range of about 0.1Hz to 3.5Hz can persist for long periods, limiting the power transfer capability of the transmission lines. These oscillations can be reduced by incorporating auxiliary controllers on generator excitation system. Power System Stabilizers (PSSs) were developed to produce additional damping by modulating the generator excitation voltage. Designing effective PSS for all operating conditions especially in large interconnected power systems still remains a difficult and challenging task. More and more power electronic based controllers have been and will be used in power systems. Many of these controllers such as Static Var Compensators (SVCs), Static Synchronous Compensators (STATCOMs) and Unified Power Flow Controllers (UPFCs) etc., are incorporated in power transmission networks to improve its operational capability. In addition, some of the energy storage systems such as Battery Energy Storage systems (BESS), Super conducting Magnetic Energy Storage System (SMES) as well large non-conventional energy sources are also increasingly being integrated with the power grid. With large integration of these devices, there is a significant impact on system stability, more importantly on small signal oscillatory instability of the power system. This thesis primarily focuses on impact of such devices on small signal oscillatory stability of the power systems. More specifically in this thesis small signal stability analysis of a Single Machine Infinite Bus (SMIB) system with a grid connected wind powered Permanent Magnet Synchronous Generator (PMSG) has been presented. A SMIB system has been purposely chosen so that general conclusions can be obtained on the behaviour of the embedded STATCOM/Energy Source (ES) system on system stability. With a better understanding of the impact of such a system it would be probably possible to analyze more complicated multimachine power system and their impact on system stability. Small signal model of the complete system which comprises the generator, transmission network, inter connecting STATCOM, the wind power generator and all associated controllers has been developed. The performances of the system following a small disturbance at various operating conditions have been analyzed. To obtain quantitative estimates of the damping and synchronizing torques generated in the system, expressions for damping and synchronizing torque clients have been developed. With these analyses, the relative impact of the STATCOM and STATCOM with ES on system performance have been assessed. It is shown that with active and reactive power modulation capabilities effective and efficient control of small signal oscillations in power systems can be achieved.

Neste trabalho é apresentada uma abordagem fuzzy para a estabilização de uma classe de sistemas não-lineares com parâmetros descritos por saltos Markovianos. Uma nova modelagem fuzzy de sistemas é formulada para representar esta classe de sistemas na vizinhança de pontos de operação escolhidos. A estrutura deste sistema fuzzy é composta de dois níveis, um para descrição dos saltos Markovianos e outro para descrição das não-linearidades no estado do sistema. Condições suficientes para a estabilização estocástica do sistema fuzzy considerado são derivadas usando uma função de Lyapunov acoplada. O projeto de controle fuzzy é então formulado a partir de um conjunto de desigualdades matriciais lineares. Em adição, um exemplo de aplicação, envolvendo a representação da operação de um sistema elétrico de potência em esquema de co-geração por um sistema com saltos Markovianos, é construído para validação dos resultados. / This work deals with the fuzzy-model-based control design for a class of Markovian jump nonlinear systems. A new fuzzy system modeling is proposed to approximate the dynamics of this class of systems. The structure of the new fuzzy system is composed of two levels, a crisp level which describes the Markovian jumps and a fuzzy level which describes the system nonlinearities. A sufficient condition on the existence of a stochastically stabilizing controller using a Lyapunov function approach is presented. The fuzzy-model-based control design is formulated in terms of a set of linear matrix inequalities. In addition, simulation results for a single-machine infinite-bus power system in cogeneration scheme, whose operation is modeled as an Markovian jump nonlinear system, are presented to illustrate the applicability of the technique.