Many environments are inaccessible or hazardous for humans. Remaining debris after earthquake and fire, ship hulls, bridge installations, and oil rigs are some examples. For these environments, major effort is being placed into replacing humans with robots for manipulation purposes such as search and rescue, inspection, repair, and maintenance. Mobility, manipulability, and stability are the basic needs for a robot to traverse, maneuver, and manipulate in such irregular and highly obstructed terrain. Hexapod walking robots are as a salient solution because of their extra degrees of mobility, compared to mobile wheeled robots. However, it is essential for any multi-legged walking robot to maintain its stability over the terrain or under external stimuli. For manipulation purposes, the robot must also have a sufficient workspace to satisfy the required manipulability. Therefore, analysis of both workspace and stability becomes very important. An accurate and concise inverse kinematic solution for multi-legged robots is developed and validated. The closed-form solution of lateral and spatial reachable workspace of axially symmetric hexapod walking robots are derived and validated through simulation which aid in the design and optimization of the robot parameters and workspace. To control the stability of the robot, a novel stability margin based on the normal contact forces of the robot is developed and then modified to account for the geometrical and physical attributes of the robot. The margin and its modified version are validated by comparison with a widely known stability criterion through simulated and physical experiments. A control scheme is developed to integrate the workspace and stability of multi-legged walking robots resulting in a bio-inspired reactive control strategy which is validated experimentally.

When designing or reviewing control systems, it is important to understand the limitations of the system's design. Many systems today are designed using numerical methods. Although the numerical model may be controllable, stabilizable, or stable, small perturbations of the system parameters can result in the loss of these properties. In this thesis, we investigate these issues for finite element approximations of a thermal convection loop. / Master of Science

A complexidade da avaliação de segurança em sistemas de potência vem se tornando elevada, principalmente devido ao aumento por demanda de energia elétrica. Diariamente são inseridas cargas de forma sucessiva nos sistemas elétricos, podendo este fato conduzir o sistema ao colapso, caso não haja um planejamento adequado que evite tal ocorrência. Visando evitar um cenário de instabilidade, metodologias de estudo relativas à determinação de máximo carregamento para sistemas elétricos de potência vem sendo estudadas e desenvolvidas. Apesar de apresentarem avanços, este trabalhos possuem limitações que os impedem de serem utilizados em estudos de pré-operação e até em tempo real nos centros de operação. Considerando estas limitações, este trabalho apresenta o desenvolvimento de uma metodologia direta e combinada para determinar o ponto de perda de estabilidade do sistema (a máxima transferência de potência, ou o aparecimento de bifurcações de Hopf), a partir de um sistema de equações diferenciais-algébricas. Esta metodologia engloba características fundamentais para os estudos supracitados como velocidade e robustez. Desta forma, um aplicativo computacional para a avaliação de segurança de um sistema de potência baseado na metodologia proposta foi desenvolvido contemplando a determinação da margem de estabilidade devido a bifurcações no sistema de forma eficiente e robusta. Para tanto, esta tese apresenta uma contextualização da necessidade desta ferramenta, realiza modificações na metodologia direta de determinação da margem de estabilidade devido a oscilações no sistema coma finalidade de elevar sua faixa de convergência e desenvolve uma metodologia direta para determinação de bifurcações Sela-Nó. Por fim, o aplicativo final foi validado, utilizando a ferramenta Organon, em diversos sistemas incluindo o sistema interligado nacional modificado, juntamente com a avaliação de uma lista de contingências para o mesmo. / Security assessment complexity in power systems is becoming higher primarily due to increased demand for electricity. Daily, loads are successively connected to the power grids, which can actually lead the system to the collapse, if there is no adequate planning to avoid it. To avoid an instability scenario, methodologies for the determination of maximum loading for a power system have been studied and developed. Inspite of their progress, these works have limitations that prevent them from being used in pre-operation studies and even in real time in operation centers. Considering these limitations, this work presents the development of a direct and combined methodology to determine the operating point where the system stability is lost (the maximum power transfer or the oscillations appearance due to Hopf bifurcation), through differential-algebric equations. This methodology includes fundamental characteristics for the aforementioned studies such as speed and robustness. Thus, a computer application for power system security assessment based on the proposed methodology was developed with the objective of determining efficiently the stability margin due to bifurcations in the system. Therefore, this thesis presents an overview of the need for this tool, as well as changes to the direct method of determining the systems stability margin due to oscilations, with the purpose of increasing its convergence range and develops a methodology for direct determination of saddle-node bifurcations points. Finally, the final developed application is validated, using the Organon tool, in several systems including the national interconnected system modified in which a list of contingencies are evaluated for this system.

A complexidade da avaliação de segurança em sistemas de potência vem se tornando elevada, principalmente devido ao aumento por demanda de energia elétrica. Diariamente são inseridas cargas de forma sucessiva nos sistemas elétricos, podendo este fato conduzir o sistema ao colapso, caso não haja um planejamento adequado que evite tal ocorrência. Visando evitar um cenário de instabilidade, metodologias de estudo relativas à determinação de máximo carregamento para sistemas elétricos de potência vem sendo estudadas e desenvolvidas. Apesar de apresentarem avanços, este trabalhos possuem limitações que os impedem de serem utilizados em estudos de pré-operação e até em tempo real nos centros de operação. Considerando estas limitações, este trabalho apresenta o desenvolvimento de uma metodologia direta e combinada para determinar o ponto de perda de estabilidade do sistema (a máxima transferência de potência, ou o aparecimento de bifurcações de Hopf), a partir de um sistema de equações diferenciais-algébricas. Esta metodologia engloba características fundamentais para os estudos supracitados como velocidade e robustez. Desta forma, um aplicativo computacional para a avaliação de segurança de um sistema de potência baseado na metodologia proposta foi desenvolvido contemplando a determinação da margem de estabilidade devido a bifurcações no sistema de forma eficiente e robusta. Para tanto, esta tese apresenta uma contextualização da necessidade desta ferramenta, realiza modificações na metodologia direta de determinação da margem de estabilidade devido a oscilações no sistema coma finalidade de elevar sua faixa de convergência e desenvolve uma metodologia direta para determinação de bifurcações Sela-Nó. Por fim, o aplicativo final foi validado, utilizando a ferramenta Organon, em diversos sistemas incluindo o sistema interligado nacional modificado, juntamente com a avaliação de uma lista de contingências para o mesmo. / Security assessment complexity in power systems is becoming higher primarily due to increased demand for electricity. Daily, loads are successively connected to the power grids, which can actually lead the system to the collapse, if there is no adequate planning to avoid it. To avoid an instability scenario, methodologies for the determination of maximum loading for a power system have been studied and developed. Inspite of their progress, these works have limitations that prevent them from being used in pre-operation studies and even in real time in operation centers. Considering these limitations, this work presents the development of a direct and combined methodology to determine the operating point where the system stability is lost (the maximum power transfer or the oscillations appearance due to Hopf bifurcation), through differential-algebric equations. This methodology includes fundamental characteristics for the aforementioned studies such as speed and robustness. Thus, a computer application for power system security assessment based on the proposed methodology was developed with the objective of determining efficiently the stability margin due to bifurcations in the system. Therefore, this thesis presents an overview of the need for this tool, as well as changes to the direct method of determining the systems stability margin due to oscilations, with the purpose of increasing its convergence range and develops a methodology for direct determination of saddle-node bifurcations points. Finally, the final developed application is validated, using the Organon tool, in several systems including the national interconnected system modified in which a list of contingencies are evaluated for this system.

This thesis studies the effects of morphological factors of hexapod robots on their locomotion stability. In particular, an offset model for such robots is proposed. The stability margin as well as the error margin are used to indicate the stability of the hexapod robot, as it walks with different gaits in arbitrary directions. Two hexapod gaits are compared, which are the symmetric gait and the metachronal gait. The former is an artificial gait and the latter, on the contrary, is a natural gait which can be observed in many multiped animals. As we investigate advantages and disadvantages of the two gaits, we find that the stability of a hexapod robot can be enhanced by increasing the offset value. This is particularly true for a robot moving in the X and oblique directions with a symmetrical gait. However, altering the offset is less useful for metachronal gaits. In general, a hexapod robot moves most stably in the Y direction with a symmetrical gait, whereas it is most stable in the X direction with a metachronal gait.

This dissertation attempts to establish an analytical and comprehensive framework to deal with two critical challenges associated with voltage stability analysis: 1. To study the new competitive environment appropriately and give more incentive for reactive power supports, one has to evaluate the impacts of distributed market forces on voltage stability, which complicates the voltage stability analysis. 2. Accurately estimating voltage stability margin online is always the goal of the industry. Industry used to apply static analysis for its computation speed at the cost of losing accuracy. On the other hand, dynamic analysis can result in more accurate estimation, but generally has a huge computation cost. So a challenge is to estimate the voltage stability margin accurately and efficiently at a reasonable cost, especially for large system. Considering the first challenge, this dissertation applied eigenvalue based bifurcation analysis to allocate the contribution of voltage stability. We investigate how parameters of the system influence the bifurcations. Three bifurcations (singularity induced bifurcation, saddle-node and Hopf bifurcation) and their relationship to several commonly used controllers are analyzed. Their parameters’ impact on these bifurcations have been investigated, from which we found a way to allocate the contribution by analyzing the relative positions of the bifurcations. For the second challenge, a new fast numerical scheme is developed to estimate voltage stability margin by intelligently adjusting the load increase ratio. A criterion, named EMD (Equilibrium Manifold Deviation) criterion, is proposed to gauge the accuracy of the estimation. And based on this criterion, a new computation scheme is proposed. The validity of our new approach is proven based on the well-known Runge-Kutta-Fehlberg method, and can be extended to other explicit single-step methods easily. Numerical tests demonstrate that the new approach is very practical and has great potential for industrial applications. This dissertation extends our new numerical scheme to stiff systems. When a system is ill-conditioned, the implicit method would be applied to achieve numerical stability. We further demonstrate the validity to combine the intelligent load adjustment technique with the implicit method to save the computation cost without loss of accuracy. This dissertation also delves into the auto detection of stiffness of the power system, and extends our new numerical scheme to general sytems.

A new approach was developed to determine the operational stability margin of a laboratory scale combustor. Applying modern and robust techniques and tools from Dynamical System Theory, the approach was based on three basic steps. In the first step, a gray-box thermoacoustical model for the combustor was derived. The second step consisted in applying System Identification techniques to experimental data in order to validate the model and estimate its parameters. The application of these techniques to experimental data under different operating conditions allowed us to determine the functional dependence of the model parameters upon changes in an experimental control parameter. Finally, the third step consisted in using that functional dependence to predict the response of the system at different operating conditions and, ultimately, estimate its operational stability margin. The results indicated that a low-order stochastic non-linear model, including two excited modes, has been identified and the combustor operational stability margin could be estimated by applying a continuation method.

Made available in DSpace on 2014-06-11T19:22:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-23Bitstream added on 2014-06-13T20:09:48Z : No. of bitstreams: 1 martins_lfb_me_bauru.pdf: 963421 bytes, checksum: 7c1f9175f040c64a63fdf8db9f7a10a1 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho foi feita uma análise comparativa entre diferentes escolhas dos pontos utilizados pelo método look ahead na estimação do ponto de máximo carregamento de um sistema elétrico de potência. O Fluxo de Cargo Continuado é utilizado na geração dos pontos de operação utilizados pelo método look ahead e para servir como referência na comparação entre os resultados previstos e o ponto de máximo carregamento real. Uma vez que a exatidão dessa estimativa é fortemente afetada pela escolha desses pontos, o FCC é modificado para fornecer pontos mais adequados para o bom funcionamento do método look ahead. A metodologia proposta é aplicada ao sistema IEEE de 300 barras, os resultados obtidos mostram o seu bom funcionamento / Here we did a comparative analysis between different choices of the points used by the look ahead method for estimating maximum loading point of a power system. The Continued Power Flow (CPF) is used in the generation of operating points used by the look ahead method and to serve as a reference in comparison between the predicted results and the real maximum loading point. Since the accurancy of this estimative is strongly affected by choicen of these points, the CPF is modified to provide the most appropriate for the proper functioning of the method look ahead. The proposed methodology system is applied to IEEE 300 buses, the results have shown its good functioning

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