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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, which exhibits an oscillatory behaviour around the equilibrium state, following any disturbance, such as sudden change in loads, fluctuations in the output of turbine and faults etc. 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. Power System Stabilizers (PSS’s) were developed as auxiliary controllers on the generators excitation system to produce additional damping by modulating the generator excitation voltage. Designing effective PSS for all operating conditions specially in large interconnected power systems still remains a difficult and challenging task. The conventionally designed Power System Stabilizer (CPSS) is the most cost-effective electromechanical damping controller till date. However, continual changes in the operating condition and network parameters in large systems result in corresponding large changes in system dynamics. This constantly changing nature of power system makes the design of CPSS a difficult 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. This thesis proposes a method for designing robust power system damping controllers that ensures a minimum robustness under model uncertainties. The minimum performance required for the PSS is set a priori and accomplished over a range of operating conditions. A generalized robust controller design methodology has been first implemented on a Single Machine Infinite Bus (SMIB) power system model. The robust controller places the closed loop rotor modes of the system to the desire location while keeping the electrical modes intact. Unlike conventional lead/lag PSS design, the proposed PSS design is based on pole assignment technique which takes into account of various model uncertainties. For the proposed stabilizer design in a multi-machine systems a new decentralized method has been used which requires system data only upto secondary bus of the unit transformer in a generating station. The proposed robust controller design based on modified Nevanlinna-Pick theory has been designed and tested extensively on SMIB and multi-machine systems to establish the efficacy of the controller in damping small signal oscillations. The thesis is organized in four chapters as follows. The first chapter discusses the basic concepts related to the rotor angle stability in power system. The conventional and other methods of countering this instability by power system stabilizers have been described. The relative merits of the various stabilization techniques have been discussed. The scope of present work, i.e design of decentralized robust power system controllers has been defined. In second chapter a modified robust power system stabilizer for SMIB system is developed. It has been shown that under specific conditions the modified Nevanlinna-Pick theory can also be applied for designing damping controllers in system with lightly damped rotor modes. Third chapter proposes a decentralized approach based on modified Nevanlinna-Pick theory for designing a power system stabilizer for interconnected power systems. The performance of the controller which is not based on external system information has been investigated on three widely used multi-machine test systems to established its efficacy in damping out low frequency oscillations. The fourth chapter gives a brief summary of the work done and also includes a section on the scope of future work relating to design of power system stabilizers.

Made available in DSpace on 2014-06-11T19:22:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-03-25Bitstream added on 2014-06-13T19:26:16Z : No. of bitstreams: 1 buzachero_lfs_me_ilha.pdf: 810037 bytes, checksum: 87b0daa8f9193eb11af167f798712fc5 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho propõem-se novas técnicas para otimização da norma de controladores robustos de sistemas dinâmicos lineares sujeitos a falhas estruturais, utilizando realimentação dos estados. As técnicas de projeto utilizadas baseiam-se em LMIs (do inglês Linear Matrix Inequalities) formuladas com base na teoria de estabilidade segundo Lyapunov, utilizando o lema de Finsler e o lema projetivo recíproco. As LMIs utilizadas tiveram o acréscimo da restrição da taxa de decaimento, incluindo o parâmetro g nas LMIs, responsável por diminuir o tempo de duração do transitório dos sistemas realimentados. Foram realizadas comparações qualitativas e quantitativas entre os métodos de projeto com otimização da norma dos controladores, visando alternativas de controladores com menor norma e melhor desempenho que atendam às restrições do projeto. O trabalho se encerra com uma seção de conclusões e perspectivas futuras / This work proposes new techniques to optimize robust controllers norm of linear systems subject to structural failures, with states feedback. The design techniques used are based on LMIs (Linear Matrix Inequalities) formulated on the basis of Lyapunov’s stability theory, using Finsler’s lemma and reciprocal projection lemma. The LMIs have used the addition of the decay rate restriction, including a parameter g in the LMIs, responsible for decreasing the settling time of the feedback system. Qualitative and quantitative comparisons were made between methods of design and optimization of the robust controllers norm, seeking alternatives with small norm and better performance that meet the design constraints. The work ends with a section of conclusions and future prospects

Orientador: Edvaldo Assunção / Banca: Marcelo Carvalho Minhoto Teixeira / Banca: Celso Correia de Souza / Resumo: Neste trabalho propõem-se novas técnicas para otimização da norma de controladores robustos de sistemas dinâmicos lineares sujeitos a falhas estruturais, utilizando realimentação dos estados. As técnicas de projeto utilizadas baseiam-se em LMIs (do inglês Linear Matrix Inequalities) formuladas com base na teoria de estabilidade segundo Lyapunov, utilizando o lema de Finsler e o lema projetivo recíproco. As LMIs utilizadas tiveram o acréscimo da restrição da taxa de decaimento, incluindo o parâmetro g nas LMIs, responsável por diminuir o tempo de duração do transitório dos sistemas realimentados. Foram realizadas comparações qualitativas e quantitativas entre os métodos de projeto com otimização da norma dos controladores, visando alternativas de controladores com menor norma e melhor desempenho que atendam às restrições do projeto. O trabalho se encerra com uma seção de conclusões e perspectivas futuras / Abstract: This work proposes new techniques to optimize robust controllers norm of linear systems subject to structural failures, with states feedback. The design techniques used are based on LMIs (Linear Matrix Inequalities) formulated on the basis of Lyapunov's stability theory, using Finsler's lemma and reciprocal projection lemma. The LMIs have used the addition of the decay rate restriction, including a parameter g in the LMIs, responsible for decreasing the settling time of the feedback system. Qualitative and quantitative comparisons were made between methods of design and optimization of the robust controllers norm, seeking alternatives with small norm and better performance that meet the design constraints. The work ends with a section of conclusions and future prospects / Mestre

Driven by the need for automation and autonomy as well as the need to reduce resources and emissions, the automotive industry is currently undergoing a major transformation. Technologically, this transformation is addressing a wide range of challenges and opportunities. The optimal control of all components is significant for the sustainable development and eco-friendly operation of vehicles. Additionally, robust control of the actuators forms the basis for the development of driver assistance systems and functions for autonomous driving. The actuators of the steering system are particularly important, as they enable safe and comfortable lateral vehicle control. Therefore, the model-based development and virtual simulation of an innovative highly robust control approach for modern Steer-by-Wire systems were conducted in this thesis. The approaches and algorithms described in this thesis allow the design of robust Steer-by-Wire systems and offer the opportunity to conduct many investigations in a computer-aided virtual environment at an early stage in the development process. This reduces time- and cost-intensive testing on prototypes, avoids unnecessary iterations in the design and significantly increases the efficiency and quality of the development. The desired high degree of robustness of the steering control also ensures that the parameterization of the steering feel generator can be freely selected for the individual application. This enables safe and comfortable vehicle lateral control.In summary, the research results described in this thesis accelerate the development of new, modern Steer-by-Wire systems whose robust design forms the basis for the realization of functions for highly automated and autonomous driving.

The implications of gait disorder, muscle weakness, and spinal cord injuries for work and age-related mobility degradation have increased the need for rehabilitation exoskeletons. Specifically, the hip rehabilitation exoskeletons due to a high percentage of the mechanical power is generated by this join during the gait cycle. Additionally, the prolonged hospitalisation after hip replacement and acetabular surgeries that affect human mobility, the social-economic impacts and the quality of life. For these reasons, a hip rehabilitation exoskeleton was our focus in this research, as it will contribute being a sustainable solution to take over the burden of physiotherapy and let patients perform their rehabilitation at home or outdoors.  This thesis details an approach of creating a hip rehabilitation exoskeleton, starting with modelling, simulating, and controlling the rehabilitation hip joint in a based-simulation environment. The mathematical model and the reason for using a series elastic actuator in the hip joint to execute the movement in a sagittal plane are more detailed. Because trajectory tracking is commonly used for controlling rehabilitation exoskeletons to ensure safe and reliable motion tracking methods; therefore, two desired torque signals were tested and analysed with the optimal linear quadratic regulator (LQR). The experiments were performed using two torque signals of a healthy hip joint—representing the sit-to-stand (STS) and the walking activity for their importance in lower limb movements. However, the mathematical model used as a basis of the optimal control strategy is usually influenced by multiple sources of uncertainties. Therefore, four case studies of various optimal control strategies were tested for a twofold reason: to choose the most optimal control strategy, and to test the energy consumption of these cases during the STS and walking movements, because the long-term goal is to produce a lightweight and reliable rehabilitation hip exoskeleton. The research showed compelling evidence that tuning the control strategy will not influence the robustness of an optimal controller only, but affect the energy consumption during the STS and walking activity, which needs to be considered in exoskeleton control design regarding its applications. / Behovet av exoskelett för rehabilitering har ökat p.g.a. komplikationer som uppstår vid arbete och åldersrelaterad försämring. Komplikationerna består bland annat av gångstörning, muskelsvaghet och ryggmärgsskador. Speciellt höftexoskelett avsett för rehabilitering är extra intressant på grund av att rehabilitering inom detta område omfattar långvarig sjukhusvistelse efter höftprotes- och acetabulära operationer. Höftleden är en av de leder som utsätts för relativt höga mekaniska påfrestningar och minskad rörelseförmåga leder inte sällan till socioekonomiska effekter och minskad livskvalité. Av denna anledning kommer höftexoskelett för rehabilitering vara det primära området i denna avhandling då det kommer att vara en lösning för att minska belastningen inom sjukvård och låta patienter utföra sin rehabilitering hemma på egen hand. Denna avhandling beskriver en metod för att skapa ett höftexoskelett avsett för rehabilitering med början i modellering, simulering och kontroll av en höftled av exoskelett i en simuleringsmiljö. Genom att använda ett serieelastiskt manöverdon för att utföra en höftledsrörelse i ett sagittalt så uppnås en mer detaljerad matematisk modell. Genom att använda banspårning, som vanligtvis används för att kontrollera exoskelett för rehabilitering för att säkerställa säkra och pålitliga rörelsespårningsmetoder, så analyserades två vridmomentssignaler mot en linjär kvadratisk regulator (LQR). Simuleringarna utfördes med hjälp av två vridmomentsignaler som representerar sitt-till-stå (STS) och gångaktivitet hos en frisk höftled. Den matematiska modellen som används för att hitta den optimala kontrollstrategin påverkas vanligtvis av flera osäkerhetskällor. Därför testades fyra fallstudier av olika optimala kontrollstrategier för två skäl: den ena för att välja den mest optimala kontrollstrategin emellan och den andra för att mäta energiförbrukningen för dessa STS och gångrörelse så att vi kan producera ett lätt och pålitligt höftexoskelett avsett för rehabilitering. Forskningen visar övertygande bevis för att inställning av styrstrategin inte bara kommer att påverka robustheten hos en optimal styrenhet utan även påverkar energiförbrukningen under STS och gångaktivitet vilket måste beaktas vid design av exoskelett.