As ligas com memória de forma (Shape Memory Alloy - SMA) consistem em um grupo de materiais metálicos que possuem a habilidade de retornar a um formato ou tamanho previamente definido quando submetidas a um ciclo térmico adequado, devido a alterações em sua estrutura cristalina. Esta mudança não é um processo termodinamicamente reversível, apresentando, conseqüentemente, histerese. Portanto, a característica principal destes materiais é a habilidade de sofrer grandes deformações e, em seguida, recuperar sua forma original quando a carga é removida ou o material é aquecido. Assim, pode-se utilizar esse fenômeno para construir atuadores leves e silenciosos, como verdadeiros músculos metálicos. O desenvolvimento de atuadores com as SMAs apresenta grande atrativo para diversos campos da engenharia, principalmente na área de robótica, substituindo os atuadores convencionais de grande peso e ruidosos, como motores, válvulas solenóides, etc. Entretanto, para o bom desempenho de atuadores SMA requer-se um complexo sistema de controle e resfriamento, reduzindo-se o tempo de resposta do atuador e minimizando-se os efeitos da histerese. Neste trabalho, propõe-se um inovador sistema de resfriamento, baseado em pastilha termo-elétrica (efeito Seebeck-Peltier). Este método possui a vantagem de ser mais compacto e simples que outros métodos de resfriamento forçado. Um modelo matemático completo foi também desenvolvido, e um protótipo experimental foi construído. Diversos experimentos foram utilizados para a validação do modelo e para a identificação de todos seus parâmetros. Analisou-se então a aplicabilidade de um controle de posição baseado em algoritmo PID, utilizando-se diversos métodos de ajuste de ganhos. Verificou-se um desempenho razoável, com uma largura de banda em malha fechada de aproximadamente 0,37Hz. Em seguida, desenvolveu-se um sistema de controle de posição baseado em teoria de modos deslizantes (sliding mode control), que utiliza o modelo matemático do sistema e leva em conta as não linearidades existentes. Embora matematicamente mais complexo, obteve-se um desempenho superior ao PID, com largura de banda de 0,69Hz. Diversos experimentos confirmaram também a robustez deste controlador e seu bom desempenho na presença de distúrbios. / Shape Memory Alloys (SMA) consist of a group of metallic materials that demonstrate the ability to return to some previously defined shape when subjected to the appropriate thermal cycle, due to shift in the materials crystalline structure. The change that occurs within SMAs crystalline structure is not a thermodynamically reversible process and results in hysteresis behavior. The key feature of these materials is the ability to undergo large plastic strains and subsequently recover these strains when a load is removed or the material is heated. Such property can be used to build silent and light actuators, similar to a mechanical muscular fiber. SMA actuators have several advantages in several engineering fields, mainly in robotics, replacing the conventional actuators like motors or solenoids. However, the good performance of the SMA actuator depends on a complex control and cooling systems, reducing the time constant and minimizing the effects of hysteresis. In the present work, a novel cooling system is proposed, based on thermo-electric effect (Seebeck-Peltier effect). Such method has the advantage of reduced weight and requires a simpler control strategy compared to other forced cooling systems. A complete mathematical model of the actuator was also derived, and an experimental prototype was implemented. Several experiments were used to validate the model and to identify all parameters. A PID position control system was developed and implemented in the prototype, using several tuning methods. A good performance was obtained, with a cut-off frequency of 0.37Hz. A position controller based on sliding mode theory was then developed, using the mathematical model of the system and taking into account the non-linear effects. Although such controller presents a more complex mathematical derivation, a better performance was obtained, with a cut-off frequency of 0.69Hz. Several experiments confirmed the robustness and disturbance filtering properties of the sliding mode controller.

Indiana University-Purdue University Indianapolis (IUPUI) / With the increasing demand of economy and environmental pollutions, more and more renewable energy systems with clean sources appear and have attracted attention of systems involving solar power, wind power and hybrid new energy powers[1]. However, there are some difficulties associated with combined utilization of solar and wind, such as their intermittent behavior and their peak hours mismatch in generation and consumption[1]. For this purpose, advanced network of a variety of renewable energy systems along with controllable load and storage units have been introduced[1-3]. This thesis proposes some configurations of hybrid energy harvesting systems, including wind-wind-storage DC power system with BOOST converters, solar-solar-storage DC power system with cascade BOOST converters, wind-solar-storage DC power system with BOOST converter and cascade BOOST converter, and wind-solar DC power system with SEPIC converter and BOOST converter. The models of all kinds of systems are built in Matlab/Simulink and the mathematical state-space models of combined renewable energy systems are also established. Several MPPT control strategies are introduced and designed to maximize the simultaneous power capturing from wind and solar, such as Perturb & Observe (P&O) algorithm for solar and wind, Tip Speed Ratio (TSR) control and Power Signal Feedback (PSF) control for wind, and Sliding Mode Extremum Seeking Control (SM-ESC) for wind and solar systems[4]. The control effects of some of these MPPT methods are also compared and analyzed. The supervisory control strategies corresponding to each configurations are also discussed and implemented to maximize the simultaneous energy harvesting from both renewable sources and balance the energy between the sources, battery and the load[2]. Different contingencies are considered and categorized according to the power generation available at each renewable source and the state of charge in the battery[2]. Applying the system architectures and control methods in the proposed hybrid new energy systems is a novel and significant attempt, which can be more general in the practical applications. Simulation results demonstrate accurate operation of the supervisory controller and functionality of the maximum power point tracking algorithm in each operating condition both for solar and for wind power[3]

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<p>Hydraulic systems are commonly used for actuation and manipulation of heavy loads. They are found in a variety of different industries, such as in automotive, manufacturing, robotics, construction, and aerospace. Conventional hydraulic systems use a centralized constant pressure supply system. Pressurized fluid is then channeled to actuators using servo-valves. The advantages of these systems are their high torque to mass ratio, and the ability to control speed and direction with relative precision. However, there are also disadvantages such as the requirement of a bulky centralized supply, leakage, noise, and reduced energy efficiency due to orifice flow and the requirement for maintaining a constant supply pressure.</p> <p>Electro-Hydrostatic Actuation systems (EHA) alleviate many of the above mentioned shortcomings of servo-valve controlled hydraulic systems. In the EHA position control is achieved by regulating the pumping action. Here, a fixed or a variable displacement pump can be used to move oil from one chamber of the actuator to the other. In these actuators, the presence of nonlinearities associated with pump/motor static friction and backlash, pressure drop in the piping system, and nonlinear friction at the load have a significant effect on the performance and positional precision of the system.</p> <p>This research will focus on developing a multiple inner-loop control strategy by implementing multiple inner-loops that utilize the differential pump/load position and velocity. The main goal will be to decrease the effect of the pump backlash as well as the nonlinear friction at the load; both of which negatively impact positional precision. Therefore, the main benefit of this method is an improvement in trajectory tracking precision, which is particularly important for high precision hydrostatic systems. Furthermore, a sliding mode control strategy will be incorporated into the design to suppress load oscillations reported in precision trajectory tracking applications. The research hypothesis states that sliding mode control in conjunction with multiple inner-loops, will improve the trajectory tracking performance of a hydrostatic actuation system by partially compensating the effects of static friction at the load. Theoretical analysis, simulation supported by experimental results are presented to demonstrate the effectiveness of the newly developed methods in suppressing the effects of nonlinearities on the EHA performance, with the downside of an increased complexity due to the increased number of controller parameters.</p> / Doctor of Philosophy (PhD)

Inflatable structures have been a subject of renewed interest in recent years for space applications such as communication antennas, solar thermal propulsion, and entry/landing systems. This is because inflatable structures are very lightweight and on-orbit deployable. In addition, they have high strength-to-mass ratio and require minimal stowage volume, which makes them especially suitable for cost-effective large space structures. An inflated toroidal structure (torus) is often used there in order to provide structural support. For these structures to be effective, their vibration must be controlled while keeping the weight low. Piezoelectric materials have become strong candidates for actuator and sensor applications in the active vibration control of such structures due to their lightweight, conformability to the host structure, and distributed nature. In this study, our main focus is to understand the dynamic characteristics of an inflatable torus and to control its vibration using piezoelectric actuators and sensors. The first part of this study is concerned with theoretical formulations. We use Sanders' shell theory to derive the governing equations of motion for a shell subjected to pressure. To take into account the prestress effects of internal pressure, we use geometric nonlinearity, and to model the follower action of pressure force, we consider the work done by internal pressure during the vibration of the shell. These equations are then specialized to obtain approximate equations presented by previous researchers. We extend this analytical formulation to derive the equivalent forces due to piezoelectric actuators in unimorph and bimorph configurations and include their mass and stiffness effects in the governing equations. A sensor equation is also developed for the shell. The actuator and sensor equations are then written in terms of modal displacements and velocities so as to evaluate their interactions with different vibratory modes. In the second part, we focus on numerical studies related to an inflated torus. At first, we perform a free vibration analysis of the inflated torus using Galerkin's method. We study how different parameters (aspect ratio, internal pressure, and wall-thickness) of the inflated torus affect the natural frequencies and mode shapes of the inflated torus. We compare the results obtained from the theory used in this research with the results from different approximate theories and commercial finite element codes. The results suggest that the use of an accurate shell theory and pressure effect is very important for the vibration analysis of an inflated torus. Next, the modal behaviors of piezoelectric actuator and sensor are analyzed. A detailed study is done in order to understand how the size and location of actuator and sensor affect the modal forces, the modal sensing constants, and the overall performance for all the considered modes. In order to determine the optimal locations and sizes of actuators and sensors, we use a genetic algorithm. Natural frequencies and mode shapes are calculated considering the passive effects of actuators and sensors. Finally, we attempt the vibration control of the inflated torus using the optimally designed actuators and sensors and sliding mode controller/observer. The numerical simulations show that piezoelectric actuators and sensors can be used in the vibration control of an inflatable torus. The robustness properties of the controller and observer against the parameter uncertainty and disturbances are verified. / Ph. D.

Unmanned Underwater Vehicles (UUVs) are widely used in commercial, scientific, and military missions for various purposes. What makes this technology challenging is the increasing mission duration and unknown environment. It is necessary to embed fault-tolerant control paradigms into UUVs to increase the reliability of the vehicles and enable them to execute and finalize complex missions. Specifically, fault-tolerant control (FTC) comprises fault detection, identification, and control reconfiguration for fault compensation. Literature review shows that there have been no systematic methods for fault-tolerant control of UUVs in earlier investigations. This study presents a hierarchical methodology of fault detection, identification and compensation (HFDIC) that integrates these functions systematically in different levels. The method uses adaptive finite-impulse-response (FIR) modeling and analysis in its first level to detect failure occurrences. Specifically, it incorporates a FIR filter for on-line adaptive modeling, and a least-mean-squares (LMS) algorithm to minimize the output error between the monitored system and the filter in the modeling process. By analyzing the resulting adaptive filter coefficients, we extract the information on the fault occurrence. The HFDIC also includes a two-stage design of parallel Kalman filters in levels two and three for fault identification using the multiple-model adaptive estimation (MMAE). The algorithm activates latter levels only when the failure is detected, and can return back to the monitoring loop in case of false failures. On the basis of MMAE, we use multiple sliding-mode controllers and reconfigure the control law with a probability-weighted average of all the elemental control signals, in order to compensate for the fault. We validate the HFDIC on the steering and diving subsystems of Naval Postgraduate School (NPS) UUVs for various simulated actuator and/or sensor failures, and test the hierarchical fault detection and identification (HFDI) with realistic data from at-sea experiment of the Florida Atlantic University (FAU) Autonomous Underwater Vehicles (AUVs). For both occasions, we model actuator and sensor failures as additive parameter changes in the observation matrix and the output equation, respectively. Simulation results demonstrate the ability of the HFDIC to detect failures in real time, identify failures accurately with a low computational overhead, and compensate actuator and sensor failures with control reconfiguration. In particular, verification of HFDI with FAU data confirms the performance of the fault detection and identification methodology, and provides important information on the vehicle performance. / Ph. D.

<p>Rad je posvećen robusnom upravljanju sistemima čiji je linearni regulator i/ili dinamika necelog reda, kao i upravljačkim problemima gde regulator necelog reda u sebi poseduje i linearnu i nelinearnu dinamiku, a koji upravlja procesima čija dinamika može i linearna i nelinearna.</p> / <p>The thesys is dedicated to robust control systems problems with linear<br />controllers and/or process dynamics of noninteger order, as well as control<br />issues with combination of linear and nonlinear controllers of noninteger<br />order that control either linear or nonlinear systems.</p>