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Dissertations / Theses on the topic 'Control and modulation strategies'

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Published: 3 June 2025

Last updated: 13 July 2025

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Darijevic, M. "Modulation and control strategies for multilevel five-phase open-end winding drives." Thesis, Liverpool John Moores University, 2016. http://researchonline.ljmu.ac.uk/4381/.

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Industrial and automotive trends clearly demonstrate an increased interest in medium- and high-power variable speed drives. Despite constant progress in the technology, the semiconductor characteristics are still the bottleneck in drive designs, due to their limitations to block high voltage (several kilovolts) and conduct high current (several hundreds of amperes per-phase). For this reason and numerous other advantages, solutions based on multilevel inverters and multiphase machines are considered in recent years. The open-end winding drives are an alternative approach for drives construction. This thesis investigates carrier based pulse width modulation schemes for five-phase open-end winding drives. Two drive topologies, with isolated dc-links of two inverters, are considered. The first one consists of two two-level inverters and a five-phase machine. The second topology utilises one three- and one two-level five-phase inverter. It is shown that the same drive structure can produce a different number of phase voltage levels, when different dc-link voltages of two inverters are in use. Hence, dc-link voltage ratio is considered as an additional degree of freedom. An open-end winding structure that comprises of two two-level inverters offers harmonic performance equivalent to three- and four-level single-sided supply. The second drive structure under analysis is able to produce four, five and six voltage levels, depending on utilised dc-link voltage ratio. Modulation schemes are classified in two categories. So-called coupled modulation schemes are developed under the assumption that open-end winding drives are equivalent to certain single-sided multilevel solutions. This enables the application of slightly modified modulation methods for multilevel inverters, to the open-end winding configurations. As a consequence, number of utilised voltage levels can be higher than the sum of two inverters’ number of levels. However, this boost in number of levels relies on simultaneous switching in two inverters’ legs connected to the same drive phase,which causes so-called dead-time spikes. The second group, referred to in this thesis as decoupled modulation schemes, rely on the separate modulation of two inverters, using voltage references obtained by splitting the overall phase voltage reference, proportionally to inverters’ dc-link voltages. Hence, this kind of modulation offers somewhat worse harmonic performance, when compared to coupled modulation schemes. Special attention is paid to the stability of dc-link voltage levels, which is one of the most important figures of merits of quality for multilevel drives. Using a novel analysis approach, it is demonstrated that utilisation of optimal harmonic performance offered by coupled modulation methods leads to unstable dc-link voltages, but only in the cases where dc-link voltage ratio is used for increment of available number of voltage levels. Decoupled modulation methods offer stable dc-link voltages, regardless of drive configuration. One of the drawbacks of the analysed open-end winding drives is the need for two isolated dc sources, which form dc-link voltages of two inverters. For that reason, a possibility to use only one dc-source in open-end winding drives with isolated inverters is considered. Analysis shows that both drive topologies can be operated using so-called bulk and conditioning inverter control, where bulk inverter is supplied from an active dc source, but operates in staircase mode, while conditioning inverter performs high-frequency pulse width modulation, in order to suppress low-order harmonic content. This kind of operation is investigated in details for two specific configurations in which two inverters never operate at the same time in PWM mode, when coupled modulation methods are used. Comparison of the results shows that topology which comprises from one three- and one two-level inverter is more suitable for this kind of control. Together with previously analysed configurations and modulation strategies, dynamic performance of this novel drive is tested under the closed-loop speed control. Experimental results show that open-end winding drives are suitable for a wide range of applications.

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Ehlers, PJ, CG Richards, DV Nicolae, E. Monacelli, and Y. Hamam. "Review of the state of the Art of modulation techniques and control strategies for matrix converters." International Review of Automatic Control, 2008. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001151.

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The reliability and stability of the Matrix Converter has improved during the last years due to the enhanced control algorithms. The traditional direct transfer function control mode has been replaced by more complex – digitally implemented control methodologies. These methodologies allow for real time calculation of the optimal switching interval of each individual switch of the matrix converter. These new switching algorithms allow optimal performances, ensuring sinusoidal outputs at any desired power factor. This paper will first revise the underlying theory of matrix converters, then review the various control limitations and finally review the current control algorithms.

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Mengoni, Michele <1981&gt. "Modulation Techniques for Multi-Phase Converters and Control Strategies for Multi-Phase Electric Drives." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2309/1/Tesi_Michele_Mengoni.pdf.

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The ever-increasing spread of automation in industry puts the electrical engineer in a central role as a promoter of technological development in a sector such as the use of electricity, which is the basis of all the machinery and productive processes. Moreover the spread of drives for motor control and static converters with structures ever more complex, places the electrical engineer to face new challenges whose solution has as critical elements in the implementation of digital control techniques with the requirements of inexpensiveness and efficiency of the final product. The successfully application of solutions using non-conventional static converters awake an increasing interest in science and industry due to the promising opportunities. However, in the same time, new problems emerge whose solution is still under study and debate in the scientific community During the Ph.D. course several themes have been developed that, while obtaining the recent and growing interest of scientific community, have much space for the development of research activity and for industrial applications. The first area of research is related to the control of three phase induction motors with high dynamic performance and the sensorless control in the high speed range. The management of the operation of induction machine without position or speed sensors awakes interest in the industrial world due to the increased reliability and robustness of this solution combined with a lower cost of production and purchase of this technology compared to the others available in the market. During this dissertation control techniques will be proposed which are able to exploit the total dc link voltage and at the same time capable to exploit the maximum torque capability in whole speed range with good dynamic performance. The proposed solution preserves the simplicity of tuning of the regulators. Furthermore, in order to validate the effectiveness of presented solution, it is assessed in terms of performance and complexity and compared to two other algorithm presented in literature. The feasibility of the proposed algorithm is also tested on induction motor drive fed by a matrix converter. Another important research area is connected to the development of technology for vehicular applications. In this field the dynamic performances and the low power consumption is one of most important goals for an effective algorithm. Towards this direction, a control scheme for induction motor that integrates within a coherent solution some of the features that are commonly required to an electric vehicle drive is presented. The main features of the proposed control scheme are the capability to exploit the maximum torque in the whole speed range, a weak dependence on the motor parameters, a good robustness against the variations of the dc-link voltage and, whenever possible, the maximum efficiency. The second part of this dissertation is dedicated to the multi-phase systems. This technology, in fact, is characterized by a number of issues worthy of investigation that make it competitive with other technologies already on the market. Multiphase systems, allow to redistribute power at a higher number of phases, thus making possible the construction of electronic converters which otherwise would be very difficult to achieve due to the limits of present power electronics. Multiphase drives have an intrinsic reliability given by the possibility that a fault of a phase, caused by the possible failure of a component of the converter, can be solved without inefficiency of the machine or application of a pulsating torque. The control of the magnetic field spatial harmonics in the air-gap with order higher than one allows to reduce torque noise and to obtain high torque density motor and multi-motor applications. In one of the next chapters a control scheme able to increase the motor torque by adding a third harmonic component to the air-gap magnetic field will be presented. Above the base speed the control system reduces the motor flux in such a way to ensure the maximum torque capability. The presented analysis considers the drive constrains and shows how these limits modify the motor performance. The multi-motor applications are described by a well-defined number of multiphase machines, having series connected stator windings, with an opportune permutation of the phases these machines can be independently controlled with a single multi-phase inverter. In this dissertation this solution will be presented and an electric drive consisting of two five-phase PM tubular actuators fed by a single five-phase inverter will be presented. Finally the modulation strategies for a multi-phase inverter will be illustrated. The problem of the space vector modulation of multiphase inverters with an odd number of phases is solved in different way. An algorithmic approach and a look-up table solution will be proposed. The inverter output voltage capability will be investigated, showing that the proposed modulation strategy is able to fully exploit the dc input voltage either in sinusoidal or non-sinusoidal operating conditions. All this aspects are considered in the next chapters. In particular, Chapter 1 summarizes the mathematical model of induction motor. The Chapter 2 is a brief state of art on three-phase inverter. Chapter 3 proposes a stator flux vector control for a three- phase induction machine and compares this solution with two other algorithms presented in literature. Furthermore, in the same chapter, a complete electric drive based on matrix converter is presented. In Chapter 4 a control strategy suitable for electric vehicles is illustrated. Chapter 5 describes the mathematical model of multi-phase induction machines whereas chapter 6 analyzes the multi-phase inverter and its modulation strategies. Chapter 7 discusses the minimization of the power losses in IGBT multi-phase inverters with carrier-based pulse width modulation. In Chapter 8 an extended stator flux vector control for a seven-phase induction motor is presented. Chapter 9 concerns the high torque density applications and in Chapter 10 different fault tolerant control strategies are analyzed. Finally, the last chapter presents a positioning multi-motor drive consisting of two PM tubular five-phase actuators fed by a single five-phase inverter.

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Zaragoza, Bertomeu Jordi. "Modulation strategies for the neutral-point-clamped converter and control of a wind turbine system." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/130900.

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Els convertidors multinivell són topologies de convertidors d’electrònica de potència que poden generar tres o més nivells de voltatge en cadascuna de les fases de sortida. Com a resultat, els voltatges i corrents generats per aquestes topologies presenten una distorsió harmònica baixa. Hi ha diferents configuracions de convertidors multinivell, les quals es basen en connectar dispositius de potència o convertidors en sèrie. El resultat d’aquestes connexions permet obtenir voltatges alts, tant en la part de corrent continu com en la de corrent altern del convertidor. A més, cada dispositiu sols ha de suportar una fracció del voltatge total del bus de corrent continu. Per aquestes raons, els convertidors multinivell són generalment utilitzats en aplicacions d’alta potència. El convertidor de tres nivells amb connexió a punt neutre (neutral-point-clamped) és el més utilitzat. La recerca d’aquesta tesis doctoral està focalitzada en aquesta topologia de convertidor, i el principal objectiu és l’aportació de noves tècniques de modulació. Aquestes tenen en compte diferents aspectes: la velocitat computacional dels algorismes, l’equilibrat de les tensions dels condensadors del bus de contínua, les pèrdues de commutació i les oscil·lacions de baixa freqüència en el punt neutre del convertidor. Totes les estratègies de modulació proposades en aquesta tesis són modulacions d’amplada de polses basades en portadora. En la primera modulació que es presenta, s’injecta un senyal comú (seqüència zero) a totes les moduladores, que es basa en els patrons de la modulació vectorial que utilitza tres vectors dels més propers al de referència (nearest-three-vector modulation). S’estudien i es comparen els resultats d’aquesta modulació amb la seva homòloga, basada en perspectiva vectorial. Una segona proposta és l’anomenada modulació d’amplada de polses de doble senyal (double-signal pulse-width modulation). Aquesta modulació és capaç d’eliminar completament les oscil·lacions de voltatge en el punt neutre del convertidor. No obstant això, es produeix un increment de les pèrdues de commutació en els dispositius de potència i, a més, no hi ha un equilibrat natural de les tensions en els condensadors del bus. Una última estratègia de modulació, anomenada modulació híbrida (hybrid pulse-width modulation), es basa en la combinació de la modulació sinusoïdal (sinusoidal pulse-width modulation) i la de doble senyal. Aquesta presenta una solució de compromís entre reduir les pèrdues de commutació, en detriment d’un augment de l’amplitud de les oscil·lacions de voltatge en el punt neutre. Una segona part d’aquesta tesis es centra en les aplicacions a generació eòlica, ja que els convertidors multinivell estan començant a ser utilitzats en aquest camp. Això es produeix fonamentalment per l’augment continu de les dimensions de les turbines eòliques. En aquesta part de la recerca s’ha considerat la configuració de dos convertidors multinivell connectats a un mateix bus de contínua (back-to-back), tot i que els convertidors han estat estudiats independentment. Inicialment s’ha estudiat el convertidor que va connectat a la xarxa elèctrica i s’ha aplicat l’estratègia de control coneguda com a control orientat a tensió (voltage-oriented control). S’han utilitzat controladors estàndard (proporcional-integral), als quals s’ha afegit un control difús que supervisa i modifica els valors de les constants dels controladors. Aquest supervisor difús millora la dinàmica de la tensió del bus de contínua davant canvis de càrrega quan el convertidor treballa com a rectificador. Per una altra part, s’ha estudiat el control d’una turbina eòlica basada en un generador d’imants permanents. En aquest cas, s’ha aplicat l’estratègia de control coneguda com a control orientat a camp (field-oriented control). S’han avaluat i comparat els avantatges i inconvenients de diferents formes de sintonitzar els controladors. Multilevel converters are power electronic topologies that can generate three or more voltage levels in each output phase. As a result, the voltage and current waveforms generated have lower total harmonic distortion. Multilevel topologies are based on connecting power devices or converters in a series. Consequently, high voltages can be handled on the dc and ac sides of the converter, while each device stands only a fraction of the total dc-link voltage. For these reasons multilevel converters are generally applied to high-power applications. The three-level neutral-point-clamped converter is the most extensively used multilevel topology. This topology is the main focus of research in this dissertation. The main objective is to propose new modulation strategies that are able to meet a compromise solution while considering computational algorithm speed, voltage balance in the dc-link capacitors, switching losses and low frequency voltage oscillations at the neutral point. All the modulation strategies proposed here are based on carrier-based pulsewidth modulation. A new modulation strategy has been implemented using a proper zero-sequence signal injected into the modulation signals. The zero sequence is determined from a space-vector modulation standpoint, particularly the nearest-threevector modulation strategy. The proposed carrier-based technique is compared with its space-vector modulation counterpart. It shows some advantages, such as easier implementation and reduced switching events; however, it still produces oscillations in the neutral-point voltage for some operating conditions. A new modulation strategy able to completely remove such voltage oscillations is also presented. It is called double-signal pulse-width modulation. The main drawback of this strategy is that it increases the switching frequency of the power devices and has no natural capacitor voltage balance. Some balancing strategies are proposed in this dissertation for this specific modulation. Furthermore, a hybrid pulse-width modulation approach is presented which is able to combine sinusoidal pulse-width modulation with doublesignal pulse-width modulation; this represents a compromise solution between switching losses and neutral-point voltage oscillation amplitudes. The second part of this thesis is focused on wind generation applications. Multilevel converters are starting to be used in such a field nowadays, and are expected to be further applied in the near future as the sizes of wind turbines grow. Two back-toback-connected power converters are considered in this application, although they are analyzed independently. First of all, the control of the grid-connected converter is studied. A voltage-oriented control is used with standard proportional-integral controllers. The originality of the method is that a fuzzy supervisor is designed and included in the structure; the fuzzy supervisor is able to modify the proportionalintegral parameters online. It is shown how the control of the total dc-link voltage improves significantly under load changes when the converter is working as a rectifier. On the other hand, a control study is performed on the wind turbine side. The variable speed wind turbine is based on a permanent magnet synchronous generator. A field-oriented control strategy is applied. The controllers are evaluated and compared using different tuning strategies which highlight the advantages and drawbacks of each.

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Pou, Félix Josep. "Modulation and control of three-phase PWM multilevel converters." Doctoral thesis, Universitat Politècnica de Catalunya, 2002. http://hdl.handle.net/10803/6327.

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La present tesi doctoral estudia els inversors trifàsics multinivell del tipus denominat de díodes de fixació (diode-clamped converters). Aquests convertidors poden generar tres o més nivells de tensió a cada fase de sortida, i normalment s'apliquen a sistemes de gran potència ja que poden treballar amb tensions majors que els inversors clàssics. L'anàlisi es centra fonamentalment en la topologia de tres nivells, tot i que també es realitzen contribucions per a convertidors de més nivells. Els principals objectius són la proposta de nous algorismes de modulació vectorial PWM de processat ràpid, l'estudi i la compensació dels efectes dels desequilibris de les tensions dels condensadors del bus de continua, i l'anàlisi de llaços de control avançat. S'han desenvolupat diversos models que han permès obtenir resultats de simulació de les tècniques de modulació i control proposades. A més, gràcies a l'estada d'un any de l'autor al Center for Power Electronics Systems (CPES) a Virginia Tech, USA, la tesi també inclou resultats experimentals que consoliden les conclusions i metodologies presentades. Les principals contribucions es resumeixen a continuació. Es presenta un nou algorisme de modulació vectorial PWM que aprofita simetries del diagrama vectorial per a reduir el temps de processat. S'analitzen i es quantifiquen les oscil·lacions de tensió de baixa freqüència que apareixen en el punt central dels condensadors del convertidor de tres nivells. Aquesta informació permet dimensionar els condensadors donades les especificacions d'una determinada aplicació. L'algorisme de modulació també s'aplica a convertidors de més nivells. Pel cas concret del convertidor de quatre nivells, es comprova l'existència de corrents continus en els punts mitjos dels condensadors que fan que els sistema sigui inestable. Es determinen gràficament les zones d'inestabilitat. Es presenta un nou i eficient algorisme de modulació vectorial feedforward en el convertidor de tres nivells que és capaç de generar tensions trifàsiques de sortida equilibrades, malgrat l'existència de desequilibris en les tensions dels condensadors. S'estudien els efectes negatius de càrregues lineals desequilibrades i càrregues no lineals en el control de les tensions dels condensadors. Es justifica que l'existència d'un quart harmònic en els corrents de càrrega pot inestabilitzar el sistema. És determina la màxima amplitud tolerable d'aquest harmònic. S'estudia la millora en l'equilibrat de les tensions d'una connexió de dos convertidors de tres nivells al mateix bus de continua (back-to-back connection). Un exemple d'aplicació pràctica és la conversió AC/DC/AC per a l'accionament de motors d'alterna treballant amb factor de potència unitari. Finalment s'aplica un controlador òptim al convertidor de tres nivells treballant com a rectificador elevador (boost). El llaç de control LQR (Linear Quadratic Regulator) es simplifica donat que la tasca d'equilibrat de les tensions dels condensadors es dur a terme en el mateix modulador.

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Li, Nan. "Digital control strategies for DC/DC SEPIC converters towards integration." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00760064.

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The use of SMPS (Switched mode power supply) in embedded systems is continuously increasing. The technological requirements of these systems include simultaneously a very good voltage regulation and a strong compactness of components. SEPIC ( Single-Ended Primary Inductor Converter) is a DC/DC switching converter which possesses several advantages with regard to the other classical converters. Due to the difficulty in control of its 4th-order and non linear property, it is still not well-exploited. The objective of this work is the development of successful strategies of control for a SEPIC converter on one hand and on the other hand the effective implementation of the control algorithm developed for embedded applications (FPGA, ASIC) where the constraints of Silicon surface and the loss reduction factor are important. To do it, two non linear controls and two observers of states and load have been studied: a control and an observer based on the principle of sliding mode, a deadbeat predictive control and an Extended Kalman observer. The implementation of both control laws and the Extended Kalman observer are implemented in FPGA. An 11-bit digital PWM has been developed by combining a 4-bit Δ-Σ modulation, a 4-bit segmented DCM (Digital Clock Management) phase-shift and a 3-bit counter-comparator. All the proposed approaches are experimentally validated and constitute a good base for the integration of embedded switching mode converters

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Pontes, José Pedro do Carmo. "A hybrid and adaptive approach to humanoid locomotion : blending rhythmic primitives and feet placement strategies." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS083.

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Cette thèse présente des recherches développées pour une optimisation adaptative et efficace des contrôleurs de locomotion des robots humanoı̈des. Elle répond à cet objectif en combinant les caractéristiques de la locomotion humanoı̈de et l’impact de différents environnements dans sa dynamique, ainsi que des techniques d’optimisation mathématique et d’analyse statistique. Les contrôleurs pour la locomotion des robots bipèdes font souvent face à des défis concernant leur optimisation vers différents objectifs et environnements. Nous proposons une architecture qui utilise les informations recueillies dans une phase d’optimisation / exploration pour s’adapter à un terrain avec des caractéristiques inconnues. Dans la phase d’exploration virtuelle des simulations sont utilisées pour optimiser les paramètres du contrôleur dans différents terrains. Les résultats de ces optimisations servent à identifier les caractéristiques inconnues du terrain et, en conséquence, à sélectionner les meilleurs valeurs des paramètres du contrôleur pour cet environnement. L’approche a été testée dans les simulations d’un robot iCub sur terrains avec un frottement variable, et du robot DARwIn-OP dans des terrains avec des pentes différentes. Ce travail s’intéresse donc au problème du choix des valeurs des paramètres des contrôleurs de locomotion bipède dans diverses situations. Les contributions apportées consistent à : 1) établir un cadre d’optimisation qui peut être appliqué à n’importe quel contrôleur avec des paramètres ouverts, et qui se traduit par des comportements à la fois sécurisés et performants ; 2) trouver des comportements de locomotion efficaces dans des environnements multiples et distincts ; 3) adapter la locomotion à des environnements aux caractéristiques variables, modélisés dans optimisations précédentes This thesis presents research developed towards adaptable and effective optimization of controllers for humanoid robots’ locomotion. It addresses this goal by combining features of humanoid locomotion and the impact of different environments in its dynamics, along with mathematical optimization and statistical analysis techniques. Controllers for the locomotion of bipedal robots often face challenges regarding their optimization towards different objectives and different environments. We propose an architecture that uses the information gathered in an optimization/exploration phase to adapt to a terrain with partially unknown characteristics. In the exploration phase virtual simulations are used to optimize the parameters of the controller in different terrains. The results of these optimizations are used to identify the unknown terrain characteristics, and these values are used to select the best parameters for this particular environment. The approach was tested in the simulations of an iCub robot on terrains with variable friction, and of the DARwIn-OP robot in ramps with varying slopes. This work brings contributions to the problem of choosing the values for the open parameters of biped locomotion controllers in various situations. Specific issues that are covered relate to: 1) establishing an optimization framework that can be applied to any controller with open parameters, and which results in both safe and well performing behaviors; 2) finding locomotion behaviors that are effective in multiple and distinct environments; 3) adapting the locomotion to environments with varying characteristics, modeled in previous optimizations

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Axelsson, Johanna, and Sarah Bernelind. "Elevator Control Strategies." Thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-134900.

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The purpose of this essay is to investigate if it is eective to switch strategies for elevators during one day in an oce building. This essay describes some of the strategies in use today, followed by a comparison and analysis of two of the strategies described. We have also implemented optimizations to one of these strategies. From our test results we can conclude that our optimized strategy worked and produced better results on average waiting time and total traveling time than the two strategies we previously implemented and that it is not necessarily eective to completely change strategies but change parts of them depending on the trac ow. Syftet med denna rapport ar att undersoka om det ar eektivt att byta strategi for hissar i en kontorsbyggnad under en dags olika trakoden. Forst beskrivs nagra av de vanligaste strategierna, vilket foljs av en jamforelse och analys av tva av dessa. For att kunna jamfora dessa strategier har en implementation av ett program som simulerar en byggnad med hissar gjorts. I programmet anvands sedan dessa strategier for att ta fram testresultat. Den mest eektiva av dessa tva strategier har optimerats och jamforts ytterligare med de tidigare resultaten. Testresultaten visar att den optimerade strategin var den mest eektiva med avseende pa genomsnittsvantetiden och den totala genomsnittsrestiden, och att det inte ar nodvandigt att helt byta strategi under dagen, men att det lonar sig att optimera delar av den, beroende pa trakodet

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Ceder, Frederick, and Alexandra Nordin. "Elevator Control Strategies." Thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-134902.

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This paper investigates the efficiency of known elevator control strategies by simulating these in an own made apartment simulator. Efficiency will be determined by the lowest product of the energy consumption (Watt/second), average waiting time, average transfer time and the maximum waiting time of a passenger, which is the output by the simulator. The apartment simulator will simulate the elevator behavior, according to a respective control strategy, and the passenger flow on each respective floor in a specific test scenario. In this test scenario, passengers always travel either to the ground floor or to their respective home floor to simulate an apartment complex on a workday. The outcome of the investigation was that a control strategy that would prioritize elevator orders, i.e. calls made from inside the elevator, remember calls and collect passengers that are on route was the most efficient, both in terms of low energy consumption and passenger satisfaction (low transit and waiting times).

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Kumar, Shubham. "Suppression and control of modulation instability." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/456080.

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Dynamical instabilities which lead to spontaneous pattern formation are present in a wide variety of nonlinear dynamical systems, both in nature as well as in technological areas. The instabilities may be saturating, leading to stationary and regular patterns, or not, leading to complex periodic structures or spatiotemporal chaos. Such pattern formation occurs universally, ranging diversely from fields such as biology and ecology to optics, hydrodynamics, condensed matter systems etc. Modulation Instability (MI), initially studied on systems such as deep-water waves, plasmas, nonlinear optics, and electromagnetics, is crucial to many current key technologies and research fields such as lasers, chemical systems, Bose-Einstein condensates of attracting atoms, high energy physics, ecology and vegetation, hydrodynamics, astrophysics etc. Despite the enormous variety of patterns in various different systems, the onset of such unstable spatiotemporal dynamics always originates through a modulation instability, when the initial, maximally-symmetric homogeneous state of the system spontaneous loses stability with respect to exponentially growing modulation modes. Therefore, the control and suppression of the MI, especially in spatially-extended systems that present a continuum (an infinite number) of unstable spatial modes, is vital for the stabilization of various such pattern-forming nonlinear systems and achieving this remains an ambitious goal. In this study, a fundamental new understanding of the MI in spatially-extended systems is developed, and a mechanism for the complete suppression of MI in such unstable systems is presented. The mechanism relies on an appropriate manipulation of the dispersion of the system, through a properly designed spatiotemporal modulation of its potential. This mechanism of MI suppression relies on a "resonant" interaction between the spatial and temporal frequencies of the modulation, which only occurs when the modulation geometry is close to the resonance. A second, much-more powerful, mechanism is also developed based on this initial understanding, in which the stabilization procedure is generalized, to form a "stabilization on demand" scheme, which achieves successful stabilization even for highly complex nonlinear systems. This method, based on the introduction of multiple "resonant" modulations of the system's potential relies on a Genetic Algorithm based optimization procedure, to suit arbitrarily complex stabilization requirements in various systems. The results bear general character, as they have been developed on the Complex Ginzburg-Landau model, which provides a universal description of MI across various systems from lasers to chemical systems, Bose-Einstein condensates, biological systems etc. Lastly, both methods are successfully applied to real-world systems, by providing a robust stabilization of MI in Broad Area Semiconductor (BAS) amplifiers and Vertical Cavity Surface Emitting semiconductor lasers. In BAS amplifiers the stabilization relays on a two-dimensional spatial modulation of the pump current, as may be provided through fishnet-like electrodes. While in the case of Vertical Cavity lasers the same may be achieved via a spatiotemporal modulation. These results have been demonstrated for realistic parameters, including large nonlinear coefficients and at high operating powers, representing a significant breakthrough in the stabilization of these widely prevalent and indispensable photonic devices. Les inestabilitats lineals que duen a la formació espontània de patrons són presents en un ampli ventall de sistemes dinàmics no lineals, tant en sistemes naturals com o sistemes tecnològics artificials. Les inestabilitats poden saturar-se, donant lloc a patrons estacionaris regulars, o no, donant lloc a estructures periòdiques complexes o a caos espai-temporal. Aquesta formació de patrons té lloc de forma universal, abraçant camps diversos, des de la biologia i l'ecologia a l'òptica, la hidrodinàmica, o sistemes de matèria condensada, etc. La Inestabilitat de Modulació (IM), inicialment estudiada en sistemes com ara ones d'aigües profundes, plasmes, òptica no lineal, i l'electromagnetisme, és crucial per a moltes tecnologies clau actuals i camps d'investigació com ara el làser, sistemes químics, condensats de Bose-Einstein d'àtoms que s’atreuen, física d'altes energia, l'ecologia i la vegetació, la hidrodinàmica, l'astrofísica, etc. Tot i l'enorme varietat de patrons en els diversos sistemes diferents, l’aparició de la inestabilitat espai-temporal dinàmica sempre s'origina a través d'una inestabilitat de modulació, quan l'estat homogeni inicial del sistema, amb màxima simetria, perd de forma espontània l’estabilitat respecte a modes de modulació de creixement exponencial. Per tant, el control i la supressió de la IM, especialment en sistemes espacials extensos que presenten un continu de modes espacials inestables, és vital per a l'estabilització de diverses tals sistemes no lineals i l'obtenció d'això continua sent un gran repte. Aquest estudi desenvolupa un nou enfoc fonamental per a la comprensió de la IM en sistemes extensos espacials, i presenta un mecanisme per a la complerta supressió de la IM en aquests sistemes inestables. El mecanisme es basa una manipulació de la dispersió del sistema de forma adequada, mitjançant una modulació espai-temporal especialment dissenyada del seu potencial. Aquest mecanisme de supressió de MI es basa en la interacció 'ressonant' entre les freqüències espacials i temporals de la modulació, que només es produeix quan el, la geometria de modulació és a prop de la ressonància. Un segon mecanisme d’estabilització, molt més potent, es desenvolupa sobre la base d'aquesta troballa inicial, en la qual es generalitza el procediment, per donar lloc a un esquema 'estabilització a demanda', que aconsegueix una estabilització exitosa fins i tot per a sistemes no lineals altament complexes. Aquest mètode, es fonamenta en la introducció de múltiples modulacions 'ressonants' en el potencial del sistemes i es basa en un procediment d'optimització mitjançant algoritmes genètics, capaç de satisfer requisits arbitràriament complexes per l’estabilització en sistemes diversos. El resultats obtinguts tenen un caràcter general, ja que han estat desenvolupats per a l’equació de Ginzburg-Landau complexa, que proporciona una descripció universal de la IM en diferents sistemes làser, sistemes químics, condensats de Bose-Einstein, sistemes biològics, etc. Finalment, tots dos mètodes s'apliquen amb èxit per a sistemes reals, proporcionant una eina potent per a l'estabilització d’amplificadors òptics de semiconductor d’àrea ampla i làsers de semiconductor de cavitat vertical. En el cas d’amplificadors òptics l’estabilització s’aconsegueix amb la modulació en dues dimensions espacials del corrent de bombeig, per exemple proporcionat a través d'elèctrodes de reixeta. D’altra banda, pels làsers de cavitat vertical s’aconsegueix a través d'una modulació espai-temporal. Aquests resultats han estat demostrat per a paràmetres realistes incloent grans coeficients no lineals i potències de funcionament elevades. Per tot això, aquest treball representa un avenç significatiu en l'estabilització d'aquests dispositius fotònics tan comuns com indispensables.

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Cruciani, Federica <1983&gt. "Therapeutic strategies for modulation of the vaginal microbiota." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4676/1/Cruciani_Federica_tesi.pdf.

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The vaginal microbiota of healthy women consists of a wide variety of anaerobic and aerobic bacteria, dominated by the genus Lactobacillus. The activity of lactobacilli is essential to protect women from genital infections and to maintain the natural healthy balance of the vaginal ecosystem. This role is particularly important during pregnancy because vaginal infection is one of the most important mechanisms for preterm birth. The most common vaginal disorder is bacterial vaginosis (BV). BV is a polymicrobial disorder, characterized by a depletion of lactobacilli and an increase in the concentration of other bacteria, including Gardnerella vaginalis, anaerobic Gram-negative rods, anaerobic Gram-positive cocci, Mycoplasma hominis, and Mobiluncus spp. An integrated molecular approach based on real-time PCR and PCR-DGGE was used to investigate the effects of two different therapeutic approaches on the vaginal microbiota composition. (i) The impact of a dietary supplementation with the probiotic VSL#3, a mixture of Lactobacillus, Bifidobacterium and Streptococcus strains, on the vaginal microbial ecology and immunological profiles of healthy women during late pregnancy was investigated. The intake was associated to a slight modulation of the vaginal microbiota and cytokine secretion, with potential implications in preventing preterm birth. (ii) The efficacy of different doses of the antibiotic rifaximin (100 mg/day for 5 days, 25 mg/day for 5 days, 100 mg/day for 2 days) on the vaginal microbiota of patients with BV enrolled in a multicentre, double-blind, randomised, placebo-controlled study was also evaluated. The molecular analyses demonstrated the ability of rifaximin 25 mg/day for 5 days to induce an increase of lactobacilli and a decrease of the BV-associated bacteria after antibiotic treatment, and a reduction of the complexity of the vaginal microbial communities. Thus, confirming clinical results, it represents the most effective treatment to be used in future pivotal studies for the treatment of BV.

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Johnson, Mackie. "Retail Inventory Control Strategies." ScholarWorks, 2016. https://scholarworks.waldenu.edu/dissertations/3171.

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Despite using computerized merchandise control systems in retail, the rate of stockouts has remained stagnant. The inability to satisfy customer needs has caused a loss of 4% in potential revenue and resulted in dissatisfied customers. The purpose of this qualitative multiple case study was to explore cost-effective inventory control strategies used by discount retail managers. The conceptual framework that grounded the study was chaos theory, which helped identify why some business leaders rely on forecasting techniques or other cost-effective strategies as an attempt to prevent stockouts. The target population was comprised of discount retail managers located throughout northeast Jacksonville, Florida. Purposeful sampling led to selecting 6 retail managers who successfully demonstrated cost-effective inventory control strategies for mitigating stockouts. Data were collected through face-to-face semistructured interviews, company websites, and company documents. Analysis included using nodes to identify similar words and axial-coding to categorize the nodes into themes. Transcript evaluation, member checking, and methodological triangulation strengthened the credibility of the findings. Five themes emerged: (a) internal stockout reduction strategies, (b) external stockout reduction strategies, (c) replenishment system strategies, (d) inventory optimization strategies, and (e) best practices for inventory control. This study may contribute to positive social change by improving inventory management, which may reduce demand fluctuations in the supply chain and reduce logistics costs in the transportation of freight thereby leading to improved customer satisfaction.

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Picas, Prat Ricard. "Control and modulation of modular multilevel converters." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/404612.

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The integration of renewable energy sources in the electrical grid is reducing our dependence on fossil fuels. However, to ensure feasibility and reliability of distributed energy generation, more efficient and higher power converters are required. The modular multilevel converter (MMC) is a modern topology of multilevel converter that is very attractive for medium- and high-voltage/power applications, including high-voltage direct current transmission systems and high-power motor drives. The main features of the MMC are modularity, scalability to different power and voltage levels, redundancy and high quality output voltages and currents. However, the operation of the MMC is complex, and there are some issues that still have to be further investigated. One of these issues is the voltage ripples of the submodule (SM) capacitors. The voltage ripples define the minimum value of the capacitances needed for the converter, and therefore its overall size and cost. The use of a proper circulating current controller can reduce the voltage ripples. In this thesis, three techniques for calculating the circulating current reference are presented: two techniques based on optimization functions for minimizing the capacitor voltage ripples; and a fast-processing technique that provides results close to optimal. The capacitor voltage ripples can also be reduced by adding a zero-sequence signal to the modulation signals. In this thesis, the application of discontinuous modulation to the MMC is proposed for the first time. This technique is based on the injection of a discontinuous zero-sequence signal and highly reduces the switching power losses and capacitor voltage ripples. Real applications of the MMC are composed of a high number of SMs. This implies a challenge in the control system, including the data acquisition system. A new technique for measuring the capacitor voltages with only a few sensors has been presented in this thesis. From the output voltage provided by a group of SMs, the individual voltage of each one of them can be acquired. Since acquisition cannot be performed at each sampling time, the capacitor voltages are calculated between samples using an estimation algorithm. Reliability is a feature required in industrial applications. The structure of the MMC facilitates the existence of redundant SMs, but faults need to be detected and localized for deactivating the faulty component. This thesis presents a robust and fast strategy for detecting, localizing and correcting faults in SMs and voltage sensors. The technique is based on three additional sensors per arm, which measure the output voltage of a group of SMs and compare it with the expected voltage. Capacitance differences between the SMs can appear due to component tolerance or ageing of the capacitors. Capacitance mismatches cause uneven distribution of the power losses, thus increasing the thermal stress of some semiconductors, and therefore, their probability of failure. A power loss balancing technique has been proposed, equalising the losses in all the SMs and therefore avoiding the concentration of power losses in some SMs. Application of the MMC to motor drive applications has also been studied in this thesis. The operation of the MMC at low motor speeds/frequencies is still a challenge, since the capacitor voltage ripples are inversely proportional to the current frequency. In this thesis, it has been demonstrated that discontinuous modulation can help to reduce capacitor voltage ripples in motor drive applications, achieving very low speed operation. The technique is compared with other state-of-the-art methods, and it achieves similar capacitor voltage ripples and a significant reduction in power losses. All the control and modulation techniques proposed in this thesis have been studied by simulation in the MATLAB/Simulink environment and corroborated experimentally on low-power laboratory prototypes. La integració de fonts d’energia renovables a la xarxa elèctrica està reduint la nostra dependència dels recursos fòssils. Però per tal d’assegurar la viabilitat i fiabilitat de la generació d’energia distribuïda, fan falta convertidors estàtics més eficients i de més potència. El convertidor multinivell modular (MMC) és una topologia de convertidor multinivell recent, molt prometedora per aplicacions de mitja i alta potència, com són els sistemes de transmissió d’energia en corrent continua o els accionaments de motors d’alta potència. Els principals avantatges del MMC són modularitat, escalabilitat en tensió i potència, redundància i gran qualitat de la tensió i corrent de sortida. El funcionament del MMC, però, és complex i encara hi ha alguns problemes que s’han d’investigar amb més profunditat. Un dels problemes és l’arrissat de tensió del condensador de sub-mòdul (SM). L’arrissat de tensió defineix el valor mínim d’aquests condensadors i per tant, el seu cost. L’ús d’un corrent circulant adequat pot reduir l’arrissat de tensió. En aquesta tesi es presenten tres tècniques per calcular la consigna del corrent circulant: dues tècniques basades en funcions d’optimització que minimitzen l’arrissat de tensió i una tècnica d’aplicació més simple, la qual proporciona resultats pròxims als òptims però que es pot calcular més ràpidament. L’arrissat de tensió també es pot reduir afegint un component homopolar en els senyals de modulació. En aquesta tesi es proposa per primera vegada l’ús de la modulació discontinua per al MMC. Aquesta tècnica, basada en la injecció d’un component homopolar, permet una gran reducció de l’arris s at de tens ió i de les pèrdues de commutació. Les aplicacions reals del convertidor MMC es componen per un gran nombre de SMs. Això implica un repte en el disseny del sistema de control, particularment en l’etapa d’adquisició de dades. Aquesta tesi presenta un nou sistema de mesura per a les tensions dels condensadors de SM, en el qual es necessiten pocs sensors. A partir de la tensió de sortida d’un grup de sensors, el sistema pot adquirir la tensió de cada un d’ells. Com que l’adquisició no es pot fer a cada període de mostreig, entre adquisicions la tensió es calcula mitjançant un algoritme d’estimació. Un dels requisits de les aplicacions industrials és la fiabilitat. L’estructura del MMC permet l’ús de SMs redundants, però les fallades s’han de detectar i localitzar per tal de desactivar el component erroni. En aquesta tesi es presenta un sistema ràpid i robust de detecció, localització i correcció de fallades en SMs i sensors de tensió. El sistema es basa en l’ús de tres sensors addicionals per semi-branca, els quals mesuren la tensió de sortida d’un grup de SMs i la comparen amb la tensió esperada. A causa de la tolerància o l’envelliment dels condensadors , poden aparèixer diferències en la capacitat dels SMs. Aquestes diferències causen una mala distribució de les pèrdues dels semiconductors, incrementant l’estrès tèrmic d’alguns dels components i la probabilitat de fallada. Per això, es proposa un algoritme d’equilibrat de pèrdues, el qual iguala les pèrdues dels SMs i n’evita la concentració en algun SM. En aquesta tesi també s’ha estudiat l’aplicació del MMC en accionaments de motors. El funcionament del MMC a baixa velocitat/freqüència del motor és un repte encara no resolt, ja que l’arrissat de tensió dels condensadors és inversament proporcional a la freqüència del corrent. Aquesta tesi demostra que la modulació discontinua es pot utilitzar per reduir l’arrissat de tensió en aquesta situació, aconseguint un bon funcionament a molt baixa velocitat. En comparació amb altres tècniques actuals de baixa velocitat, la modulació discontinua aconsegueix un arrissat de tensió similar i una reducció de les pèrdues. Totes les tècniques proposades en aquesta tesi s’han estudiat mitjançant simulació en l’entorn MATLAB/Simulink i s’han corroborat experimentalment en prototips de laboratori.

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Scheiner, Ricarda, Arnd Baumann, and Wolfgang Blenau. "Aminergic control and modulation of honeybee behaviour." Universität Potsdam, 2006. http://opus.kobv.de/ubp/texte_eingeschraenkt_verlag/2010/4610/.

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Biogenic amines are important messenger substances in the central nervous system and in peripheral organs of vertebrates and of invertebrates. The honeybee, Apis mellifera, is excellently suited to uncover the functions of biogenic amines in behaviour, because it has an extensive behavioural repertoire, with a number of biogenic amine receptors characterised in this insect. In the honeybee, the biogenic amines dopamine, octopamine, serotonin and tyramine modulate neuronal functions in various ways. Dopamine and serotonin are present in high concentrations in the bee brain, whereas octopamine and tyramine are less abundant. Octopamine is a key molecule for the control of honeybee behaviour. It generally has an arousing effect and leads to higher sensitivity for sensory inputs, better learning performance and increased foraging behaviour. Tyramine has been suggested to act antagonistically to octopamine, but only few experimental data are available for this amine. Dopamine and serotonin often have antagonistic or inhibitory effects as compared to octopamine. Biogenic amines bind to membrane receptors that primarily belong to the large gene-family of GTP-binding (G) protein coupled receptors. Receptor activation leads to transient changes in concentrations of intracellular second messengers such as cAMP, IP3 and/or Ca2+. Although several biogenic amine receptors from the honeybee have been cloned and characterised more recently, many genes still remain to be identified. The availability of the completely sequenced genome of Apis mellifera will contribute substantially to closing this gap. In this review, we will discuss the present knowledge on how biogenic amines and their receptor-mediated cellular responses modulate different behaviours of honeybees including learning processes and division of labour.

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Kuo, Yu-Ting. "Imaging appetite control and modulation in vivo." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542967.

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Ives, Robert W. "Error Control Coding for Multi-Frequency Modulation." Thesis, Monterey, California: Naval Postgraduate School, 1990. http://hdl.handle.net/10945/27762.

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Approved for public release; distribution is unlimited. Multi-frequency modulation (MFM) has been developed at NPS using both quadrature-phase-shift-keyed (QPSK) and quadrature-amplitude-modulated (QAM) signals with good bit error performance at reasonable signal-to-noise ratios. Improved performance can be achieved by the introduction of error control coding. This report documents a Fortran simulation of the implementation of error control coding into an MFM communication link with additive white Gaussian noise. Four Reed-Solomon codes were incorporated, two for 16-QAM and two for 32- QAM modulation schemes. The error control codes used were modified from the conventional Reed-Solomon codes in that one information symbol was sacrificed to parity in order to use a simplified decoding algorithm which requires no iteration and enhances error detection capability. Bit error rates as a function of SNR and EbN0 were analyzed, and bit error performance waa weighed against reduction in information rate to determine the value of the codes.

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Graaf, Rick de. "Venous graft remodeling novel mechanisms and pharmaco-modulation strategies /." [S.l.] : Maastricht : D & L Graphics ; University Library, Universiteit Maastricht [host], 2008. http://arno.unimaas.nl/show.cgi?fid=13503.

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Grewal, Sukhminder Singh. "Digital signal processor implementation of novel PWM strategies." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246284.

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Kahriman, Edin, and Srdjan Jovanovic. "Alternative Strategies for Engine Control." Thesis, Linköpings universitet, Reglerteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-119470.

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The existing powertrain control system in Volvo CE's vehicles consists of various types of physical quantities that are controlled. One of them is the engine speed. The purpose of this thesis is to investigate whether there are other control strategies suitable for engine speed control, than the existing one. Currently, the existing control system requires re-calibration of the control parameters if hardware in the vehicle is replaced. The current controller is a gain-scheduled PID controller with control parameters that varies over the operating range. The aim has been to develop several different adaptive control strategies. Adaptive control methods are expected to adapt to the changes of the system that a replacement of hardware can bring. The performance and robustness of the developed controllers have been compared with the existing controller. The approach has been to implement the control strategies in Matlab/Simulink and simulate the process with existing engine software provided by Volvo CE. The next step was to test and verify the controllers in a real machine. The focus in this thesis work has been on the adaptive control strategies MRAC (Model-Reference Adaptive Control) and L1 Adaptive Control. In the MRAC structure the desired performance is specified in terms of a reference model that the real system is supposed to follow. Each time an error is generated, by comparing actual and desired output, a suitable algorithm is used in order to obtain the control signal that can minimize the error. In addition, modeling errors and disturbances are estimated so that the controller can compensate for these. L1 Adaptive Control is an extension of the MRAC structure. The difference is that before the control signal is fed to the real system, it is low-pass filtered. This is done in order to prevent feeding high frequencies into the system. The results show that adaptive control has potential to be used in engine speed control. Reference following and disturbance rejection is well handled and simulations have furthermore shown that the developed controllers can deal with changes in the hardware. One of the developed L1-controllers was implemented in a real machine with promising results. Det existerande styrsystemet i Volvo CE:s maskiner har till uppgift att styra och reglera flera olika fysikaliska storheter. En av dessa storheter är motorvarvtalet. Syftet med detta examensarbete är att undersöka alternativa reglerstrategier som kan användas för att styra motorvarvtalet. Problemet idag är att det nuvarande styrsystemet kräver omkalibrering av regulatorparametrar när befintlig hårdvara i maskinen behöver ersättas på grund av föråldring eller slitage. Den nuvarande regulatorn är en parameterstyrd PID-regulator där regulatorparametrarna beror av aktuell arbetspunkt. Målet har varit att utveckla och prova flera olika adaptiva reglerstrategier. Dessa metoder förväntas kunna hantera förändringar och adaptera sig mot nya förhållanden och omständigheter som en hårdvaruförändring kan medföra. Prestanda och robusthet som de utvecklade regulatorerna erhåller har jämförts mot den existerande regulatorstrukturen. Tillvägagångssättet har varit att implementera reglerstrategierna i Matlab/Simulink samt simulera med tillhörande motormjukvara som Volvo CE tillhandahållit. I nästa fas skulle regulatorerna testas och verifieras i en riktig maskin. Fokuset har under detta examensarbete riktats mot de två adaptiva reglerstrategierna Model-Reference Adaptive Control (MRAC) och L1 Adaptive Control. MRAC-strukturen bygger på att specificera prestandan genom en referens-modell som det riktiga systemet skall följa. Varje gång en avvikelse uppstår så beräknas en lämplig styrsignal genom att beakta och försöka minimera skillnaden mellan det riktiga systemet och den önskade referens-modellen. Till detta modelleras och skattas störningar som regulatorn skall kompensera för. Tekniken inom L1 Adaptive Control är en utvidgning av MRAC. Önskat beteende specificeras även för denna regulatorstruktur men största skillnaden är att innan styrsignalen matas in till systemet så lågpassfiltreras den. Detta görs i förebyggande syfte för att inte släppa in onödigt höga frekvenser in i systemet. Resultaten visar att adaptiv reglering av motorvarvtalet har potential. Referensföljning och undertryckning av störningar hanteras väl och simuleringar har dessutom visat att de utvecklade regulatorerna kan hantera hårdvaruändringar. En av de utvecklade L1-regulatorerna implementerades i en riktig maskin och resultaten såg lovande ut.

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Ng, Kwai Choi Stanley. "Regulation strategies for process control." Thesis, University of Sunderland, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337287.

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Goel, Anukul. "Control strategies for supercavitating vehicles." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE0000537.

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Haviland, Jesse. "Control strategies for reactive manipulation." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/236551/1/Jesse%2BHaviland%2BThesis%282%29.pdf.

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For a robot to operate in the real world, which is dynamic, unstructured, and unknowable, it must be able to react and adapt to the ever-changing state of the robot, environment, and goal. This thesis develops novel reactive motion controllers, which, unlike prior approaches, can rapidly, robustly and safely operate in real-world environments. The thesis also provides extensive software and educational materials to encourage the adoption and ongoing development of this new reactive robot motion paradigm.

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Antonopoulos, Antonios. "Control, Modulation and Implementation of Modular Multilevel Converters." Licentiate thesis, KTH, Elektriska maskiner och effektelektronik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-34188.

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Denna avhandling behandlar analys och styrning av den modulära multinivå omvandlaren (M2C). M2C är en lovande omvandlarteknologi för högspända högeffekttillämpningar. Anledningen till detta är låg distorsion i utstorheterna kan uppnås med låg medelswitchfrekvens per switch och utan utgångsfilter. Med M2C har utspänningen så lågt övertonsinnehåll att drift av högeffektmotorer är möjlig utan reduktion av märkeffekten. Emellertid innebär det stora antalet styrda switchar att styrningen blir mer komplex än för motsvarande tvånivåomvandlare. Styrningen av M2C måste måste konstrueras så att submodulernas kondensatorspänningar balanseras och är stabila oberoende av driftfall. En aktiv mekanism för val av submoduler, som är integrerad i modulatorn, har visat sig vara effektiv för att ombesörja den interna balanseringen av omvandlararmarna. Utöver balanseringen av de individuella kondensatorerna krävs en strategi för styrning av den totalt upplagrade energin i omvandlaren. Med utgångspunkt i en analytisk beskrivning av omvandlaren föreslås styrlagar för både öppen styrning och sluten reglering, vilka genom både simuleringar och med hjälp av experiment har visat sig vara stabila i hela arbetsområdet. Den potentiella växelverkan mellan den inre omvandlarstyrningen och en yttre strömreglering undersöks också. Både simuleringar och experiment bekräftar att eventuell interaktion inte innebär några avsevärda problem vare sig för omvandlaren eller motorn. En hårdvaruimplementering av en nedskalad trefasig 10kVA-omvandlare har genomförts för att verifiera modellering och styrning. Implementeringen av styrningen beskrivs i detalj. Styrningen är anmärkningsvärt snabb och kan utökas till godtyckligt antal nivåer. Den kan därför användas för en fullskaleimplementering i MW-klassen. This thesis deals with the analysis and control of the modular multilevel converter (M2C). The M2C is a promising converter technology for various high-voltage high-power applications. The reason to this is that low-distortion output quantities can be achieved with low average switching frequencies per switch and without output filters. With the M2C the output voltage has such a low harmonic content that high-power motors can be operated without any derating. However, the apparent large number of devices, requires more complex converter control techniques than a two-level counterpart. The internal control of an M2C must be designed so that the submodule capacitor voltages are equalized and stable independent of the loading conditions. An active submodule selection mechanism, included in the modulator, has been shown able to provide voltage sharing inside the converter arm. Apart from the individual capacitor voltage sharing, a strategy has to be designed to ensure that the total amount of energy stored inside the converter will always be controlled. Based on an analytical description of the converter, both feedback and open-loop control methods are suggested, simulated and experimentally evaluated, which will ensure stable operation in the whole operation range. The potential interaction of the internal controllers with an external motor current controller is also investigated. Both simulation and experimental results show that any interaction will not result in any problems neither for the converter nor for the motor control itself. A hardware implementation of a down-scaled 10 kVA three-phase laboratory prototype converter is performed, in order to evaluate the modeling and the controllers developed. The controller implementation is described in detail, as it exhibits remarkably fast response, and can be expanded up to an arbitrary number of levels. Therefore it can be used even by a full-scale converter implementation in the MW range. QC 20110628

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Poulsen, Catherine. "Motivational modulation of on-line attention control processes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq54385.pdf.

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Larbes, Cherif. "Boost modulation : control of AC variable speed drives." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304281.

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Uhl, Brecken. "Direct Spatial Antenna Modulation for Wideband Phase Control." International Foundation for Telemetering, 2010. http://hdl.handle.net/10150/604278.

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ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California Direct spatial antenna modulation (DSAM) is a new approach to phased array control that opens up new "smart antenna" architecture possibilities. The DSAM technique leverages the inherent spatial differences of excitation in an antenna in a novel way to achieve the equivalent of conventional modulation and beam control effects. Smart antenna techniques are of potentially increasing importance to test range operations given a trend toward more flexible, internetworked, and autonomous test activities. The DSAM technique has been demonstrated through several generations of analysis, simulation, and prototyping, but has previously only been applied to narrowband antenna designs. Furthermore, the IQ DSAM approach in particular has not been previously implemented in hardware. This paper details the application of IQ DSAM to achieve wideband phase control using a commercial off the shelf (COTS) antenna. The phase control performance of IQ DSAM over a range of 1.5 GHz to 4 GHz is measured across relative field control angles of +/- 45 degrees. The measured IQ DSAM performance is compared to what could be expected from a conventional phased array element control architecture.

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Keeler, Joshua Finn. "Instrumental response sequencing : dopaminergic modulation and behavioural control." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648582.

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Celanovic, Nikola. "Space Vector Modulation and Control of Multilevel Converters." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/29164.

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This dissertation is the result of research and development of a power conditioning system for Superconductive Magnetic Energy Storage System. The dominant challenge of this research was to develop the power conditioning system that can match slowly varying dc voltage and dc current on the super conductive magnet side with the ac voltages and ac currents on the utility side. At the same time the power conditioning system was required to provide a bi-directional power flow to the superconductive magnet. The focus of this dissertation is a three-level diode clamped dc-ac converter which is a principle part of the power conditioning system. Accordingly, this dissertation deals with the space vector modulation of three-level converters and introduces a computationally very efficient three-level space vector modulation algorithm that is experimentally verified. Furthermore, the proposed space vector modulation algorithm is successfully generalized to allow equally efficient, real time implementation of space vector modulation to dc-ac converters with virtually any number of levels. The most important advantage of the proposed concept is in the fact that the number of instructions required to implement the algorithm is almost independent from the number of levels in a multilevel converter. More on the side of the control of multilevel converters, the particular attention in this dissertation is paid to the problem of charge balance in the split dc-link capacitors of three-level neutral-point-clamped converters. It is a known fact that although the charge balance in the neutral point can be maintained on a line cycle level, a significant third harmonic current flows into the neutral point for certain loading conditions, causing the neutral point voltage ripple. The logical consequence of that ripple is the deteriorated quality of the output voltage waveforms as well as the increased voltage stress on the switching devices. This was the motivation to more carefully explore the loading conditions that cause the unbalance, as well as to study the fundamental limitations of dc-link capacitor charge balancing algorithms. As a part of that work, a new model of the neutral point current in the rotating coordinate frame is developed as a tool in investigation of theoretical limitations and in providing some intuitive insight into the problem. Additionally, the low frequency ripple is quantified and guidelines are offered that can help size the dc-link capacitors. Because the study of the neutral point balance identified the loading conditions, that under some possible system constraints, cause an unavoidable neutral point voltage ripple, a feed forward type of control method is developed next. The proposed feed forward algorithm can effectively prevent the neutral point voltage ripple from creating distortions in the converter output voltage under all loading conditions and without causing additional disturbance in the neutral point voltage. The feed forward method is developed for a sine triangle as well as for the space vector type PWM algorithm. The simulation results that include the full dynamic model of the converter and load system validate the feed forward approach and prove that the feed forward algorithm can effectively compensate the effect of the neutral point voltage ripple. The simulation results are than experimentally verified. Ph. D.

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Ko, Youngjong [Verfasser]. "Thermally-Compensated Modulation Strategies for Modular Power Converters / Youngjong Ko." Kiel : Universitätsbibliothek Kiel, 2019. http://d-nb.info/1185485198/34.

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ZUCCOLINI, PAOLO. "STRATEGIES FOR AN OPTOGENETIC MODULATION OF THE PACEMAKER CURRENT IF." Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/634438.

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HCN4 channels control pacemaking of the heart. They are activated by negative voltage and modulated by cAMP. Recently it had been discovered that cyclic di-nucleotides bind to a second site in the channel C-terminus. This counteracts the effect of cAMP on shifting channel activation positive. A bacterial cyclase, which synthesizes c-di-GMP in response to red light, allows engineering of an optogenetic system for remote HCN4 modulation and hence for controlling the heart pace. Two cyclases were used in this work: one constitutively active (Slr1143) and one red ligh-regulated (BphS). Because the latter has some dark activity, it is co-expressed with a phosphodiesterase (YhjH). Recordings of HCN4 activity in HEK293T cells show that Slr1143 affects the voltage dependence of the channel, shifting the activation curve negative with respect to the control. Experiments with BphS show no difference in HCN4 activity between light and dark treated cells. The combined BphS-YhjH expression seemed to be unable to increase the c-di-GMP concentration in a light dependent manner. To examine the effect of light on c-di-GMP production we quantified the cyclic di-nucleotide with an established ELISA assays in HEK293T cells and with an immune-fluorescence method. The latter consisted of monitoring expression of interferon-β in BphS-YhjH expressing T cells. Cyclic di-nucleotides can activate the STING pathway, which augments synthesis of interferon-β. Both methods underlined that Slr1143 and BphS-YhjH system increased the level of c-di-GMP in cells. This activity, however, was not light regulated. The immuno-fluorescence data indicate a slightly higher expression of the constitutive compared to the light-regulated cyclase. This may explain why we observed an effect of the former but not of the latter on HCN4 gating. Eliminating YhjH did not affect the level of c-di-GMP, suggesting that the phosphodiesterase is insufficient for eliminating c-di-GMP dark production. The data confirm previous results in that c-di-GMP is able to modulate HCN4 activity. BphS is not yet suitable as an optogenetic tool because of its high dark activity. This problem may be overcome by increasing the expression/activity of the phosphodiesterase in the next iteration of engineering an optogenetic tool.

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Ibrahim, Khan M. "Tuberculosis in Pakistan improving control strategies /." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=969899300.

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Kørte, Steffen Østensjø. "Guidance & Control Strategies for UUVs." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16228.

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Focus on safety and effectiveness in the oil and gas industry has increased the need for advanced control system for underwater vehicles. For remotely operated vehicles (ROVs) effectiveness when conducting deep sea operation is extremely critical both concerning safety and cost. For AUVs conducting survey missions, energy and collision avoidance are critical factors. A control system for ROV Minerva is being developed through the AUR-Lab at the Institute of Marine Technology at NTNU. Several guidance features have been investigated, with respect to different mission the ROV should be able to do. A guidance system has been developed, where basic functions such as a DP system with station keeping and trajectory tracking was the focus of the project thesis of the author. More advanced functionality with respect to path following has been developed, where focus have been set on different strategies to apply when the ROV is following a path. Simulations based on different strategies for following a lawnmower pattern have been simulated and evaluated with respect to time, energy and control objective. Full scale experiments with the ROV Minerva show that especially the forward speed versus arc radius is an important issue. The results show that the ROV is able to follow a path made out of straight lines and circular arcs, and particularly lawnmower patterns. For an underwater vehicle to be able to operate autonomously, stationary and dynamic obstacles have to be taken into account. A collision avoidance system based on local collision avoidance algorithms has been implemented, where focus has been on reactivity with respect to unmapped obstacles. The collision avoidance system has been through initial full scale tests with ROV Minerva, and the result are promising.

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Al-Mudhaffar, Azhar. "Impacts of Traffic Signal Control Strategies." Doctoral thesis, Stockholm : Division of transports and logistics, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4268.

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Zolotas, Argyrios C. "Advanced control strategies for tilting trains." Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/4279.

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The use of tilting bodies on railway vehicles is becoming increasingly widespread: a number of well-established services using tilt technology already exist around the world, and will appear again in the UK over the next year or so. The motivation for tilting railway vehicles is that they give a cost-effective means of achieving a substantial reduction in journey time by increasing the vehicle speed during curves. Early tilt controller designs were based upon local vehicle measurements, however at that time this approach did not prove very successful. Nowadays most European manufacturers use the so called ‘precedence' control scheme, utilising measurements from precedent vehicles to achieve ‘precedence' information. However, achieving a satisfactory local tilt control strategy is still an important research target because of the system simplifications and more straightforward failure detection. The thesis describes a comprehensive study of tilt control, and its aim is to employ advanced control techniques - based upon practical sensors - with the particular objective of identifying effective strategies which can be applied to each vehicle independently, i.e. without using precedence control. The sensors employed for control design are in particular mounted on the vehicle passenger coach. Most of the work has been undertaken using Matlab, and this has included a proper assessment of the ride quality issues.

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Chacón, Vásquez Mercedes. "Strategies for wireless networked control systems." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28771.

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Networked Control Systems (NCS) and Wireless Networked Control Systems (WNCS) are control systems where controllers, sensors and final elements of control are connected to a mutual communication network. The inclusion of the network introduces delays and dropouts, which greatly influence the stability and robustness of the controller. While there is wealth in theoretical contributions to NCS, it is still imperative to study more applications and investigate the effects of networks in a real-time operation. There are also open problems that require further study of the impact of disturbances, constraints and strong interactions in complex NCS. This thesis is concerned with the design of control strategies for WNCS mainly focused on Model-Based Predictive Control (MBPC), Proportional Integral Derivative (PID) and decentralised schemes with the aim of creating control laws suitable for compensating time-varying delays and dropouts. These strategies rely on optimisation problems which incorporate robustness and performance restrictions to compute the optimum controller. The performance and robustness of the controllers are evaluated through extensive experiments in a network simulator. A new adaptive Internal Model Control (IMC) controller has been developed to adapt to the network requirements and compute the IMC model parameters online. A new robust PID for NCS under random delays has been created by solving a new constrained optimisation problem that included constraints of maximum sensitivity to guarantee robustness. A novel optimal immune PID is developed to improve the performance of NCS under time-varying delays and dropouts. Simulation results show that the controller offers greater flexibility and improves the performance and robustness with respect to the other methods studied. Four more controllers have been tested and extensive tests have indicated stability for a limited percentage of process model variations and dropouts. Predictive PID controllers, with similar properties to MBPC, are developed to compensate dropouts in WNCS. A quadratic programming problem optimises a new MBPC cost function to find the optimal PID gains. The approach successfully maximises the performance by changing the controller gains at every sampling time and allowing maximum variations of system parameters and dropouts. Also, a new constrained predictive PID controller is presented to deal with input saturation. Simulation results show the superiority of the design in comparison with the control schemes studied earlier. Furthermore, a decentralised wireless networked model predictive control design for complex industrial systems has been developed. Also, the method has been applied to wind farm control. The proposed decentralised control offers an effective and innovative solution to improve the performance of large industrial applications.

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Chen, Xin 1973. "Coordinating inventory control and pricing strategies." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29598.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2003. Includes bibliographical references (p. 127-130). Traditional inventory models focus on effective replenishment strategies and typically assume that a commodity's price is exogenously determined. In recent years, however, a number of industries have used innovative pricing strategies to manage their inventory effectively. These developments call for models that integrate inventory control and pricing strategies. Such models are clearly important not only in the retail industry, where price-dependent demand plays an important role, but also in manufacturing environments in which production/distribution decisions can be complemented with pricing strategies to improve the firm's bottom line. To date, the literature has confined itself mainly to models with variable ordering costs but no fixed costs. Extending some of these models to include a fixed cost component is the main focus of this thesis. In this thesis, we start by analyzing a single product, periodic review joint inventory control and pricing model, and characterizing the structure of the optimal policy under various conditions. Specifically, for the finite horizon periodic review case, we show, by employing the classical k-convexity concept, that a simple policy, called (s, S, p), is optimal when the demand functions are additive. For the model with more general demand functions, we show that an (s, S, p) policy is not necessarily optimal. We introduce a new concept, the symmetric k-convex functions, and apply it to provide a characterization of the optimal policy. Surprisingly, in the infinite horizon periodic review case, the concept of symmetric k-convex functions allows us to show that a stationary (s, S, p) policy is optimal for both discounted and average profit models even for general demand functions. (cont.) Our approach developed for the infinite horizon periodic review joint inventory control and pricing problem is then extended to a corresponding continuous review model. In this case, we prove that a stationary (s, S, p) policy is optimal under fairly general assumptions. Finally, the symmetric k-convexity concept developed in this thesis is employed to characterize the optimal policy for the stochastic cash balance problem. by Xin Chen. Ph.D.

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Abuzeid, Mustafa R. "Advanced braking control strategies for trains." Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/32027.

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The thesis describes modelling methods that are being developed to support the design and evaluation of intelligent railway braking control systems. A particular feature is that the models include higher order vehicle and train dynamics, the effects of which are expected to become important as the performance of braking systems improve. The thesis describes mathematical techniques for modelling braking systems starting with braking of a single wheelset on its own, then a single braked wheelset in a bogie, followed by a single braked wheelset in a complete vehicle and finally four wheelsets braked in a complete vehicle. The mathematical model for the braking system combines the non-linear creep laws governing the braking forces generated between wheel and rail with the suspension dynamics of a typical high speed railway vehicle.

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Round, Philip A. "Simulation of robot manipulator control strategies." Thesis, Aston University, 1988. http://publications.aston.ac.uk/11918/.

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The high capital cost of robots prohibit their economic application. One method of making their application more economic is to increase their operating speed. This can be done in a number of ways e.g. redesign of robot geometry, improving actuators and improving control system design. In this thesis the control system design is considered. It is identified in the literature review that two aspects in relation to robot control system design have not been addressed in any great detail by previous researchers. These are: how significant are the coupling terms in the dynamic equations of the robot and what is the effect of the coupling terms on the performance of a number of typical independent axis control schemes?. The work in this thesis addresses these two questions in detail. A program was designed to automatically calculate the path and trajectory and to calculate the significance of the coupling terms in an example application of a robot manipulator tracking a part on a moving conveyor. The inertial and velocity coupling terms have been shown to be of significance when the manipulator was considered to be directly driven. A simulation of the robot manipulator following the planned trajectory has been established in order to assess the performance of the independent axis control strategies. The inertial coupling was shown to reinforce the control torque at the corner points of the trajectory, where there was an abrupt demand in acceleration in each axis but of opposite sign. This reduced the tracking error however, this effect was not controllable. A second effect was due to the velocity coupling terms. At high trajectory speeds it was shown, by means of a root locus analysis, that the velocity coupling terms caused the system to become unstable.

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Devereux, David. "Control strategies for whole arm grasping." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/control-strategies-for-whole-arm-grasping(02ddb06c-3264-46e1-818a-8632b1bb05c4).html.

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Grasping is a useful ability that allows manipulators to restrain objects to a desired location or trajectory. Whole arm grasps are grasps that use the entire surface of the manipulator to apply contacts to an object. The problem of determining the shape of an object and planning a grasp for that object with a snake-like robot are considered in this work. Existing algorithms that attempt to allow robots to plan and perform whole arm grasps are lacking, they either use restrictive assumptions or have unrealistic demands in terms of required hardware. The work presented here allows even the most basic of robots to plan grasps on unknown objects whilst using a minimum of assumptions.The new developed Octograsp algorithm is a method of gaining information regarding the shape of the object to be grasped through tactile information alone. This contact information is processed using an inverse convex hull algorithm to build a model of the object's shape and position. The performance of the algorithms are examined using both simulations and experimental hardware, it is shown that accuracy errors as low as 3.1% can be obtained. The accuracy of the model depends upon factors such as the complexity of the object and the suitability of the robot. Manipulators consisting of a large number of small links with relaxed rotational constraints outperform other configurations. It is also shown that the accuracy can be improved by between 11% and 17% by contacting the object from multiple orientations, whilst also encircling from multiple positions can provide a very large improvement of between 56% to 86%. These methods allow even the coarse contact information provided by the experimental equipment to attain a model with an accuracy error of only 26%.A second novel algorithm is described that uses the information provided from the first algorithm to plan strong grasps over the desired object. The algorithm takes, on average, 25.1 seconds to plan the grasp. The mean strength of the planned grasps is 0.3816 using the wrench ball measure, this is firmly in the very good region. Several robotic configurations, as well as objects, are used to test the performance of the algorithm. The optimal parameters of the algorithm are investigated by using the results of 51030 different tests. It is again shown that robots that consist of a large number of small links and with high rotational ability perform the best.

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Auret, Erika Elizabeth. "Control strategies for citrus postharvest diseases." Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-06192006-084845.

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Linser, Katrin. "Unconscious modulation of the conscious experience of voluntary control." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1181000414782-24817.

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How does the brain generate our experience of being in control over our actions and their effects? Here I argue that the perception of events as self-caused emerges from a comparison between anticipated and actual action-effects: if the representation of an event that follows an action is activated before the action, the event is experienced as caused by one’s own action, whereas in the case of a mismatch it will be attributed to an external cause rather than to the self. In a subliminal priming paradigm I show that participants overestimated how much control they had over objectively uncontrollable stimuli, which appeared after free- or forced-choice actions, when a masked prime activated a representation of the stimuli immediately before each action. This prime-induced control-illusion was independent from whether primes were consciously perceived. Results indicate that the conscious experience of control is modulated by unconscious anticipations of action-effects.

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Trichard, Marc Henri. "Study of Trellis Coded Modulation and error control coding." Thesis, University of Ottawa (Canada), 1995. http://hdl.handle.net/10393/9658.

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In this thesis, we examine some general theoretical features of Trellis Coded Modulation. The codes in use are the recursive Ungerboeck convolutional codes and they are combined with Quadrature Amplitude Modulation over an Additive White Gaussian Noise channel. The search of optimum mappings is first treated and the question of having some smaller punctured constellations from a larger one is considered. Performance evaluation of TCM codes is provided according to geometric conditions that the mappings must stand in order to reduce the complexity of the calculation. Computation of transfer function is provided and this leads to a theoretical analysis for probability expressions of even, symbol and bit errors. A second order term expression is also elaborated which takes into consideration both error events on the trellis and errors on parallel transitions. Computer simulations have been run along with High Density Television transmission parameters. The results are presented and discussed. The use of error control coding techniques makes a great improvement in performance. For this purpose, Reed-Solomon codes have been concatenated with TCM codes, and gone through interleaving to ensure a higher error recovery efficiency.

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Venkatesan, Priya. "Modulation of airway neural control and the cough reflex." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326081.

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Anderson, Duncan J. "Modulation and control of diode lasers for optical interferometers." Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1519.

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Amos, Brian John. "Control and modulation of pH in mammalian central neurones." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307596.

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Sethuraman, Shanthi. "Variable sampling interval control strategies for a process control problem." Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/40313.

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Skelton, Claude Eugene II. "Mixed Control Moment Gyro and Momentum Wheel Attitude Control Strategies." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/9677.

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Attitude control laws that use control moment gyros (CMGs) and momentum wheels are derived with nonlinear techniques. The control laws command the CMGs to provide rapid angular acceleration and the momentum wheels to reject tracking and initial condition errors. Numerical simulations of derived control laws are compared. A trend analysis is performed to examine the benefits of the derived controllers. We describe the design of a CMG built using commercial off-the-shelf (COTS) equipment. A mixed attitude control strategy is implemented on the spacecraft simulator at Virginia Tech. Master of Science

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Sabattini, Lorenzo <1983&gt. "Nonlinear Control Strategies for Cooperative Control of Multi-Robot Systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4465/1/sabattini_lorenzo_tesi.pdf.

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This thesis deals with distributed control strategies for cooperative control of multi-robot systems. Specifically, distributed coordination strategies are presented for groups of mobile robots. The formation control problem is initially solved exploiting artificial potential fields. The purpose of the presented formation control algorithm is to drive a group of mobile robots to create a completely arbitrarily shaped formation. Robots are initially controlled to create a regular polygon formation. A bijective coordinate transformation is then exploited to extend the scope of this strategy, to obtain arbitrarily shaped formations. For this purpose, artificial potential fields are specifically designed, and robots are driven to follow their negative gradient. Artificial potential fields are then subsequently exploited to solve the coordinated path tracking problem, thus making the robots autonomously spread along predefined paths, and move along them in a coordinated way. Formation control problem is then solved exploiting a consensus based approach. Specifically, weighted graphs are used both to define the desired formation, and to implement collision avoidance. As expected for consensus based algorithms, this control strategy is experimentally shown to be robust to the presence of communication delays. The global connectivity maintenance issue is then considered. Specifically, an estimation procedure is introduced to allow each agent to compute its own estimate of the algebraic connectivity of the communication graph, in a distributed manner. This estimate is then exploited to develop a gradient based control strategy that ensures that the communication graph remains connected, as the system evolves. The proposed control strategy is developed initially for single-integrator kinematic agents, and is then extended to Lagrangian dynamical systems.

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