35 research outputs found

    Control and management of energy storage systems in microgrids

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    The rate of integration of the renewable energy sources in modern grids have significantly increased in the last decade. These intermittent, non-dispatchable renewable sources, though environment friendly tend to be grid unfriendly. This is precisely due to the issues pertaining to grid congestion, voltage regulation and stability of grids being reported as a result of the incorporation of renewable sources. In this scenario, the use of energy storage systems (ESS ) in electric grids is being widely proposed to overcome these issues. However, integrating energy storage systems alone will not compensate for the issue created by renewable generation. The control and management of the ESS should be done optimally so that their full capabilities are exploited to overcome the issues in the power grids and to ensure their lower cost of investment by prolonging ESS lifetime through minimising degradation. Motivated by this aspect this Ph.D work focusses on developing an efficient, optimal control and management strategy for ESS in a microgrid, especially hybrid ESS. The Ph.D work addresses this issue by proposing a hierarchical control scheme comprising of a lower power management and higher energy management stage with contributions in each stage. In the power management stage this work focusses on improving aspects of real time control of power converters interfacing ESS to grid and the microgrid system as whole. The work proposes control systems with improved dynamic behaviour for power converters based on the reset control framework. In the microgrid control the work presents a primary+secondary control scheme with improved voltage regulation performance under disturbances, using an observer. The real time power splitting strategies among hybrid ESS accounting for the ESS operating efficiencies and degradation mechanisms will also be addressed in the primary+secondary control of power management stage. The design criteria, stability and robustness analysis will be carried out, along with simulation or experimental verifications. In the higher level energy management stage, the contribution of this work involves application of an economic MPC framework for the management of ESS in microgrids. The work specifically addresses the problems of mitigating grid congestion from renewable power feed-in, minimising ESS degradation and maximising self consumption of generated renewable energy using the MPC based energy management system. A survey of the forecasting methods that can be used for MPC will be carried out and a neural network based forecasting unit for time series prediction will be developed. The practical issue of accounting for forecasting error in the decision making of MPC will be addressed and impact of the resulting conservative decision making on the system performance will be analysed. The improvement in performance with the proposed energy management scheme will be demonstrated and quantified.La integraci贸n de las fuentes de energ铆a renovables en las redes modernas ha aumentado significativamente en la 煤ltima d茅cada. Estas fuentes renovables, aunque muy convenientes para el medio ambiente son de naturaleza intermitente, y son no panificables, cosa que genera problemas en la red de distribuci贸n. Esto se debe precisamente a los problemas relacionados con la congesti贸n de la red y la regulaci贸n del voltaje. En este escenario, el uso de sistemas de almacenamiento de energ铆a (ESS) en redes el茅ctricas est谩 siendo ampliamente propuesto para superar estos problemas. Sin embargo, la integraci贸n de sistemas de almacenamiento de energ铆a por s铆 solos no compensar谩 el problema creado por la generaci贸n renovable. El control y la gesti贸n del ESS deben realizarse de manera 贸ptima, de modo que se aprovechen al m谩ximo sus capacidades para superar los problemas en las redes el茅ctricas, garantizar un coste de inversi贸n razonable y prolongar la vida 煤til del ESS minimizando su degradaci贸n. Motivado por esta problem谩tica, esta tesis doctoral se centra en desarrollar una estrategia de control y gesti贸n eficiente para los ESS integrados en una microrred, especialmente cuando se trata de ESS de naturaleza. El trabajo de doctorado propone un esquema de control jer谩rquico compuesto por un control de bajo nivel y una parte de gesti贸n de energ铆a operando a m谩s alto nivel. El trabajo realiza aportaciones en los dos campos. En el control de bajo nivel, este trabajo se centra en mejorar aspectos del control en tiempo real de los convertidores que interconectan el ESS con la red y el sistema de micro red en su conjunto. El trabajo propone sistemas de control con comportamiento din谩mico mejorado para convertidores de potencia desarrollados en el marco del control de tipo reset. En el control de microrred, el trabajo presenta un esquema de control primario y uno secundario con un rendimiento de regulaci贸n de voltaje mejorado bajo perturbaciones, utilizando un observador. Adem谩s, el trabajo plantea estrategias de reparto del flujo de potencia entre los diferentes ESS. Durante el dise帽o de estos algoritmos de control se tienen en cuenta los mecanismos de degradaci贸n de los diferentes ESS. Los algoritmos dise帽ados se validar谩n mediante simulaciones y trabajos experimentales. En el apartado de gesti贸n de energ铆a, la contribuci贸n de este trabajo se centra en la aplicaci贸n del un control predictivo econ贸mico basado en modelo (EMPC) para la gesti贸n de ESS en microrredes. El trabajo aborda espec铆ficamente los problemas de mitigar la congesti贸n de la red a partir de la alimentaci贸n de energ铆a renovable, minimizando la degradaci贸n de ESS y maximizando el autoconsumo de energ铆a renovable generada. Se ha realizado una revisi贸n de los m茅todos de predicci贸n del consumo/generaci贸n que pueden usarse en el marco del EMPC y se ha desarrollado un mecanismo de predicci贸n basado en el uso de las redes neuronales. Se ha abordado el an谩lisis del efecto del error de predicci贸n sobre el EMPC y el impacto que la toma de decisiones conservadoras produce en el rendimiento del sistema. La mejora en el rendimiento del esquema de gesti贸n energ茅tica propuesto se ha cuantificado.La integraci贸 de les fonts d'energia renovables a les xarxes modernes ha augmentat significativament en l鈥櫭簂tima d猫cada. Aquestes fonts renovables, encara que molt convenients per al medi ambient s贸n de naturalesa intermitent, i s贸n no panificables, cosa que genera problemes a la xarxa de distribuci贸. Aix貌 es deu precisament als problemes relacionats amb la congesti贸 de la xarxa i la regulaci贸 de la tensi贸. En aquest escenari, l鈥櫭簊 de sistemes d'emmagatzematge d'energia (ESS) en xarxes el猫ctriques est脿 sent 脿mpliament proposat per superar aquests problemes. No obstant aix貌, la integraci贸 de sistemes d'emmagatzematge d'energia per si sols no compensar脿 el problema creat per la generaci贸 renovable. El control i la gesti贸 de l'ESS s'han de fer de manera _optima, de manera que s'aprofitin al m脿xim les seves capacitats per superar els problemes en les xarxes el猫ctriques, garantir un cost d鈥檌nversi贸 raonable i allargar la vida 煤til de l'ESS minimitzant la seva degradaci贸. Motivat per aquesta problem脿tica, aquesta tesi doctoral es centra a desenvolupar una estrat猫gia de control i gesti贸 eficient per als ESS integrats en una microxarxa, especialment quan es tracta d'ESS de natura h铆brida. El treball de doctorat proposa un esquema de control jer脿rquic compost per un control de baix nivell i una part de gesti贸 d'energia operant a m茅s alt nivell. El treball realitza aportacions en els dos camps. En el control de baix nivell, aquest treball es centra a millorar aspectes del control en temps real dels convertidors que interconnecten el ESS amb la xarxa i el sistema de microxarxa en el seu conjunt. El treball proposa sistemes de control amb comportament din脿mic millorat per a convertidors de pot猫ncia desenvolupats en el marc del control de tipus reset. En el control de micro-xarxa, el treball presenta un esquema de control primari i un de secundari de regulaci贸 de voltatge millorat sota pertorbacions, utilitzant un observador. A m茅s, el treball planteja estrat猫gies de repartiment de el flux de pot猫ncia entre els diferents ESS. Durant el disseny d'aquests algoritmes de control es tenen en compte els mecanismes de degradaci贸 dels diferents ESS. Els algoritmes dissenyats es validaran mitjanant simulacions i treballs experimentals. En l'apartat de gesti贸 d'energia, la contribuci贸 d'aquest treball se centra en l鈥檃plicaci贸 de l'un control predictiu econ貌mic basat en model (EMPC) per a la gesti贸 d'ESS en microxarxes. El treball aborda espec铆ficament els problemes de mitigar la congesti贸 de la xarxa a partir de l鈥檃limentaci贸 d'energia renovable, minimitzant la degradaci贸 d'ESS i maximitzant l'autoconsum d'energia renovable generada. S'ha realitzat una revisi贸 dels m猫todes de predicci贸 del consum/generaci贸 que poden usar-se en el marc de l'EMPC i s'ha desenvolupat un mecanisme de predicci贸 basat en l鈥櫭簊 de les xarxes neuronals. S'ha abordat l鈥檃n脿lisi de l'efecte de l'error de predicci贸 sobre el EMPC i l'impacte que la presa de decisions conservadores produeix en el rendiment de el sistema. La millora en el rendiment de l'esquema de gesti贸 energ猫tica proposat s'ha quantificat

    Control strategies and motion planning for nanopositioning applications with multi-axis magnetic-levitation instruments

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    This dissertation is the first attempt to demonstrate the use of magnetic-levitation (maglev) positioners for commercial applications requiring nanopositioning. The key objectives of this research were to devise the control strategies and motion planning to overcome the inherent technical challenges of the maglev systems, and test them on the developed maglev systems to demonstrate their capabilities as the next-generation nanopositioners. Two maglev positioners based on novel actuation schemes and capable of generating all the six-axis motions with a single levitated platen were used in this research. These light-weight single-moving platens have very simple and compact structures, which give them an edge over most of the prevailing nanopositioning technologies and allow them to be used as a cluster tool for a variety of applications. The six-axis motion is generated using minimum number of actuators and sensors. The two positioners operate with a repeatable position resolution of better than 3 nm at the control bandwidth of 110 Hz. In particular, the Y-stage has extended travel range of 5 mm 脙脗 5 mm. They can carry a payload of as much as 0.3 kg and retain the regulated position under abruptly and continuously varying load conditions. This research comprised analytical design and development, followed by experimental verification and validation. Preliminary analysis and testing included open-loop stabilization and rigorous set-point change and load-change testing to demonstrate the precision-positioning and load-carrying capabilities of the maglev positioners. Decentralized single-input-single-output (SISO) proportional-integral-derivative (PID) control was designed for this analysis. The effect of actuator nonlinearities were reduced through actuator characterization and nonlinear feedback linearization to allow consistent performance over the large travel range. Closed-loop system identification and order-reduction algorithm were developed in order to analyze and model the plant behavior accurately, and to reduce the effect of unmodeled plant dynamics and inaccuracies in the assembly. Coupling among the axes and subsequent undesired motions and crosstalk of disturbances was reduced by employing multivariable optimal linear-quadratic regulator (LQR). Finally, application-specific nanoscale path planning strategies and multiscale control were devised to meet the specified conflicting time-domain performance specifications. All the developed methodologies and algorithms were implemented, individually as well as collectively, for experimental verification. Some of these applications included nanoscale lithography, patterning, fabrication, manipulation, and scanning. With the developed control strategies and motion planning techniques, the two maglev positioners are ready to be used for the targeted applications

    Applications of equivalent representations of fractional- and integer-order linear time-invariant systems

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    Nicht-ganzzahlige - fraktionale - Ableitungsoperatoren beschreiben Prozesse mit Ged盲chtniseffekten, deshalb werden sie zur Modellierung verschiedenster Ph盲nomene, z.B. viskoelastischen Verhaltens, genutzt. In der Regelungstechnik wird das Konzept vor allem wegen des erh枚hten Freiheitsgrades im Frequenzbereich verwendet. Deshalb wurden in den vergangenen Dekaden neben einer Verallgemeinerung des PID-Reglers auch fortgeschrittenere Regelungskonzepte auf nicht-ganzzahlige Operatoren erweitert. Das Ged盲chtnis der nicht-ganzzahligen Ableitung ist zwar essentiell f眉r die Modellbildung, hat jedoch Nachteile, wenn z.B. Zust盲nde gesch盲tzt oder Regler implementiert werden m眉ssen: Das Ged盲chtnis f眉hrt zu einer langsamen, algebraischen Konvergenz der Transienten und da eine numerische Approximation ist speicherintensiv. Im Zentrum der Arbeit steht die Frage, mit welchen Ma脽nahmen sich das Konvergenzverhalten dieser nicht ganzzahligen Systeme beeinflussen l盲sst. Es wird vorgeschlagen, die Ordnung der nicht ganzzahligen Ableitung zu 盲ndern. Zun盲chst werden Beobachter f眉r verschiedene Klassen linearer zeitinvarianter Systeme entworfen. Die Entwurfsmethodik basiert dabei auf einer assoziierten Systemdarstellung, welche einen Differenzialoperator mit h枚herer Ordnung verwendet. Basierend auf dieser Systembeschreibung k枚nnen Beobachter entworfen werden, welche das Ged盲chtnis besser mit einbeziehen und so schneller konvergieren. Anschlie脽end werden ganzzahlige lineare zeitinvariante Systeme mit Hilfe nicht-ganzzahliger Operatoren dargestellt. Dies erm枚glicht eine erh枚hte Konvergenz im Zeitintervall direkt nach dem Anfangszeitpunkt auf Grund einer unbeschr盲nkten ersten Ableitung. Die periodische L枚schung des so eingef眉hrten Ged盲chtnisses wird erzielt, indem die nicht ganzzahlige Dynamik periodisch zur眉ckgesetzt wird. Damit wird der algebraischen Konvergenz entgegen gewirkt und exponentielle Stabilit盲t erzielt. Der Reset reduziert den Speicherbedarf und induziert eine unterlagerte zeitdiskrete Dynamik. Diese bestimmt die Stabilit盲t des hybriden nicht-ganzzahligen Systems und kann genutzt werden um den Frequenzgang f眉r niedrige Frequenzen zu bestimmen. So lassen sich Beobachter und Regler f眉r ganzzahlige System entwerfen. Im Rahmen des Reglerentwurfs k枚nnen durch den Resets das Verhalten f眉r niedrige und hohe Frequenzen in gewissen Grenzen getrennt voneinander entworfen werden.Non-integer, so-called fractional-order derivative operators allow to describe systems with infinite memory. Hence they are attractive to model various phenomena, e.g. viscoelastic deformation. In the field of control theory, both the higher degree of freedom in the frequency domain as well as the easy generalization of PID control have been the main motivation to extend various advanced control concepts to the fractional-order domain. The long term memory of these operators which helps to model real life phenomena, has, however, negative effects regarding the application as controllers or observers. Due to the infinite memory, the transients only decay algebraically and the implementation requires a lot of physical memory. The main focus of this thesis is the question of how to influence the convergence rates of these fractional-order systems by changing the type of convergence. The first part is concerned with the observer design for different classes of linear time-invariant fractional-order systems. We derive associated system representations with an increased order of differentiation. Based on these systems, the observers are designed to take the unknown memory into account and lead to higher convergence rates. The second part explores the representation of integer-order linear time-invariant systems in terms of fractional-order derivatives. The application of the fractional-order operator introduces an unbounded first-order derivative at the initial time. This accelerates the convergence for a short time interval. With periodic deletion of the memory - a reset of the fractional-order dynamics - the slow algebraic decay is avoided and exponential stability can be achieved despite the fractional-order terms. The periodic reset leads to a reduced implementation demand and also induces underlying discrete time dynamics which can be used to prove stability of the hybrid fractional-order system and to give an interpretation of the reset in the frequency domain for the low frequency signals. This concept of memory reset is applied to design an observer and improve fractional-order controllers for integer-order processes. For the controller design this gives us the possibility to design the high-frequency response independently from the behavior at lower frequencies within certain limits

    LINC-NIRVANA Piston Control and Near-Infrared Polarization Images of the Orion Proplyds

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    This thesis is focussed on the development of optimized techniques to overcome limitations of astrophysical observations. The goal is an optimal signal estimation in noisy measurements by the consideration of underlying physical processes. This principle was applied to two different fields in astrophysics: intrumental design and analysis of polarimetric observations. In the observational part of this thesis near-infrared images of young stellar objects in the Orion constellation are studied. Limitations in resolution and sensitivity of current astronomical instruments prohibit the detailed analysis of interesting proto-stellar sources to improve theories of star formation. Radiation from the astronomical targets is not only characterized by its spectral energy, but also by polarization properties. The modeling of typical configurations of star-disk systems and the simulation of their polarization patterns helped to understand and interprete features, that were found in observations. For the case of a proto-stellar systems with both a disk and an envelope analysis techniques were developed, which are based on polarimetric effects of the scattering of light by dust. These techniques substantially improve the sensitivity and resolution and are reliable under different observing conditions. Although the obtained data did not allow investigations of substructures of the circumstellar material, the techniques are suitable to obtain constraints on star formation processes. With larger telescopes, such as the Large Binocular Telescope (LBT), the analysis of principles down to the scale of planet formation will be possible. LINC-NIRVANA, the near-infrared imaging system at the LBT, will provide unprecedented resolution and sensitivity performance combined with a wide field of view. The interferometric combination of light from two telescopes imposes new challenges in the instrument design. A so-called fringe tracker is mandatory for the interference of light at the detector by compensating optical path differences with an actuated mirror. The performance suffers from structural vibrations, limited sensitivity of sensors and processing latencies. The dynamics of actuators with significant amount of moving masses are limited. These effects are studied in the instrumental part of this thesis. Giant telescopes with large mirrors and high-resolution instruments are complex, expensive projects. The telescope time, i.e. the allocated time to the observations of individual astronomical topics, is very limited and hence valuable. It is of great importance to improve the performance in terms of sensitivity and resolution of observations under difficult conditions. By modeling all performance related subsystems of the interferometric instrument critical parameters were identified. For a realistic model several precision measurements of the telescope and parts of the LINC-NIRVANA instrument were necessary. Simulations of atmospheric effects completed the model. Several approaches for the optimization of the instrument performance were proposed. The determination of atmospheric and instrumental optical path difference or differential piston is improved by the detailed analysis of the statistical variation and appropriate filtering. The application of modern control theory provides stability and optimal dynamic response of the mirror actuator. Since both parts of this thesis deal with the impact of the atmosphere on the observational result of astronomical instruments, chapter 1 gives an overview on the basic principles and techniques. Chapter 2 presents the modeling and control analysis of the fringe tracker for the LINC-NIRVANA instrument. A software simulation is introduced and first results of a laboratory experiment are denoted. Chapter 3 gives a short introduction into star formation theories and unsolved problems, followed by the detailed description of polarimetric observations of proto-stellar objects in the Orion constellation in chapter 4. Some concepts and atmospheric effects as introduced in chapter 1 are discussed. Promising findings of one source of the sample led to extensive modeling and analysis of polarimetric properties of proto-stars and the development of innovative analysis techniques, presented in chapter 5. In the last chapter these methods are applied to the observational data and the obtained configuration parameters are compared to results of previous investigations in the literature

    A Course in Harmonic Analysis

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    These notes were written to accompany the courses Math 6461 and Math 6462 (Harmonic Analysis I and II) at Missouri University of Science & Technology during the 2018-2019 academic year. The goal of these notes is to provide an introduction to a range of topics and techniques in harmonic analysis, covering material that is interesting not only to students of pure mathematics, but also to those interested in applications in computer science, engineering, physics, and so on

    Regularisierte Optimierungsverfahren f眉r Rekonstruktion und Modellierung in der Computergraphik

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    The field of computer graphics deals with virtual representations of the real world. These can be obtained either through reconstruction of a model from measurements, or by directly modeling a virtual object, often on a real-world example. The former is often formalized as a regularized optimization problem, in which a data term ensures consistency between model and data and a regularization term promotes solutions that have high a priori probability. In this dissertation, different reconstruction problems in computer graphics are shown to be instances of a common class of optimization problems which can be solved using a uniform algorithmic framework. Moreover, it is shown that similar optimization methods can also be used to solve data-based modeling problems, where the amount of information that can be obtained from measurements is insufficient for accurate reconstruction. As real-world examples of reconstruction problems, sparsity and group sparsity methods are presented for radio interferometric image reconstruction in static and time-dependent settings. As a modeling example, analogous approaches are investigated to automatically create volumetric models of astronomical nebulae from single images based on symmetry assumptions.Das Feld der Computergraphik besch盲ftigt sich mit virtuellen Abbildern der realen Welt. Diese k枚nnen erlangt werden durch Rekonstruktion eines Modells aus Messdaten, oder durch direkte Modellierung eines virtuellen Objekts, oft nach einem realen Vorbild. Ersteres wird oft als regularisiertes Optimierungsproblem dargestellt, in dem ein Datenterm die Konsistenz zwischen Modell und Daten sicherstellt, w盲hrend ein Regularisierungsterm L枚sungen f枚rdert, die eine hohe A-priori-Wahrscheinlichkeit aufweisen. In dieser Arbeit wird gezeigt, dass verschiedene Rekonstruktionsprobleme der Computergraphik Instanzen einer gemeinsamen Klasse von Optimierungsproblemen sind, die mit einem einheitlichen algorithmischen Framework gel枚st werden k枚nnen. Dar眉ber hinaus wird gezeigt, dass vergleichbare Optimierungsverfahren auch genutzt werden k枚nnen, um Probleme der datenbasierten Modellierung zu l枚sen, bei denen die aus Messungen verf眉gbaren Daten nicht f眉r eine genaue Rekonstruktion ausreichen. Als praxisrelevante Beispiele f眉r Rekonstruktionsprobleme werden Sparsity- und Group-Sparsity-Methoden f眉r die radiointerferometrische Bildrekonstruktion im statischen und zeitabh盲ngigen Fall vorgestellt. Als Beispiel f眉r Modellierung werden analoge Verfahren untersucht, um basierend auf Symmetrieannahmen automatisch volumetrische Modelle astronomischer Nebel aus Einzelbildern zu erzeugen

    An introduction to continuous optimization for imaging

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    International audienceA large number of imaging problems reduce to the optimization of a cost function , with typical structural properties. The aim of this paper is to describe the state of the art in continuous optimization methods for such problems, and present the most successful approaches and their interconnections. We place particular emphasis on optimal first-order schemes that can deal with typical non-smooth and large-scale objective functions used in imaging problems. We illustrate and compare the different algorithms using classical non-smooth problems in imaging, such as denoising and deblurring. Moreover, we present applications of the algorithms to more advanced problems, such as magnetic resonance imaging, multilabel image segmentation, optical flow estimation, stereo matching, and classification
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