Spacecraft formation flying (SFF) offers robust observations of multi-scale ionospheric space weather. A number of hardware-in-the-loop (HIL) SFF simulation testbeds based on Global-Navigation-Satellite-Systems (GNSS) have been developed to support GNSS-based SFF mission design, however, none of these testbeds has been directly applied to ionospheric space weather studies. The Virginia Tech Formation Flying Testbed (VTFFTB), a GNSS-based HIL simulation testbed, has been developed in this work to simulate closed-loop real-time low Earth orbit (LEO) SFF scenarios. The final VTFFTB infrastructure consists of three GNSS hardware signal simulators, three multi-constellation multi-band GNSS receivers, three navigation and control systems, an STK visualization system, and an ionospheric remote sensing system. A fleet of LEO satellites, each carrying a spaceborne GNSS receiver for navigation and ionospheric measurements, is simulated in scenarios with ionospheric impacts on the GPS and Galileo constellations. Space-based total electron density (TEC) and GNSS scintillation index S4 are measured by the LEO GNSS receivers in simulated scenarios. Four stages of work were accomplished to (i) build the VTFFTB with a global ionospheric modeling capability, and (ii) apply the VTFFTB to incubate future ionospheric measurement techniques. In stage 1, a differential-TEC method was developed to use space-based TEC measurements from a pair of LEO satellites to determine localized electron density (Ne). In stage 2, the GPS-based VTFFTB was extended to a multi-constellation version by adding the Galileo. Compared to using the GPS constellation only, using both GPS and Galileo constellations can improve ionospheric measurement quality (accuracy, precision, and availability) and relative navigation performance. Sensitivity studies found that Ne retrieval characteristics are correlated with LEO formation orbit, the particular GNSS receivers and constellation being used, as well as GNSS carrier-to-noise density C/N0. In stage 3, the VTFFTB for dual-satellite scenarios was further extended into a 3-satellite version, and then implemented to develop a polar orbit scenario with more fuel-efficient natural motion. In stage 4, a global 4-dimensioanl ionospheric model (TIE-CGM) was incorporated into the VTFFTB to significantly improve the modelling fidelity of multi-scale ionospheric space weather. Equatorial and polar space weather structures (e.g. plasma bubbles, tongues-of-ionization) were successfully simulated in 4-dimensional ionospheric scenarios on the enhanced VTFFTB. The dissertation has demonstrated the VTFFTB is a versatile GNSS-based SFF mission incubator to study ionospheric space weather impacts and develop next-generation multi-scale ionospheric observation missions. / Doctor of Philosophy / Spacecraft formation flying (SFF) is a space mission architecture with a group of spacecraft flying together and working as a team. SFF provides new opportunities for robust, flexible and low-cost observations of various phenomena in the ionized layer of Earth's atmosphere (called the ionosphere). Several hardware SFF simulation platforms based on Global Navigation Satellite Systems (GNSS) have been established to develop GNSS-based SFF missions, however, none of these platforms has ever directly used on-board GNSS receivers to study the impact of space weather on ionospheric density structures. The Virginia Tech Formation Flying Testbed (VTFFTB), a hardware simulation infrastructure using multiple GNSS signals, has been built in this work to emulate realistic SFF scenarios in low altitude orbits. The overall VTFFTB facility comprises three GNSS hardware signal emulators, three GNSS signal receivers, three navigation and control components, a software visualization component, and an ionospheric measurement component. Both Global-Positioning-System (GPS) and Galileo (the European version GNSS) are implemented in the VTFFTB. The objectives of this work are to (i) develop the VTFFTB with a high-fidelity ionospheric modeling capability, and (ii) apply the VTFFTB to incubate future ionospheric measurement techniques with GNSS receivers in space. A fleet of two or three spacecraft, each having a GNSS receiver to navigate and sense the ionosphere is emulated in several space environments. The electron concentration of the ionosphere and the GNSS signal fluctuation are measured by the GNSS receivers from space in simulated scenarios. These measurements are advantageous to study the location, size and structure of irregular ionospheric phenomena nearby the trajectory of spacecraft fleet. The culmination of this study is incorporation of an external global ionospheric model with temporal variations into the VTFFTB infrastructure to model a variety of realistic ionospheric structures and space weather impacts. Equatorial and polar space weather phenomenon were successfully simulated on the VTFFTB to verify a newly developed space-borne electron density measurement technique in the 3-dimensional ionosphere. Overall, it was successfully demonstrated that the VTFFTB is a versatile GNSS-based SFF mission incubator to study multiple kinds of ionospheric space weather impacts and develop next-generation space missions for ionospheric measurements.

The transition from fossil fuel-based energy sources involves exploring different sources of energy that can be reliably integrated into the power grid. One such existing resource is the CHPs, which are distributed throughout the US electric grid. The integration of the CHPs into the grid requires technological innovations. One idea is to design an F-CHP converter that would facilitate the CHPs to interconnect seamlessly with the electrical grid. This thesis presents the development and testing of different components of a testbed that would facilitate the testing of the F-CHP converter. It also presents the integration of a PMU and a communication interface for the F-CHP converter. The phasor estimation of the F-CHP PMU has been compared with a commercial PMU and its performance has been validated. / Master of Science / The transition from fossil fuel based energy sources involves exploring different sources of energy that can reliably integrated into the power grid. One such existing resource is the CHPs, that are distributed throughout the US electric grid. The integration of the CHPs into the grid required technological innovations. One idea is to design a power electronics converter that would facilitate the CHPs to connect with the electrical grid. This thesis presents the development and testing of different components of a testbed that would facilitate the testing of the converter. This work also integrates a technology for estimating the voltage and current at the point of interconnection between the converter and the electrical grid.

The popularity and demand for safe autonomous vehicles are on the rise. Advances in semiconductor technology have led to the integration of a wide range of sensors with high-performance computers, all onboard the autonomous vehicles. The complexity of the software controlling the vehicles has also seen steady growth in recent years. Verifying the control software using traditional verification techniques is difficult and thus increases their safety concerns. Runtime verification is an efficient technique to ensure the autonomous vehicle's actions are limited to a set of acceptable behaviors that are deemed safe. The acceptable behaviors are formally described in linear temporal logic (LTL) specifications. The sensor data is actively monitored to verify its adherence to the LTL specifications using monitors. Corrective action is taken if a violation of a specification is found. An unmanned aerial vehicle (UAV) development platform is proposed for the validation of monitors on configurable hardware. A high-fidelity simulator is used to emulate the UAV and the virtual environment, thereby eliminating the need for a real UAV. The platform interfaces the emulated UAV with monitors implemented on configurable hardware and autopilot software running on a flight controller. The proposed platform allows the implementation of monitors in an isolated and scalable manner. Scenarios violating the LTL specifications can be generated in the simulator to validate the functioning of the monitors. / Master of Science / Safety is one of the most crucial factors considered when designing an autonomous vehicle. Modern vehicles that use a machine learning-based control algorithm can have unpredictable behavior in real-world scenarios that were not anticipated while training the algorithm. Verifying the underlying software code with all possible scenarios is a difficult task. Runtime verification is an efficient solution where a relatively simple set of monitors validate the decisions made by the sophisticated control software against a set of predefined rules. If the monitors detect an erroneous behavior, they initiate a predetermined corrective action. Unmanned aerial vehicles (UAVs), like drones, are a class of autonomous vehicles that use complex software to control their flight. This thesis proposes a platform that allows the development and validation of monitors for UAVs using configurable hardware. The UAV is emulated on a high-fidelity simulator, thereby eliminating the time-consuming process of flying and validating monitors on a real UAV. The platform supports the implementation of multiple monitors that can execute in parallel. Scenarios to violate rules and cause the monitors to trigger corrective actions can easily be generated on the simulator.

An autoclave is an advanced machine that sterilizes objects using high-pressure and high heat, with water steam as the medium. Autoclaves are frequently found in hospitals and other places where sterility is required. This project aims to meet the company's need to create a digital twin (DT) of an autoclave. The purpose is to test the control unit that controls the physical autoclave by exposing the DT to the same program as a real autoclave. A DT is a virtual model of a physical system, and in this project, it represented the autoclave and its sensors. The model was programmed in a graphical programming language NI LabView, with the same input and output signals as a real autoclave. The model was based on data-driven logic rather than physical based logic. From a real autoclave run where signals were recorded every second, conclusions could be drawn about how much each unique analog signal changed in combination with other signals through interpolation. The interpolation of the analog signals was used to capture the characteristics of these signals.  For validation, the DT was loaded into a Hardware In the Loop (HIL) system that simulates the autoclave with the DT but retains the control unit from the autoclave, which is the unit the company wants to test. The developed DT was tested against three goals describing how closely the values should align over an accumulated time. The results were compared each second between the real run and the DT run. The data-driven DT model met one of the three goals set, however, the DT model's characteristics resembled those of the real run, making the model useful as the control system does not interrupt the simulation for disallowed or deviant values. / En autoklav är en avancerad maskin som rengör objekt till en steril nivå med ett högt tryck och hög temperatur, där vattenånga används som medium. Autoklaven har ett vanligt förekommande på sjukhus och andra platser där sterilitet är ett krav. Det här projektet går ut på att möta företagets behov av att skapa en digital tvilling (DT) av en autoklav. Syftet är att testa kontrollenheten som styr den fysiska autoklaven genom att en DT ska utsättas för samma programkörning som en verklig autoklav. En DT är en virtuell modell av ett fysiskt system och i detta projekt var autoklaven och sensorerna i maskinen en DT. Modellen programmerades i ett grafiskt programmeringsspråk, NI LabVIEW med samma in- och utsignaler som en verklig autoklav. Modellen utgår ifrån en datadriven metod och inte en fysikalisk formulerad logik. Datan samlades in från en körning av en verklig autoklav, där signalerna sparades varje sekund. Slutsatser för hur mycket varje unik analog signal förändrades i kombination med övriga signaler kunde dras med hjälp av interpolering. Interpoleringen av de analoga signalera kunde användas för att fånga deras karakteristik.  För validering integrerades DT i ett Hardware In the Loop (HIL) system som hjälper till att simulera autoklaven. HIL-systemet har kontrollenheten kvar från autoklaven som är den enhet företaget vill utföra tester på. Den framtagna DT testades mot tre mål som beskriver hur nära värdena skall ligga under en ackumulerad tid. Resultatet jämfördes för varje sekund mellan den verkliga och DT körningen. Den datadrivna DT modellen uppfyllde 1 av 3 mål som ställdes, men DT modellens karakteristik efterliknade den från verkliga körningen vilket gör modellen användbar då kontrollsystemet inte avbryter simuleringen för ej tillåtna eller avvikande värden.

La qualité de la puissance injectée au réseau électrique est une problématique importante pour le développement des énergies marines renouvelables, et en particulier de l'énergie des vagues, ou énergie houlomotrice. En effet la puissance produite par les systèmes houlomoteurs à entrainement direct est très fluctuante (fluctuations de l'ordre de la seconde) à cause de la nature oscillante de la ressource. Afin d'étudier l'impact de l'intégration des ces systèmes sur les réseaux électriques, un modèle permettant de représenter la chaîne depuis la vague jusqu'au réseau électrique a été développé. Les simulations effectuées à l'aide de ce modèle pour différents types de réseau électrique et différents états de mer ont montré que la mise en place de solutions pour améliorer la qualité de la puissance produite était nécessaire. Ainsi l'effet du regroupement et de la dispersion spatiale des systèmes houlomoteurs sur la qualité de la puissance a été étudiée. L'insertion d'un système de stockage dans la chaîne wave-to-wire afin de lisser la puissance a aussi été considérée. Enfin, une partie du modèle a pu être validée à l'aide d'un banc de test Hardware-in-the-loop comprenant un banc moteur, des armoires de puissance pour émuler électronique de puissance et le réseau électrique et un module de supercondensateurs. / Power quality is an important issue for the development of marine renewable energies, in particular wave energy. Due to the oscillatory nature of the oceans waves, the wave energy converters output power profile can present fluctuations in the range of seconds. The impact of these devices on the electric grid therefore needs to be investigated for wave farms to be connected to the grid. In order to emulate an operating direct drive wave energy converter, study power quality improvement and test different control strategies, a wave-to-wiremodel has been developed.Simulations carried out with this model for different grid strengths and different levels of sea-state showed that it is necessary to foster solutions to improve power quality. Thus, the wave energy converters aggregating and dispersion effects on power quality have been investigated. As it does not seem sufficient to meet the grid codes requirements, another solution have been considered, consisting of the insertion of an energy storage system into the chain. Finally, a part of the model has been validated using a hardware-in-the-Loop test bench including a motorbench, power modules to emulate the grid and power electronic's control and super capacitors module.

Submitted by Viviane Lima da Cunha (viviane@biblioteca.ufpb.br) on 2016-02-16T14:54:49Z No. of bitstreams: 1 arquivovotal.pdf: 4473573 bytes, checksum: 152c2f0d263c50dcbea7d500d5f7f5da (MD5) / Made available in DSpace on 2016-02-16T14:54:49Z (GMT). No. of bitstreams: 1 arquivovotal.pdf: 4473573 bytes, checksum: 152c2f0d263c50dcbea7d500d5f7f5da (MD5) Previous issue date: 2015-08-17 / Este trabalho propõe um ambiente para verificação de sistemas embarcados heterogêneos através da cossimulação distribuída. A verificação ocorre de maneira síncrona entre o software do sistema e o sistema embarcado usando a High Level Architecture (HLA) como middeware. A novidade desta abordagem não é apenas fornecer suporte para simulações, mas também permitir a integração sincronizada com todos os dispositivos de hardware físico. Neste trabalho foi utilizado o Ptolemy como uma plataforma de simulação. A integração do HLA com Ptolemy e os modelos de hardware abre um vasto conjunto de aplicações, como o de teste de vários dispositivos ao mesmo tempo, executando os mesmos, ou diferentes aplicativos ou módulos, a execução de multiplos dispositivos embarcados para a melhoria de performance. Além disso a abordagem de utilização do HLA, permite que sejam interligados ao ambiente, qualquer tipo de robô, assim como qualquer outro simulador diferente do Ptolemy. Estudo de casos são apresentado para provar o conceito, mostrando a integração bem sucedida entre o Ptolemy e o HLA e a verificação de sistemas utilizando Hardware-in-the-loop e Robot-in-the-loop. / This work proposes an environment for verification of heterogeneous embedded systems through distributed co-simulation. The verification occurs in real-time co-simulating the system software and hardware platform using the High Level Architecture (HLA) as a middleware. The novelty of this approach is not only providing support for simulations, but also allowing the synchronous integration with any physical hardware devices. In this work we use the Ptolemy framework as a simulation platform. The integration of HLA with Ptolemy and the hardware models open a vast set of applications, like the test of many devices at the same time, running the same, or different applications or modules, the usage of Ptolemy for real-time control of embedded systems and the distributed execution of different embedded devices for performance improvement. Furthermore the use of HLA approach allows them to be connected to the environment, any type of robot, as well as any other Ptolemy simulations. Case studies are presented to prove the concept, showing the successful integration between Ptolemy and the HLA and verification systems using Hardware-in-the-loop and Robot-in-the-loop.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-18T14:49:13Z No. of bitstreams: 1 igordiasnetodesouza.pdf: 13872772 bytes, checksum: 45517d7a6da7ae06ecacec6a7fb7ebd8 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-18T14:50:11Z (GMT) No. of bitstreams: 1 igordiasnetodesouza.pdf: 13872772 bytes, checksum: 45517d7a6da7ae06ecacec6a7fb7ebd8 (MD5) / Made available in DSpace on 2017-04-18T14:50:11Z (GMT). No. of bitstreams: 1 igordiasnetodesouza.pdf: 13872772 bytes, checksum: 45517d7a6da7ae06ecacec6a7fb7ebd8 (MD5) Previous issue date: 2017-02-17 / Esta dissertação apresenta um estudo de um conversor emulador de rede (CER) que faz parte de uma estrutura Power-Hardware-in-the-Loop (PHIL). O PHIL será futuramente utilizado para verificar os impactos causados pela integração de sistemas de geração fotovoltaico (PV) à rede elétrica, assim como a operação do sistema PV frente a distúrbios na rede. O CER, composto por um conversor fonte de tensão (VSC) de dois níveis e filtro de saída LC, é responsável por alimentar cargas isoladas emulando uma rede elétrica. A modelagem do conversor emulador de rede é feita no sistema de coordenadas estacionário (αβ0), fornecendo um sistema de equações diferenciais usado para descrever o comportamento dinâmico do sistema. O conversor é controlado no modo de tensão, através da estratégia de modulação vetorial. Duas malhas de controle em cascata são projetadas. A malha interna utiliza compensadores em avanço digitais para amortecer a ressonância do filtro LC sem a necessidade de uma realimentação interna de corrente. Já a externa utiliza controladores ressonantes digitais modificados para rejeitar distúrbios harmônicos e garantir a qualidade da forma de onda da tensão no ponto de acoplamento comum. Os controladores ressonantes são conectados em série e o projeto é baseado no amortecimento dos zeros. Resultados experimentais, obtidos com o protótipo de laboratório, cujos controladores foram implementados em um processador digital de sinais TMS320F28335 da Texas Instruments, são usados para validar as estratégias de controle propostas. / This dissertation presents a study on a grid-former converter (GFC) which is a part of a Power-Hardware-in-the-Loop (PHIL) structure. The PHIL will be used to verify the impacts caused by the integration of photovoltaic (PV) generation systems into grid, as well as to study the PV operation under grid disturbances. The GFC, composed by a two-level voltage source converter with a LC output filter, is responsible to feed isolated loads emulating an electrical grid. The modeling of the grid-former converter is done in the stationary frame (αβ0), providing a set of differential equations that describes the dynamical behavior of the system. The converter is controlled in voltage mode by means of the space vector modulation (SVM) strategy. Two control loops are designed to control the static converter. At the inner loop a novel discrete-time active damping technique is proposed in order to damp the filter resonance without the need of current feedback. The method is based on an inner feedback loop with digital lead compensator on the feedback path while the external loop uses a discretetime integrator and a modified digital resonant controller to guarantee a decreasing frequency response and ensure the quality of the voltage waveform at the point of common coupling, respectively. The resonant controllers are connected in series and the design is based on its zeros damping. Experimental results obtained with the prototype, which controllers were implemented in a Texas Instruments TMS320F28335 are used to validate the proposed control strategies.

Les travaux présentés dans ce mémoire portent sur les convertisseurs continu-continu (DC/DC) pour les réseaux de transport à Courant Continu (HVDC) dans un contexte de réseau maillé de type Multi Terminaux DC (MTDC). Dans ce genre de réseau, les convertisseurs DC/DC sont nécessaires pour interconnecter ces réseaux. L’objectif de ce travail est donc d’étudier un convertisseur DC/DC pour des applications à haute tension et forte puissance. De nombreux convertisseurs DC/DC classiques existent, mais ne sont pas adaptés à ces niveaux de tension et puissance. Le volume et coût sont les points clés de l’étude pour l’industrialisation des structures dédiées aux réseaux HVDC. Parmi les structures identifiées, le convertisseur DC-DC Modulaire Multiniveaux (M2DC), récent et compact, a été finalement choisi. Le travail proposé développe l’étude du M2DC en régime établi et une modélisation en modèle moyen de ce convertisseur. Ensuite, des lois de contrôle sont proposées pour valider les analyses précédentes sur la base du principe de l’inversion du modèle. Le travail vise enfin à valider les analyses et le contrôle à l’aide de la maquette du Convertisseur Modulaire Multiniveaux (MMC) du L2EP. Pour cela, un dimensionnement du M2DC basé sur le MMC existant est proposé. Enfin, des simulations HIL (Hardware-In-the-Loop) valident les analyses et montrent la faisabilité du prototypage du M2DC / This work is based on Multi Terminal Direct Current (MTDC) grids. In the MTDC grid, DC/DC converter stations are needed to connect different HVDC grids. A lot of DC/DC converters have been studied and developed, but are not suitable for high voltage and great power constraints. Therefore, the objective of this work is the study of a DC/DC converter for high voltage and great power applications. For the potentially HVDC applications, the volume and costs are major criteria. According to this, a high voltage and great power potential DC/DC converter is selected, which is the DC-DC Modular Multilevel Converter (M2DC). Focusing on the M2DC, the work proposes analyses in steady state and builds an average model for the converter. Based on the average model, the basic control algorithm for the converter is developed to validate the previous analysis. Since the thesis aims to use the existing L2EP Modular Multilevel Converter (MMC) to test the M2DC model and control, a design of the M2DC based on MMC is proposed. Finally, the M2DC HIL (Hardware In-the-Loop) simulations results are presented confirming previous analyses and allowing to go on to prototyping the M2DC on the base of the existing MMC

Cette thèse développe une nouvelle approche de contrôle pour les avions à échelle réduite. Les lois de commande proposées exploitent un modèle non linéaire simple mais pertinent des forces aérodynamiques appliquées à l’aéronef. Ils reposent sur une structure hiérarchique de contrôle non linéaires, et sont synthétisées sur la base d’analyse de stabilité et de convergence théoriques. Ils sont conçus pour fonctionner sur un large domaine de vol. En particulier, ils évitent les singularités associées à la paramétrisation de l'attitude et la direction de la vitesse. Dans un premier temps, le problème de stabilisation de trajectoires de référence est résolu en étendant la méthode du "thrust vectoring", utilisée pour les véhicules à voilure tournante, au cas des aéronefs à voilure fixe. Dans le cas des avions, le principal défi est de prendre en compte les forces aérodynamiques dans la conception des systèmes de commande. Afin de résoudre ce problème, le contrôle proposé est conçu et analysé sur la base du modèle de forces aérodynamique proposé. Le domaine d'utilisation de cette loi de commande est élargi et englobe les trajectoires d'équilibre (trim trajectories) qui sont classiquement utilisées dans la littérature. Cette solution est ensuite adaptée au problème de suivi de chemin, afin de concevoir des lois de guidage cinématique et de contrôle dynamique applicables à presque tout chemin 3D régulier. Les lois de contrôle proposées contiennent des termes intégraux qui robustifient le contrôle vis-à-vis de dynamiques non modélisées. Plusieurs problèmes pratiques sont adressés et les lois de commande proposées sont validées par des simulations du type "hardware-in-the-loop". Enfin, des résultats d'essais en vol illustrent la performance des lois de contrôle proposées. / The present thesis develops a new control approach for scale-model airplanes. The proposed control solutions exploit a simple but pertinent nonlinear model of aerodynamic forces acting on the aircraft. Nonlinear controllers are based on a hierarchical structure, and are derived on the basis of theoretical stability and convergence analyses. They are designed to operate on a large spectrum of operating conditions. In particular, they avoid the singularities associated with the parameterization of the attitude and the heading of the vehicle, and do not rely on a decoupling between longitudinal and lateral dynamics. First, the trajectory tracking problem is addressed by extending the thrust vectoring method used for small rotor vehicles to the case of fixed wing vehicles. In the case of airplanes, the main challenge is to take into account the aerodynamic forces in the design of control systems. In order to solve this problem, the proposed control is designed and analyzed on the basis of the proposed aerodynamic forces model. The flight envelope is thus broadened beyond trim trajectories which are classically used in the literature. This solution is then adapted to the path following problem, and kinematic guidance and dynamic control laws are developed within a single coherent framework that applies to almost any regular 3D path. The proposed control laws incorporate integral terms that robustify the control with respect to unmodelled dynamics. Several practical issues are addressed and the proposed control laws are validated via hardware-in-the-loop simulations. Finally, successful flight test results illustrate the soundness and performance of the proposed control laws.

No description available.