Rozprawy doktorskie na temat „Contrôle en admittance”

Les transducteurs à ultrasons ont été largement utilisés dans le diagnostic médical, la thérapie, l'évaluation non destructive, le nettoyage, le sonar et d'autres applications. Le bon fonctionnement du transducteur lui-même est un facteur clé de la fiabilité globale du système. Cependant, en raison d'une mauvaise utilisation par l’opérateur ou d'une dégradation des matériaux, des défauts peuvent survenir tels que des ruptures dans le câblage, des fissures dans les matériaux passifs, l’endommagement des matériaux actifs, une délamination entre les couches constitutives du dispositif ... Ce travail de thèse porte sur une analyse détaillée de l'influence de délaminations sur les performances du transducteur, visant à déterminer des procédures pour faciliter le suivi du comportement du transducteur pendant sa durée de vie et la détection des dégradations avant qu'elles n'affectent significativement les performances du système dans son ensemble.Dans le cadre de ce travail, un modèle analytique bidimensionnel original pour l’étude des vibrations couplées dans les résonateurs piézoélectriques est proposé. Des solutions générales pour toutes les grandeurs physiques dans les systèmes de coordonnées cartésiennes et cylindriques sont déduites des équations tensorielles de la piézoélectricité. Elles sont exprimées sous forme de séries de fonctions trigonométriques ou de Bessel. L'impédance électrique, la forme du mode et le spectre de fréquences des céramiques piézoélectriques sont calculés par la méthode analytique proposée ainsi que par la méthode des éléments finis. La comparaison des résultats de ces deux méthodes montre un excellent accord.Une étude systématique de l'influence de différents types de délaminations sur les performances des transducteurs ultrasonores monoéléments et multi-éléments est présentée. Des modèles par éléments finis sont développés pour montrer l'impact des différents types de délaminations ainsi que d'autres facteurs sur l'admittance électromécanique (EMA) de transducteurs composés soit d'un disque soit de parallélépipèdes de céramiques piézoélectriques, d'un milieu arrière et d'une lame adaptatrice. Des études expérimentales sont mises en place pour valider les modèles et des indicateurs quantitatifs sont proposés. Des éléments sont réalisés en impression 3D (milieu arrière, lame adaptatrice) et montés sur des échantillons de céramiques piézoélectriques pour obtenir un transducteur modèle intact et des transducteurs modèles avec délaminations. La comparaison entre les résultats numériques et expérimentaux montre un bon accord et permet d’affirmer que des modifications de l'EMA peuvent révéler l'apparition et l'étendue d'une délamination entre les éléments constitutifs d’une sonde échographique
Ultrasonic transducers have been widely used in medical diagnostic, therapy, non-destructive evaluation, cleaning, underwater sonar, and other applications. The proper functioning of the transducer itself is a key factor in the reliability of the entire system. However, due to the misuse of operators or material degradation, defects may occur, such as breakages in cables, cracks, damaged or weakened crystals, and delamination between layers. This contribution focuses on a detail analysis of the influence of bonding delamination on the performance of the transducer, aiming to determine procedures to facilitate the monitoring of the behavior of the transducer during its lifetime and the detection of degradations before they significantly affect the performance of the system.In the frame of this work, an original two-dimensional analytical model for coupled vibrations of finite piezoelectric resonators is proposed. General solutions for all the physical quantities in Cartesian and cylindrical coordinate systems are deduced from the governing equations. They are expressed as a series of trigonometric or Bessel functions. Electrical impedance, mode shape, and frequency spectrum of piezoceramics are calculated by the proposed analytical method as well as by the finite element method. Comparison of the results of these two methods shows an excellent agreement.A systematic investigation of the influence of different kinds of bonding delamination on the performance of single-element and linear array ultrasonic transducers is presented. Finite element models are developed to show the impact of bonding delamination as well as other factors on the electromechanical admittance (EMA) of ultrasonic transducers, which are composed of a piezoceramic disk or parallelepiped, a backing, and a matching layer. Experimental studies are set up to validate the models and quantitative indicators are proposed. 3D printed backings and matching layers are mounted on piezoceramic elements to obtain an intact model transducer and delaminated ones. Comparison between numerical and experimental results show a good agreement, which allows to affirm that changes in EMA can reveal the occurrence and extent of a delamination in an ultrasound probe

Les robots sont de plus en plus amenés à interagir avec des humains ou des environnements anthropiques en vue de collaboration. La connaissance des propriétés visco-élastiques cartésiennes humaines durant des interactions physiques avec des environnements procure un éclairage au champ des sciences du mouvement humain, et aussi à la robotique collaborative pour la conception de commandes innovantes bio-inspirées. Dans cette thèse, la focalisation est placée sur une modélisation linéaire très simple en impédance mécanique du membre supérieur, qui fait entrer en jeu les paramètres cartésiens apparents en raideur, amortissement et masse. Cette modélisation permet d'approcher des comportements en rejet de perturbations qui interviennent notamment lors d'interactions physiques.Une expérience a été mise en œuvre avec un robot articulé piloté en admittance cartésienne, pour permettre des estimations d'impédance mécanique du bras de participants pendant une tâche de référence permettant de générer des mouvements rythmiques, avec des retours haptiques. Une méthode permettant l'estimation des paramètres du modèle en impédance, basée sur l'approximation des trajectoires virtuelles en position et force lors de faibles perturbations ne gênant pas la réalisation de la tâche, est proposée. Les trajectoires virtuelles sont approchées par des interpolations de splines ou des optimisations de sinusoïdes.Une trentaine de participants ont pris part aux expériences proposées pour permettre des estimations significatives de variations des paramètres visco-élastiques apparents et mieux comprendre leurs implications dans la réalisation d'une tâche en interaction avec un robot. Le compromis stabilité-transparence du couplage du robot avec un environnement en impédance a finalement été analysé pour proposer une amélioration des réglages du contrôle en admittance cartésienne
Robots are more inclined to interact with humans or their environment for collaborative purposes. Knowledge on the human endpoint vis-coelastic properties during physical interactions provides insights for the field of human movement science and also for the design of innovative bio-inspired collaborative robotic control strategies. In this work, the focus is placed on a simplistic linear mechanical model of the human arm, with endpoint apparent parameters like stiffness, damping and mass. Perturbation rejection behaviours occuring remarkably during physical interactions can be met using this modelling.In order to estimate those properties for the human arm, an experimental test-bed was designed using an endpoint admittance controled polyarticulated robot. A benchmark task was used so that rhythmic movements emerged, while haptic feedback were introduced by the robot. A methodology to identify the linear parameters of the chosen impedance model was designed, tackling the issue of the estimation of virtual trajectories of the arm during dynamic movements. The estimations of the arm's virtual trajectories both in position and force relied on spline interpolations and sine optimisations, for small deviations that did not alter the performances of the task.A cohort of participants took part in experiments proposed to observe significant variations of the viscoelastic apparent parameters, and improve the understanding of the implications of such variations during a physical interaction with a robot. The famous trade-off between stability and transparency while the robot is coupled with an environment was then study thanks to the obtained estimations, to enhance the tuning of the endpoint admittance control empirically designed

To enhance the transient stability and the power oscillation damping of the powergrid, supplementary controllers can be applied to the embedded point-to-point High-Voltage Direct Current (HVDC) links. The work presented in this report aimed tovalidate the Dynamic Virtual Admittance Control (DVAC) designed in SuperGridInstitute, in Software- and Hardware-In-The-Loop (SIL and HIL) simulations.The DVA control was first studied analytically and implemented in an offlinesimulation, on a basic test-system. A two-area test-system was then modelled as thebase for validation of the stabilising control. The fault applied to test the controller’sefficiency was a three-phase short-circuit on one of the AC transmission lines linkingthe two areas. The DVAC was validated on the test-system, first by SIL, and thenby HIL real-time simulation. For the purpose of turning the simulation into an HILsimulation, the DVAC was implemented in code C in a Raspberry Pi computer, andthe IEC 61850 communication protocol was studied in detail to be configured for theHIL simulation’s set-up.The SIL and HIL simulations of the DVAC on a three-phase short-circuit provedthe control’s ability to damp power oscillations in around 5 seconds, twice as fast asif no control is implemented.
För att förbättra elnätets transientstabilitet och dämpning kan kompletterandestyrenheter användas på inbäddade högspänningslikströmslänkar (HVDC). Arbetetsom presenteras i denna rapport syftade till att validera Dynamic Virtual Admittance(DVA) reglering, utvecklat i SuperGrid Institute, i simuleringar med mjukochhårdvara-i-loop (SIL & HIL).DVA studerades först analytiskt och implementerades i en offlinesimulering, påett grundläggande provsystem. Ett testsystem i två områden modellerades sedansom bas för validering av regleringens stabilisering. Felet som användes för attprova styrenhetens effektivitet var en trefas kortslutning på en av de växelströmsledningarsom förbinder de två områdena. DVAC validerades på provsystemet,först av SIL och sedan av HIL realtidssimulering. För att omvandla simuleringen tillen HIL-simulering implementerades DVAC i kod C i en Raspberry Pi-dator, och IEC61850-kommunikationsprotokollet studerades i detalj för att konfigureras för HILsimuleringensuppsättning.SIL och HIL simulering av DVAC validerades för en trefasig kortslutning ochbekräftade att regleringen kunde dämpa ut effektoscillationerna inom 5 sekunder,dubbelt så snabbt jämfört med om ingen reglering var implementerad.

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The population that requires devices for motion improvement has increased considerably, due to aging and neurological impairments. Robotic devices, such as robotic orthosis, have greatly advanced with the objective of improving both the mobility and quality of life of people. Clinical researches remark that these devices, working in constant interaction with the neuromuscular and skeletal human system, improves functional compensation and rehabilitation. Hence, the users become an active part of the training/rehabilitation, facilitating their involvement and improving their neural plasticity. For this purpose, control approaches based on motion intention have been presented as a novel control framework for robotic devices. This work presents the development of a novel robotic knee exoskeleton controlled by motion intention based on sEMG, which uses admittance modulation to assist people with reduced mobility and improve their locomotion. For recognition of the lower-limb motion intention, sEMG signals from trunk are used, which implies a new approach to control robotic assistive devices. The control system developed here includes a stage for human-motion intention recognition (HMIR) system, which is based on techniques to classify motion classes related to knee joint. The motion classes that are taken into account are: stand-up, sit-down, knee flexionextension, walking, rest in stand-up position and rest sit-down position. For translation of the users intention to a desired state for the robotic knee exoskeleton, the system includes a finite state machine, in addition to admittance, velocity and trajectory controllers, which has also the function of stopping the movement according to the users intention. This work also proposes a method for on-line knee impedance modulation, which generates variable gains through the gait cycle for stance control during gait. The proposed HMIR system showed, in off-line analysis, an accuracy between 76% to 83% to recognize motion intention of lower-limb muscles, and 71% to 77% for trunk. Experimental on-line results of the controller showed that the admittance controller proposed here offers knee support in 50% of the gait cycle, and assists correctly the motion classes. A positive effect of the controller on users regarding safety during gait was also found, with a score of 4 in a scale of 5. Thus the robotic knee exoskeleton introduced here is an alternative method to empower knee movements using motion intention based on sEMG signals from lower limb and trunk muscles.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Book, Wayne; Committee Member: Glezer, Ari; Committee Member: Sadegh, Nader. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Cette thèse se place dans un contexte médical de traitements oncologiques, plus particulièrement en protonthérapie robotisée. L’objectif de cette thèse, réalisée sous contrat Cifre avec la société LEONI CIA Cable Systems, est le développement d’une commande en co-manipulation sûre dédiée à un robot médical sériel. Cette commande doit permettre à un opérateur de manipuler intuitivement et précisément un robot de grande inertie positionneur de patients. Les contributions portent sur deux axes, d’une part le développement et l’implémentation sur le robot Orion de l’entreprise LEONI CIA Cable Systems d’une commande en admittance ainsi que la comparaison de trois dispositifs haptiques, et d’autre part le développement d’un mécanisme de détection de collisions proprioceptif permettant l’amélioration de la sécurité de fonctionnement. À partir d’une revue de la littérature concernant les commandes compliantes, nous avons développé et implémenté une commande en admittance dédiée au robot Orion en tenant compte de la discrétisation de la commande par le contrôleur spécifique de ce robot. Une expérience de comparaison sur le robot nous a permis d’identifier le dispositif haptique le mieux adapté au cas clinique considéré. Après une étude de l’état de l’art des mécanismes de détection de collisions, une approche fréquentielle de la modélisation du couple axial prenant en compte les rapports de réduction élevés et de technologie différente du robot a été proposée. Elle permet de modéliser finement le couple théoriquement fourni par les moteurs ; celui-ci est ensuite comparé avec la mesure du couple réellement produit afin de détecter une éventuelle collision
This PhD thesis takes place in a medical context of oncological treatments, more particularly in robotised protontherapy. The objective of this thesis, carried out under a CIFRE contract with LEONI CIA Cable Systems, is the development of a safe comanipulation control dedicated to a serial medical robot. This control law should allow an operator to intuitively and precisely manipulate a robot of high inertia for accurate patients positioning. The contributions of this thesis focus on the development and implementation of an admittance-controlled Orion robot from LEONI CIA Cable Systems and the comparison of three haptic devices, and on the other hand, on the development of a proprioceptive collision detection mechanism allowing the improvement of operational safety. Based on a review of the literature on compliant controls, we have developed and implemented an admittance control approach dedicated to the Orion robot, taking into account the discretization of the control by the controller specific to this robot. A comparison experiment on the robot allowed us to identify the haptic device best suited to the clinical case considered. Based on a state of the art of collision detection mechanisms analysis, a frequency approach of the modeling of the axial torque taking into account the high reduction ratios and different robot technology has been proposed. It allows us to finely model the torque theoretically provided by the motors ; The latter is then compared with the measurement of the torque actually produced in order to detect a possible collision

The ability to maintain postural control is a complex task and, although it is natural for healthy subjects, it is often disrupted in stroke patients. The control of posture, in fact, results from the integration of several sensory inputs, both from the body and the external environment; these inputs are real-time processed to implement a dynamic equilibrium configuration for the entire musculoskeletal system. Postural rehabilitation has grown remarkably in the neuro-rehabilitation field and has met new challenges in the so-called cortical plasticity¬, which is also the rationale for rehabilitation robotics. This principle, in fact, states the ability of the CNS to reorganize itself, even after a cerebrovascular accident. This reason led to the introduction, during the last years, of a huge number of robotic platforms to improve the postural rehabilitation process, both in the fields of Research and clinical routine. The lack, in the literature, of a motorized, 2 DOFs platform, able to interact with the subjects standing upon it, led to the design of a device with these requirements, intended for use by the pediatric patients of the MARlab (Movement Analysis and Robotics laboratory, Ospedale Pediatrico “Bambino Gesù”, Palidoro, RM). After the dimensioning of the selected components, the platform has been designed in a CAD environment. The final layout is a Cartesian robot with a 15x15 cm2 workspace and a low profile (170 mm), and it is ideal to be installed, in the future, below the floor. Two linear induction motors are used to power the two motion axis and, in order to make the platform compliant with the patient, each motor slider was sensorized with a 1DOF load cell. A study was then conducted to evaluate the influence of the inertial forces over the load cell output. The goal of this project was to design and realize a robot prototype, called SlideBiT2D, with an open, evolvable architecture. For this reason we chose to install the network of sensors and actuators over a CAN fieldbus; we also selected, as the network master node, a PCI card CANopen-compliant, which could be programmed in LabVIEW environment. As regards the software, it has been designed on a three-level structure, two of which has already been developed. In this way it is not mandatory to have a good knowledge of the CANopen protocol in order to develop the user interface. To make the platform a real haptic interface, ie able to respond to the external forces imposed by the patient, we used, for both motors, the speed control mode; in addition, a superior control loop was imposed to simulate a 2DOFs spring, placed in parallel with a damper of coefficient C. The control thus produced was tested first with a test bench, along a single dimension, and was then successfully implemented in 2D, over the platform. Since the platform is a medical device, some special attentions were used throughout the design activities. As regards the requirements for electrical safety, the development of the electrical panel was demanded to a certified company (MPD Ltd – Induno Olona, VA). The use of the platform before its installation under the floor will be conducted in combination with the use of the overhead crane installed in the MARlab of Santa Marinella. Finally, the platform commissioning/start-up will require further calibration phase for motors and load cells, in order to assure quality measurements and safe interaction of the robot with the patient.
Il mantenimento della postura è un compito complesso, pur nella sua apparente naturalezza, ed è spesso compromesso in pazienti con patologie a carico del Sistema Nervoso Centrale (SNC). Questo compito è, infatti, frutto dell’integrazione di numerosi input sensoriali, propriocettivi ed esterocettivi, da parte del SNC; tali input vengono elaborati per attuare, in ogni istante, durante tutte le attività quotidiane, una configurazione di equilibrio per l’intero apparato muscoloscheletrico. La riabilitazione del mantenimento della postura ha acquistato importanza sempre crescente nel campo della neuro-riabilitazione ed ha conosciuto nuovi stimoli nel razionale della terapia mediata da robot, la quale si fonda sul concetto della plasticità corticale, ossia sulla capacità del SNC di riorganizzarsi anche a seguito di accidenti cerebrovascolari. Per questo motivo, gli ultimi decenni hanno visto l’introduzione di numerose piattaforme robotiche sia in Ricerca che in Clinica, allo scopo di migliorare il processo di recupero dell’equilibrio e la sua oggettivazione. L’assenza, in letteratura, di una piattaforma motorizzata a 2 gdl (gradi di libertà), e in grado di interagire con i soggetti posti al di sopra di essa, hanno portato alla progettazione di un dispositivo con queste caratteristiche, destinato all’utilizzo da parte dei pazienti pediatrici del MARlab (Movement Analysis and Robotics laboratory) dell’OPBG (Ospedale Pediatrico “Bambino Gesù”) di Palidoro (RM). Dopo l’individuazione delle specifiche di progetto, la scelta e il dimensionamento dei componenti, la piattaforma è stata disegnata in ambiente CAD, risultando un robot cartesiano con un workspace di 15x15 cm2 ed un basso profilo (170 mm), ideale per essere in futuro installata al di sotto del pavimento. Il cuore del dispositivo è costituito dai due motori lineari a induzione elettromagnetica LinMot, che consentono di attivare ciascuno una direzione del moto. Al fine di rendere la piattaforma interattiva, è stato necessario sensorizzare ciascun motore con una cella di carico, così da rilevare la volontà esterna di muovere il robot. Inoltre, trattandosi di un dispositivo destinato a pazienti pediatrici, aventi cioè massa corporea confrontabile con quella della piattaforma, è stato condotto uno studio per valutare la possibilità di compensare in accelerazione le uscite delle celle di carico, depurandole dalla forza di inerzia associata proprio al moto della piattaforma. La filosofia di approccio alla costruzione di questo prototipo, denominato SlideBiT2D, è quella di un sistema aperto ed evolvibile, sia dal punto di vista dell’hardware che del software, pronto ad accogliere nuove necessità espresse da parte del personale medico. Per questo, si è scelto di installare la rete di sensori e attuatori su bus di campo CAN, scegliendo come master della rete un nodo CANopen-compliant, programmabile però in ambiente LabVIEW. Il software è stato concepito come articolato su tre livelli e ne sono stati sviluppati i due più bassi, in modo da svincolare la creazione di una interfaccia utente da qualsiasi conoscenza del CANopen, protocollo molto efficiente ma anche complesso da apprendere. Per rendere la piattaforma una vera e propria interfaccia aptica, in grado cioè di rispondere alle sollecitazioni imposte dall’esterno, i motori sono stati controllati in velocità e, in più, è stato sviluppato un controllore di livello superiore per simulare una molla a 2 gdl, di rigidezza variabile K, posta in parallelo ad uno smorzatore con coefficiente C. Il controllo così realizzato è stato testato dapprima con un banco di prova, lungo una sola dimensione, ed è stato poi implementato con successo in 2D sulla piattaforma. Avere a che fare con un prototipo di un dispositivo medico ha richiesto alcune attenzioni particolari durante tutta la attività di progettazione. Anzitutto, per ciò che riguarda la sicurezza elettrica, il quadro elettrico è stato sviluppato da una ditta certificata (MPD srl – Induno Olona, VA). L’utilizzo stesso della piattaforma, in attesa che essa sia interrata, sarà auspicabilmente condotto in combinazione con l’utilizzo di un carroponte in dotazione al MARlab dell’OPBG di Santa Marinella. Infine, come si conviene ad ogni dispositivo di misura, la messa in opera del robot richiederà una ulteriore fase di taratura dei motori e delle catene di misura presenti, al fine di garantire la qualità delle misure e la sicurezza nella interazione per il paziente.. Infine, come si conviene a un qualsiasi dispositivo di misura, la messa in opera del robot richiederà una ulteriore fase di taratura dei motori e delle catene di misura presenti, al fine di garantire la qualità delle misure e la sicurezza nella interazione per il paziente.

I serpenti robot sono una classe di meccanismi iper-ridondanti che appartiene alla robotica modulare. Grazie alla loro forma snella ed allungata e all'alto grado di ridondanza possono muoversi in ambienti complessi con elevata agilità. L'abilità di spostarsi, manipolare e adattarsi efficientemente ad una grande varietà di terreni li rende ideali per diverse applicazioni, come ad esempio attività di ricerca e soccorso, ispezione o ricognizione. I robot serpenti si muovono nello spazio modificando la propria forma, senza necessità di ulteriori dispositivi quali ruote od arti. Tali deformazioni, che consistono in movimenti ondulatori ciclici che generano uno spostamento dell'intero meccanismo, vengono definiti andature. La maggior parte di esse sono ispirate al mondo naturale, come lo strisciamento, il movimento laterale o il movimento a concertina, mentre altre sono create per applicazioni specifiche, come il rotolamento o l'arrampicamento. Un serpente robot con molti gradi di libertà deve essere capace di coordinare i propri giunti e reagire ad ostacoli in tempo reale per riuscire a muoversi efficacemente in ambienti complessi o non strutturati. Inoltre, aumentare la semplicità e ridurre il numero di controllori necessari alla locomozione alleggerise una struttura di controllo che potrebbe richiedere complessità per ulteriori attività specifiche. L'obiettivo di questa tesi è ottenere un comportamento autonomo cedevole che si adatti alla conformazione dell'ambiente in cui il robot si sta spostando, accrescendo le capacità di locomozione del serpente robot. Sfruttando la cedevolezza intrinseca del serpente robot utilizzato in questo lavoro, il SEA Snake, e utilizzando un controllo che combina cedevolezza attiva ad una struttura di coordinazione che ammette una decentralizzazione variabile del robot, si dimostra come tre andature possano essere modificate per ottenere una locomozione efficiente in ambienti complessi non noti a priori o non modellabili.

The dissertation presents a generalized average-current-mode control technique (GACMC), which is an extension of the average-current-mode control (ACMC) for single-phase ac-dc boost converters with power factor correction (PFC). Traditional ACMC is generalized in a sense that it offers improved performance in the form of significant reduction of the current control loop bandwidth requirement for a given line frequency in unidirectional and bidirectional boost PFC converters, and additional functionality in the form of reactive power control capability in bidirectional converters. These features allow using a relatively low switching frequency and slow-switching power devices such as insulated-gate bipolar transistors (IGBTs) in boost PFC converters, including those designed for higher ac line frequencies such as in aircraft power systems (360â 800 Hz). In bidirectional boost PFC converters, including multilevel topologies, the GACMC offers a capability to supply a prescribed amount of reactive power (with leading or lagging current) independently of the dc load power, which allows the converter to be used as a static reactive power compensator in the power system.

A closed-loop dynamic model for the current control loop of the boost PFC converter with the ACMC has been developed. The model explains the structure of the converter input admittance, the current phase lead phenomenon, and lays the groundwork for development of the GACMC. The leading phase admittance cancellation (LPAC) principle has been proposed to completely eliminate the current phase lead phenomenon and, consequently, the zero-crossing distortion in unidirectional converters. The LPAC technique has been adapted for active compensation of the input filter capacitor current in bidirectional boost PFC converters.

The dynamic model of the current control loop for bidirectional boost PFC converters was augmented to include a reactive power controller. The proposed control strategy enables the converter to process reactive power and, thus, be used as a reactive power compensator, independently of the converter operation as an ac-dc converter.

Multiple realizations of the reactive power controller have been identified and examined in a systematic way, along with their merits and limitations, including susceptibility to the ac line noise. Frequency response characteristics of reactive elements emulated by means of these realizations have been described.

Theoretical principles and practical solutions developed in this dissertation have been experimentally verified using unidirectional and bidirectional converter prototypes. Experimental results demonstrated validity of the theory and proposed practical implementations of the GACMC.
Ph. D.

This dissertation aims to present a detailed analysis of the grid voltage disturbance in frequency domain for the current control design in the grid-tie inverter applications and to propose current control techniques in order to minimize its impact and maximize feasibility of the power conditioning system in distributed generations. Because the grid voltage is constantly changing, the inverter must be able to response to it. If the inverter is unable to respond properly, then the grid voltage power comes back to the system and damages the fuel cell power conditioning systems. A closed-loop dynamic model for the current control loop of the grid-tie inverter has been developed. The model explains the structure of the inverter admittance terms. The disturbance of the grid voltages has been analyzed in frequency domain. The admittance compensator has been proposed to prevent the grid voltage effect. The proposed lead-lag current control with admittance compensator transfers current properly without system failure. In order to get rid of the steady-state error of the feedback current, a proportional-resonant controller (PR) has been adopted. A PR control with admittance compensation provides great performance from zero power to full power operation. In addition, active and reactive power flow controller has been proposed based on the PR controller with admittance compensation. The proposed active and reactive power flow control scheme shows a wide range power flow control from pure leading power to pure lagging power. Finally, the proposed controller scheme has been verified its feasibility in three phase grid-tie inverter applications. First of all, a half-bridge grid-tie inverter has been designed with PR controller and admittance compensation. Then three individual grid-tie inverters has been combined and produced three phase current to the three phase grid in either balanced condition or unbalanced condition. The proposed control scheme can be applied not only single phase grid-tie inverter application, but also three phase grid-tie inverter application. This research can be applicable to the photovoltaic PCS as well. This technology makes renewable energy source more plausible for distributed generations.
Ph. D.

With the rapid increase in electrical energy demand, power generation in the form of distributed generation is becoming more important. However, the connections of distributed generators (DGs) to a distribution network or a microgrid can create several protection issues. The protection of these networks using protective devices based only on current is a challenging task due to the change in fault current levels and fault current direction. The isolation of a faulted segment from such networks will be difficult if converter interfaced DGs are connected as these DGs limit their output currents during the fault. Furthermore, if DG sources are intermittent, the current sensing protective relays are difficult to set since fault current changes with time depending on the availability of DG sources. The system restoration after a fault occurs is also a challenging protection issue in a converter interfaced DG connected distribution network or a microgrid. Usually, all the DGs will be disconnected immediately after a fault in the network. The safety of personnel and equipment of the distribution network, reclosing with DGs and arc extinction are the major reasons for these DG disconnections. In this thesis, an inverse time admittance (ITA) relay is proposed to protect a distribution network or a microgrid which has several converter interfaced DG connections. The ITA relay is capable of detecting faults and isolating a faulted segment from the network, allowing unfaulted segments to operate either in grid connected or islanded mode operations. The relay does not make the tripping decision based on only the fault current. It also uses the voltage at the relay location. Therefore, the ITA relay can be used effectively in a DG connected network in which fault current level is low or fault current level changes with time. Different case studies are considered to evaluate the performance of the ITA relays in comparison to some of the existing protection schemes. The relay performance is evaluated in different types of distribution networks: radial, the IEEE 34 node test feeder and a mesh network. The results are validated through PSCAD simulations and MATLAB calculations. Several experimental tests are carried out to validate the numerical results in a laboratory test feeder by implementing the ITA relay in LabVIEW. Furthermore, a novel control strategy based on fold back current control is proposed for a converter interfaced DG to overcome the problems associated with the system restoration. The control strategy enables the self extinction of arc if the fault is a temporary arc fault. This also helps in self system restoration if DG capacity is sufficient to supply the load. The coordination with reclosers without disconnecting the DGs from the network is discussed. This results in increased reliability in the network by reduction of customer outages.

abstract: Admittance control with fixed damping has been a successful control strategy in previous human-robotic interaction research. This research implements a variable damping admittance controller in a 7-DOF robotic arm coupled with a human subject’s arm at the end effector to study the trade-off of agility and stability and aims to produce a control scheme which displays both fast rise time and stability. The variable damping controller uses a measure of intent of movement to vary damping to aid the user’s movement to a target. The range of damping values is bounded by incorporating knowledge of a human arm to ensure the stability of the coupled human-robot system. Human subjects completed experiments with fixed positive, fixed negative, and variable damping controllers to evaluate the variable damping controller’s ability to increase agility and stability. Comparisons of the two fixed damping controllers showed as fixed damping increased, the coupled human-robot system reacted with less overshoot at the expense of rise time, which is used as a measure of agility. The inverse was also true; as damping became increasingly negative, the overshoot and stability of the system was compromised, while the rise time became faster. Analysis of the variable damping controller demonstrated humans could extract the benefits of the variable damping controller in its ability to increase agility in comparison to a positive damping controller and increase stability in comparison to a negative damping controller.
Dissertation/Thesis
Masters Thesis Mechanical Engineering 2019