Full Bridge MMC Converter Optimal Design to HVDC Operational Requirements

This project is funded by RTE, Paris, FrancePeer reviewedPostprin

Application of digital computer to magnetic data interpretation using surface integral method

A simple method is developed for the calculation of the magnetic effect due to three-dimensional bodies. The method is based on the use of surface integration instead of volume integration. Thus, any three-dimensional body can be considered as having two surfaces, upper and lower, with magnetic pole distributions. Simple equations based on potential theory have been derived for the calculation of the vertical component and total intensity due to these surface distributions of poles. The anomalous field of the body can be obtained by subtracting the effect due to one of the surfaces from that of the other. The method can be applied to the interpretation of magnetic anomalies arising mainly from structures or polarization contrasts in the magnetic basement rocks. The calculations have been programmed in a fixed point system for the Royal McBee LGP-30 electronic digital computer. The programs may be used for either vertical magnetometer data or total intensity data. Application to some theoretical models establishes the relative accuracy of the method. The technique has been presented as an application of the digital computer to magnetic interpretation where the time required to obtain computed results is an economic factor --Abstract, page ii

Modélisation et simulation d'une liaison HVDC de type VSC-MMC

RÉSUMÉ Le transport d’énergie en courant continu à haute tension (CCHT ou HVDC) est aujourd’hui en pleine expansion dans le monde. Deux principaux facteurs sont à l’origine de cet engouement. Le premier est lié à la difficulté de construire de nouvelles lignes aériennes pour assurer le développement du réseau à haute tension qui fait que le recours à des câbles souterrains est de plus en plus fréquent. Or l’utilisation de ces câbles est limitée en longueur à quelques dizaines de km à cause du courant capacitif généré par le câble lui-même. Au-delà de cette longueur limite, la solution consiste généralement à transporter en courant continu. Le second facteur est lié au développement de l’éolien offshore qui nécessite de raccorder des puissances de plusieurs centaines de MW au réseau continental au moyen de câbles dont les longueurs peuvent atteindre quelques centaines de km et ce qui nécessite donc le transport en HVDC. De façon concrète, plusieurs projets de transmission HVDC ont été planifiés par le gestionnaire du réseau de transport français RTE. Le projet INELFE, par exemple, est une interconnexion HVDC entre la France et l’Espagne, pour la transmission de 2000 MW. Cette thèse est financée par RTE, dans le but de modéliser, simuler en temps réel et étudier les risques d’interaction entre ces liaisons HVDC. La particularité des ouvrages de transport en courant continu est de faire appel à un contrôle commande dédié qui va en grande partie déterminer le comportement dynamique de la liaison tant sur des grosses perturbations (défauts sur le réseau) qu’en régime de petites variations. Il existe différentes topologies VSC (Voltage Source Converter), comme les convertisseurs à deux niveaux, les convertisseurs multi-niveaux avec des diodes et les convertisseurs multiniveaux avec des condensateurs flottants. Toutefois, en raison de la complexité des commandes et des limites pratiques, les installations de système HVDC-VSC ont été limitées à des convertisseurs à deux niveaux et à trois niveaux. Récemment, la mise au point de la technologie modulaire appelé MMC (Modular Multilevel Converter [Siemens]-[Alstom]) ou CTL (Cascaded Two Level topology [ABB]) en fonction des industriels, a permis de surmonter les limites des autres topologies multi-niveaux pour les applications HVDC. Cette topologie est constituée de plusieurs sous-modules connectés en séries. Chaque sous-module contient deux IGBTs avec leurs diodes antiparallèles et un condensateur qui sert comme accumulateur d’énergie.----------ABSTRACT High-voltage direct current transmission systems (HVDC) are rapidly expanding in the world. Two main factors are responsible for this expansion. The first is related to the difficulty of building new overhead lines to ensure the development of high-voltage AC grids, which makes the usage of underground cables more common. However, the use of such cables is limited in length to a few tens of km because of the capacitive current generated by the cable itself. Beyond this length limit, the solution is usually to transmit in DC. The second factor is related to the development of offshore wind power plants that require connecting powers of several hundred of MW to the mainland grid by cables whose lengths can reach several hundreds of km and consequently require HVDC transmission system. Several HVDC projects are currently planned and developed by the French transmission system operator RTE. One of such projects is the INELFE interconnection project, with a capacity of 2,000 MW, between France and Spain. This thesis has been funded by RTE, in order to model and simulate in off-line and real time modes, modern HVDC interconnections. The delivered simulation means are used to examine targeted HVDC system performances and risks of abnormal interactions with surrounding power systems. The particularity of the INELFE HVDC system is the usage of a dedicated control system that will largely determine the dynamic behaviour of the system for both large disturbances (faults on the network) and small perturbations (power step changes). Various VSC topologies, including the conventional two-level, multi-level diode-clamped and floating capacitor multi-level converters, have been proposed and reported in the literature. However, due to the complexity of controls and practical limitations, the VSC-HVDC system installations have been limited to the two-level and three-level diode-clamped converters. Recently, the development of modular technology called MMC (Modular Multilevel Converter [Siemens] - [Alstom]) or CTL (Cascaded Two Level topology [ABB]) has allowed to overcome existing limitations. This topology consists of several sub-modules connected in series. Each submodule contains two IGBTs with antiparallel diodes and a capacitor that act as energy storage. The control of these IGBTs allows connecting and disconnecting the capacitor on the network

Low Energy Protection System for DC Grids Based on Full Bridge MMC Converters

This project is funded by RTE, Paris, France. D. Jovcic and W. Lin are with the School of Engineering, University of Aberdeen, AB24 3UE, U.K. ( [email protected], [email protected]). S. Nguefeu and H. Saad are with the Réseau de Transport d’Electricité, Paris 92932, France ([email protected], [email protected] )Peer reviewedPostprin

Evaluation of Coronary Artery Bypass by CT Coronary Angiography

Coronary computed tomography angiography (CCTA) is an accurate method for graft imaging and assessment than invasive coronary angiography (ICA). CTA has excellent sensitivity and specificity. The chapter describes the role of CTA in evaluation of coronary bypass graft. It covers the appropriate indications for performing CTA after bypass operation, patient preparation, as well as protocol and technique of CTA. The chapter describes the post-examination processing of the images and how to interpret CTA images for detection of graft patency or dysfunction as occlusion, partial thrombosis, poor blood flow, and stealing flow from native artery. According to the American College of Cardiology, the American College of Radiology, and the North American Society for Cardiovascular Imaging, graft patency assessment with CTA is an appropriate approach in symptomatic patients at risk for graft stenosis/occlusion. Cardiac CT can be used to assess the patency of coronary artery bypass graft (CABG) with high diagnostic accuracy compared with ICA and even with a better performance compared to the assessment of native coronaries

Understanding the Significance of Patient Empowerment in Health Care Services and Delivery

To address emerging challenges in empowering patients through telehealth, this dissertation has the following objectives: (a) find the key characteristics that enable patient empowerment [PE], (b) determining when will PE work as a solution, (c) find the optimal telehealth care method that enables PE, and (d) evaluate the impact of telehealth on health care outcomes (such as, patient satisfaction, patient trust with primary care providers, etc.) that ultimately enhances PE. These objectives are addressed in three studies presented here as three essays. Collectively, these essays contribute to the knowledge on PE, patient trust, and telehealth by providing insights on leveraging PE towards better health care services and delivery systems. Essay 1 aims to systemically map the concept of PE using principles of systems thinking with the Boardman soft systems methodology that enables a graphical visualization (i.e., systemigrams). Essay 2 investigates the practical and theoretical implications of connecting patients to empowerment care plans and minimizing wait times in healthcare service delivery using electronic prescriptions (s-scripts), phone calls, and video calls. In Essay 3, the mediating role of telehealth services between patient empowerment and patient satisfaction was analyzed, along with patient trust was assessed as a moderator between telehealth usability and patient satisfaction. Two hundred sixty-two responses from patients in North America with chronic illnesses were collected through an online survey questionnaire were analyzed using partial least squares-structural equation modeling (PLS-SEM). The findings of the research show that patients with chronic illnesses in North America feel empowered by using telehealth as they can get diagnosis of the illness even in remote areas and face no obstacle

Design of Compact Monopole Antenna using Double U-DMS Resonators for WLAN, LTE, and WiMAX Applications

This paper is under in-depth investigation due to suspicion of possible plagiarism on a high similarity indexIn this research, a novel wide-band microstrip antenna for wideband applications is proposed. The proposed antenna consists of a square radiating patch and a partial ground plane with a smal rectangular notch-shape. Two symmetrical U-slots are etched in radiating patch. The defected microstrip U-shapes and the small notch improve the antenna characterestics such impedance wideband and the gain along the transmission area. The proposed antenna is simulated on an FR4 substrate of a dielectric constant of 4.3, thickness 1.6 mm, permittivity 4.4, and loss tangent 0.018. The simulation and optimization results are carried out using CST software.The antenna topology occupies an area of 30 × 40 × 0.8 mm3 or about 0.629λg × 0.839λg × 0.017λg at 3 GHz (the centerresonance frequency). The antenna covers the range of 2.1711 to 4.0531 GHz, which meet the requirements of the wireless local area network (WLAN), worldwide interoperability for microwave access (WiMAX) and LTE (Long Term Evolution) band applications. Good VSWR, return loss and radiation pattern characteristics are obtained in the frequency band of interest. The obtained Simulation results for this antenna depict that it exhibits good radiation behavior within the transmission frequency range

Aspects quantitatifs et qualitatifs des eaux transitant par la grotte karstique de Hammamet Algérie

International audienceLes travaux portant sur la connaissance et le fonctionnement sont rares, en effet les derniers travaux effectués sur cette grotte sont très anciens. Cette situation freine les travaux actuels. Pour réaliser notre travail, nous nous sommes intéressés à la morphologie externe de la grotte. Le constat réalisé montre une morphologie gondolée traduisant la présence de petites dolines, ces dernières permettent l'infiltration des eaux dans les cavités. L'étude réalisée montre également la présence de sources sur la partie droite de la grotte en dessous de l'épikarst. Ce constat nous a permis de déduire une dissymétrie de la fissuration. En effet le coté gauche de la grotte est étanche, aucun écoulement ne se fait par contre le coté droit est très fissuré, ce qui favorise l'infiltration et la circulation des eaux. Les apports en eau sont soit directs, par infiltration des eaux de pluies soit indirects à partir des Djebels entourant la grotte, tel que le Djebel Tazbent, situé à plus haute altitude. Les débits jaugés à la sortie de la grotte varient en fonction des saisons et leur pluviosité. De ce fait à la sortie de la grotte les débits sont importants et peuvent atteindre 1 913L/s, par contre au niveau de l'oued Bouakous caractérisant la zone aval, le débit n'excède pas 10L/s. Les jaugeages différentiels effectués montrent une infiltration de 541L/s. Ces eaux vont modifier la composition chimique des eaux souterraines, ce dernier est bicarbonaté en période pluvieuse et devient chloruré en période sèche. Ce changement est accentué par la mise en solution des minéraux

A Compact Wideband Monopole Antenna using Single Open Loop Resonator for Wireless Communication Applications

A novel single layer, microstrip line fed compact wideband monopole antenna using open loop resonator has been designed and analyzed. The proposed antenna occupies a compact size of only 30 36.5 1.6 mm3. A partial ground plane is employed to enhance the operating bandwidth and reflection coefficient of the proposed antenna. The variations in operating bandwidth of the proposed antenna can be easily controlled by properly adjusting the position of the gap in the open loop resonator.The antenna prototype is fabricated on FR4 substrate with a dielectric constant 4.2. In this design, the antenna exhibits 10dB wide impedance bandwidth of 61% from 2.0174 to 3.7903 GHz.The antenna can be easily fed using a 50 Ω microstrip feed line and it covers the bandwidth requirements of a number of modern wireless communication systems such as IEEE 502.11b WLAN band (2.4 2.5 GHz), extended UMTS (2.5 2.69 GHz), IMT (2.7 2.9 GHz), and IEEE 802.16 Wi MAX band (3.3 3.6 GHz) applications. The desired antenna is designed and simulated using Computer Simulation Technology (CST). An extensive analysis of the antenna parameters (reflection coefficient, radiation pattern, directivity, and VSWR) including surface current distributions is presented and discussed in this paper. Good agreement between simulated and measured result is obtained

An Improved Retraining Scheme for Convolutional Neural Network

A feed-forward neural network artificial model, or multilayer perceptron (MLP), learns input samples adaptively and solves non-linear problems for data that are noisy and imprecise. Another variant of MLP, known as Convolutional Neural Network (CNN) has additional features such as weight sharing, local receptive field, and subsampling, making CNN superior in handling challenging pattern-recognition tasks. Although CNN has improved the performance of MLP, the complexity of its structure has caused retraining processes to become inefficient whenever new categories or neurons using a winner-takes-all approach are added at the classifier stage. Thus, it is necessary to retrain the complete network set when new categories are added to the network. However, such a retraining incurs additional cost and training time. In this paper, we propose a retraining scheme that could overcome the mentioned problem. The proposed retraining scheme generalizes the feature of extraction layers, hence the retraining process only involves the last two layers instead of the whole network. The design was evaluated on AT&T and JAFFE databases. The results obtained have proved that training an additional category is approximately more than 70 times faster than retraining the whole network architectur