Protection and Disturbance Mitigation of Next Generation Shipboard Power Systems

Today, thanks to modern advances mainly in the power electronics field, megawatt-level electric drives and magnetic levitation are being integrated into the marine power grids. These technologies operate based on Direct Current (DC) power which require Alternating Current (AC) to DC conversion within the current grid. Medium-voltage Direct Current (MVDC) and Flywheel Energy Storage Systems (FESS) are the next state-of-the-art technologies that researchers are leaning on to produce, convert, store, and distribute power with improved power quality, reliability, and flexibility. On the other hand, with the extensive integration of high-frequency power electronic converters, system stability analysis and the true system dynamic behaviors assessment following grid disturbances have become a serious concern for system control designs and protection. This dissertation first explores emerging shipboard power distribution topologies such as MVDC networks and FESS operation with charge and discharge dynamics. Furthermore, the important topic of how these systems perform in dynamic conditions with pulsed power load, faults, arc fault and system protection are studied. Secondly, a communication-based fault detection and isolation system controller that improves upon a directional AC overcurrent relay protection system is proposed offering additional protection discrimination between faults and pulsed-power Load (PPL) in MVDC systems. The controller is designed to segregate between system dynamic short-circuit fault and bus current disturbances due to a PPL. Finally, to validate the effectiveness of the proposed protection controller, different bus current disturbances are simulated within a time-domain electromagnetic transient simulation of a shipboard power system including a PPL system operating with different ramp rate profiles, pulse widths, peak powers, and fault locations. This overarching goal of this work is to address some of the critical issues facing the US Navy as warfighter mission requirements increase exponentially and move towards advanced and sophisticated pulsed power load devices such as high energy weapon systems, high energy sensor and radar systems. The analyses and proposed solutions in this dissertation support current shipbuilding industry priorities to improve shipboard power system reliability and de-risk the integration of new power system technologies for next generation naval vessels

Randomized permutation routing in multihop ad hoc networks with unknown destinations

A large variety of permutation routing protocols in a single-hop Network are known to day. Since they are single hop, there is always a wireless path connecting two nodes. One way to solve this problem in a multiple hop environment is to partition nodes into clusters, where a node in each cluster called clusterhead is responsible for the routing service. In this paper, we propose a clustering mechanism to perform permutation routing in multi-hop ad hoc Networks having p stations and in which n data items are saved. We first develop a clustering algorithm to partition stations into clusters. Secondly, we run a locally permutation routing to broadcast items to their local destinations in each group. Finally we use a multicast procedure to transmit outgoing items to their final cluster destination.1st IFIP International Conference on Ad-Hoc NetWorkingRed de Universidades con Carreras en Informática (RedUNCI

A survey of the mental healthcare systems in five Francophone countries in West Africa: Bénin, Burkina Faso, Côte d'Ivoire, Niger and Togo

Sub-Saharan Africa has a wide mental health treatment gap, with low levels of access to mental health services. This paper presents the findings of systematic situation analyses carried out in five Francophone countries in West Africa, which are among the poorest in the world. The findings showed low levels of budgetary allocation to mental health, poor health infrastructure (especially at primary level) and unequal distribution of human and financial resources. In this challenging context, there are signs of reform of services, based on international best-practice guidelines and practical considerations such as decentralisation of services, task-sharing and strengthening stakeholder skills to advocate for change.</jats:p

Contribution d’une analyse du discours à l’étude des stratégies d’actions et de régulation des agents en situation d’écoute téléphonique

Dans cette étude, nous avons analysé les représentations d’opérateurs de la téléphonie sociale en particulier les écoutants du numéro d’urgence 115, afin d’évaluer les difficultés liées à leur activité de travail et les stratégies qu’ils mettent en œuvre pour y faire face. Cette analyse a été faite sur la base du recueil d’entretiens portant sur le vécu des écoutants. La relation d’aide au téléphone met en œuvre de multiples compétences acquises dans des domaines variés. Toutefois, elle apparaît fondée sur de multiples paradoxes qui impactent considérablement l’activité des écoutants. D’autres facteurs d’ordre organisationnel contribuent également à rendre difficile ce travail : de nombreux appels polluants sans relation directe avec leur activité, la dépendance du dispositif à d’autres structures du secteur social, etc. Dans ce contexte, les écoutants développent des stratégies individuelles et collectives pour mieux gérer les contraintes de certains appels ou bien le déficit en places du dispositif d’hébergement.In this study we analyzed the representations of listener-operators of the emergency hotline “115” for the homeless, to assess the difficulties linked to their work and the strategies which they implement to deal with them. Our analysis was based on recorded interviews relating listener-operator experiences. The relation involved in assistance by telephone requires a number of skills in a range of fields. However it appears to be based on a series of paradoxes which impact considerably on the listening activity. Other factors of an organizational nature also add to the work’s difficulties, such as polluting calls having no direct connection with the assistance activity, hotline dependence on other social structures, etc. In this situation, the 115 hotline agents develop individual and collective strategies to better manage constraints resulting from certain calls or lack of places in the shelter program.En este estudio hemos analizado las representaciones de los teleoperadores del número de urgencia 115 del servicio de telefonía social, a fin de evaluar las dificultades relacionadas a su actividad de trabajo y las estrategias que emplean para afrontarlas. Este análisis fue realizado a partir de entrevistas destinadas a relevar lo vivido por los teleoperadores. La relación de ayuda telefónica implica el despliegue de múltiples competencias adquiridas en diversos ámbitos. Sin embargo, ésta aparece fundada en diversas paradojas que impactan considerablemente la actividad de los teleoperadores. Asimismo, otros factores de carácter organizacional, contribuyen a dificultar este trabajo : numerosos llamados contaminantes sin relación directa con su actividad, la dependencia del dispositivo con respecto a otras estructuras del sector social, etc. En este contexto, los teleoperadores desarrollan estrategias individuales y colectivas para gestionar más adecuadamente las exigencias que plantean ciertos llamados o el déficit de plazas que ofrece el dispositivo de albergue de las personas sin techo

Fault Protection Considerations for MVDC Shipboard Power Systems Operating With Pulsed-Power Loads

Medium Voltage Direct Current (MVDC) power distribution architectures are of immense interest for various shipboard power applications due to their advantages over classical MVAC distribution systems with respect to power quality, power density, and efficiency. However, MVDC are far away from maturity when compared to MVAC with respect to fault detection and isolation. Currently, there are no standards available for applying MVDC protection systems in shipboard applications. Furthermore, due to the absence of zero crossings in DC waveforms and unique transient fault signatures, it is challenging to design effective protection system schemes to isolate faults via conventional protection systems. This paper investigates and analyses various types of shipboard MVDC dynamic fault behaviours and signatures under different DC bus disturbances such as: bus to ground, bus to bus to ground, and impact of Pulsed-Power Load (PPL) with and without faults on a shipboard MVDC distribution system. Furthermore, a communication-based fault detection and isolation system controller that improves upon a directional ac overcurrent relay protection system is proposed offering additional protection discrimination between faults and PPLs in MVDC systems. To validate the effectiveness of the proposed protection controller, different bus current disturbances are simulated within a time-domain electromagnetic transient simulation of a shipboard power system including a PPL system operating with different ramp rate profiles, pulse widths, peak powers, and fault locations

Effet de l’irradiation gamma des semences de tomate (Lycopersicon esculentum Mill) sur la résistance au NaCl et l’accumulation de la proline dans les feuilles

L’objectif de cette expérience est de sélectionner des variétés de tomates (Lycopersicon esculentum Mill) résistantes au NaCl grâce à l’irradiation gamma. Son but est d'évaluer l'effet de l’irradiation des graines de tomate sur leur résistance au NaCl et de confirmer celle-ci par l’évaluation de la concentration en proline contenue dans les feuilles des plantes régénérées. Des traitements gamma au cobalt 60 (60Co) ont été  appliqués sur des semences de tomate à la température ambiante. Quatre doses d’irradiation ont été appliquées sur les graines à savoir : 0 (témoins) ; 100 ; 150 ; et 200 gray (Gy) à une fréquence de 20 rad.min-1. Les graines ont ensuite été semées sur le milieu MS additionné de différentes concentrations de NaCl. Les résultats ont montré que la germination des graines a été affectée par l'addition du NaCl dans le milieu de culture. Avec l’ajout de 60 mM de sel dans le milieu de culture, une réduction de 50% du taux de germination chez les graines irradiées et non irradiées a été observée. A des concentrations en sel plus élevées (100 mM), seul quelques génotypes parmi les graines irradiées sont capables de germer mais avec un pourcentage de germination trop faible. La durée de germination est plus longue pour les graines irradiées que pour les témoins. 50% et 100% de jours supplémentaires sont nécessaires respectivement pour des concentrations de 60 et 100 mM de NaCl dans le milieu comparativement aux graines non irradiées. La concentration de proline contenue dans les feuilles des plantes régénérées a été  déterminée. Les doses d’irradiation appliquées sur les semences ont un effet sur l’accumulation de la proline dans les feuilles de tomate. En effet, le taux de proline augmente avec l’augmentation des doses de radiation.Mots clés: Lycopersicon esculentum Mill, irradiation gamma, NaCl, proline