Contribution à la commande non linéaire robuste des systèmes d'alimentation en air des piles à combustible de type PEM

La pile à combustible (PàC) est un dispositif qui produit de l'électricité à partir d'une réaction chimique entre l'hydrogène et l'oxygène. Le système à PàC nécessite un certain nombre d'auxiliaires pour fonctionner. Pour cela, un système de commande est indispensable pour optimiser la performance de la PàC.Dans ce travail de thèse, nous nous sommes intéressés à trois types de problématiques de commande de la PàC. La première est celle de l'optimisation de la puissance délivrée par la PàC en contrôlant le rapport d'excès d'oxygène via le débit d'air du compresseur ; en prenant en compte les variations paramétriques, les incertitudes et les perturbations externes. Ce problème est résolu en utilisant la commande non-linéaire par mode glissant d'ordre 2. Deux types d'algorithme sont synthétisés, l'algorithme du mode glissant d'ordre 2 sous-optimal et l'algorithme du Super Twisting adaptatif. Les performances de ces lois de commande ont été validées grâce à un simulateur Hardware In Loop. La deuxième concerne la maximisation de la puissance nette fournie par la pile, tout en maintenant le fonctionnement du compresseur centrifuge dans sa zone nominale et tout en évitant le manque d'oxygène à la cathode, lors des variations rapides de charge. La solution proposée pour résoudre ce problème est un gestionnaire de charge qui consiste en un filtre à coefficient de filtrage ajustable. Deux approches d'ajustement de ce coefficient basées sur la technique de l'Extremum Seeking sont appliquées, comparées et validées expérimentalement. La troisième problématique abordée dans cette thèse est celle de la régulation de la différence de pression entre l'anode et la cathode, lors de variations de charge en présence de variations paramétriques et d'incertitudes. Une solution basée sur un contrôleur multi-variable par mode glissant d'ordre 2 associé à une étude de robustesse est proposée.The PEM fuel cell is a device which generates electricity from a chemical reaction between hydrogen and oxygen. The PEM fuel cell requires many ancillaries to operate the system. A control system is needed to optimize the performance of the PEMFC. This thesis is focused upon three specific control problems related to PEM fuel cell systems. The first problem is the control of the air (oxygen source) entering in the cathode side of fuel cell. The objective is to regulate the oxygen excess ratio in order to maintain the optimum net power output. This problem has been addressed using nonlinear second order sliding mode controllers, which are robust against parametric uncertainty and external disturbance. The SOSM controllers are based on two algorithms: sub-optimal and adaptive Super Twisting. Their performance is validated through Hardware In Loop simulation. The second problem is to maintain the centrifugal compressor in its operating zone, while avoiding the oxygen starvation in the cathode side during rapid load variations. The proposed solution to this problem is a load governor, which is similar to a variable bandwidth first order linear filter. Two adjustment algorithms have been applied for the bandwidth coefficient, based on the Extremum Seeking technique. Their performance has been validated experimentally. The third problem addressed in this thesis is the regulation of the pressure difference between the anode and the cathode during load variations. The control objective is achieved using second order sliding mode MIMO controller, which has been shown to be robust against parametric uncertainty and external disturbance.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF

Evaluating the Impact of Computerized Provider Order Entry on Medical Students Training at Bedside: A Randomized Controlled Trial

Objective: To evaluate the impact of computerized provider order entry (CPOE) at the bedside on medical students training. Materials and Methods We conducted a randomized cross-controlled educational trial on medical students during two clerkship rotations in three departments, assessing the impact of the use of CPOE on their ability to place adequate monitoring and therapeutic orders using a written test before and after each rotation. Students’ satisfaction with their practice and the order placement system was surveyed. A multivariate mixed model was used to take individual students and chief resident (CR) effects into account. Factorial analysis was applied on the satisfaction questionnaire to identify dimensions, and scores were compared on these dimensions. Results: Thirty-six students show no better progress (beginning and final test means = 69.87 and 80.98 points out of 176 for the control group, 64.60 and 78.11 for the CPOE group, p = 0.556) during their rotation in either group, even after adjusting for each student and CR, but show a better satisfaction with patient care and greater involvement in the medical team in the CPOE group (p = 0.035*). Both groups have a favorable opinion regarding CPOE as an educational tool, especially because of the order reviewing by the supervisor. Conclusion: This is the first randomized controlled trial assessing the performance of CPOE in both the progress in prescriptions ability and satisfaction of the students. The absence of effect on the medical skills must be weighted by the small time scale and low sample size. However, students are more satisfied when using CPOE rather than usual training

Methode de description de reseaux locaux industriels heterogenes

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 83236 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Approche dirigée par les modèles pour la spécification, la vérification formelle et la mise en oeuvre de services Web composés

Dans ce travail, une approche pour la spécification, la vérification formelle et la mise en oeuvre de services Web composés est proposée. Il s'agit d'une approche dirigée par les modèles fidèle aux principes de MDA définis par l'OMG. Elle permet au développeur de s'abstraire des difficultés liées à l'implémentation en travaillant sur les modèles de haut niveau, indépendants de la plateforme ou de la technologie d'implémentation cible. Les modèles sont réalisés à l'aide du langage de modélisation UML. Plus précisément, une extension à UML nommée UML-S est proposée pour adapter le langage au domaine de la composition de services. Les modèles UML-S sont suffisamment expressifs et précis pour être directement transformés en code exécutable tout en conservant leur lisibilité. Ces modèles peuvent également être transformés en descriptions formelles LOTOS afin de procéder à leur vérification formelle. L'approche proposée contribue à réduire les temps et les coûts de développement tout en assurant la fiabilité des services composés.In this work, an approach is proposed to specify, formally verify and implement composite Web services. This model-driven approach embraces the principles of the Model-Driven Architecture (MDA) as promoted by the OMG. It allows for the developer to work at a high level of abstraction by handling graphical models that are independent from programming concepts and implementation technologies. These models are described using the UML modeling language. Specifically, an extension to UML called UML-S is proposed to adapt the language to the specific needs of the Web service composition domain. UML-S models are expressive and precise enough to support direct transformation into low-level execution code while being easily readable. These models can also be transformed into formal descriptions in LOTOS to support the formal verification of the composition. The approach proposed contributes to reducing development time and costs while contributing to the robustness of the service composition.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF

Model-driven engineering of composite web services using uml-s

UML was already considered to describe Web services composition. In [8], an approach using UML activity diagrams to do so was presented by Skogan et al. They provide a way to model the coordination and the sequencing of the interactions between Web services. Although they present basic transformation rules between UML diagrams and BPEL [1] or WorkSCo, they do not consider flow control patterns. Their study is limited to basic activities such as variable assignment, Web service invocation, parameters reception and response output. In [11], Wohed et al. proposed a pattern based analysis of BPEL4WS. The main purpose of this paper was to evaluate the capabilities and limitations of BPEL4WS. They studied how the main flow control patterns could be expressed in BPEL. Unfortunately, they reported that some patterns such as multiple merge, discriminator and its generalization, the N-out-of-M join are unsupported by BPEL and most of the implementation solutions provided require editing to be correct in latest WS-BPEL 2.0. In [4], Dumez et al. introduced UML-S, an UML 2.0 profile to model Web services as well as their composition. Web services interfaces are modeled using UML-S class diagrams although their interactions are represented using activity diagrams, due to the dynamism involved. In [7], Nait-Sidi-Moh et al. provide the necessary means to verify and validate UML-S models. Since UML is a semi-formal language, it lacks sufficient formalism to apply directly on its diagram mathematical techniques. Therefore, they provide transformation rules between UML-S and adapted Petri nets to solve said issue. The properties which should be verified are idenhal-00347220

Sensor Networks Applications Performance Measures for IEEE802.11n WiFi Security Protocols

International audienceThis paper presents a study for performance implementation of IEEE 802.11i WPA2 (Wi-Fi Protected Access 2) security protocol in Sensor Network applications. This research compared the implementation of the WPA2 security protocols over Sensor Networks to estimate the security impacts on sensor networks applications and evaluate the quality of service (QoS) parameters and network degradation related to service time and packet delay. The results showed that the network applications performance depends on network design, security protocol headers, which adds a significant impact related to the packet delays, the number of users, and the transmitted data packet size over the network