Resource allocation consists in allocating spectrum and power on every link of a network, possibly under power and rate requirements. In the context of cognitive radios, almost 15 years of research produced an impressive amount of theoretical contributions, exploring a wide range of possibilities. However, despite the ever-growing list of imaginable scenarios, we observe in Chapter 2 that most of these studies are based on similar working hypotheses. Our first contribution is to challenge some of these hypotheses, and propose a novel resource allocation scheme. Sticking to realistic assumptions, we show how our scheme reduces both computational complexity and control traffic, compared to other state-of-the-art techniques.<p><p>Due to a majority of the abovementioned studies making some constraining assumptions, realistic system designs and experimental demonstrations are much more quiet and unharvested fields. In an effort to help this transition from theory to practice, our second contribution is a four-nodes cognitive network demonstrator, presented in Chapter 3. In particular, we aim at providing a modular platform available for further open collaboration: different options for spectrum sensing, resource allocation, synchronisation and others can be experimented on this demonstrator. As an example, we develop a simple protocol to show that our proposed resource allocation scheme is fully implementable, and that primary users can be avoided using our approach.<p><p>Chapter 4 aims at removing another working hypothesis made when developping our resource allocation scheme. Indeed, resource alloca- tion is traditionally a Media Access Control (MAC) layer problem. This means that when solving a resource allocation problem in a network, the routing paths are usually assumed to be known. Conversely, the routing problem, which is a network layer issue, usually assumes that the available capacities on each link of the network (which depend on resource allocation) are known. Nevertheless, these two problems are mathematically entangled, and a cross-layer allocation strategy can best decoupled approaches in several ways, as we discuss in Chapter 4. Accordingly, our third and last contribution is to develop such a cross-layer allocation scheme for the scenario proposed in previous chapters.<p><p>All conclusions are summarised in Chapter 5, which also points to a few tracks for future research. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Les antennes microruban et en particulier l’antenne microruban rectangulaire sont étudiées et utilisées depuis plusieurs dizaines d’années.<p>Comme pour toute antenne, il est important de disposer pour ces antennes d’un modèle analytique qui permette une bonne compréhension du fonctionnement et fournisse de manière rapide des valeurs pour les principaux paramètres (fréquence de travail, impédance, gain, rendement et bande passante).<p>Au fil des ans, deux modèles, chacun comprenant de nombreuses variantes, ont été développés :le modèle dit « de la ligne de transmission » et le modèle dit « de la cavité ». Ces modèles sont soit peu rigoureux, soit complexes et donnent souvent des résultats assez éloignés de la réalité.<p>L’objectif de ce travail est double :définir un modèle qui soit d’une part aussi simple et direct que possible et d’autre part aussi précis que possible.<p>Le premier objectif est atteint dans la mesure où on n’utilise que la loi fondamentale du rayonnement des courants réels (électriques) en excluant tout recours à des courants virtuels (magnétiques).<p>Concernant l’objectif de précision, des comparaisons nombreuses avec des résultats d’un simulateur purement numérique et des mesures indiquent une amélioration pour tous les paramètres mais en particulier pour l’impédance qui est le point faible de tous les modèles existants.<p><p><p>Microstrip antennas and the rectangular microstrip antenna in particular have been studied and used for several decades.<p>As every antenna, the microstrip antenna requires a good analytical model that provides physical insight and an easy prediction of the antenna parameters (resonance frequency, impedance, gain, efficiency and bandwidth).<p>Over the years, two families of models have been developed, each involving many variants: the “transmission line” and the “cavity” models. These models either lack accuracy or are very complex and produce results that may be far away from reality. <p>The objective of this work is double: defining a model as simple and direct as possible and on the other hand as accurate as possible.<p>The first objective has been reached as all our calculations rest on the fundamental radiation formula by real (electrical) currents excluding any virtual (magnetic) currents.<p>Regarding accuracy, comparisons to numerical simulations and measurements show an improvement, in particular with regard to the prediction of the impedance parameters, which is the weak point of all existing models.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

High Impedance Faults (HIFs) are undetectable by conventional protection technology under certain<p>conditions. These faults occur when an energized conductor makes undesired contact with a<p>quasi-insulating object, such as a tree or a road. This contact restricts the level of the fault current to a very low value, from a few mA up to 75A. In solidly grounded distribution networks where the value of the residual current under normal conditions is considerable, overcurrent devices do not protect against HIFs. However, such a protection is essential for guaranteeing public security, because of the possibility of reaching the fallen conductor and the risk of fire. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Wind generation is one of the most successful sources of renewable energy for the production of electrical energy. Wind power offers relatively high capacities, with generation costs that are becoming competitive with conventional energy sources. However, a major problem to its effective use as a power source is the fact that it is both intermittent and diffuse as wind speed is highly variable and site-specific. This is translated in large voltage and frequency excursions and dynamically unstable situations when fast wind power changes. Very high wind speeds will result in sudden loss of wind generator production. The requirement to ensure that sufficient spinning reserve capacity exists within the system to compensate for sudden loss of generation becomes crucial. From the utilities operators’point of view, the primary objective is the security of the system, followed by the quality of the supplied power.<p>In order to guard the system security and quality of supply and retain acceptable levels, a maximum allowed wind power penetration (wind margin) is normally assumed by the operators. Very conservative methods are used to assess the impact of wind power and the consequences turn to under-exploitation of the wind power potential in a given region. This thesis presents the study of actual methods of wind power assessment, divided into three parts:<p>1. Part I: Impact on the Security of Power Systems<p>2. Part II: Impact on the Power Quality<p>3. Part III: Impact on the Dynamic Security of Power Systems / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

In satellite communications, non-linear interference is created by the non-linear power amplifier aboard the satellite. Even in the case of a memoryless power amplifier, the channel is a non-linear system with memory due to the presence of linear filters on ground and aboard the satellite. The non-linear interference degrades the system performance, especially when considering high-order modulations or in case of several signals being amplified by the same power amplifier. In this thesis, we have proposed algorithms at the transmitter and at the receiver to digitally compensate this interference. In particular, a new predistortion algorithm has been proposed, which significantly improves state-of-the-art algorithms. Since the complexity of this algorithm is an issue, low-complexity algorithms have also been proposed and achieve almost the same performance as the initial algorithm. We have also proposed joint predistortion and turbo-equalization algorithms to further improve the system performance. / En communications par satellite, de l’interférence non-linéaire est créée par l’amplificateur de puissance non-linéaire à bord du satellite. Même si l’amplificateur peut être considéré comme sans mémoire, le canal est malgré tout un système non-linéaire avec mémoire de par la présence de filtres linéaires au sol ou à bord du satellite. L'interférence non-linéaire dégrade les performances du système, en particulier lorsqu’on considère des modulations d’ordre élevé ou plusieurs signaux amplifiés par le même amplificateur de puissance. Dans cette thèse, nous avons proposé des algorithmes à l’émetteur et au récepteur pour compenser numériquement cette interférence. En particulier, nous avons proposé un nouvel algorithme de prédistorsion qui améliore de façon significative les algorithmes de l’état-de-l’art. La complexité de l’algorithme étant très élevée, nous avons proposé des algorithmes de plus faible complexité atteignant pratiquement les mêmes performances par rapport à l’algorithme initial. Nous avons aussi proposé des algorithmes de prédistorsion et d’égalisation conjointes, permettant d'atteindre des performances plus élevées qu'avec la prédistorsion seule. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

This work takes place in the context of distribution grids with high level of distributed generation, for example in microgrids. With high level of distributed generation, it has been shown that selective, fast and sensitive network protection is expected to be more difficult. Furthermore, during system restoration, the accurate fault location could be more challenging to assess, thereby increasing the average outage duration.<p>Thanks to cost reductions and improvement of information and communication technologies, future distribution networks will probably have advanced communication infrastructures and more measurement devices installed in order to manage the increasing complexity of those networks, which is primarily caused by the introduction of distributed generation at the distribution level.<p>Therefore this thesis investigates how the monitoring, protection and fault location functions can be improved by using system-wide measurements, i.e. real-time measurements such as synchronized voltage and current measurements recorded at different network locations. Distributed synchronized measurements bring new perspectives for these three functions: protection and fault location are usually performed with local measurements only and synchronized measurements are not common in monitoring applications. For instance, by measuring distributed generators infeed together with some feeder measurements, the protection is expected to be more sensitive and selective and the fault location to be more accurate.<p>The main contribution of this work is the use of state estimation, which is normally only used for network monitoring, for the protection and the fault location. <p>The distribution system state estimation is first developed using the classical transmission system approach. The impact of the placement of the measurement devices and of a relatively low measurement redundancy on the accuracy, on the bad data detection and on the topology error identification capabilities of the estimator are discussed and illustrated. This results in recommendations on the placement of the meters.<p>Then, a backup protection algorithm using system-wide measurements is presented. The coherence of the measurements and the healthy network model are checked thanks to a linear three-phase state estimation. If the model does not fit to the measurements and if the estimated load is too high or unbalanced, a fault is detected. The advantages of the method are that the voltage measurement redundancy is considered, improving the detection sensitivity, and that load models may be considered in the algorithm, avoiding the need to install measurement devices on every line of the network.<p>Finally, two new impedance-based fault location algorithms using distributed voltage and current recordings are proposed. By defining statistical errors on the measurements and the network parameters, a method to compute a confidence interval of the fault distance estimate is proposed. The fault location accuracy and its sensitivity to the fault conditions (e.g. fault resistance or fault type) and to the different sources of error are assessed on a simulated distribution system. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Détection précoce de crises<p>d’épilepsie à l’aide d’une<p>modélisation du comportement<p>oscillatoire neuronal / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

State estimation is an important tool for power system monitoring and the present study involves integrating phasor measurement units in the state estimation process. Based on measurements taken throughout the network, the role of a state estimator is to estimate the state variables of the power system while checking that these estimates are consistent with the measurement set. In the case of power system state estimation, the state variables are the voltage phasors at each network bus.\\<p><p>The classical state estimator currently used is based on SCADA (Supervisory Control and Data Acquisition) measurements. Weaknesses of the SCADA measurement system are the asynchronicity of the measurements, which introduce errors in the state estimation results during dynamic events on the electrical network.\\<p><p>Wide-area monitoring systems, consisting of a network of Phasor Measurement Units (PMU) provide synchronized phasor measurements, which give an accurate snapshot of the monitored part of the network at a given time. The objective of this thesis is to integrate PMU measurements in the state estimator. The proposed state estimators use PMU measurements exclusively, or both classical and PMU measurements.\\ <p><p>State estimation is particularly useful to filter out measurement noise, detect and eliminate bad data. A sensitivity analysis to measurement errors is carried out for a state estimator using only PMU measurements and a classical state estimator. Measurement errors considered are Gaussian noise, systematic errors and asynchronicity errors. Constraints such as zero injection buses are also integrated in the state estimator. Bad data detection and elimination can be done before the state estimation, as in pre-estimation methods, or after, as in post-estimation methods. For pre-estimation methods, consistency tests are used. Another proposed method is validation of classical measurements by PMU measurements. Post-estimation is applied to a measurement set which has asynchronicity errors. Detection of a systematic error on one measurement in the presence of Gaussian noise is also analysed. \\<p><p>The state estimation problem can only be solved if the measurements are well distributed over the network and make the network observable. Observability is crucial when trying to solve the state estimation problem. A PMU placement method based on metaheuristics is proposed and compared to an integer programming method. The PMU placement depends on the chosen objective. A given PMU placement can provide full observability or redundancy. The PMU configuration can also take into account the zero injection nodes which further reduce the number of PMUs needed to observe the network. Finally, a method is proposed to determine the order of the PMU placement to gradually extend the observable island. \\<p><p>State estimation errors can be caused by erroneous line parameter or bad calibration of the measurement transformers. The problem in both cases is to filter out the measurement noise when estimating the line parameters or calibration coefficients and state variables. The proposed method uses many measurement samples which are all integrated in an augmented state estimator which estimates the voltage phasors and the additional parameters or calibration coefficients. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Electromagnetic acceleration has the potential for various applications stemming from space electric propulsion systems to future air breathing hypersonic augmentation.<p>Electromagnetic acceleration uses electromagnetic body force produced by the interactions of currents carried in plasma which is either externally applied or self-induced magnetic fields to accelerate the whole body of gas. Historically, these plasmas sources have been arc jets, shock tube and microwaves. Never has an electromagnetic accelerator been powered by an inductively coupled plasma (ICP) source.<p>The von Karman Institute has experimentally investigated the acceleration of an electrically conductive fluid produce by a subsonic ICP source. This ICP source was powered with a 15 kW and 27.1 MHz radio frequency facility called the Minitorch. The electromagnetic acceleration was accomplished with the design, fabrication and testing of a linear Hall current magnetofluiddynamic accelerator (MFDA) channel. The channel was geometrically orientated into the Hall configuration to accounts for the large Hall Effect. This channel used a single pair of copper annulus electrodes powered by a 10 kW direct current power supply. The channel was water cooled and contained various diagnostics to provide greater insight to the electromagnetic acceleration process. This was the first successful magnetofluiddynamic acceleration of an ICP source and validates the proof of concept.<p>One-dimensional MFD modeling was formulated and used to determine the necessary performance requirements of the MFDA channel E and B field subsystems. An interaction parameter of approximately 2.25 was required for the doubling of an inlet velocity of 300 m/sec. The required subsystem need to provide a current density was 6 Amps/cm2 with a magnetic field strength of 0.50 Tesla over an acceleration length of 0.1 meters. Additional the most critical constraint was the thermal management subsystem which was designed to overcome large heat transfer fluxes to achieve a steady state condition over a test run of 10 minutes.<p>The dynamic pressure measured increase the inlet velocity 101% for an argon plasma flowing at 1.01 g/s at a magnetic field strength of 0.49 Tesla. his strong acceleration of the plasma was most notable near the region of the electrodes at the exit of the 0.1 m long channel. The central region of the plasma has less dynamic pressure increase corresponding to only a maximum of 15% increase in velocity at a magnetic strength of 0.49 Tesla. Experimental results showed that axial discharge voltages increased with increased magnetic fields, indicating a strong Hall Effect in the accelerator as expected.<p>Theoretical analysis was accomplished using the one-dimensional equation of motion and was compared to utilizing only the momentum equation. Experimental force fluxes were compared to the calculated values of the one-dimensional equation of motion and momentum equation. The reference area for the current density was selected from intensity measurement using a high speed camera with the MFDA channel on. There was significant error in the analysis concerning using the momentum Lorentz force only versus the one-dimensional equations of motion; which included joule heating. This analysis summarized the necessity to include joule heating in the formulation of the problem. / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Nous présentons notre contribution sur la régulation et l’optimisation de la production d’électricité.La première partie concerne l’optimisation de la gestion d’un micro réseau. Nous formulons le programme de gestion comme un problème de commande optimal en temps continu, puis nous résolvons ce problème par programmation dynamique à l’aide d’un solveur développé dans ce but : BocopHJB. Nous montrons que ce type de formulation peut s’étendre à une modélisation stochastique. Nous terminons cette partie par l’algorithme de poids adaptatifs, qui permet une gestion de la batterie du micro réseau intégrant le vieillissement de celle-ci. L’algorithme exploite la structure à deux échelles de temps du problème de commande.La seconde partie concerne des modèles de marchés en réseaux, et en particulier ceux de l’électricité. Nous introduisons un mécanisme d’incitation permettant de diminuer le pouvoir de marché des producteurs d’énergie, au profit du consommateur. Nous étudions quelques propriétés mathématiques des problèmes d’optimisation rencontrés par les agents du marché (producteurs et régulateur). Le dernier chapitre étudie l’existence et l’unicité des équilibres de Nash en stratégies pures d’une classe de jeux Bayésiens à laquelle certains modèles de marchés en réseaux se rattachent. Pour certains cas simples, un algorithme de calcul d’équilibre est proposé.Une annexe rassemble une documentation sur le solveur numérique BocopHJB. / We present our contribution on the optimization and regulation of electricity produc- tion.The first part deals with a microgrid Energy Management System (EMS). We formulate the EMS program as a continuous time optimal control problem and then solve this problem by dynamic programming using BocopHJB, a solver developed for this application. We show that an extension of this formulation to a stochastic setting is possible. The last section of this part introduces the adaptative weights dynamic programming algorithm, an algorithm for optimization problems with different time scales. We use the algorithm to integrate the battery aging in the EMS.The second part is dedicated to network markets, and in particular wholesale electricity markets. We introduce a mechanism to deal with the market power exercised by electricity producers, and thus increase the consumer welfare. Then we study some mathematical properties of the agents’ optimization problems (producers and system operator). In the last chapter, we present some pure Nash equilibrium existence and uniqueness results for a class of Bayesian games to which some networks markets belong. In addition we introduce an algorithm to compute the equilibrium for some specific cases.We provide some additional information on BocopHJB (the numerical solver developed and used in the first part of the thesis) in the appendix.