Dans le domaine du transport de l'électricité, les qualités intrinsèques des réseaux alternatifs s'estompent devant la difficulté imposée par le transport de la puissance réactive lorsque les lignes aériennes ou, plus particulièrement, les câbles souterrains ou sous-marins atteignent des longueurs critiques. Dans le cadre des réflexions visant à exploiter au mieux les énergies renouvelables d'origine éolienne off-shore ou hydrolienne, l'hypothèse de la création d'un réseau électrique à haute tension continue pour acheminer ces énergies jusqu'aux centres de consommation est considérée. Ce travail de thèse est en lien avec le projet européen TWENTIES (Transmission system operation with large penetration of Wind and other renewable Electricity sources in Networks by means of innovative Tools and Integrated Energy Solutions, ref 249812), financé dans le cadre du programme FP7 de la Commission Européenne. Ces travaux traitent de la protection des réseaux à courant continu contre les défauts d'isolement dans les câbles et au niveau des jeux de barre. L'étude se concentre sur des réseaux multi-terminaux bouclés et/ou maillés, et propose d'étudier la faisabilité d'un plan de protection comportant un algorithme principal et un secours en cas de défaillance d'un disjoncteur. / In the area of power transmission grids, the inherent qualities of alternative current networks fade behind the difficulty imposed by the transmission of the reactive power when overhead lines or, particularly, underground or undersea cables reach critical lengths. As part of thought aimed for operate at best renewable energy resources, namely wind or marine resources, the assumption of the creation of a high voltage direct current power grid to dispatch those energies to the consumption centers is considered. This Ph.D work is linked to the European project TWENTIES (Transmission system operation with large penetration of Wind and other renewable Electricity sources in Networks by means of innovative Tools and Integrated Energy Solutions, ref 249812), funded as a part of the 7th framework program of the European Commission. This work deal with the protection of DC grids against insulation faults occurring in the cables or at a busbar. The study focusses on meshed and/or looped multi-terminal grids, and proposes to study the feasibility of a protection plan including a main protection algorithm and a backup in case of breaker failure.

La portée des communications quantiques est limitée à quelques dizaines de km en raison de l’atténuation dans les fibres. Les répéteurs quantiques (relais quantiques synchronisés par des mémoires quantiques photoniques) furent introduits afin d’accroître ces distances. Or, pour le moment, les mémoires les plus performantes fonctionnent à des longueurs d’onde n’appartenant pas à la bande C télécom. Afin de profiter de ces mémoires, l’utilisation d’interfaces quantiques (milieu non linéaire quadratique) fut proposée comme alternative. En ajoutant ainsi par somme de fréquences un photon de pompe de longueur d’onde appropriée au photon télécom portant l’information, on transfère l’information à une longueur d’onde compatible avec les mémoires, et ceci sans dégradation de l’information portée initialement par le photon télécom. Notre but est ainsi de construire un oscillateur paramétrique optique continu simplement résonant (SRO) qui fournira un faisceau à 1648 nm qui sera sommé en fréquence aux photons télécom à 1536 nm pour transférer l’information vers un photon stockable dans une mémoire à base d’atomes alcalins. Pour transférer efficacement l’information, le SRO doit satisfaire quelques critères : une haute finesse spectrale (largeur de raie ~kHz), une forte puissance (~1W) et une longueur d’onde plus grande que celle du photon télécom à convertir. Pour ce faire, nous utilisons le faisceau non-résonant d’un SRO continu. Le premier travail réalisé dans cette thèse a été de faire la démonstration de la possibilité d’avoir un faisceau à la fois intense et pur spectralement en sortie d’un SRO continu. En réutilisant un SRO déjà développé durant nos travaux antérieurs, nous avons pu stabiliser au niveau du kHz la fréquence du faisceau non résonant à 947 nm (onde signal) de ce SRO, tout en émettant une puissance de plus d’un watt. Ensuite, nous avons conçu le SRO dont le faisceau non résonant à 1648 nm (onde complémentaire) a été stabilisé à court terme en-dessous du kHz avec une puissance de l’ordre du watt. Nous avons ensuite étudié la stabilité à long terme de la longueur d’onde du complémentaire à 1648 nm. Nous avons mesuré des dérives de fréquences de l’ordre de 10 MHz/mn. Ces dérives, venant essentiellement de la cavité de référence sur laquelle le SRO est asservi, peuvent être réduites en contrôlant activement la cavité d’une part, et en utilisant des techniques de stabilisation en fréquence robustes, d’autre part. / Long distance quantum communications are limited to few tens of km due to the attenuation of light in telecom fibres. Quantum repeaters (quantum relays synchronized by photonic quantum memories) were introduced in order to increase distances. Or, currently, the most efficient memories do not operate at wavelengths in the telecom C band. In order to take advantage of these memories, the use of quantum interfaces (second order nonlinear medium) was proposed as an alternative. Thus, by adding by sum frequency generation a pump photon at an appropriate wavelength to the telecom photon carrying the information, one transfers the information to a wavelength compatible with these memories, and this with a preservation of the information initially carried by the telecom photon. Our aim is thus to build a continuous-wave singly resonant optical parametric oscillator (cw SRO) which will provide a wave at 1648 nm that will be frequency summed to telecom photons at 1536 nm to transfer the information to a photon storable into alkali atoms based memory. To efficiently transfer the information, the cw SRO has to fulfill some requirements: a high spectral purity (linewidth ~kHz), a high output power (~1 W) and a wavelength longer than that of the telecom photon to be converted. To this aim, we use the non-resonant wave of a cw SRO. The first work done during this thesis was to experimentally prove the possibility to have both high output power and high spectral purity from a cw SRO. By reusing a cw SRO already built during our previous works, we were able to stabilize at the kHz level the frequency of the non-resonant wave at 947 nm (signal wave) of this SRO, with an output power of more than one watt. Then, we built the cw SRO of which non-resonant wave at 1648 nm (idler wave) has been frequency stabilized below the kHz level along with an output power of the order of one watt. We next studied the long term stability of the idler wavelength at 1648 nm. We have measured frequency drifts of the order of 10 MHz/mn. These drifts originating mainly from the reference cavity to which the SRO is locked, can be reduced by, firstly, an active control of the cavity and by, secondly, the use of robust frequency stabilization techniques.

Discrete silicon carbide (SiC) power devices have unique characteristics that outpace those of silicon (Si) counterparts. The improved physical features have provided better faster switching, greater current densities, lower on-resistance, and temperature performances. However, there is lack of suitable commercial gate drivers that are compatible for high-voltage, and high-speed devices. There has been a great research effort required for the advancement of gate drivers for high voltage SiC transistors. A drive circuit for a SiC MOSFET needs to be optimized in normal operation to give best efficiency and same drive circuit should secure the MOSFET under unsuitable conditions. To ensure the rapid switching of these advanced SiC MOSFETs, a gate driver capable of providing the high current capability is required. In this work, three different high-power-density, high-speed, and high-noise-immunity gate driver modules for 10 kV SiC MOSFET were built and optimized.  Double-pulse test was developed for the dynamic characterization of SiC MOSFETs and gate drivers. This setup provided clean measurements of DUT voltage and current under well-defined conditions and correlated to simulation results. Designed gate drivers have thoroughly investigated to test and compare it with our future design. The influential parameters such as dV/dt, dI/dt, and gate driving capability of gate driver were adjusted according to the requirements. The short circuit protection test was performed to check the reliability of driver modules in worst conditions. Furthermore, a DC-DC converter was designed and tested with the advanced gate drivers. The driver modules were tested in designed converter under different load conditions and influential parameters were successfully demonstrated. The driver modules effectively helped in reducing the EMI and switching losses. These designed gate drivers and prototype converter provide all the attractive features and can be widely implemented in industrial applications for energy efficient systems.

This thesis focuses on optimization and increasing the efficiency of high-power DC/DC switching converters with transformer (switching power supplies). The work focuses mainly on using converters with flyback topology for high power, even though it is a common belief that this type of converter is not suitable for high power. This topology was selected because of potentially better achievable parameters, especially the efficiency, in comparison to a commonly used forward converter – in a flyback converter, losses are produced only in one magnetic component (transformer) in contrast to two components (transformer and inductor) in the forward converter. Compared to resonant and quasi-resonant converters, the flyback converter is easily controllable in the whole output voltage and current range. To make the flyback converter favorable for a high-power use, some innovative circuit modifications were made and modern semiconductor and passive components were used. Theoretical part of the work deals with efficiency optimization of the flyback converter, based on analytical solution. Operating parameters of the converter – switching frequency and parameters of the transformer (flux density and numbers of turns) are commonly only guessed or chosen from experience. The objective of this part is a mathematically exact determination of these parameters to achieve lowest total losses of the converter for given input parameters. In a certain case, it was possible to obtain the final solution analytically, in other cases the final solution step had to be done with a help of software. A prototype of a 12-kW switching power supply with a flyback converter was constructed to validate the proposed solutions and methods. The power supply fits into a space of only 33x33x16 cm. Modern semiconductors based on the silicon-carbide (SiC) technology (MOS-FET transistors and diodes) were used. After bringing the converter to a full-power operation, an efficiency of 96.8 % of the DC/DC converter was measured. High efficiency was obtained for a wide range of output parameters. A certain comparison with a forward converter with the same output parameters is done in the work. Not only from an efficiency point of view, the flyback converter seems very perspective.

The aim of my master’s thesis is the design of the LED lighting system for breeding and growing purposes as replacement for the classical high-pressure sodium lamps and other sources of light used today. The whole system can be controlled locally by buttons or remotely by web server using Ethernet interface. LEDs are powered by five-channel step-down converter with current feedback. Converters are controlled by pulse width modulation generated by microcontroller.

<p>Nonlinear transmission lines (NLTLs) are of great interest for high power microwave (HPM) generation because they can sharpen pulses to create an electromagnetic shockwave to produce oscillations from 100 MHz to low GHz. NLTLs provide frequency agility, compactness, durability and reliability, providing a solid-state radiofrequency (RF) source for producing HPM. The essential component of NLTLs is the nonlinear material, typically a dielectric that varies with voltage or a magnetic material whose permeability varies with current, incorporated in the transmission line in various topologies. This thesis presents an alternative approach involving designing composites comprised of nonlinear dielectric inclusions (barium strontium titanate (BST)) and/or nonlinear inductive inclusions (nickel zinc ferrites (NZF)) in a polymer base host material, analogous to electromagnetic interference designs that incorporate stainless steel inclusions of various shapes in a plastic to tune the composite’s electromagnetic properties at GHz. Appropriately designing NLTL composites requires predicting these effective properties both in linear (for a fixed and low voltage and current) and nonlinear regions (permittivity and permeability become voltage dependent and current dependent, respectively) prior to designing HPM systems comprised of them. As a first step, this thesis evaluates and benchmarks composites models in the commercial software CST Microwave Studios (CST MWS) to various effective medium theories (EMTs) to predict the permittivity and permeability of composites of BST and/or NZF inclusions in the linear regime, compared with experimental measurements. The manufacturing and measurement of the nonlinear composites will be briefly discussed with an analysis of the homogeneity of a composite sample using 3D X-ray scan. Long-term application of these approaches to predicting the effective nonlinear composite permittivity and permeability and future work will be discussed.</p>

L’amplification par dérive de fréquence démontrer en 1985 a permis la création d’installations laser en impulsions courtes tels que Petal (Petawatt Aquitaine Laser). La montée en puissance de ces lasers est limitée par la résistance au flux laser des composants placés après la compression. L’objectif de cette thèse est d’améliorer la résistance au flux laser de ces composants qui sont des miroirs qui consiste en un empilement multicouches. Trois approches sont envisagées le changement de designs des empilements couches minces (nombre de couche, épaisseurs), de matériaux et/ou de procédés de fabrication. Une étude numérique a permis d’envisager théoriquement le changement de matériaux et/ou de design et de quantifier les améliorations possibles. Cette étude a mené au développement d’un algorithme d’optimisation des designs qui nécessite la caractérisation préalable des matériaux. Par conséquent, une variété de matériaux déposés en monocouches a été testée au flux laser et caractérisé optiquement pour évaluer l’adéquation matériaux et technique de dépôt. Les résultats obtenus montrent une forte dispersion qui ne peut être expliqué par des lois préalablement établi dans la littérature. Cependant, une bonne corrélation entre le seuil de tenue au flux laser intrinsèque dans l’infrarouge et l’absorption dans l’ultraviolet a été observé ce qui confirme l’influence de l’absorption multi-photonique sur l’endommagement laser en impulsions courtes. Pour finir, l’ensemble de ces résultats expérimentaux et de l’algorithme d’optimisation ont permis la fabrication d’échantillons de miroirs qui montrent une amélioration du seuil de tenue au flux laser de 73% par rapport à des miroirs quart d’onde classiques. / The chirped pulse amplification demonstrated in 1985 allowed the development of petawatt class laser such as Petal (Petawatt Aquitaine Laser). The increase of power of those facilities is limited by the resistance to laser-induced damage of the optical components placed after the compression stage. The aim of this thesis is to improve the laser-induced damage threshold of those components which are multilayer dielectric mirrors. Three paths of improvement are considered the change of design (number of layer, thicknesses), of materials and/or deposition process. A numerical study allows evaluating the potential improvement brought by two of those paths. This led to the development of a design optimization algorithm that required the prior characterization materials. Consequently, various materials deposited as single layers were laser damage tested and optically characterized to evaluate the adequacy of the materials with the deposition process. The results show a wide discrepancy that cannot be explained by the laws exposed in the literature. However, a good correlation was found between the intrinsic laser-induced damage thresholds in the infrared with the absorption in the ultraviolet confirming the influence of the multiphoton absorption in the laser-induced damage mechanisms. Finally, those experimental results combined with the optimization algorithm allowed the development of mirror samples that exhibit laser-induced damage threshold 73% higher than one of classical mirrors.

The Swedish transport sector will need to undergo a major restructuring to achieve the established climate and environmental goals. The biggest change is that fossil fuels will be phased out and a larger part of the vehicle fleet will be electrified. This study deals with the electrification of heavy-duty trucks and how high-power charging stations affect the local electricity grid. Charging of heavy-duty trucks depends largely on the logistics of the transport system, which reduces the demand flexibility of power. High-power charging entails a risk of increased power peaks, which can affect the bus-voltage profiles, losses and loads on grid components. This thesis has been conducted as general study based on the case with the high-power charging station at Vädermotet in the area Hisingen of Gothenburg. The purpose was to build a generic model of the electricity grid at Hisingen and then investigate the consequences of high-power charging for the grid for two charging scenarios: the first scenario with four ABB Terra 360 chargers, and the second scenario with six ABB Terra 360 chargers and one MCS. The electricity network model and simulations were performed in PSS®SINCAL. The two charging scenarios, as well as the scenario before chargers were installed, were then simulated for three different system-load cases: maximum, average, and low load. The results showed that high-power charging of trucks had the biggest impacts for the voltage profiles during the case of low load. For the medium load and maximum load cases, the effect of the high-power charge decreased. Furthermore, electricity network losses increased for the low load case, but decreased slightly for the average and maximum load case. The reason was a more even load balance between the bus that connected the charging station to the grid and the rest of the network for the average and maximum load cases. In summary, the study indicated that grid implementation of a high-power charging station will have consequences for the local power system. However, the magnitude of the effects is not validated and can therefore only be regarded as indications. The outcome can be partly explained by the assumptions and simplifications of the model compared to the real system.

<p>Nonlinear transmission lines (NLTLs) provide a solid state alternative to conventional vacuum based high power microwave (HPM) sources. The three most common NLTL implementations are the lumped element, split ring resonator (SRR), and the nonlinear bulk material based NLTLs. The nonlinear bulk material implementation provides the highest power output of the three configurations, though they are limited to pulse voltages less than 50 kV; higher voltages are possible when an additional insulator is used, typically SF₆ or dielectric oil, between the nonlinear material and the outer conductor. The additional insulator poses a risk of leaking if structural integrity of the outer conductor is compromised. The desire to provide a fieldable NLTL based HPM system makes the possibility of a leak problematic. The work reported here develops a composite based NLTL system that can withstand voltages higher than 50 kV and not pose a risk of catastrophic failure due to a leak while also decreasing the size and weight of the device and increasing the output power.</p> <p>Composites with barium strontium titanate (BST) or nickel zinc ferrite (NZF) spherical inclusions mixed in a silicone matrix were manufactured at volume fractions ranging from 5% to 25%. The dielectric and magnetic parameters were measured from 1-4 GHz using a coaxial airline. The relative permittivity increased from 2.74±0.01 for the polydimethylsiloxane (PDMS) host material to 7.45±0.33 after combining PDMS with a 25% volume fraction of BST inclusions. The relative permittivity of BST and NZF composites was relatively constant across all measured frequencies. The relative permeability of the composites increased from 1.001±0.001 for PDMS to 1.43±0.04 for a 25% NZF composite at 1 GHz. The relative permeability of the 25% NZF composite decreased from 1.43±0.05 at 1 GHz to 1.17±0.01 at 4 GHz. The NZF samples also exhibited low dielectric and magnetic loss tangents from 0.005±0.01 to 0.091±0.015 and 0.037±0.001 to 0.20±0.038, respectively, for all volume fractions, although the dielectric loss tangent did increase with volume fraction. For BST composites, all volume fraction changes of at least 5% yielded statistically significant changes in permittivity; no changes in BST volume fraction yielded statistically significant changes in permeability. For NZF composites, the change in permittivity was statistically significant when the volume fraction varied by more than 5% and the change in permeability was statistically significant for variations in volume fraction greater than 10%. The DC electrical breakdown strength of NZF composites decreased exponentially with increasing volume fraction of NZF, while BST composites exhibited no statistically significant variation with volume fraction. </p> <p>For composites containing both BST and NZF, increasing the volume fraction of either inclusion increased the permittivity with a stronger dependence on BST volume fraction. Increasing NZF volume fraction increased the magnetic permeability, while changing BST volume fraction had no effect on the composite permeability. The DC dielectric breakdown voltage decreased exponentially with increased NZF volume fraction. Adding as little as 5% BST to an NZF composite more than doubled the breakdown threshold compared to a composite containing NZF alone. For example, adding 10% BST to a 15% NZF composite increased the breakdown strength by over 800%. The combination of tunability of permittivity and permeability by managing BST and NZF volume fractions with the increased dielectric breakdown strength by introducing BST make this a promising approach for designing high power nonlinear transmission lines with input pulses of hundreds of kilovolts.</p> <p>Coaxial nonlinear transmission lines are produced using composites with NZF inclusions and BST inclusions and driven by a Blumlein pulse generator with a 10 ns pulse duration and 1.5 ns risetime. Applying a 30 kV pulse using the Blumlein pulse generator resulted in frequencies ranging from 1.1 to 1.3 GHz with an output power over 20 kW from the nonlinear transmission line. The output frequencies increased with increasing volume fraction of BST, but the high power oscillations characteristic of an NLTL did not occur. Simulations using LT Spice demonstrated that an NLTL driven with a Blumlein modulator did not induce high power oscillations while driving the same NLTL with a pulse forming network did. </p> <p>Finally, a composite-based NLTL could be driven directly by a high voltage power supply without a power modulator to produce oscillations both during and after the formed pulse upon reaching a critical threshold. The output frequency of the NLTLs is 1 GHz after the pulse and ranged from 950 MHz to 2.2 GHz during the pulse. These results demonstrate that the NLTL may be used as both a pulse forming line and high power microwave source, providing a novel way to reduce device size and weight, while the use of composites could provide additional flexibility in pulse output tuning. </p>

The trend of electrification in transportation applications has led to the fast development of high-power-density power electronics converters. High-switching-frequency and high-temperature operations are the two key factors towards this target. Both requirements, however, are challenging the fundamental limit of silicon (Si) based devices. The emerging wide-bandgap, silicon carbide (SiC) power devices have become the promising solution to meet these requirements. With these advanced devices, the technology barrier has now moved to the compatible integration technology that can make the best of device capabilities in high-power-density converters. Many challenges are present, and some of the most important issues are explored in this dissertation. First of all, the high-temperature performances of the commercial SiC MOSFET are evaluated extensively up to 200 degree C. The static and switching characterizations show that the device has superior electrical performances under elevated temperatures. Meanwhile, the gate oxide stability of the device - a known issue to SiC MOSFETs in general - is also evaluated through both high-temperature gate biasing and gate switching tests. Device degradations are observed from these tests, and a design trade-off between the performance and reliability of the SiC MOSFET is concluded. To understand the interactions between devices and circuit parasitics, an experimental parametric study is performed to investigate the influences of stray inductances on the MOSFETs switching waveforms. A small-signal model is then developed to explain the parasitic ringing in the frequency domain. From this angle, the ringing mechanism can be understood more easily and deeply. With the use of this model, the effects of DC decoupling capacitors in suppressing the ringing can be further explained in a more straightforward way than the traditional time-domain analysis. A rule of thumb regarding the capacitance selection is also derived. A Power Electronics Building Block (PEBB) module is then developed with discrete SiC MOSFETs. Integrating the power stage together with the peripheral functions such as gate drive and protection, the PEBB concept allows the converter to be built quickly and reliably by simply connecting several PEBB modules. The high-speed gate drive and power stage layout designs are presented to enable fast and safe switching of the SiC MOSFET. Based on the PEBB platform, the state-of-the-art Si and SiC power MOSFETs are also compared in the device characteristics, temperature influences, and loss distributions in a high-frequency converter, so that special design considerations can be concluded for the SiC MOSFET. Towards high-temperature, high-frequency and high-power operations, integrated wire-bond phase-leg modules are also developed with SiC MOSFET bare dice. High-temperature packaging materials are carefully selected based on an extensive literature survey. The design considerations of improved substrate layout, laminated bus bars, and embedded decoupling capacitors are all discussed in detail, and are verified through a modeling and simulation approach in the design stage. The 200 degree C, 100 kHz continuous operation is demonstrated on the fabricated module. Through the comparison with a commercial SiC phase-leg module designed in the traditional way, it is also shown that the design considerations proposed in this work allow the SiC devices in the wire-bond structure to be switched twice as fast with only one-third of the parasitic ringing. To further push the performance of SiC power modules, a novel hybrid packaging technology is developed which combines the small parasitics and footprint of a planar module with the easy fabrication of a wire-bond module. The original concept is demonstrated on a high-temperature rectifier module with SiC JFET. A modified structure is then proposed to further improve design flexibility and simplify module fabrication. The SiC MOSFET phase-leg module built in this structure successfully reaches the switching speed limit of the device almost without any parasitic ringing. Finally, a new switching loop snubber circuit is proposed to damp the parasitic ringing through magnetic coupling without affecting either conduction or switching losses of the device. The concept is analyzed theoretically and verified experimentally. The initial integration of such a circuit into the power module is presented, and possible improvements are proposed. / Ph. D.