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Palomera-Arias, Rogelio 1972. "PIN diode switch circuit for short time high current pulse signal." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/47505.
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Lanz, B. (Brigitte). "Compact current pulse-pumped GaAs–AlGaAs laser diode structures for generating high peak-power (1–50 watt) picosecond-range single optical pulses." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526213569.
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Abstract Although gain-switching is a simple, well-established technique for obtaining ultrashort optical pulses generated with laser diodes, the optical energy in a pulse achievable from commercial structures using this technique is no more than moderate and the ‘spiking’ behaviour seen at turn-on is likely to evolve into trailing oscillations. This thesis investigates, develops and improves laser diodes in order to offer experimentally verified solutions for maximizing the optical energy so as to achieve a peak power of several watts in a single optical pulse of picosecond-range duration in the gain-switching operation regime, and for suppressing the energy located in any trailing pulses to a negligible level relative to the total optical pulse energy. This was addressed by means of either (i) an ultrashort pump current pulse with an amplitude range ~(1–10) A or (ii) custom laser diode structures, both options being capable of operating uncooled at room temperature (23±3°C). For the first solution a unique superfast gallium arsenide (GaAs) avalanche transistor was utilized as a switch in order to achieve an injection current pulse with a duration of < 1 ns, which is short enough to generate only a first optical ‘spike’ when pumping a commercial laser diode. The most promising structure with regard to the second solution was an edge-emitting semiconductor laser having a strongly asymmetric broadened double heterostructure with a relatively thick active layer. Laser pulses with full width at half maximum (FWHM) of ~100 ps and an optical energy of >3 nJ but with some trailing oscillations were achieved in experiments employing injection current pulses in the nanosecond range with an amplitude of ≤17 A, generated using inexpensive silicon (Si) electronics. The performance was improved by introducing a saturable absorber (SA) into the laser cavity, which suppressed the formation of trailing oscillations, resulting in a single optical pulse<br>Tiivistelmä ”Gain switching” (vahvistuskytkentä) on tunnettu tekniikka lyhyiden (<100 ps) optisten pulssien generoimiseen laserdiodeilla. Kaupallisia laserdiodirakenteita käyttäen optinen energia rajoittuu kuitenkin 10…100 pJ:n tasolle. Tällöinkin, erityisesti suurilla energiatasoilla, optisessa pulssissa ilmenee voimakkaita jälkioskillaatioita. Tässä väitöskirjassa tutkittiin ja kehitettiin kokeellisesti varmennettuja laserdiodilähetinrakenteita tavoitteena saavuttaa >1 nJ:n optisen pulssin energia ja ~100 ps:n pulssinpituus gain-switching -toimintamoodissa. Tavoitteena oli myös minimoida jälkipulssien energia. Tutkimuksen pääsisältönä on kaksi toimintaperiaatetta: Toisessa tekniikassa päähuomio kohdistuu laseridiodin virta-ajuriin, johon kehitettiin elektroniikka, joka kykenee tuottamaan nopeita virtapulsseja laajalla pulssivirta-alueella. Virtapulssin nopeuden kasvattamisen (<1 ns) osoitettiin edistävän gain switching -ilmiötä. Toisena tekniikkana tutkittiin räätälöityä laserdiodirakennetta, joka sisäisen toimintansa perusteella tuottaa dynaamisessa ohjaustilanteessa tehokkaan ja nopean laserpulssin. Kummankin periaatteen osoitettiin toimivan huonelämpötilassa (23±3°C) ilman erillistä jäähdytystä. Ensimmäisessä ratkaisussa käytettiin nopeaa gallium-arsenidi (GaAs) -avalanchetransistoria virtakytkimenä, jolla saavutettiin <1 ns FWHM injektiovirtapulssi 10 A:n virtatasolla. Tällainen virtapulssi on riittävän lyhyt virittämään ”gain switching” -ilmiön nJ-energiatasolla. Lupaavin rakenne toiseksi ratkaisuksi oli reunaemittoiva puolijohdelaseri, jossa epäsymmetrinen aaltoputki ja aktiivinen alue ovat sijoitettu normaalista laserdiodirakenteesta poiketen rinnakkain. Tällä rakenteella voitiin tuottaa ~100 ps levyisiä (FWHM) ja >3 nJ optisen kokonaisenergian omavia laserpulsseja edullisella pii-pohjaisella (Si) elektroniikalla luoduilla 1.5–2 ns:n (FWHM) ≤17 A injektiovirtapulsseilla. Suorituskykyä saatiin edelleen parannettua istuttamalla saturoiva absorbaattori (SA) laserin optiseen onteloon. Tämän osoitettiin vähentävän jälkioskillaatioiden muodostumista
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Bendixsen, Luis Sebastian Caballero. "The design and construction of a compact, high-current pulsed power generator based on multiple low impedance pulse forming lines and networks." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526548.
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Bloomfield, Aaron Paul. "A High Frequency Alternating Current Battery Heater for Military Vehicles." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1302312903.
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Gamir, Luis Palafox. "A new method for the determination of the entry position of #gamma#-rays in high purity germanium detectors by current pulse analysis." Thesis, Cranfield University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387640.
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Palafox, Gamir Luis. "A new method for the determination of the entry position of γ-rays [gamma rays] in high purity germanium detectors by current pulse analysis". Thesis, Cranfield University, 1997. http://dspace.lib.cranfield.ac.uk/handle/1826/850.
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A new method for determining the entry point of gamma-rays in closed ended HPGe detectors has been developed. Exploiting the position dependence shown by the current pulses generated when a gamma-ray interacts with the detector, it is possible to electronically divide the crystal in the radial coordinate and thus increase the effective granularity of the detector. Position resolution is particularly important for correcting the Doppler peak broadening observed in many in-beam gamma-spectroscopy experiments. Position resolution within coaxial crystals is accomplished by combining the angular information gained by segmenting the outer contact with the determination of the event radius by current pulse shape analysis. With increasing gamma-energy, more than one interaction is in general required to completely stop a gamma-ray in a germanium detector. The concept of a main interaction, defined as that depositing the largest fraction of the original gamma-energy, is introduced and seen to be the dominant contribution to the event current pulses. A Monte Carlo simulation for the positions and energies of the interactions in an event has been performed in order to establish the physical limits for the position resolution that can be measured in a segmented CLUSTER module. A varying fraction of events, from 55% at a gamma-energy of 400 keV to 85% at 1800 keV, have their main interaction within 5 mm from the entry point. The position of the main interaction can therefore be successfully used to measure the entry position of the gamma-ray in the detector. In order to provide high quality charge/energy and current outputs from the detector signal, a new preamplifier for large volume HPGe detectors has been developed. The intrinsic equivalent noise contribution from the preamplifier was measured at 0.65 keV + 35 eV /pF. The measured energy resolution when the input FET is operated at cryogenic temperature is 2.30 keV at 1333 keV with 3 μs shaping time. Using this preamplifier and the first prototype of a two-fold segmented CLUSTER module, a radial resolution of ±4mm has been measured with the new method both at 662 and 1333 keV. The method can be incorporated into an analogue electronic circuit and is therefore directly applicable in in-beam gamma-spectroscopy experiments.
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Palafox, Gamir Luis. "A new method for the determination of the entry position of y-rays [gamma rays] in high purity germanium detectors by current pulse analysis." Thesis, Cranfield University, 1997. http://hdl.handle.net/1826/850.
Full textAbstract:
A new method for determining the entry point of gamma-rays in closed ended HPGe
detectors has been developed. Exploiting the position dependence shown by the
current pulses generated when a gamma-ray interacts with the detector, it is possible
to electronically divide the crystal in the radial coordinate and thus increase the
effective granularity of the detector.
Position resolution is particularly important for correcting the Doppler peak
broadening observed in many in-beam gamma-spectroscopy experiments. Position resolution
within coaxial crystals is accomplished by combining the angular information
gained by segmenting the outer contact with the determination of the event
radius by current pulse shape analysis.
With increasing gamma-energy, more than one interaction is in general required
to completely stop a gamma-ray in a germanium detector. The concept of a main
interaction, defined as that depositing the largest fraction of the original gamma-energy,
is introduced and seen to be the dominant contribution to the event current pulses.
A Monte Carlo simulation for the positions and energies of the interactions in an
event has been performed in order to establish the physical limits for the position
resolution that can be measured in a segmented CLUSTER module. A varying
fraction of events, from 55% at a gamma-energy of 400 keV to 85% at 1800 keV, have
their main interaction within 5 mm from the entry point. The position of the
main interaction can therefore be successfully used to measure the entry position
of the gamma-ray in the detector.
In order to provide high quality charge/energy and current outputs from the
detector signal, a new preamplifier for large volume HPGe detectors has been
developed. The intrinsic equivalent noise contribution from the preamplifier was
measured at 0.65 keV + 35 eV /pF. The measured energy resolution when the
input FET is operated at cryogenic temperature is 2.30 keV at 1333 keV with
3 μs shaping time.
Using this preamplifier and the first prototype of a two-fold segmented
CLUSTER module, a radial resolution of ±4mm has been measured with the
new method both at 662 and 1333 keV. The method can be incorporated into
an analogue electronic circuit and is therefore directly applicable in in-beam gamma-
spectroscopy experiments.
8
Hinde, David Derek. "Corona discharges on the surfaces of high voltage composite insulators." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/29320/2/David_Hinde_Thesis.pdf.
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The degradation of high voltage electrical insulation is a prime factor that can significantly influence the reliability performance and the costs of maintaining high voltage electricity networks. Little information is known about the system of localized degradation from corona discharges on the relatively new silicone rubber sheathed composite insulators that are now being widely used in high voltage applications.
This current work focuses on the fundamental principles of electrical corona discharge phenomena to provide further insights to where damaging surface discharges may localize and examines how these discharges may degrade the silicone rubber material. Although water drop corona has been identified by many authors as a major cause of deterioration of silicone rubber high voltage insulation until now no thorough studies have been made of this phenomenon.
Results from systematic measurements taken using modern digital instrumentation to simultaneously record the discharge current pulses and visible images associated with corona discharges from between metal electrodes, metal electrodes and water drops, and between waters drops on the surface of silicone rubber insulation, using a range of 50 Hz voltages are inter compared. Visual images of wet electrodes show how water drops can play a part in encouraging flashover, and the first reproducible visual images of water drop corona at the triple junction of water air and silicone rubber insulation are presented.
A study of the atomic emission spectra of the corona produced by the discharge from its onset up to and including spark-over, using a high resolution digital spectrometer with a fiber optic probe, provides further understanding of the roles of the active species of atoms and molecules produced by the discharge that may be responsible for not only for chemical changes of insulator surfaces, but may also contribute to the degradation of the metal fittings that support the high voltage insulators.
Examples of real insulators and further work specific to the electrical power industry are discussed. A new design concept to prevent/reduce the damaging effects of water drop corona is also presented.
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Hinde, David Derek. "Corona discharges on the surfaces of high voltage composite insulators." Queensland University of Technology, 2009. http://eprints.qut.edu.au/29320/.
Full textAbstract:
The degradation of high voltage electrical insulation is a prime factor that can significantly influence the reliability performance and the costs of maintaining high voltage electricity networks. Little information is known about the system of localized degradation from corona discharges on the relatively new silicone rubber sheathed composite insulators that are now being widely used in high voltage applications.
This current work focuses on the fundamental principles of electrical corona discharge phenomena to provide further insights to where damaging surface discharges may localize and examines how these discharges may degrade the silicone rubber material. Although water drop corona has been identified by many authors as a major cause of deterioration of silicone rubber high voltage insulation until now no thorough studies have been made of this phenomenon.
Results from systematic measurements taken using modern digital instrumentation to simultaneously record the discharge current pulses and visible images associated with corona discharges from between metal electrodes, metal electrodes and water drops, and between waters drops on the surface of silicone rubber insulation, using a range of 50 Hz voltages are inter compared. Visual images of wet electrodes show how water drops can play a part in encouraging flashover, and the first reproducible visual images of water drop corona at the triple junction of water air and silicone rubber insulation are presented.
A study of the atomic emission spectra of the corona produced by the discharge from its onset up to and including spark-over, using a high resolution digital spectrometer with a fiber optic probe, provides further understanding of the roles of the active species of atoms and molecules produced by the discharge that may be responsible for not only for chemical changes of insulator surfaces, but may also contribute to the degradation of the metal fittings that support the high voltage insulators.
Examples of real insulators and further work specific to the electrical power industry are discussed. A new design concept to prevent/reduce the damaging effects of water drop corona is also presented.
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Shahriari, Ejlal. "Commutateurs à semi-conducteurs rapides et à courant élevé pour les applications de puissance pulsée." Electronic Thesis or Diss., Pau, 2024. https://theses.hal.science/tel-04818494.
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Des impulsions de courant d'amplitude élevée (plusieurs centaines de kA) dans la gamme des microsecondes peuvent être appliquées pour générer des champs magnétiques de l'ordre du mégagauss. Cette technologie relative au domaine des haute puissances pulsées a été utilisée pour des travaux de recherche sur la fusion par confinement inertiel, le X-pinch ou la physique des hautes densités d'énergie. De plus, un certain nombre d'applications industrielles telles que le soudage par impulsion magnétique et la fracturation des roches nécessitent une puissance moyenne élevée, une répétabilité et un générateur d'impulsions de forts courants fiable avec une longue durée de vie. Par conséquent, le développement d'un interrupteur à semi-conducteurs rapide fonctionnant dans la gamme de plusieurs centaines de kA est d'une importance considérable.Un interrupteur rapide à courant élevé est l'un des composants les plus complexes d'un générateur de hautes puissances pulsées. Historiquement, seuls les interrupteurs remplis de gaz pouvaient fonctionner dans de telles conditions extrêmes. Cependant, les interrupteurs remplis de gaz présentent plusieurs inconvénients bien connus, notamment une faible fréquence de répétition des impulsions, une durée de vie courte et une instabilité lors du déclenchement. Ils sont également coûteux à utiliser, nécessitant souvent des systèmes de flux de gaz et des chambres de recirculation de gaz pour une opération répétitive. Ces inconvénients ont freiné l'adoption généralisée des technologies de hautes puissances pulsées.Les récents progrès en physique et technologie des semi-conducteurs ont introduit les interrupteurs à semi-conducteurs dans le domaine des hautes puissances pulsées. En particulier, les structures en silicium à haute tension déclenchées en mode onde d'ionisation par impact représentent une solution prometteuse pour les interrupteurs à semi-conducteurs rapides à très fort courant (dizaines à centaines de kA et gradient de courant de plusieurs dizaines de kA/μs).L'objectif principal de cette thèse est de démontrer expérimentalement la capacité des thyristors à haute tension à commuter rapidement des impulsions de courant d'amplitude élevée. Pour atteindre cet objectif, des études expérimentales et théoriques sont entreprises. Dans les travaux expérimentaux, l'accent principal est porté sur une limitation critique mise en évidence dans la littérature, à savoir la surface de section transversale du thyristor. Pour s'affranchir de cette limitation, plusieurs solutions ont été étudiées dans cette thèse, notamment (i) le déclenchement du plus grand thyristor disponible dans le commerce, d'un diamètre de 100 mm avec une tension de claquage statique de 5,2 kV, (ii) le déclenchement en parallèle d'un ensemble de deux et quatre thyristors à haute tension, (iii) la configuration série-parallèle afin d'augmenter simultanément la tension de blocage et la capacité de courant de l'interrupteur. En termes d'étude théorique, la simulation numérique est réalisée pour apporter une meilleure compréhension des phénomènes de claquage par avalanche en mode de commutation par ionisation d'impact<br>Micro-second range high-current pulses (100s kA) are applied to generate megagauss-range magnetic fields. This high pulsed power technology has been employed in inertial fusion research, X-pinch, and high-energy-density physics. Moreover, a number of industrial applications such as magnetic pulse welding and rock fracturing require high average power, repeatability, and a reliable high-current pulse generator with a long lifespan. Hence, a fast solid-state switch development operating in the range of several hundred kA is of considerable importance.A fast high-current switch is one of the most complex components in a pulsed power generator. Historically, only gas-filled switches could operate under such extreme conditions. However, gas-filled switches have several well-known disadvantages, including low pulse repetition frequency, short lifetimes, and instability in triggering. They are also expensive to use, often requiring gas flow systems, costly gases, and recirculating chambers of gas for repetitive operation. These disadvantages have hindered the widespread adoption of pulsed power technologies.Recent advancements in semiconductor physics and technology have introduced solid-state switches into the pulsed power domain. In particular, silicon high-voltage structures triggered in impact-ionization wave mode present a promising solution for fast high-current solid-state switches (10s-100s kA and 10s kA/μs).The main goal of this thesis is to experimentally demonstrate the capability of high-voltage thyristors to switch fast-high current pulses. to accomplish this goal, two major axes of study are defined as the experimental and theoretical studies. In the experimental work, the main focus is determined based on a key limitation highlighted in the literature, i.e., the cross-sectional area of the thyristor. To eliminate this limitation several solutions have been investigated in this thesis including (i) triggering the largest commercially available thyristor, 100 mm wafer diameter with 5.2 kV static voltage breakdown. (ii) Parallel triggering of an assembly of two and four high-voltage thyristors. (iii) Series-parallel configuration in order to further increase blocking voltage and current capability of the switch simultaneously. In terms of theoretical study, the numerical simulation is conducted to shed light on the avalanche breakdown phenomena in impact-ionization switching mode
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Zabihi, Sasan. "Flexible high voltage pulsed power supply for plasma applications." Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/48137/1/Sasan_Zabihi_Sheykhrajeh_Thesis.pdf.
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Demands for delivering high instantaneous power in a compressed form (pulse shape) have widely increased during recent decades. The flexible shapes with variable pulse specifications offered by pulsed power have made it a practical and effective supply method for an extensive range of applications. In particular, the release of basic subatomic particles (i.e. electron, proton and neutron) in an atom (ionization process) and the synthesizing of molecules to form ions or other molecules are among those reactions that necessitate large amount of instantaneous power. In addition to the decomposition process, there have recently been requests for pulsed power in other areas such as in the combination of molecules (i.e. fusion, material joining), gessoes radiations (i.e. electron beams, laser, and radar), explosions (i.e. concrete recycling), wastewater, exhausted gas, and material surface treatments. These pulses are widely employed in the silent discharge process in all types of materials (including gas, fluid and solid); in some cases, to form the plasma and consequently accelerate the associated process.
Due to this fast growing demand for pulsed power in industrial and environmental applications, the exigency of having more efficient and flexible pulse modulators is now receiving greater consideration. Sensitive applications, such as plasma fusion and laser guns also require more precisely produced repetitive pulses with a higher quality. Many research studies are being conducted in different areas that need a flexible pulse modulator to vary pulse features to investigate the influence of these variations on the application. In addition, there is the need to prevent the waste of a considerable amount of energy caused by the arc phenomena that frequently occur after the plasma process. The control over power flow during the supply process is a critical skill that enables the pulse supply to halt the supply process at any stage.
Different pulse modulators which utilise different accumulation techniques including Marx Generators (MG), Magnetic Pulse Compressors (MPC), Pulse Forming Networks (PFN) and Multistage Blumlein Lines (MBL) are currently employed to supply a wide range of applications. Gas/Magnetic switching technologies (such as spark gap and hydrogen thyratron) have conventionally been used as switching devices in pulse modulator structures because of their high voltage ratings and considerably low rising times. However, they also suffer from serious drawbacks such as, their low efficiency, reliability and repetition rate, and also their short life span. Being bulky, heavy and expensive are the other disadvantages associated with these devices. Recently developed solid-state switching technology is an appropriate substitution for these switching devices due to the benefits they bring to the pulse supplies. Besides being compact, efficient, reasonable and reliable, and having a long life span, their high frequency switching skill allows repetitive operation of pulsed power supply. The main concerns in using solid-state transistors are the voltage rating and the rising time of available switches that, in some cases, cannot satisfy the application’s requirements. However, there are several power electronics configurations and techniques that make solid-state utilisation feasible for high voltage pulse generation. Therefore, the design and development of novel methods and topologies with higher efficiency and flexibility for pulsed power generators have been considered as the main scope of this research work. This aim is pursued through several innovative proposals that can be classified under the following two principal objectives.
• To innovate and develop novel solid-state based topologies for pulsed power generation
• To improve available technologies that have the potential to accommodate solid-state technology by revising, reconfiguring and adjusting their structure and control algorithms.
The quest to distinguish novel topologies for a proper pulsed power production was begun with a deep and through review of conventional pulse generators and useful power electronics topologies. As a result of this study, it appears that efficiency and flexibility are the most significant demands of plasma applications that have not been met by state-of-the-art methods. Many solid-state based configurations were considered and simulated in order to evaluate their potential to be utilised in the pulsed power area. Parts of this literature review are documented in Chapter 1 of this thesis.
Current source topologies demonstrate valuable advantages in supplying the loads with capacitive characteristics such as plasma applications. To investigate the influence of switching transients associated with solid-state devices on rise time of pulses, simulation based studies have been undertaken. A variable current source is considered to pump different current levels to a capacitive load, and it was evident that dissimilar dv/dts are produced at the output. Thereby, transient effects on pulse rising time are denied regarding the evidence acquired from this examination. A detailed report of this study is given in Chapter 6 of this thesis.
This study inspired the design of a solid-state based topology that take advantage of both current and voltage sources. A series of switch-resistor-capacitor units at the output splits the produced voltage to lower levels, so it can be shared by the switches. A smart but complicated switching strategy is also designed to discharge the residual energy after each supply cycle. To prevent reverse power flow and to reduce the complexity of the control algorithm in this system, the resistors in common paths of units are substituted with diode rectifiers (switch-diode-capacitor). This modification not only gives the feasibility of stopping the load supply process to the supplier at any stage (and consequently saving energy), but also enables the converter to operate in a two-stroke mode with asymmetrical capacitors. The components’ determination and exchanging energy calculations are accomplished with respect to application specifications and demands. Both topologies were simply modelled and simulation studies have been carried out with the simplified models. Experimental assessments were also executed on implemented hardware and the approaches verified the initial analysis. Reports on details of both converters are thoroughly discussed in Chapters 2 and 3 of the thesis.
Conventional MGs have been recently modified to use solid-state transistors (i.e. Insulated gate bipolar transistors) instead of magnetic/gas switching devices. Resistive insulators previously used in their structures are substituted by diode rectifiers to adjust MGs for a proper voltage sharing. However, despite utilizing solid-state technology in MGs configurations, further design and control amendments can still be made to achieve an improved performance with fewer components. Considering a number of charging techniques, resonant phenomenon is adopted in a proposal to charge the capacitors. In addition to charging the capacitors at twice the input voltage, triggering switches at the moment at which the conducted current through switches is zero significantly reduces the switching losses. Another configuration is also introduced in this research for Marx topology based on commutation circuits that use a current source to charge the capacitors. According to this design, diode-capacitor units, each including two Marx stages, are connected in cascade through solid-state devices and aggregate the voltages across the capacitors to produce a high voltage pulse. The polarity of voltage across one capacitor in each unit is reversed in an intermediate mode by connecting the commutation circuit to the capacitor. The insulation of input side from load side is provided in this topology by disconnecting the load from the current source during the supply process. Furthermore, the number of required fast switching devices in both designs is reduced to half of the number used in a conventional MG; they are replaced with slower switches (such as Thyristors) that need simpler driving modules. In addition, the contributing switches in discharging paths are decreased to half; this decrease leads to a reduction in conduction losses. Associated models are simulated, and hardware tests are performed to verify the validity of proposed topologies. Chapters 4, 5 and 7 of the thesis present all relevant analysis and approaches according to these topologies.
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Mejecaze, Guillaume. "Analyse des destructions d'alimentations électroniques soumises à un courant impulsionnel fort niveau." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0204.
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Depuis plus d'une trentaine d'années, la menace d'impulsion électromagnétique provoquée par une explosion à haute altitude (IEMN-HA) d'une arme nucléaire est un sujet d'actualité avec les préoccupations croissantes de sécurité. L'IEMN-HA se couple de manière privilégiée sur les lignes aériennes de distribution en électricité permettant d'alimenter les habitations et les usines. Une fois couplée à ces lignes, la contrainte générée peut alors se propager de façon conduite jusqu'aux premiers systèmes qu'elle rencontrera, et les perturber voire les détruire. Dans la majorité des cas, ces systèmes sont les alimentations des appareils domestiques ou industriels. Dans ce cadre, les effets de destruction d'alimentations électroniques lors de l'injection d'un courant impulsionnel de forte amplitude sont étudiés grâce à un moyen d'injection appelé PIC pour Plateforme d'Injection en Courant. Une alimentation à découpage de type flyback, représentative d'une majorité des alimentations actuelles, a été conçue pour la thèse afin de maîtriser entièrement sa topologie et ses constituants. Les composants les plus susceptibles dans une alimentation à découpage ont été mis en évidence, et il a été montré qu'ils sont détruits à cause d'une amplitude trop importante de courant pendant une durée excessive par rapport aux maximums de leurs capacités. Des analyses aux rayons~X et au microscope optique ont été réalisées sur les composants pour aider à la compréhension. Celles-ci ont permis de fournir des premières hypothèses sur la cause de leur destruction, qui ont ensuite été confirmées par des mesures de courants et de tensions autour de chaque composant lors de l'injection de l'impulsion en entrée de l'alimentation. Enfin, le moyen d'injection ainsi que l'alimentation conçue ont été modélisés sous un logiciel de simulation électronique de type Spice. Cette thèse est la première étape d'un travail dont l'objectif final est de modéliser la susceptibilité des alimentations à découpage afin de prédire leur niveau de destruction<br>For thirty years, the threat of electromagnetic pulses caused by a high-altitude nuclear explosion (NEMP / HEMP) is still an actual concern in the field of security and safety. NEMP couples efficiently on aerial lines of the electricity network allowing to supply houses and factories. Once coupled to these lines, the generated interference can then be propagated to the first encountered systems and disturb or destroy them. In most cases, these systems are household or industries appliances power supplies. In this context, destruction effects of electronic power supplies due to high level current pulse injectionare studied thanks to an injection generator called PIC for Current Injection Platform. A flyback switch mode power supply (SMPS), representative of a majority of common power supplies, has been designed for the thesis in order to fully control its topology and components. The most susceptible components in SMPS have been identified and have been destroyed due to a too high level current over an excessive duration compared to their maximum ratings. These understandings have been supported by X-rays and optical microscope analyzes. These ones allowed to provide first hypotheses on their destruction cause, which were then confirmed by current and voltage measurements on each component during the pulse injection. Finally, PIC and the designed SMPS have been modeled using a Spice electronic simulation software. This thesis is the first step of a work whose final objective is to model the susceptibility of SMPS in order to predict their destruction level
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Chazottes-Leconte, Aurélien. "Conception et fabrication d'un dispositif de mise en compression par impulsions électro magnétiques (EMP)." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1082.
Full textAbstract:
Les procédés de traitement de surface sont utilisés à l'échelle industrielle pour améliorer les performances de pièces mécaniques en introduisant des contraintes résiduelles de compression. Cette mise en compression de surface permet de limiter l'amorçage et la propagation de fissures dans le matériau. Ceci permet d'augmenter de façon significative la durée de vie en fatigue des pièces mécaniques ainsi traitées. L'utilisation de ces procédés dans l'industrie a démontré leur efficacité, mais aussi leurs limitations et inconvénients. Les défauts récurrents consistent en une profondeur traitée faible, une dégradation de l'état de surface (rugosité), des difficultés de contrôle, une contamination du matériau traité, etc. Ces défauts ont conduit à l'élaboration de nouveaux procédés innovants qui permettent de meilleures performances en évitant certains des inconvénients succinctement évoqués. Parmi ces procédés innovants, le traitement de surface par impulsion électromagnétique semble particulièrement intéressant. Ce procédé met en œuvre un puissant champ magnétique transitoire pour engendrer des forces de Laplace dans une pièce métallique et induire des contraintes résiduelles. Il n'existe que peu d'informations dans la littérature et il n'existe aucun dispositif expérimental de ce procédé. Cette thèse est dédiée à la conception et la réalisation d'un prototype de mise en compression électromagnétique. Le premier chapitre de cette thèse est un état de l'art des technologies de mise en compression et du procédé de mise en compression par impulsion électromagnétique. Ainsi, les besoins de ce procédé sont identifiés et les technologies pouvant répondre à ces besoins sont explorées. Le deuxième chapitre, après une sélection de la structure globale du dispositif, va consister aux dimensionnements des éléments du prototype EMP. Cette étude commencera avec une étude sur l'inducteur qui va être utilisé avant de continuer sur le dimensionnement du stockage d'énergie et de l'interrupteur de décharge. Afin de valider le dimensionnement des composants précédents, une simulation électromagnétique 3D du système est réalisée. L'assemblage du prototype est présenté dans le troisième chapitre ainsi qu'une première campagne d'essai sur un alliage d'aluminium. Deux types d'éprouvettes sont testées : une éprouvette fine pour vérifier visuellement la mise en compression (essai Almen) et une éprouvette massive afin d'évaluer la profondeur traitée. Une modélisation multiphysique 3D du procédé est réalisée afin de corréler ces résultats avec l'expérience. Dans un dernier chapitre, une étude exploratoire est menée sur un matériau ferromagnétique, le mumétal, pour visualiser l'influence des contraintes résiduelles sur les propriétés magnétiques de ce dernier<br>Penning processes are widely used in industries to apply compressive residual stresses into the most solicited part of mechanical pieces. In that way, the compressive residual stresses limit the priming and the propagation of micro-cracks in the material. This increases significantly the lifespan of the treated mechanical piece under fatigue stresses. These existing peening processes have proved their efficiency and also their limitations and weaknesses. The main recurrent defaults are a shallow depth of treatment, a degradation of the surface condition, a random control of the treatment, a material contamination, etc. These problems have led towards the development of news innovative peening processes which allow better performance avoiding some previous defaults briefly evoked. Among these news processes, the electromagnetic peening process seems especially interesting. This process uses high energy electromagnetic fields to induce Lorentz forces into a metallic piece and thus residual stresses. Actually, there is not much information about this process in the literature and no prototype was ever built. The work of this thesis is dedicated to development and realization of an electromagnetic peening prototype. The first chapter of this thesis adresses the state of the art of major peening processes actually in industrial use. Next, the electromagnetic peening process, or EMP process, is described and the electrical needs are exposed. A second state of the art is made about the technological solutions to respond to the EMP needs. The second chapter is about the conception of the EMP prototype with the electrical structure adopted in the previous chapter. The first step is about the inductor sizing to generate an electromagnetic field sufficient enough for a peening application. Next, the storage system is designed depending on the inductor parameters and finally the closing switch is created considering the electrical parameters used for the EMP process. To validate the previous results, a 3D electromagnetic simulation is done. The prototype assembly is presented in the third chapter and also the first experimental test on the EMP prototype. To begin with, an aluminium alloy with low yield strength is selected to be treated. Two different samples forms are used, a thin one, to realize a similar test to the Almen test and thick one to check the EMP depth of treatment. A 3D multiphysics simulation of these experiments is made and these numeric results are next correlated to the experimental ones. In the fourth chapter, an exploratory study is realized on the effects of the residual stresses on magnetic properties of ferromagnetic material, the mumetal
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Alexander, Eric Douglas. "Pulsed-Power Busbar Design for High-Powered Applications." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71329.
Full textAbstract:
The use of high-powered electrical energy systems requires an efficient and capable
means to move electrical energy from one location to another while reducing energy
losses. This paper describes the design and construction process of a high-powered
busbar system that is to be implemented in pulsed-power applications. In order to
obtain a robust system capable of handling in excess of 25kJ, both mechanical and
electrical analyses were performed to verify a capable design. The following methodology
describes how the Lorentz force was balanced with mechanical forces during the
design process and then validated after construction was completed using the fundamental
Maxwell equations and computer simulations. Main focuses include handling
of EMF, high current density concentrations, and overall mechanical stability of the
system and how these effects determine the physical design and implementation. In
the end, a repeatable methodology is presented in the form of a design process that
can be implemented in any system given the design criteria.<br>Master of Science
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Welsh, David S. "Current density limitations in a fast-pulsed high-voltage vacuum diode." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23850.
Full textAbstract:
Approved for public release: distribution is unlimited.<br>An investigation into the limitations on the enhanced field-emitted current density
in a fast-pulsed (rise-time = ns), high voltage (> 106 V), 1-inch vacuum diode was
conducted using a computer simulation based on the Fowler-Nordheim equation.
Oscillations in the emitted current density (due to the change in the amount of
space charge within the gap) were found to quickly decay into a final steady-state for
the voltages applied. Steady-state values for a wide variety of work functions, electric
field enhancement factors (based on the theory that "whiskers" on the cathode surface
experience varying degrees of enhancement), and applied potentials were compared
to two benchmarks: the amount of current density required to explode a whisker in
< 10 ns by joule heating (J E = 109 A/cm2
); and the Child-Langmuir (C-L) spacecharge-
limited current density. Steady-state values were found to be less than J E . One model of the formation
process of a plasma at the cathode surface requires that J E be met or exceeded by
the steady-state value. Thus, such a model is not supported by this project's findings.
The C-L limit is based on a thermionic-type emission process. As only pure field
emission (i.e., no thermionic emission included) was considered, the steady-state
values were, in all conclusive cases, less than the corresponding C-L limited values.
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Веселова, Надія Вікторівна. "Становлення і розвиток харківських наукових шкіл у галузі техніки та електрофізика високих напруг (1930–2010 рр.)". Thesis, НТУ "ХПІ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/17177.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата історичних наук за спеціальністю 07.00.07 – історія науки і техніки. – Національний технічний університет "Харківський політехнічний інститут". – Харків, 2015. У дисертації комплексно досліджується створення та розвиток харківських наукових шкіл у галузі техніки та електрофізики високих напруг у 1930–2010 рр. В роботі визначені харківські наукові школи в цій галузі, а саме: наукова школа високовольтних прискорювачів в УФТІ, яку очолив академік АН УРСР А. К. Вальтер; наукова школа техніки високих напруг ХПІ, засновником якої став академік АН УРСР В. М. Хрущов; наукова школа магнітно-імпульсної обробки металів ХПІ, що була заснована проф. І. В. Білим. Проведено цілісний науково-історичний аналіз процесу виникнення технічних рішень в електрофізиці і створення установок високої напруги в провідних харківських наукових центрах. Розкрито процес формування складу наукових установ і лабораторій, внесок окремих вчених у розвиток техніки і електрофізики високих напруг в м. Харкові. Показана важливість та унікальність створених високовольтних установок, визначено передумови їх створення та досліджено застосування цих пристроїв у вітчизняній науці та промисловості.<br>The thesis for the competition of the academic degree of the candidate of the historical sciences, the speciality 07.00.07 – The history of science and technique. – National Technical University "Kharkiv Polytechnic Institute". – Kharkiv, 2015. The thesis is devoted to the complex research of the establishment and the development of Kharkiv scientific schools in the field of the technique and the electrophysics of the high-voltages in 1930's – 2010's. In this work the Kharkiv scientific schools in this field were identified for the first time. They are: the scientific school of the high-voltage accelerators in the UFTI headed by academician of USSR A.K. Walter; the scientific school of the technique of high-voltages in the KhPI, the founder of which was the acacademician of the Academy of Sciences of USSR V. M. Khrushchev; the scientific school of magnetic-pulse treatment of metals in KhPI which was founded by professor I. V. Belii. A holistic scientific-historical analysis of the process of technical solutions in electrophysics and the creation of high-voltage installations in leading scientific centers of Kharkiv is carried out in this work. The importance and uniqueness of the high-voltage installations is shown here. The importance and the uniqueness of the high-voltage structures, the conditions of their creation usage in home industry and science are shown here.
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Howe, Daniel Steven. "A WIRELESS ELECTRICAL STIMULATION SYSTEMFOR WOUND HEALING THERAPYWITH BIPHASIC HIGH-VOLTAGE PULSED CURRENT OUTPUT." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1365179992.
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Zhang, Xiangdong. "Surface modification of Ti- and Ni-base alloys by High Current Pulsed Electron Beam." Thesis, Metz, 2011. http://www.theses.fr/2011METZ008S.
Full textAbstract:
Modification de surface des alliages à base de Ti et de Ni par faisceau d'électrons de haute courant pulsé a été effectuée avec des intentions de la compréhension de la modification de la couche fondue et les mécanismes de pénétration de trempe que les deux devraient dépendre de la nature du matériau et son orientation. Il a été constaté que α 'ou α''martensite a été formée sur la surface Ti alliage traité. Le taux de refroidissement a été estimée en utilisant la taille des grains avant-β dans les alliages Ti TA15. Le niveau de stress induit par le traitement HCPEB a été estimée en utilisant le déclenchement des contraintes de stress induite transformation de phase martensitique α''. La croissance épitaxiale a été observée dans la surface fondue couches de la HCPEB traités à base de nickel alliages monocristallins AM1 (100) et (111). Une zone de substrat durcis en raison de la présence de dislocations à haute densité et un substrat adoucir la zone en raison de la brutalité des précipités ont été trouvés. Il a été constaté densité de cratères des superalliages à base de nickel monocristallin est un ou deux ordres de grandeur plus faible que celle des matériaux métalliques étudiés précédemment. En examinant la morphologie du cratère, trois étapes de la formation de cratères ont également été proposés<br>Surface modification of Ti and Ni base alloys by high current pulsed electron beam has been carried out with intentions of understanding of the modification in the melted layer and the mechanisms of deep hardening that both should depend on the nature of the material and its orientation. It was found that α’ or α’’ martensite has been formed on the treated titanium alloy surface. The cooling rate was estimated by using an empirical equation with the size of the prior-β grains in TA15 titanium alloys. The stress level induced by HCPEB treatment was experimentally estimated by using the triggering stress for stress-induced α’’ martensitic phase transformation. Epitaxial growth was observed in the surface melted layers of the HCPEB treated Ni-base single crystal superalloys AM1 (100) and AM1 (111). Significant difference in deep hardening between the AM1 (100) and AM1 (111) samples are also observed. A substrate hardened zone due to the presence of high density dislocations induced by the stress generated by the HCPEB treatment and a substrate soften zone due to the coarsening of the precipitates have been found. It was found crater density of the Ni-base single crystal superalloys is one or two orders of magnitude lower that of the previously studied metallic materials. Through examining the crater morphologies in details, three stages of the formation of craters have also been proposed
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Веселова, Надія Вікторівна. "Становлення і розвиток харківських наукових шкіл у галузі техніки та електрофізика високих напруг (1930–2010 рр.)". Thesis, НТУ "ХПІ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/17176.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата історичних наук за спеціальністю 07.00.07 – історія науки і техніки. – Національний технічний університет "Харківський політехнічний інститут". – Харків, 2015.
У дисертації комплексно досліджується створення та розвиток харківських наукових шкіл у галузі техніки та електрофізики високих напруг у 1930–2010 рр. В роботі визначені харківські наукові школи в цій галузі, а саме: наукова школа високовольтних прискорювачів в УФТІ, яку очолив академік АН УРСР А. К. Вальтер; наукова школа техніки високих напруг ХПІ, засновником якої став академік АН УРСР В. М. Хрущов; наукова школа магнітно-імпульсної обробки металів ХПІ, що була заснована проф. І. В. Білим. Проведено цілісний науково-історичний аналіз процесу виникнення технічних рішень в електрофізиці і створення установок високої напруги в провідних харківських наукових центрах. Розкрито процес формування складу наукових установ і лабораторій, внесок окремих вчених у розвиток техніки і електрофізики високих напруг в м. Харкові. Показана важливість та унікальність створених високовольтних установок, визначено передумови їх створення та досліджено застосування цих пристроїв у вітчизняній науці та промисловості.<br>The thesis for the competition of the academic degree of the candidate of the historical sciences, the speciality 07.00.07 – The history of science and technique. – National Technical University "Kharkiv Polytechnic Institute". – Kharkiv, 2015.
The thesis is devoted to the complex research of the establishment and the development of Kharkiv scientific schools in the field of the technique and the electrophysics of the high-voltages in 1930's – 2010's. In this work the Kharkiv scientific schools in this field were identified for the first time. They are: the scientific school of the high-voltage accelerators in the UFTI headed by academician of USSR A.K. Walter; the scientific school of the technique of high-voltages in the KhPI, the founder of which was the acacademician of the Academy of Sciences of USSR V. M. Khrushchev; the scientific school of magnetic-pulse treatment of metals in KhPI which was founded by professor I. V. Belii. A holistic scientific-historical analysis of the process of technical solutions in electrophysics and the creation of high-voltage installations in leading scientific centers of Kharkiv is carried out in this work. The importance and uniqueness of the high-voltage installations is shown here. The importance and the uniqueness of the high-voltage structures, the conditions of their creation usage in home industry and science are shown here.
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Wu, Jiang. "Nanostructures of Zr-based bulk metallic glasses : induced by ball milling and high-current pulsed electron beams." Thesis, Metz, 2010. http://www.theses.fr/2010METZ022S.
Full textAbstract:
Contrairement aux métaux conventionnels, les verres métalliques amorphes présentent des arrangements atomiques à courte distante. Ce résultat conduit à des propriétés physiques et chimiques fondamentalement différentes de leurs homologues cristallins. Cette étude porte sur la caractérisation et la compréhension de la nanocristallisation de verres métalliques amorphes massifs (BMG) Zr-Al-Ni-Cu induite par traitement thermique, broyage mécanique et faisceaux d’électrons pulsés à fort courant (HCPEB). Deux alliages amorphes massifs ont été cristallisés par broyage mécanique et HCPEB : le classique Zr65Al7.5Ni10Cu17.5 et un nouvel alliage Zr58Al16Ni11Cu15 développé en utilisant un modèle basé sur l’association de clusters. Les échantillons initiaux et traités ont été caractérisés en combinant les microscopies électroniques en transmission (MET) et à balayage (MEB), la diffraction d’électrons rétrodiffusés (EBSD), l’analyse thermique différentielle (ATD) et la spectroscopie Raman afin d’analyser finement les évolutions microstructurales. Les nanocristallisations induites par broyage et HCPEB sont très différentes de celles obtenues par traitements thermiques. Ces travaux de recherche permettent une avancée dans la compréhension des mécanismes de cristallisations mécanique et sous irradiation. Les résultats peuvent être utilisés pour réaliser des structures composites de BMGs avec l’objectif final d’améliorer leur ductilité<br>Unlike conventional metals, the atomic arrangements in metallic glasses have only short-range order. This results in many physical and chemical properties that are fundamentally different from those of their crystalline counterparts. This study is devoted to charactering and understanding nanostructures and nanocrystallization of Zr-Al-Ni-Cu bulk metallic glasses induced by thermal annealing, ball milling, and high-current pulsed electron beam (HCPEB) treatment. Two Zr-Al-Ni-Cu BMGs were used: the classic Zr65Al7.5Ni10Cu17.5 alloy and a new Zr58Al16Ni11Cu15 alloy developed by using a cluster-based approach. The initial and treated samples were characterized by the combination of transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), differential thermal analysis (DTA) and Raman spectroscopy in order to analyze accurately the microstructure evolution encountered in the materials. The nanocrystallization behaviour under ball mill and HCPEB is significantly different from the one observed via thermal annealing. The significance of this research is the advancement of the fundamental understanding of mechanical and the electron beam irradiation-induced crystallizations. This research may be used for the design of BMG-related composite structures with the ultimate goal of improving their ductility
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Cimmperman, Piotras. "Plonųjų manganitų sluoksnių tyrimas stipriuose impulsiniuose elektriniuose ir magnetiniuose laukuose." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2006. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2006~D_20061003_100516-61918.
Full textAbstract:
The main aim of this work was to investigate electrical conductivity of La-Ca(Sr)-MnO thin films at high pulsed electric and magnetic fields and to clear up the possibilities to use these materials for high pulsed magnetic field sensor and fault current limiter applications.
The dissertation consists of the preface, six chapters, summary and main conclusions, references, list of publications and abstract (in Lithuanian).
The main objectives of the work, scientific novelty, goals, validation of results, and statements for defense are presented in the preface.
Chapter 1 presents an introduction and review of previous works on electroresistance (ER) and magnetoresistance (MR) phenomena in manganites.
Chapter 2 presents a description of two deposition techniques which were used for preparation of thin manganite films: metal organic chemical vapour deposition (MOCVD) and pulsed laser deposition (PLD).
Measurement equipment and methods are described in Chapter 3. The resistance dependence on voltage was investigated using electric pulses with duration of 5–30 ns and amplitude up to 1000 V in the temperature range of 4.2–300 K. For magnetoresistance measurements a pulsed magnetic field generator, which generates magnetic field pulses of 0.6–2 ms duration with amplitude up to 50 T was used.
Chapter 4 presents an investigation of surface morphology of prepared films and a characterization of their properties at low electric and magnetic fields. The electric and magnetic properties... [to full text]
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Zou, Jianxin. "Mécanismes fondamentaux du traitement de surfaces par bombardements électroniques pulsés : application aux matériaux métalliques et intermétalliques." Metz, 2007. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/2007/Zou.Jianxim.SMZ0718.pdf.
Full textAbstract:
La technique de "High-Current Pulsed Electron Beam" (HCPEB) a été développée récemment pour le traitement de surface des matériaux. Des impulsions très courtes avec une importante densité d'énergie d'électrons induisent des cycles thermo-mécaniques ultra-rapides en surface. Ces cycles peuvent conduire à la fusion - voir éventuellement à l'évaporation - de la couche superficielle ainsi qu'à la formation d’un champ de contrainte dynamique qui est à l’origine d’une déformation intense en sous-couche. Ce manuscrit propose une revue des développements récents concernant la technique HCPEB qui ont été obtenus dans le cadre de nos travaux. Nous montrons l'importance de la distinction entre les trois différents modes de traitement : le mode "chauffage", le mode "fusion" et le mode "évaporation". Tout d’abord, des modèles physiques associés à ces modes ont été proposés. L'analyse expérimentale a ensuite été réalisée sur différents métaux et alliages intermétalliques. Les modifications de surface et certains phénomènes spéciaux liés aux différents modes de traitement ont été détaillés. Finalement, nous avons discuté les applications potentielles de cette technique pour améliorer les propriétés des matériaux. Il apparaît clairement que le potentiel de la technique HCPEB nécessite un bon contrôle des paramètres de traitement pour modifier la surface des matériaux en utilisant le mode de traitement le plus approprié<br>High-Current Pulsed Electron Beam (HCPEB) is a recently developed technique for surface treatment of materials. The high-density electron pulses of short durations induce dynamic temperature fields in the surface layers giving rise to superfast heating, possible melting and evaporating. This is followed by a rapid solidification and cooling of the material surface. In addition, a dynamic stress field is formed that causes intense deformation in the material sub-layers. The development and research work carried out using the HCPEB technique have been reviewed in this thesis by underlying its effects under the "melting", "heating" and "evaporating" treatment modes. At first, different physical models for the HCPEB treatment of materials under the three different treatment modes have been proposed. Subsequently, the intriguing surface modifications associated with the HCPEB treatment were detailed. Finally, the potential applications of the HCPEB technique to improve the materials’ properties have been pointed out. Under all the three treatment modes, HCPEB treatment is proved to be an efficient way to modify the surface of metallic and intermetallic materials to taylor their properties. Overall, this review clearly demonstrate that the high potential of the HCPEB technique can be better achieved by a good control of the processing parameter in order to treat the sample surfaces under the most appropriate mode
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Saleh, Paul Matthew. "Characterisation of practical high temperature superconductors in pulsed magnetic fields and development of associated technology." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365786.
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Ghasemi, Negareh. "Improving ultrasound excitation systems using a flexible power supply with adjustable voltage and frequency to drive piezoelectric transducers." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/61091/1/Negareh_Ghasemi_Thesis.pdf.
Full textAbstract:
The ability of a piezoelectric transducer in energy conversion is rapidly expanding in several applications. Some of the industrial applications for which a high power ultrasound transducer can be used are surface cleaning, water treatment, plastic welding and food sterilization. Also, a high power ultrasound transducer plays a great role in biomedical applications such as diagnostic and therapeutic applications. An ultrasound transducer is usually applied to convert electrical energy to mechanical energy and vice versa. In some high power ultrasound system, ultrasound transducers are applied as a transmitter, as a receiver or both. As a transmitter, it converts electrical energy to mechanical energy while a receiver converts mechanical energy to electrical energy as a sensor for control system. Once a piezoelectric transducer is excited by electrical signal, piezoelectric material starts to vibrate and generates ultrasound waves. A portion of the ultrasound waves which passes through the medium will be sensed by the receiver and converted to electrical energy. To drive an ultrasound transducer, an excitation signal should be properly designed otherwise undesired signal (low quality) can deteriorate the performance of the transducer (energy conversion) and increase power consumption in the system. For instance, some portion of generated power may be delivered in unwanted frequency which is not acceptable for some applications especially for biomedical applications.
To achieve better performance of the transducer, along with the quality of the excitation signal, the characteristics of the high power ultrasound transducer should be taken into consideration as well. In this regard, several simulation and experimental tests are carried out in this research to model high power ultrasound transducers and systems. During these experiments, high power ultrasound transducers are excited by several excitation signals with different amplitudes and frequencies, using a network analyser, a signal generator, a high power amplifier and a multilevel converter. Also, to analyse the behaviour of the ultrasound system, the voltage ratio of the system is measured in different tests. The voltage across transmitter is measured as an input voltage then divided by the output voltage which is measured across receiver. The results of the transducer characteristics and the ultrasound system behaviour are discussed in chapter 4 and 5 of this thesis.
Each piezoelectric transducer has several resonance frequencies in which its impedance has lower magnitude as compared to non-resonance frequencies. Among these resonance frequencies, just at one of those frequencies, the magnitude of the impedance is minimum. This resonance frequency is known as the main resonance frequency of the transducer. To attain higher efficiency and deliver more power to the ultrasound system, the transducer is usually excited at the main resonance frequency. Therefore, it is important to find out this frequency and other resonance frequencies. Hereof, a frequency detection method is proposed in this research which is discussed in chapter 2.
An extended electrical model of the ultrasound transducer with multiple resonance frequencies consists of several RLC legs in parallel with a capacitor. Each RLC leg represents one of the resonance frequencies of the ultrasound transducer. At resonance frequency the inductor reactance and capacitor reactance cancel out each other and the resistor of this leg represents power conversion of the system at that frequency. This concept is shown in simulation and test results presented in chapter 4.
To excite a high power ultrasound transducer, a high power signal is required. Multilevel converters are usually applied to generate a high power signal but the drawback of this signal is low quality in comparison with a sinusoidal signal. In some applications like ultrasound, it is extensively important to generate a high quality signal. Several control and modulation techniques are introduced in different papers to control the output voltage of the multilevel converters. One of those techniques is harmonic elimination technique. In this technique, switching angles are chosen in such way to reduce harmonic contents in the output side. It is undeniable that increasing the number of the switching angles results in more harmonic reduction. But to have more switching angles, more output voltage levels are required which increase the number of components and cost of the converter. To improve the quality of the output voltage signal with no more components, a new harmonic elimination technique is proposed in this research. Based on this new technique, more variables (DC voltage levels and switching angles) are chosen to eliminate more low order harmonics compared to conventional harmonic elimination techniques. In conventional harmonic elimination method, DC voltage levels are same and only switching angles are calculated to eliminate harmonics. Therefore, the number of eliminated harmonic is limited by the number of switching cycles. In the proposed modulation technique, the switching angles and the DC voltage levels are calculated off-line to eliminate more harmonics. Therefore, the DC voltage levels are not equal and should be regulated. To achieve this aim, a DC/DC converter is applied to adjust the DC link voltages with several capacitors. The effect of the new harmonic elimination technique on the output quality of several single phase multilevel converters is explained in chapter 3 and 6 of this thesis.
According to the electrical model of high power ultrasound transducer, this device can be modelled as parallel combinations of RLC legs with a main capacitor. The impedance diagram of the transducer in frequency domain shows it has capacitive characteristics in almost all frequencies. Therefore, using a voltage source converter to drive a high power ultrasound transducer can create significant leakage current through the transducer. It happens due to significant voltage stress (dv/dt) across the transducer. To remedy this problem, LC filters are applied in some applications. For some applications such as ultrasound, using a LC filter can deteriorate the performance of the transducer by changing its characteristics and displacing the resonance frequency of the transducer. For such a case a current source converter could be a suitable choice to overcome this problem. In this regard, a current source converter is implemented and applied to excite the high power ultrasound transducer. To control the output current and voltage, a hysteresis control and unipolar modulation are used respectively. The results of this test are explained in chapter 7.
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Allard, Florian. "Etude de nouvelles architectures modulaires d'alimentations électriques pour les applications de hautes puissances pulsées." Thesis, Pau, 2018. http://www.theses.fr/2018PAUU3005/document.
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De nos jours, pour accroître le potentiel applicatif des machines de hautes puissances pulsées, il est nécessaire de développer des modulateurs compacts capables de délivrer des impulsions de l’ordre de plusieurs Mégawatts de durée pouvant atteindre plusieurs centaines de microsecondes. Cette amélioration requiert le développement de structures innovantes dont le but est de produire aussi bien des puissances moyennes que des puissances crêtes importantes. Les modulateurs étudiés dans ce mémoire sont basés sur l’utilisation de divers transformateurs pour la génération d’impulsions de très forte puissance. Le projet AGIR (acronyme de « Architecture pour la Génération d’Impulsions Rectangulaires de forte de puissance ») est réalisé dans le cadre d’un RAPID (Régime d’Appui Pour l’Innovation Duale) financé par la Direction Générale de l’Armement (DGA). Le projet est une collaboration avec EFFITECH, une entreprise spécialisée dans les puissances pulsées. L’objectif est de développer deux générateurs pour deux gammes de puissance crête (jusqu’à 10MW pour l’un et 1GW pour l’autre). Le premier modulateur « AGIR1 » repose sur l’association d’un convertisseur AC-DC et de 12 convertisseurs résonants DC-DC qui permettent la génération de plusieurs types d’impulsions (fort courant ou forte tension) en fonction de la configuration choisie. Le second modulateur repose sur le développement d’un transformateur impulsionnel à quatre primaires synchronisés. Chaque primaire est relié à un système de mise en forme de type Blumlein dont le déclenchement est assuré par un éclateur pressurisé à trois électrodes. La synchronisation des quatre éclateurs est assurée par un générateur impulsionnel innovant à faible gigue. La principale difficulté du travail effectué au laboratoire réside dans l’étude des différents transformateurs haute-tension utilisés (résonant ou impulsionnel) et du système de synchronisation des éclateurs. Chaque élément constituant le système est étudié et simulé de manière électrostatique, électromagnétique ou électrique avant d’être réalisé et assemblé. Des essais ponctue l’étude afin de valider le fonctionnement en récurrent avec un système de dissipation thermique adapté<br>Nowadays, to increase the application potential of high power pulsed machines, it is necessary to develop compact modulators able to deliver pulses in the range of several megawatts with duration of up to several hundred microseconds. This improvement requires the development of innovative structures whose purpose is to produce both average power and large peak power. Modulators studied in this thesis are based on the use of various transformers for the generation of very high power pulses. The AGIR project (French acronym for "Architecture for Rectangular High Pulse power generation") is achieved within the framework of a RAPID (Dual Innovation Support Regime) funded by the French Defense (DGA). The project is carried on by a collaboration with EFFITECH, a company specialized in pulsed powers. The goal is to develop two generators for two peak power ranges (up to 10MW for one and 1GW for the other). The first modulator "AGIR1" is based on the association of an AC-DC converter and 12 DC-DC resonant converters allowing the generation of several types of pulses (high current or high voltage) depending on the chosen configuration. The second modulator is based on the development of a four synchronized primary pulse transformer. Each primary is connected to a Blumlein pulse forming line triggered by a three-electrode pressurized spark gap. The synchronization of the four spark gaps is ensured by an innovative pulse generator with low jitter. The main difficulty of the work which was completed in the laboratory relies in the study of the different high-voltage transformers used (resonant or pulse) and the spark gap synchronization system. Each element constituting the system is studied and simulated electrostatically, electromagnetically or electrically before being realized and assembled. Trials punctuate the study to validate the recurrent operation with a suitable heat dissipation system
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Adabi, Firouzjaee Jafar. "Remediation strategies of shaft and common mode voltages in adjustable speed drive systems." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/39293/1/Jafar_Adabi_Firouzjaeel_Thesis.pdf.
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AC motors are largely used in a wide range of modern systems, from household appliances to automated industry applications such as: ventilations systems, fans, pumps, conveyors and machine tool drives. Inverters are widely used in industrial and commercial applications due to the growing need for speed control in ASD systems. Fast switching transients and the common mode voltage, in interaction with parasitic capacitive couplings, may cause many unwanted problems in the ASD applications. These include shaft voltage and leakage currents.
One of the inherent characteristics of Pulse Width Modulation (PWM) techniques is the generation of the common mode voltage, which is defined as the voltage between the electrical neutral of the inverter output and the ground. Shaft voltage can cause bearing currents when it exceeds the amount of breakdown voltage level of the thin lubricant film between the inner and outer rings of the bearing. This phenomenon is the main reason for early bearing failures.
A rapid development in power switches technology has lead to a drastic decrement of switching rise and fall times. Because there is considerable capacitance between the stator windings and the frame, there can be a significant capacitive current (ground current escaping to earth through stray capacitors inside a motor) if the common mode voltage has high frequency components. This current leads to noises and Electromagnetic Interferences (EMI) issues in motor drive systems.
These problems have been dealt with using a variety of methods which have been reported in the literature. However, cost and maintenance issues have prevented these methods from being widely accepted. Extra cost or rating of the inverter switches is usually the price to pay for such approaches. Thus, the determination of cost-effective techniques for shaft and common mode voltage reduction in ASD systems, with the focus on the first step of the design process, is the targeted scope of this thesis. An introduction to this research – including a description of the research problem, the literature review and an account of the research progress linking the research papers – is presented in Chapter 1.
Electrical power generation from renewable energy sources, such as wind energy systems, has become a crucial issue because of environmental problems and a predicted future shortage of traditional energy sources. Thus, Chapter 2 focuses on the shaft voltage analysis of stator-fed induction generators (IG) and Doubly Fed Induction Generators DFIGs in wind turbine applications. This shaft voltage analysis includes: topologies, high frequency modelling, calculation and mitigation techniques. A back-to-back AC-DC-AC converter is investigated in terms of shaft voltage generation in a DFIG. Different topologies of LC filter placement are analysed in an effort to eliminate the shaft voltage.
Different capacitive couplings exist in the motor/generator structure and any change in design parameters affects the capacitive couplings. Thus, an appropriate design for AC motors should lead to the smallest possible shaft voltage. Calculation of the shaft voltage based on different capacitive couplings, and an investigation of the effects of different design parameters are discussed in Chapter 3. This is achieved through 2-D and 3-D finite element simulation and experimental analysis.
End-winding parameters of the motor are also effective factors in the calculation of the shaft voltage and have not been taken into account in previous reported studies. Calculation of the end-winding capacitances is rather complex because of the diversity of end winding shapes and the complexity of their geometry. A comprehensive analysis of these capacitances has been carried out with 3-D finite element simulations and experimental studies to determine their effective design parameters. These are documented in Chapter 4. Results of this analysis show that, by choosing appropriate design parameters, it is possible to decrease the shaft voltage and resultant bearing current in the primary stage of generator/motor design without using any additional active and passive filter-based techniques.
The common mode voltage is defined by a switching pattern and, by using the appropriate pattern; the common mode voltage level can be controlled. Therefore, any PWM pattern which eliminates or minimizes the common mode voltage will be an effective shaft voltage reduction technique. Thus, common mode voltage reduction of a three-phase AC motor supplied with a single-phase diode rectifier is the focus of Chapter 5. The proposed strategy is mainly based on proper utilization of the zero vectors.
Multilevel inverters are also used in ASD systems which have more voltage levels and switching states, and can provide more possibilities to reduce common mode voltage. A description of common mode voltage of multilevel inverters is investigated in Chapter 6.
Chapter 7 investigates the elimination techniques of the shaft voltage in a DFIG based on the methods presented in the literature by the use of simulation results. However, it could be shown that every solution to reduce the shaft voltage in DFIG systems has its own characteristics, and these have to be taken into account in determining the most effective strategy.
Calculation of the capacitive coupling and electric fields between the outer and inner races and the balls at different motor speeds in symmetrical and asymmetrical shaft and balls positions is discussed in Chapter 8. The analysis is carried out using finite element simulations to determine the conditions which will increase the probability of high rates of bearing failure due to current discharges through the balls and races.
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Nami, Alireza. "A new multilevel converter configuration for high power and high quality applications." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/33216/1/Alireza_Nami_Thesis.pdf.
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The Queensland University of Technology (QUT) allows the presentation of theses for the Degree of Doctor of Philosophy in the format of published or submitted papers, where such papers have been published, accepted or submitted during the period of candidature. This thesis is composed of ten published /submitted papers and book chapters of which nine have been published and one is under review. This project is financially supported by an Australian Research Council (ARC) Discovery Grant with the aim of investigating multilevel topologies for high quality and high power applications, with specific emphasis on renewable energy systems. The rapid evolution of renewable energy within the last several years has resulted in the design of efficient power converters suitable for medium and high-power applications such as wind turbine and photovoltaic (PV) systems. Today, the industrial trend is moving away from heavy and bulky passive components to power converter systems that use more and more semiconductor elements controlled by powerful processor systems. However, it is hard to connect the traditional converters to the high and medium voltage grids, as a single power switch cannot stand at high voltage. For these reasons, a new family of multilevel inverters has appeared as a solution for working with higher voltage levels. Besides this important feature, multilevel converters have the capability to generate stepped waveforms. Consequently, in comparison with conventional two-level inverters, they present lower switching losses, lower voltage stress across loads, lower electromagnetic interference (EMI) and higher quality output waveforms. These properties enable the connection of renewable energy sources directly to the grid without using expensive, bulky, heavy line transformers. Additionally, they minimize the size of the passive filter and increase the durability of electrical devices. However, multilevel converters have only been utilised in very particular applications, mainly due to the structural limitations, high cost and complexity of the multilevel converter system and control. New developments in the fields of power semiconductor switches and processors will favor the multilevel converters for many other fields of application. The main application for the multilevel converter presented in this work is the front-end power converter in renewable energy systems. Diode-clamped and cascade converters are the most common type of multilevel converters widely used in different renewable energy system applications. However, some drawbacks – such as capacitor voltage imbalance, number of components, and complexity of the control system – still exist, and these are investigated in the framework of this thesis. Various simulations using software simulation tools are undertaken and are used to study different cases. The feasibility of the developments is underlined with a series of experimental results. This thesis is divided into two main sections. The first section focuses on solving the capacitor voltage imbalance for a wide range of applications, and on decreasing the complexity of the control strategy on the inverter side. The idea of using sharing switches at the output structure of the DC-DC front-end converters is proposed to balance the series DC link capacitors. A new family of multioutput DC-DC converters is proposed for renewable energy systems connected to the DC link voltage of diode-clamped converters. The main objective of this type of converter is the sharing of the total output voltage into several series voltage levels using sharing switches. This solves the problems associated with capacitor voltage imbalance in diode-clamped multilevel converters. These converters adjust the variable and unregulated DC voltage generated by renewable energy systems (such as PV) to the desirable series multiple voltage levels at the inverter DC side. A multi-output boost (MOB) converter, with one inductor and series output voltage, is presented. This converter is suitable for renewable energy systems based on diode-clamped converters because it boosts the low output voltage and provides the series capacitor at the output side. A simple control strategy using cross voltage control with internal current loop is presented to obtain the desired voltage levels at the output voltage. The proposed topology and control strategy are validated by simulation and hardware results. Using the idea of voltage sharing switches, the circuit structure of different topologies of multi-output DC-DC converters – or multi-output voltage sharing (MOVS) converters – have been proposed. In order to verify the feasibility of this topology and its application, steady state and dynamic analyses have been carried out. Simulation and experiments using the proposed control strategy have verified the mathematical analysis. The second part of this thesis addresses the second problem of multilevel converters: the need to improve their quality with minimum cost and complexity. This is related to utilising asymmetrical multilevel topologies instead of conventional multilevel converters; this can increase the quality of output waveforms with a minimum number of components. It also allows for a reduction in the cost and complexity of systems while maintaining the same output quality, or for an increase in the quality while maintaining the same cost and complexity. Therefore, the asymmetrical configuration for two common types of multilevel converters – diode-clamped and cascade converters – is investigated. Also, as well as addressing the maximisation of the output voltage resolution, some technical issues – such as adjacent switching vectors – should be taken into account in asymmetrical multilevel configurations to keep the total harmonic distortion (THD) and switching losses to a minimum. Thus, the asymmetrical diode-clamped converter is proposed. An appropriate asymmetrical DC link arrangement is presented for four-level diode-clamped converters by keeping adjacent switching vectors. In this way, five-level inverter performance is achieved for the same level of complexity of the four-level inverter. Dealing with the capacitor voltage imbalance problem in asymmetrical diodeclamped converters has inspired the proposal for two different DC-DC topologies with a suitable control strategy. A Triple-Output Boost (TOB) converter and a Boost 3-Output Voltage Sharing (Boost-3OVS) converter connected to the four-level diode-clamped converter are proposed to arrange the proposed asymmetrical DC link for the high modulation indices and unity power factor. Cascade converters have shown their abilities and strengths in medium and high power applications. Using asymmetrical H-bridge inverters, more voltage levels can be generated in output voltage with the same number of components as the symmetrical converters. The concept of cascading multilevel H-bridge cells is used to propose a fifteen-level cascade inverter using a four-level H-bridge symmetrical diode-clamped converter, cascaded with classical two-level Hbridge inverters. A DC voltage ratio of cells is presented to obtain maximum voltage levels on output voltage, with adjacent switching vectors between all possible voltage levels; this can minimize the switching losses. This structure can save five isolated DC sources and twelve switches in comparison to conventional cascade converters with series two-level H bridge inverters. To increase the quality in presented hybrid topology with minimum number of components, a new cascade inverter is verified by cascading an asymmetrical four-level H-bridge diode-clamped inverter. An inverter with nineteen-level performance was achieved. This synthesizes more voltage levels with lower voltage and current THD, rather than using a symmetrical diode-clamped inverter with the same configuration and equivalent number of power components. Two different predictive current control methods for the switching states selection are proposed to minimise either losses or THD of voltage in hybrid converters. High voltage spikes at switching time in experimental results and investigation of a diode-clamped inverter structure raised another problem associated with high-level high voltage multilevel converters. Power switching components with fast switching, combined with hard switched-converters, produce high di/dt during turn off time. Thus, stray inductance of interconnections becomes an important issue and raises overvoltage and EMI issues correlated to the number of components. Planar busbar is a good candidate to reduce interconnection inductance in high power inverters compared with cables. The effect of different transient current loops on busbar physical structure of the high-voltage highlevel diode-clamped converters is highlighted. Design considerations of proper planar busbar are also presented to optimise the overall design of diode-clamped converters.
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Weber, Johannes [Verfasser], Linus [Akademischer Betreuer] Maurer, Linus [Gutachter] Maurer, and Robert [Gutachter] Weigel. "Pulsed High Current Characterization of Highly Integrated Circuits and Systems / Johannes Weber ; Gutachter: Linus Maurer, Robert Weigel ; Akademischer Betreuer: Linus Maurer ; Universität der Bundeswehr München, Fakultät für Elektrotechnik und Informationstechnik." Neubiberg : Universitätsbibliothek der Universität der Bundeswehr München, 2019. http://d-nb.info/1201593816/34.
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Weber, Johannes [Verfasser], Linus [Akademischer Betreuer] Maurer, Linus Gutachter] Maurer, and Robert [Gutachter] [Weigel. "Pulsed High Current Characterization of Highly Integrated Circuits and Systems / Johannes Weber ; Gutachter: Linus Maurer, Robert Weigel ; Akademischer Betreuer: Linus Maurer ; Universität der Bundeswehr München, Fakultät für Elektrotechnik und Informationstechnik." Neubiberg : Universitätsbibliothek der Universität der Bundeswehr München, 2019. http://nbn-resolving.de/urn:nbn:de:bvb:706-6303.
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Tajalli, Alaleh. "Characterization and Study of Reliability Aspects in GaN High ElectronMobility Transistors." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3427319.
Full textAbstract:
GaN-based high electron mobility transistors (HEMTs) have excellent performance for power applications. Indeed, characteristics such as the high breakdown electric filed (3.3 MV/cm), the low ON-Resistance (RON) and the good thermal dissipation make the GaN-based diode and transistor a good potential for high frequency and power applications. The other outstanding feature of GaN-based HEMTs is the high electron mobility (1200 cm2/V.s) of the 2-dimensional electron gas (2DEG), formed at the interface between AlGaN and GaN, which leads to a low channel resistance and a high current density.
This thesis presents an overview of the most relevant trapping and degradation mechanisms that limit the performance and lifetime of GaN-based transistors for power electronics applications. To that end, pulsed I-V and drain current transient measurements are employed in order to investigate the trapping effects. The degradations of AlGaN/GaN MIS-HEMTs submitted to the gate step-stress experiments are investigated in the first part of this thesis. The results, that are obtained by a combined electrical and optical characterization over the different voltages, are discussed in chapter 2 which indicate the existence of a field- and hot-electron induced phenomena as the AlGaN/GaNMIS-HEMTs degradation mechanism.
A specific discussion is devoted to investigate the proton irradiation effect on the dynamic-Ron in HEMTs and is presented in chapter 3. It is shown that the proton irradiation is an effective and controllable method to reduce the dynamic-Ron in AlGaN/GaN HEMTs. Indeed, it is shown that samples that are submitted to a proton irradiation at high fluences (1.5£1014 cm– 2, 3MeV) exhibit a complete suppression of dynamic-Ron (complete voltage range, 150°C). This chapter further continuous to describe the voltage and temperature-dependent pulsed I-V characteristics of 650 V-rated transistors. It also points out the physical origin of dynamic RON in these devices.
Furthermore, owing to the positive and stable threshold voltage, the low on-resistance and the high breakdown field, the p-GaN gate GaN-based transistors are commonly accepted as promising devices for application in power converters. To that end, chapter 4 deals with the mechanisms that limit the dynamic performance and the reliability of normally-off GaN-based transistors. This chapter proposed the suppression of threshold voltage instability by a suitable passivation on the p-GaN sidewall. The improved reliability of device highlights that hole trapping mostly takes place on the sidewalls.
Finally, in chapter 5, a low leakage current and a state-of-the-art vertical breakdown voltage of above 1400 V a carbon-free GaN-on-Si device are demonstrated. These characteristics are achieved thanks to a thick and excellent crystal quality of GaN buffer. Indeed, low trapping effects are observed all the way to 1200 V with a low dependency of the substrate bias on the current density. The first demonstration of trap-free at such high voltage with this material system, could paves the way for 1200 V applications with GaN-on-Si resulting in a lower Ron and thus higher efficiency as compared to SiC and Si devices.
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Weerasekara, Aruna Bandara. "Electrical and Optical Characterization of Group III-V Heterostructures with Emphasis on Terahertz Devices." Digital Archive @ GSU, 2007. http://digitalarchive.gsu.edu/phy_astr_diss/16.
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Electrical and optical characterizations of heterostructures and thin films based on group III-V compound semiconductors are presented. Optical properties of GaMnN thin films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on GaN/Sapphire templates were investigated using IR reflection spectroscopy. Experimental reflection spectra were fitted using a non - linear fitting algorithm, and the high frequency dielectric constant (ε∞), optical phonon frequencies of E1(TO) and E1(LO), and their oscillator strengths (S) and broadening constants (Γ) were obtained for GaMnN thin films with different Mn fraction. The high frequency dielectric constant (ε∞) of InN thin films grown by the high pressure chemical vapor deposition (HPCVD) method was also investigated by IR reflection spectroscopy and the average was found to vary between 7.0 - 8.6. The mobility of free carriers in InN thin films was calculated using the damping constant of the plasma oscillator. The terahertz detection capability of n-type GaAs/AlGaAs Heterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) structures was demonstrated. A threshold frequency of 3.2 THz (93 µm) with a peak responsivity of 6.5 A/W at 7.1 THz was obtained using a 0.7 µm thick 1E18 cm−3 n - type doped GaAs emitter layer and a 1 µm thick undoped Al(0.04)Ga(0.96)As barrier layer. Using n - type doped GaAs emitter layers, the possibility of obtaining small workfunctions (∆) required for terahertz detectors has been successfully demonstrated. In addition, the possibility of using GaN (GaMnN) and InN materials for terahertz detection was investigated and a possible GaN base terahertz detector design is presented. The non - linear behavior of the Inter Pulse Time Intervals (IPTI) of neuron - like electric pulses triggered externally in a GaAs/InGaAs Multi Quantum Well (MQW) structure at low temperature (~10 K) was investigated. It was found that a grouping behavior of IPTIs exists at slow triggering pulse rates. Furthermore, the calculated correlation dimension reveals that the dimensionality of the system is higher than the average dimension found in most of the natural systems. Finally, an investigation of terahertz radiation efect on biological system is reported.
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Tobolová, Marie. "Mikrostimulátor." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219499.
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The theoretical part of the thesis deals with the explanation of the actions that occur during the stimulation of tissues with the electric current. A significant analogy with electrical circuits is used to describe the phenomena at the molecular and cellular level. The models of membrane and cell are necessary for understanding the behaviour of more complex structures, such as tissues and organs. A considerable attention is paid to the conditions of electrical stimulation which bring about response in the stimulated area. Next, the cumulative effect of the subthreshold stimulation is analysed. The mechanisms of common treatment effects of the electrotherapeutic methods are outlined. The research results in the practical part of the thesis – the design for a microstimulator. Properties of the microstimulator and compliance with standard requirements are verified by testing the electromagnetic compatibility and electrical safety, conducted by the Institute for testing and certification, JSC. The effects of microstimulation on living organisms are experimentally investigated on horses, in collaboration with the Veterinary and Pharmaceutical University. For the first time, thermodynamic sensors are used for the objective assessment of the microstimulation therapeutic effect. These miniature sensors are placed on the horse´s front legs and monitor the changes in thermal activity while only one limb is really stimulated and the other is just considered as a reference. Comparison and statistical evaluation of the measured signals could provide a more detailed view of the thermal changes within the stimulated area, which is significantly related to blood circulation in limbs, and with the support of the reduction of edema. The course of the experiment which deals with the effect of microstimulation on edema of the horse´s legs caused by minor injuries (tendinitis, sprains, etc.), is documented in photographs or videos that are significant for possible evaluation of the effectiveness of the stimulation in this application.
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Aboelhassan, Mustafa Osman Elrayah. "Robustní řízení synchronního stroje s permanentními magnety a spínaným tokem." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-233605.
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Je jasné, že nejúspěšnější konstrukce zahrnuje postup vícefázového řízení, ve kterém každá fáze může být považována za samostatný modul. Provoz kterékoliv z jednotek musí mít minimální vliv na ostatní, a to tak, že v případě selhání jedné jednotky ostatní mohou být v provozu neovlivněny. Modulární řešení vyžaduje minimální elektrické, magnetické a tepelné ovlivnění mezi fázemi řízení (měniče). Synchronní stroje s pulzním tokem a permanentními magnety se jeví jako atraktivní typ stroje, jejíž přednostmi jsou vysoký kroutící moment, jednoduchá a robustní konstrukce rotoru a skutečnost, že permanentní magnety i cívky jsou umístěny společně na statoru. FS-PMSM jsou poměrně nové typy střídavého stroje stator-permanentní magnet, které představují významné přednosti na rozdíl od konvenčních rotorů - velký kroutící moment, vysoký točivý moment, v podstatě sinusové zpětné EMF křivky, zároveň kompaktní a robustní konstrukce díky umístění magnetů a vinutí kotvy na statoru. Srovnání výsledků mezi FS-PMSM a klasickými motory na povrchu upevněnými PM (SPM) se stejnými parametry ukazuje, že FS-PMSM vykazuje větší vzduchové mezery hustoty toku, vyšší točivý moment na ztráty v mědi, ale také vyšší pulzaci díky reluktančnímu momentu. Pro stroje buzené permanentními magnety se jedná o tradiční rozpor mezi požadavkem na vysoký kroutící moment pod základní rychlostí (oblast konstantního momentu) a provozem nad základní rychlostí (oblast konstantního výkonu), zejména pro aplikace v hybridních vozidlech. Je předložena nová topologie synchronního stroje s permanentními magnety a spínaným tokem odolného proti poruchám, která je schopná provozu během vinutí naprázdno a zkratovaného vinutí i poruchách měniče. Schéma je založeno na dvojitě vinutém motoru napájeném ze dvou oddělených vektorově řízených napěťových zdrojů. Vinutí jsou uspořádána takovým způsobem, aby tvořila dvě nezávislé a oddělené sady. Simulace a experimentální výzkum zpřesní výkon během obou scénářů jak za normálního provozu, tak za poruch včetně zkratových závad a ukáží robustnost pohonu za těchto podmínek. Tato práce byla publikována v deseti konferenčních příspěvcích, dvou časopisech a knižní kapitole, kde byly představeny jak topologie pohonu a aplikovaná řídící schémata, tak analýzy jeho schopnosti odolávat poruchám.
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Zhou, Hua. "Harmonic current control in a high-power current source rectifier system." Master's thesis, 2011. http://hdl.handle.net/10048/1702.
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Line current distortion is an important issue to a high-power current source rectifier(CSR) system. There are two main challenges related to this issue. First, the CSR input LC resonance can be affected by the variation of the source inductance from the power system and the effects of the CSR DC side circuit, which may lead to a line current distortion higher than expected. Another challenge is that the traditional high-power CSR using Selective Harmonic Elimination (SHE) pulse-width modulation (PWM) technique attempts to eliminate certain harmonics in the PWM current, which limits its ability for line current harmonic control. To control the CSR line current harmonics, this thesis focuses on two aspects: 1) the analysis and design of CSR input filter to avoid unexpected input LC resonance, and 2) the development of a new PWM scheme that can compensate the effects of the grid voltage harmonics and DC link current ripples. The thesis work has been validated by simulations and on an experimental CSR prototype.<br>Power Engineering and Power Electronics
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Chao, Kuan-Yu, and 趙冠宇. "Nickel Hexacyanoferrate-Modified LiFePO4 Cathodes with High-Rate and High-Pulse Current Charge-Discharge Capabilities." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/57004706193694668747.
Full textAbstract:
碩士<br>逢甲大學<br>綠色能源科技碩士學位學程<br>104<br>Nickel hexacyanoferrate (NiHCF) was synthesized by reverse micelle method and was coated on LiFePO4 (LFP) cathodes to improve the high-rate and pulse-current charge-discharge performances. This NiHCF has a low-strain open framework structure and exhibits a redox potential similar to that of LFP. The NiHCF-modified LFP cathodes show improved high-rate capability, with a 10 C discharge capacity that is 15% higher than that of pristine LFP. The NiHCF-modified LFP can endure high-pulse current charge-discharge, which is well suited for green energy grids. The modified and pristine LFP cathodes were operated with alternate pulse currents of 0.01 C and 5 C introduced into a 0.2 C discharge/charge process to simulate the conditions of green grids. The modified LFP cathodes exhibited a capacity retention of 92% after 50 cycles, whereas the pristine sample showed a capacity retention of only 75%. These results can be attributed to the reduction of electrode/electrolyte interface resistances due to NiHCF coating, as demonstrated by electrochemical impedance spectroscopy.
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Ma, Yu-Sheng, and 馬佑昇. "A Digital-Type GaN Driver with Current-Pulse-Balancer Technique Achieving Sub-nanosecond Current Pulse Width for High Resolution and Dynamic Effective Range LiDAR System." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/e7ysm8.
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YANG, FU-KUO, and 楊富國. "White LED Driver with High Current Matching and Pulse-Width-Modulation Brightness Control." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/7y7v74.
Full textAbstract:
碩士<br>國立臺北科技大學<br>電腦與通訊研究所<br>96<br>The use of white LED can accord with the current issue in energy saving and environmental protection in the world. Due to the features of small size and longer life, this LED is widely used in the backlight of portable device display. The backlight can change the life time of battery and the brightness of display. In the thesis, switching mode boost DC-DC converter can make higher efficiency, and current sensing circuit can increase current matching of each output, and make the brightness of every white LED lightbulbs uniform.
The structure of whole system is consisted of three major parts:(1) Boost DC-DC converter will offer the voltage for white LED, and the circuit includes a compensator, a pulse-width-modulation, a non-overlapping circuit and a driver circuit. The pulse-width-modulation circuit is composed of ring oscillator and pseudo hyperbola charge current generator, and it can enhance the efficiency because the power consumption is lower than sawtooth generator. (2)Current sensing circuit is composed of current mirror and operational amplifier. (3)White LED brightness control circuit can be adjusted to the suitable brightness.
White LED driver is implemented by TSMC 0.35μm 2P4M CMOS 5V process and whole chip area is 1.503x1.218mm2 without pads. The range of the operation voltage is from 2.7V to 3.7V, and the output voltage is 4V. The output maximum current is at 105mA, the driver efficiency will reach to 90%, and the minimum mean error of each output current can reach to 1.6% matching.
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Ling, Kian Siong. "A PWM (pulse width modulated) transconductance amplifier for high current numerical protective relay testing." 2006. http://hdl.handle.net/1993/20820.
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唐, 永鹏, and Yongpeng TANG. "A study on restoration of fatigue damage in stainless steel by high-density pulse current." Thesis, 2013. http://hdl.handle.net/2237/19335.
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Sivaprasad, Sreenivasa J. "Control, Modulation and Testing of High-Power Pulse Width Modulated Converters." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3310.
Full textAbstract:
Experimental research on high-power converters, particularly in an academic environment, faces severe infrastructural constraints. Usually, power source and loads of required ratings are not available. Further, more importantly, the energy consumption is huge. One possibility is to establish an experimental research platform, comprising of a network of high-power converters, through which power is circulated and which draws only the losses from the mains.
This work deals with the establishment of a circulating power test set-up, comprising of two line-side PWM converters, inclusive of control and modulation methods for the two converters. Two types of circulating power test setups are developed. In the first setup, the converters are connected in parallel, on ac as well as dc sides, such that real and/or reactive power is circulated between them. In the second test setup, the dc buses of the converters are separated; hence, only reactive power circulation is possible. These setups are used to conduct heat-run tests with low energy expenditure on the PWM converters at various operating conditions up to power levels of 150 kVA. Further, these are used to validate analytically-evaluated thermal characteristics of high-power PWM converters. A safe thermal limit is derived for such converters in terms of apparent power (kVA) handled, power factor and switching frequency. The effects of voltage sag and of unequal current sharing between parallel IGBT modules on the safe thermal limit are studied.
While the power drawn by the circulating-power setup from the grid is much lower than the ratings of the individual converters, the harmonic injection into the mains by the setup could be significant since the harmonics drawn by both converters tend to add up. This thesis investigates carrier interleaving to improve the waveform quality of grid current, drawn by the circulating-power test setup. The study of carrier interleaving is quite general and covers various applications of parallel-connected converters such as unity power factor rectification, static reactive power compensation and grid-connected renewable energy systems.
In literature, carrier interleaving has been employed mainly for unity power factor rectifiers, sharing a common dc load equally. In such case, the fundamental components of the terminal voltages of the parallel converters are equal. However, when the power sharing between the two converters is unequal, or when power is circulated between the two converters, the terminal voltages of the two converters are not equal. A method to estimate rms grid current ripple, drawn by parallel-connected converters with equal and/or unequal terminal voltages, in a synchronous reference frame is presented. Further, the influence of carrier interleaving on the rms grid current ripple is studied. The optimum interleaving angle, which minimizes the rms grid current ripple under various applications, is investigated. This angle is found to be a function of modulation index of the converters in the equal terminal voltages case. In the unequal terminal voltages case, the optimum interleaving angle is shown to be a function of the average modulation index of the two parallel converters.
The effect of carrier interleaving is experimentally studied on the reactive power circulation setup at different values of kVA and different dc bus voltages. The grid current ripple is measured for different values of interleaving angle. It is found experimentally that the optimum interleaving angle reduces the rms grid current ripple by between 37% and 48%, as compared without interleaving, at various operating conditions.
Further, the reactive power circulation test set-up is used to evaluate and compare power conversion losses corresponding to different PWM techniques such as conventional space-vector PWM (CSVPWM), bus-clamping PWM (BCPWM) and advanced bus-clamping PWM methods for static reactive power compensator (STATCOM) application at high power levels. It is demonstrated theoretically as well as experimentally that an advanced bus-clamping PWM method, termed minimum switching loss PWM (MSLPWM), leads to significantly lower power conversion loss than CSVPWM and BCPWM techniques at a given average switching frequency.
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Sivaprasad, Sreenivasa J. "Control, Modulation and Testing of High-Power Pulse Width Modulated Converters." Thesis, 2013. http://etd.iisc.ernet.in/2005/3310.
Full textAbstract:
Experimental research on high-power converters, particularly in an academic environment, faces severe infrastructural constraints. Usually, power source and loads of required ratings are not available. Further, more importantly, the energy consumption is huge. One possibility is to establish an experimental research platform, comprising of a network of high-power converters, through which power is circulated and which draws only the losses from the mains.
This work deals with the establishment of a circulating power test set-up, comprising of two line-side PWM converters, inclusive of control and modulation methods for the two converters. Two types of circulating power test setups are developed. In the first setup, the converters are connected in parallel, on ac as well as dc sides, such that real and/or reactive power is circulated between them. In the second test setup, the dc buses of the converters are separated; hence, only reactive power circulation is possible. These setups are used to conduct heat-run tests with low energy expenditure on the PWM converters at various operating conditions up to power levels of 150 kVA. Further, these are used to validate analytically-evaluated thermal characteristics of high-power PWM converters. A safe thermal limit is derived for such converters in terms of apparent power (kVA) handled, power factor and switching frequency. The effects of voltage sag and of unequal current sharing between parallel IGBT modules on the safe thermal limit are studied.
While the power drawn by the circulating-power setup from the grid is much lower than the ratings of the individual converters, the harmonic injection into the mains by the setup could be significant since the harmonics drawn by both converters tend to add up. This thesis investigates carrier interleaving to improve the waveform quality of grid current, drawn by the circulating-power test setup. The study of carrier interleaving is quite general and covers various applications of parallel-connected converters such as unity power factor rectification, static reactive power compensation and grid-connected renewable energy systems.
In literature, carrier interleaving has been employed mainly for unity power factor rectifiers, sharing a common dc load equally. In such case, the fundamental components of the terminal voltages of the parallel converters are equal. However, when the power sharing between the two converters is unequal, or when power is circulated between the two converters, the terminal voltages of the two converters are not equal. A method to estimate rms grid current ripple, drawn by parallel-connected converters with equal and/or unequal terminal voltages, in a synchronous reference frame is presented. Further, the influence of carrier interleaving on the rms grid current ripple is studied. The optimum interleaving angle, which minimizes the rms grid current ripple under various applications, is investigated. This angle is found to be a function of modulation index of the converters in the equal terminal voltages case. In the unequal terminal voltages case, the optimum interleaving angle is shown to be a function of the average modulation index of the two parallel converters.
The effect of carrier interleaving is experimentally studied on the reactive power circulation setup at different values of kVA and different dc bus voltages. The grid current ripple is measured for different values of interleaving angle. It is found experimentally that the optimum interleaving angle reduces the rms grid current ripple by between 37% and 48%, as compared without interleaving, at various operating conditions.
Further, the reactive power circulation test set-up is used to evaluate and compare power conversion losses corresponding to different PWM techniques such as conventional space-vector PWM (CSVPWM), bus-clamping PWM (BCPWM) and advanced bus-clamping PWM methods for static reactive power compensator (STATCOM) application at high power levels. It is demonstrated theoretically as well as experimentally that an advanced bus-clamping PWM method, termed minimum switching loss PWM (MSLPWM), leads to significantly lower power conversion loss than CSVPWM and BCPWM techniques at a given average switching frequency.
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Shao, Zhen-Ting, and 邵振庭. "Study and Implementation of A Boost Converter with Low Current Ripple and High Voltage Gain Based on Complementary Single-Sided Multiple Pulse Width Modulation." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/13760487010847230289.
Full textAbstract:
碩士<br>國立中央大學<br>電機工程學系<br>104<br>The thesis presents an improved non-isolated boost DC-DC converter. The boost DC-DC converter has been widely applied on renewable generation and energy storage. Improved circuit proposed in this thesis is divided into two stages through three IGBT switches to perform the control. The first stage is a modified circuit architecture of the input current ripple complementary boost converter. The current ripple through two switches can be effectively reduced by inversely operating. This approach not only enables a more stable input source but also reduces the high current carrying stress of single inductor. Through the proposed single-sided multiple pulse width modulation control the input current ripple can be maintained in a minimum range at any duty ratio.
The second stage apply switched-inductors replaced for a single inductor to increase the voltage gain ratio. Finally, a boost converter with an input voltage of 40~60 V, an output voltage of 150~400 V, and output power of 300 W is implemented. The experimental results are verified with theoretical analysis of the proposed structure.
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Σακκάς, Σωτήρης. "Ανάλυση συστήματος μεταφοράς με διασύνδεση Σ.Ρ. και PWM ρυθμιζόμενους μετατροπείς". Thesis, 2012. http://hdl.handle.net/10889/5757.
Full textAbstract:
Τα τελευταία χρόνια έχει αρχίσει να διαδίδεται με γρήγορους ρυθμούς η μέθοδος μεταφοράς ισχύος μέσω συνεχούς ρεύματος. Προς αυτή την κατεύθυνση ώθηση έδωσε η ανάπτυξη νέων ημιαγωγικών διακοπτικών στοιχείων οδηγώντας σε περεταίρω ανάπτυξη και χρήση των συστημάτων μεταφοράς με συνεχές ρεύμα. Σε αυτή τη διπλωματική εργασία μελετάται ένα σύστημα μεταφοράς ισχύος με διασύνδεση συνεχούς ρεύματος (HVDC), που συνδέεται ανάμεσα σε δυο εναλλασσόμενα ηλεκτρικά δίκτυα με και χωρίς φορτίο. Την διασύνδεση συνεχούς ρέματος πραγματοποιούν δυο back-to-back AC/DC μετατροπείς VSC, που αναλαμβάνουν τους ρόλους του ανορθωτή και του αντίστροφα ισχύος. Οι μετατροπείς χρησιμοποιούν την διαμόρφωση πλάτους παλμού PWM. Αρχικά μελετάται θεωρητικά το μοντέλο των μετατροπέων και του back-to-back HVDC συστήματος και στην συνέχεια σχεδιάζεται και αναλύεται η λειτουργία του ανάμεσα σε δυο δίκτυα εναλλασσομένου ρεύματος με ή χωρίς την ταυτόχρονη παρουσία φορτίου. Τέλος προσομοιώνεται το σύστημα μέσω του λογισμικού Matlab και συγκεκριμένα της εφαρμογής Simulink για την εξαγωγή συμπερασμάτων.<br>In the past few years the method of power transmission by means of direct current has expanded rapidly. To this direction a push forward has been given by the development of new semi-conductive switching valves leading to a further development of transmission systems by direct current. In this thesis what is considered is a power transmission system via direct current HVDC connected between two AC electric networks with or without load. The direct current connection is achieved through back-to-back AC/DC converters VSC which undertake the role of rectifier and that of inverter of power. The converters use the Pulse Width Modulation (PWM). At first the converter model and the back-to-back HVDC system is theoretically approached and in the process what is designed and analyzed is its function between two networks of AC current with or without the simultaneous presence of load. Finally the system is simulated through software Matlab and specifically the application of simulink in order to draw conclusions.
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Lukic, Zdravko. "Design and Practical Implementation of Advanced Reconfigurable Digital Controllers for Low-power Multi-phase DC-DC Converters." Thesis, 2012. http://hdl.handle.net/1807/33855.
Full textAbstract:
The main goal of this thesis is to develop practical digital controller architectures for multi-phase dc-dc converters utilized in low power (up to few hundred watts) and cost-sensitive applications. The proposed controllers are suitable for on-chip integration while being capable of providing advanced features, such as dynamic efficiency optimization, inductor current estimation, converter component identification, as well as combined dynamic current sharing and fast transient response.
The first part of this thesis addresses challenges related to the practical implementation of digital controllers for low-power multi-phase dc-dc converters. As a possible solution, a multi-use high-frequency digital PWM controller IC that can regulate up to four switching converters (either interleaved or standalone) is presented. Due to its configurability, low current consumption (90.25 μA/MHz per phase), fault-tolerant work, and ability to operate at high switching frequencies (programmable, up to 10 MHz), the IC is suitable to control various dc-dc converters. The applications range from dc-dc converters used in miniature battery-powered electronic devices consuming a fraction of watt to multi-phase dedicated supplies for communication systems, consuming hundreds of watts.
A controller for multi-phase converters with unequal current sharing is introduced and an efficiency optimization method based on logarithmic current sharing is proposed in the second part. By forcing converters to operate at their peak efficiencies and dynamically adjusting the number of active converter phases based on the output load current, a significant improvement in efficiency over the full range of operation is obtained (up to 25%). The stability and inductor current transition problems related to this mode of operation are also resolved.
At last, two reconfigurable digital controller architectures with multi-parameter estimation are introduced. Both controllers eliminate the need for external analog current/temperature sensing circuits by accurately estimating phase inductor currents and identifying critical phase parameters such as equivalent resistances, inductances and output capacitance. A sensorless non-linear, average current-mode controller is introduced to provide fast transient response (under 5 μs), small voltage deviation and dynamic current sharing with multi-phase converters. To equalize the thermal stress of phase components, a conduction loss-based current sharing scheme is proposed and implemented.