No description available.

The dissertation studies the nonlinear resonance problems of power systems. Generally speaking, ferroresonance has usually occurred in low-voltage distribution system, especially for potential transformers. Due to the considerable increase of power consumption, the power system is more complex than before. Besides, a number of under-ground cables are used, and transformers¡¦ loss reduce due to improvement of core iron material. These factors could probably result in ferroresnance occurring in extra-high-voltage power system. The dissertation proposed three-phase representation method to analyze unbalance and non-linear system. This method employ magnetically coupled electrical circuit techniques and the original voltage equations can be used without the need for any transformations, which improves significantly computation accuracy. Consequently, it is quite suitable for power system design and incident investigation. Since the traditional d-q-0 model is not well suited for the study of unbalanced faults and requires further transformation, the analytical solution becomes rather complicated and the solutions are still inaccurate. At last we simulated the ferroresonant overvoltages occurring at a nuclear power station in Taiwan in order to investigate the causes and afford mitigation. The simulation results were enough to prove accuracy and practicability of this method.

A pulse hysteresisgraph system was constructed capable outputting current source and voltages source waveforms. MATLAB scripts were created to analyze the collected data. Three toroidal samples of soft magnetic materials were prepared. Theoretical modeling was done to predict the variation of effective applied magnetic fields inside the toroids from ideal assumptions due to three effects: wire spacing, cylindrical spreading, and eddy current generated fields. Data was collected under sinusoidal voltage source and sinusoidal current source excitation at 1 kHz. Large differences in core loss were noted especially at higher field excitations. Core loss under sinusoidal current source excitation was found to always be greater than or equal to core loss under sinusoidal voltage source. Normal magnetization curves under sinusoidal current and voltage source excitation were also compared. Significant differences were apparent in the magnetization curves of one sample toroid, and slight differences noted in the curves of the other two samples. Eddy currents were offered as a primary mechanism for the difference in core loss between sinusoidal current source and sinusoidal voltage source. A formula to predict the relative eddy current losses to be expected from an arbitrary, periodic voltage waveform shape is given. / text

Šio darbo tyrimo tikslas – ištirti elektros energijos apskaitos prietaisų, indukcinių ir elektroninių, charakteristikas. Buvo atlikta informacijos šaltinių analizė apie indukcinių ir elektroninių elektros energijos skaitiklių ir srovės matavimo transformatorių parametrus, apsprendžiančius jų charakteristikas. Remiantis informacijos šaltinių apibendrinimu suformuota hipotezė: ne visos elektroninių elektros energijos prietaisų charakteristikos geresnės už indukcinių elektros energijos apskaitos prietaisų charakteristikas. Suformuoti tyrimo uždaviniai: ištirti elektroninių ir indukcinių elektros energijos prietaisų paklaidų priklausomybes nuo apkrovos srovės, galios koeficiento, eksploatacijos laiko, pasvyros kampo ir srovės matavimo transformatorių srovinės paklaidas. Padarytos išvados, nurodomas naudotos literatūros sąrašas. / The aim of this paper is to investigate the electricity metering devices, i.e. inductive and electronic, characteristics. It was made the analysis of the sources about the inductive and electricity meters and current transformers for measuring the parameters that define their characteristics. According to sources of information was formed the hypothesis: not all electronic power devices characteristics are better than inductive energy metering devices characteristics. The study objectives are to investigate experimentally the electronic and inductive power devices values of the load current, power factor, operating time, against an adverse list angle and current measuring transformer errors stream. Findings are discussed; the list of references is presented.

This diploma thesis is focused on investigation of metallic thin films and nanostructures using scanning probe microscopy. Magnetic properties of these objects are studied by magnetic force microscopy, which is modification of scanning probe microscopy. In the theoretical part basic principles of scanning probe microscopy and magnetic force microscopy are summarized, and also principle of creation of magnetic domains and some special properties of ferromagnetic and antiferromagnetic materials. Further, two techniques of fabricating nanostructures are described. Experimental part is focused on imaging and simulating of magnetic domains. Further, exchange bias is revealed. This phenomenon is present in systems composed from ferromagnetic and antiferromagnetic materials. One part of this diploma thesis is also focused on discussion of problems with magnetic force microscopy.

Les matériaux piézoélectriques et ferroélectriques présentent un comportementélectromécanique couplé. Cette particularité leur a permis d’être utilisés dans de nombreusesapplications telles que les applications de capteur, actionneur, transformateur et récupérateurd’énergie. En outre, en raison de leur comportement non linéaire et dissipatif, les matériauxferroélectriques sont de plus en plus utilisés dans le domaine de l’électronique en tant quecapacité accordable, mémoire non volatile, oscillateur et filtre. La performance et la fiabilitéde ces systèmes dépendent directement des propriétés ferroélectriques et piézoélectriques dumatériau, qui nécessite par conséquent d’être caractérisé. Les propriétés piézoélectriques,ferroélectriques, ferroélastiques et diélectriques des matériaux ferroélectriques ont été le sujetde nombreuses études. Pourtant, les conditions d’essai restent difficiles à maîtriser car lespropriétés thermiques, mécaniques et électriques de ces matériaux sont fortement couplées.Dans cette thèse, un dispositif de mesure de champ de déformation a été conçu pourcaractériser le comportement piézoélectrique et ferroélectrique des céramiquesferroélectriques. Ce dispositif utilise un banc optique ainsi qu’un algorithme de Corrélationd’Images Numériques (CIN) 2D appelé CorreliRT3. Cet algorithme est basé sur une approcheglobale et réduit les erreurs de mesure de déplacement en s’appuyant sur les équationsd’équilibre de la mécanique des solides. Grâce au banc de caractérisation par CIN, il estmontré que les déformations piézoélectriques et ferroélectriques peuvent être mesurées avecune incertitude d’environ 10-5. Cette incertitude est atteinte aussi bien pour des sollicitationssimples que couplées (champ électrique et/ou contrainte mécanique). Il est aussi montré quele banc expérimental permet de vérifier les conditions d’essai en caractérisant l’hétérogénéitédes déformations lors d’un essai matériau.Dans les deux derniers chapitres, un matériau ferroélectrique est caractérisé souschamp électrique et sous contrainte mécanique. Le comportement du matériau est présenté etdiscuté dans les différentes configurations de chargement. Les propriétés matériau, telles queles coefficients piézoélectriques (d33, d31), sont extraites et étudiées en fonction du champélectrique et de la contrainte. Les résultats montrent que la CIN est capable de mesurer etcaractériser le comportement et les propriétés des matériaux ferroélectriques etpiézoélectriques. L’avantage de la CIN étant que, contrairement aux méthodes de mesureclassiques, celle-ci ne perturbe pas les conditions d’essai (mesure sans contact) et permette dedétecter la présence d’erreurs systématiques. / Piezoelectric and ferroelectric materials exhibit a coupled electromechanicalbehaviour. This property allows a use in various kinds of applications such as sensors,actuators, harvesting devices or converters. In addition, due to their non-linear and dissipativebehaviour, ferroelectric materials are increasingly used in electronic applications such astunable capacitors, non-volatile memory, oscillators and filters. The performance andreliability of such devices depend on the material electromechanical properties, whichconsequently need to be characterised. In the past decades, such characterisation was largelydeveloped and the piezoelectric, ferroelectric, ferroelastic and dielectric properties offerroelectrics were the subject of numerous studies. Yet the test conditions are difficult tocontrol due to the strong interplay between thermal, mechanical and dielectric properties.In this work, a full-field measurement apparatus has been designed to characterise thepiezoelectric and ferroelectric strain behaviour of ferroelectric ceramics. This apparatus usesan optical setup and a 2D Digital Image Correlation (DIC) algorithm named CorreliRT3. Thealgorithm is based on a global approach and reduces the displacement field errors using thebalance equations of solid mechanics. It is shown that piezoelectric and ferroelectric strainscan be measured with an uncertainty around 10-5 by using the developed setup. Thisuncertainty is reached under uncoupled or coupled loading (electric field and/or stress). It isalso shown that the experimental setup can control the test conditions by characterising thestrain heterogeneity during the test.In the two last chapters, a ferroelectric material is characterised under electric field andstress. The material behaviour is presented and discussed in the different loadingconfigurations. Material properties, such as the longitudinal and transverse piezoelectriccoefficients (d33, d31) are extracted and analysed as a function of the electric field and stress.The results show that the DIC technique is able to measure and characterise the behaviour andthe properties of ferroelectric and piezoelectric materials. The main benefits of this techniqueis that, contrary to classical measurement techniques, the measurement does not alter the testconditions. Moreover, DIC is able to detect test anomalies such as strain heterogeneities

The erosion and transport of fertile topsoil is a serious problem in the U.S., Australia, China and throughout Europe. It results in extensive environmental damage, reduces soil fertility and productivity, and causes significant environmental loss. It is as big a threat to the future sustainability of global populations as climate change, but receives far less attention. With both chemicals (fertilizers, pesticides, herbicides) and biological pathogens (bacteria, viruses) preferentially sorbing to silt and clay sized soil particles, estimating contaminant fluxes in eroded soil also requires predicting the transported soils particle size distribution. The Hairsine-Rose (HR) erosion model is considered in this thesis as it is one of the very few that is specifically designed to incorporate the effect of particle size distribution, and differentiates between non-cohesive previously eroded soil compared with cohesive un-eroded soil. This thesis develops a new extended erosion model that couples the HR approach with the one-dimensional St Venant equations, and an Exner bed evolution equation to allow for feedback effects from changes in the local bed slope on surface hydraulics and erosion rates to be included. The resulting system of 2I +3 (where I = number of particle size classes) nonlinear hyperbolic partial differential equations is then solved numerically using a Liska-Wendroff predictor corrector finite difference scheme. Approximate analytical solutions and series expansions are derived to overcome singularities in the numerical solutions arising from either boundary or initial conditions corresponding to a zero flow depth. Three separate practical applications of the extended HR model are then considered in this thesis, (i) flow through vegetative buffer strips, (ii) modelling discharge hysteresis loops and (iii) the growth of antidunes, transportational cyclic steps and travelling wave solutions. It is shown by comparison against published experimental flume data that predictions from the extended model are able to closely match measurements of deposited sediment distribution both upstream and within the vegetative buffer strip. The experiments were conducted with supercritical inflow to the flume which due to the increased drag from the vegetative strip, resulted in a hydraulic jump just upstream of the vegetation. As suspended sediment deposited at the jump, this resulted in the jump slowly migrating upstream. The numerical solutions were also able to predict the position and hydraulic jump and the flow depth throughout the flume, including within the vegetative strip, very well. In the second application, it is found that the extended HR model is the first one that can produce all known types of measured hysteresis loops in sediment discharge outlet data. Five main loop types occur (a) clockwise, (b) counter-clockwise, (c,d) figure 8 of both flow orientations and (e) single curve. It is clearly shown that complicated temporal rainfall patterns or bed geometry are not required to developed complicated hysteresis loops, but it is the spatial distribution of previously eroded sediment that remains for the start of a new erosion event, which primarily governs the form of the hysteresis loop. The role of the evolution of the sediment distribution in the deposited layer therefore controls loop shape and behavior. Erosion models that are based solely on suspended sediment are therefore unable to reproduce these hysteretic loops without a priori imposing a hysteretic relationship on the parameterisations of the erosion source terms. The rather surprising result that the loop shape is also dominated by the suspended concentration of the smallest particle size is shown and discussed. In the third application, a linear stability analysis shows that instabilities, antidunes, will grow and propagate upstream under supercritical flow conditions. Numerical simulations are carried out that confirm the stability analysis and show the development and movement of antidunes. For various initial parameter configurations a series of travelling antidunes, or transportational cyclic steps, separated by hydraulic jumps are shown to develop and evolve to a steady form and wave speed. Two different forms arise whereby (a) the deposited layer completely shields the underlying original cohesive soil so that the cohesive layer plays no role in the speed or shape of the wave profile or (b) the cohesive soil is exposed along the back of the wave such that both the non-cohesive and cohesive layers affect the wave profile. Under (a) the solutions are obtained up to an additive constant as the actual location of the boundary of the cohesive soil is not required, whereas for (b) this constant must be determined in order to find the location on the antidune from where the cohesive soil becomes accessible. For single size class soils the leading order travelling wave equations are fairly straightforward to obtain for both cases (a) and (b). However for multi-size class soils, this becomes much more demanding as up to 2I + 3 parameters must be found iteratively to define the solution as each size class has its own wave profile in suspension and in the antidune.

Dans les applications de l’électronique de puissance, les inductances sont généralement utilisées avec des formes d’ondes triangulaire et rectangulaire. Dans ces conditions, les inductances ne peuvent pas être caractérisées avec des formes d’ondes sinusoïdales. Il existe dans la littérature plusieurs méthodes de caractérisation des inductances. Aucune de ces méthodes ne permet de caractériser les composants magnétiques intégrés dans des conditions compatibles avec les formes d’onde de l’électronique de puissance. Une nouvelle méthode de caractérisation en temps réel convenable aux composants magnétiques planaires intégrées est développée dans cette thèse. Le composant sous test est utilisé dans un convertisseur DC-DC. A partir du courant i(t) et de la tension u(t) relevés à ses bornes, il est possible de déterminer la caractéristique φ(i) du composant. Connaissant le cycle d’hystérésis φ(i), les principaux paramètres du composant tels que la valeur de l’inductance, le niveau de saturation du matériau magnétique, les pertes fer peuvent être déterminées. Il convient de préciser qu’après l’enregistrement de u(t) et de i(t), un traitement des données approprié est effectué pour obtenir des signaux exploitables. L’approche a été testée avec succès sur des inductances discrètes et planaires intégrées pour des fréquences de mesure allant jusqu’au MHz. Nous avons ainsi montré que cette méthode permet de relever des cycles mineurs jusqu’à la saturation du matériau magnétique et de tracer l’évolution de l’inductance en fonction de la composante continue du courant. Les résultats montrent que pour de très faibles courants, on a des fortes valeurs de l’inductance qui sont quasiment constantes, en revanche à des courants moyens, l’inductance diminue fortement et à des forts courants, le circuit magnétique se sature et la valeur de l’inductance devient donc très faible. Cette méthode permet également d’étudier l’évolution des pertes fer dans les mêmes conditions d’utilisation que celles rencontrées en électronique de puissance / In applications of power electronics, inductors are generally used with triangular and rectangular waveforms. In these conditions, inductors cannot be characterized with sinusoidal waveforms. Many methods of characterization are developed, but none of them allow the characterization of integrated magnetic components under conditions compatible with power electronics waveforms. A new real-time characterization method suitable for integrated magnetic components is developed in this thesis. The Device under test is inserted in a DC-DC converter. From u(t) voltage and i(t) current recordings, it is possible to determine the φ(i) hysteresis loop that allows main inductor parameters to be determined: inductance value, core losses, and saturation of the magnetic material. It should be made clear when u(t) and i(t) are recorded, suitable signal processing is completed in order to obtain usable signals. The method has been successfully tested on discrete and integrated inductors with measurement frequencies up to MHz. We have thus shown that this method makes it possible to determine minor loops up to the saturation of the magnetic material and to plot the evolution of the inductance versus the DC bias current.The results show that for very low current values, we have obtained strong values of inductor and these values are constant. However, for the mean current, the inductance value decreases drastically and for strong current values, the magnetic material is saturated which causes very small values of inductor. This method also makes it possible to study the evolution of iron losses under the same conditions of use as those encountered in power electronics

Battery Management System (BMS) is an essential part in battery powered applications where large battery packs are in use. BMS ensures protection, controlling, supervision and accurate state estimation of battery pack to provide efficient energy management. However the particular application determines the accuracy and requirements of BMS where it has to implement; in electric vehicles (EVs) accuracy cannot be compromised. The software part of BMS estimates the states of the battery pack and takes the best possible decision. In EVs one of the key tasks of BMS’s software part is to provide the actual state of charge (SOC), which represents a crucial parameter to be determined, especially in lithium iron phosphate (LiFePO4) batteries, due to the presence of the high hysteresis behavior in the open circuit voltage than other kind of lithium batteries. This hysteresis phenomena appears with two different voltage curves during the charging and discharging process. The value of the voltage that the battery is going to assume during the off-loading operation depends on several factors, such as temperature, loop direction and ageing. In this research work, hybrid method is implemented in which advantages of several methods are achieved by implementing one technique combined with another. In this work SOC is calculated from coulomb counting method and in order to correct the error of SOC, an hysteresis model is developed and used due to presence of hysteresis effect in LiFePO4 batteries. An hysteresis model of the open circuit voltage (OCV) for a LiFePO4 cell is developed and implemented in MATLAB/Simulink© in order to reproduce the voltage response of the battery when no current from the cell is required (no load condition). Then the difference of estimated voltage and measured voltage is taken in order to correct the error of SOC calculated from coulomb counting or current integration method. To develop the hysteresis model which can reproduce the same voltage behavior, lot of experiments have been carried out practically in order to see the hysteresis voltage response and to see that how voltage curve change with the variation of temperature, ageing and loop direction. At the end model is validated with different driving profiles at different ambient temperatures.

This work is focused on study of mechanical properties of NiTi alloy which shows pseudoelastic and shape memory behaviour. Functional and structural fatigue of the material is examined. The main aim of this work was to perform and to evaluate a series of fatigue tests. The material was supplied in the form of wire which was gripped in the machine using special grips. In the first part of the experiment, tensile tests are evaluated and the reproducibility of measurements is demonstrated. Then, a series of cyclic tests was performed. Results were analysed together with previous measurements. One part of discussion concerned changes of the hysteresis loops during cycling and their dependence on strain rate. The fatigue life curves were plotted. It was found that these curves have non-standard shapes. The reasons for this are explained in the work.