Tesi sul tema "Electromagnetic losses"

The operation of a wide variety of applications in today's modern society are heavily dependent on the magnetic properties of ferromagnetic materials and their interaction with electromagnetic fields. The understanding of these interactions and the associated loss mechanisms is therefore crucial for the improvement and future development of such applications. This thesis is concerned with electromagnetic waves in media with ferromagnetic losses. We model the dynamics of the magnetization of a ferromagnetic material with the nonlinear Landau-Lifshitz-Gilbert (LLG) equation and study stability conditions on static solutions. Furthermore, with the aid of a small signal analysis this equation is linearized around a stable static solution. From this analysis we obtain a small signal permeability, which shows that ferromagnetic material in general are gyrotropic with a resonant frequency behavior similar to that of a Lorentz material. In difference to dielectric Lorentz material, this resonance frequency can be shifted with the aid of a bias field. For a specific bias field we obtain a frequency behavior that mimics that of a material with electric conductivity losses. In terms of losses per unit volume it is then possible to define a magnetic conductivity which is independent of frequency. We treat composite materials built from ferromagnetic inclusions in a nonmagnetic and nonconductinig background material. The composite material inherits the gyrotropic structure and resonant behavior of the single particle. The resonance frequency of the composite material is found to be independent of the volume fraction, unlike dielectric composite materials. For small enough particles, typically around 100 nm, it becomes energetically favorable to form a single domain in the particle, where disturbances in the magnetization can propagate in the form of spin waves. We study the possibility of exciting spin waves and derive a susceptibility that takes spin waves into account. It is found that spin wave resonances are excited in the gigahertz range and this could offer a way to increase the losses in a composite material. We also discuss some concerns regarding stability and causality of effective material parameters for biased ferromagnetic materials. Finally, we discuss the possibility of using magnetic materials in absorbing applications. We analyze the scattering of electromagnetic waves from a metal surface covered with a thin magnetic lossy sheet. It is found that very thin magnetic layers can provide substantial specular absorption over a wide frequency band. However, magnetic specular absorbers, where the waves propagates just a fraction of the wavelength in the material, seem to require a certain amount of ferromagnetic material which make them quite heavy and thereby limit its practical use. On the other hand, for nonspecular absorbers where the waves propagates several wavelengths in the material, the amount of magnetic material required for efficient absorption seems to be substantially less than for specular absorbers. Thus, as nonspecular absorbers, magnetic lossy materials could offer very thin and light designs.
QC 20100906

High-speed permanent magnet machines are currently being developed for a number of applications including gas-turbine generator sets and machine tools. Due to the high peripheral speed of the rotor and the relatively high conductivity of the magnets used, rotor eddy current loss can be substantial. Quite low levels of loss may present a serious problem if rotor cooling is poor. The accurate calculation of these losses, and appreciation of their dependence on machine parameters, are therefore of great importance for reasons of both efficiency and temperature rise. In this, thesis, a method has been developed to evaluate the asynchronously rotating harmonics with respect to the rotor and to calculate rotor power loss caused by these harmonics. The harmonics are determined by double Fourier analysis of the normal flux density data over the rotor surface. The data is obtained from finite element magnetostatic analysis of the machine at different rotor positions, with all possible harmonic sources present, except rotor induced eddy currents whose effect on harmonics was found to be negligible. Rotor power loss is calculated for each harmonic using a 2D rectilinear current sheet model of the machine. The magnitude of the current sheet, which is placed on the inner surface of a toothless stator, is adjusted to produce the same magnetostatic normal flux density over the rotor surface as that of the corresponding harmonic. The 2D current sheet model does not allow for 3D end effects and magnet segmentation. The accuracy of the analytical rectilinear current sheet model was verified by comparison with a cylindrical FE current sheet model, and by solving a benchmark eddy current problem that can be also solved using FE steady-state AC analysis. The current sheet model was used to calculate rotor loss in a number of generic machines, with two basic types of rotor construction: 1) non-salient rotor with arc shaped surface magnets and 2) salient rotor with chord shaped surface magnets. The results show that rotor loss depends strongly on the ratio of slot opening to slot pitch (s/X.) and on the ratio of total airgap to slot pitch (g/X). For the same fundamental airgap flux density, rotor loss reduces dramatically by increasing airgap length and reducing slot opening. Increasing the number of slots also reduces the loss. The results also show that rotor loss in a generator increases as the power factor moves from lagging to leading due to the armature reaction effect. Using a conducting sleeve, instead of a non-conducting one, with conductivity in the range of practical values, increases rotor losses dramatically. Reducing magnet conductivity reduces rotor loss. Rotor power loss in machines with non-conducting sleeve is concentrated on the surface of the magnet and a small part on the surface of the hub. In machines with chord shaped magnets, the power loss density can be very high in the parts of the steel hub near the intersection of two poles where local total airgap is small. The harmonics caused by inverter switching in a motor or rectifier switching in an alternator can cause a very significant increase in rotor loss, compared to a machine with a sinusoidal mmf. The results also show that the loss depends strongly on the switching strategy, e.g., switching harmonics in 6 step mmf waveform produce 3 times more loss than a 12 step mmf waveform. Although the developed method for calculation of rotor power loss does not take the effect of magnet peripheral discontinuity or segmentation into account, it is clear that segmentation reduces power loss by interrupting the eddy current return path, specially for harmonics with long wavelengths. The effect of segmentation requires further study.

Geomagnetic disturbances that result from solar activities can affect technological systems such as power networks. They may cause DC currents in power networks and saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomena result in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and malfunction of protective relays menaces the power network stability. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon. Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC. Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis. In this project, a new algorithm for digital measurement of the magnetic materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Two and three dimensional finite element models of various core types of power transformers are created to study the effect of DC magnetization on transformers. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a novel topological based time step transformer model has been outlined. The model can employ a detailed magnetic circuit and consider nonlinearity, hysteresis and eddy current effects of power transformers. Furthermore, the proposed model can be used in the design process of transformers and even extend other application such as analysis of electrical machines. The numerical and experimental studies in this project lead to understanding the mechanism that a geomantic disturbance affects power transformers and networks. The revealed results conclude with proposals for mitigation strategies against these phenomena.

QC 20150210

Planar magnetic elements are becoming a replacement for their conventional rivals. Among the reasons supporting their application, is their smaller size. Taking less bulk in the electronic package is a critical advantage from the manufacturing point of view. The planar structure consists of the PCB copper tracks to generate the desired windings .The windings on each PCB layer could be connected in various ways to other winding layers to produce a series or parallel connection. These windings could be applied coreless or with a core depending on the application in Switched Mode Power Supplies (SMPS). Planar shapes of the tracks increase the effective conduction area in the windings, brings about more inductance compared to the conventional windings with the similar copper loss case. The problem arising from the planar structure of magnetic inductors is the leakage current between the layers generated by a pulse width modulated voltage across the inductor. This current value relies on the capacitive coupling between the layers, which in its turn depends on the physical parameters of the planar scheme. In order to reduce this electrical power dissipation due to the leakage current and Electromagnetic Interference (EMI), reconsideration in the planar structure might be effective. The aim of this research is to address problem of these capacitive coupling in planar layers and to find out a better structure for the planar inductance which offers less total capacitive coupling and thus less thermal dissipation from the leakage currents. Through Finite Element methods (FEM) several simulations have been carried out for various planar structures. The labs prototypes of these structures are built with the similar specification of the simulation cases. The capacitive couplings of the samples are determined with Spectrum Analyser whereby the test analysis verified the simulation results.

The advent and proliferation of planar technologies for power converters are driven in part by the overall trends in analog and digital electronics. These trends coupled with the demands for increasingly higher power quality and tighter regulations raise various design challenges. Because inductors and transformers constitute a rather large part of the overall converter volume, size and performance improvement of these structures can subsequently enhance the capability of power converters to meet these application-driven demands. Increasing the switching frequency has been the traditional approach in reducing converter size and improving performance. However, the increase in switching frequency leads to increased power loss density in windings and core, with subsequent increase in device temperature, parasitics and electromagnetic radiation. An accurate set of reduced-order modeling methodologies is presented in this work in order to predict the high-frequency behavior of inductors and transformers. Analytical frequency-dependent expressions to predict losses in planar, foil windings and cores are given. The losses in the core and windings raise the temperature of the structure. In order to ensure temperature limitation of the structure is not exceeded, 1-D thermal modeling is undertaken. Based on the losses and temperature limitation, a methodology to optimize performance of magnetics is outlined. Both numerical and analytical means are employed in the extraction of transformer parasitics and cross-coupling. The results are compared against experimental measurements and are found to be in good accord. A simple near-field electromagnetic shield design is presented in order to mitigate the amount of radiation. Due to inadequacy of existing winding technology in forming suitable planar windings for PCB application, an alternate winding scheme is proposed which relies on depositing windings directly onto the core.
Master of Science

In order to design a power transformer it is important to understand its internal electromagnetic behaviour. That can be obtained by measurements on physical transformers, analytical expressions and computer simulations. One benefit with simulations is that the transformer can be studied before it is built physically and that the consequences of changing dimensions and parameters easily can be assessed. In this thesis a time-domain transformer model is presented. The model includes core phenomena as magnetic static hysteresis, eddy current and excess losses. Moreover, the model comprises winding phenomena as eddy currents, capacitive effects and leakage flux. The core and windings are first modelled separately and then connected together in a composite transformer model. This results in a detailed transformer model. One important result of the thesis is the feasibility to simulate dynamic magnetization including the inhomogeneous field distribution due to eddy currents in the magnetic core material. This is achieved by using a Cauer circuit combined with models for static and dynamic magnetization. Thereby, all magnetic loss components in the material can be simulated accurately. This composite dynamic magnetization model is verified through experiments showing very good correspondence with measurements. Furthermore, the composite transformer model is verified through measurements. The model is shown to yield good correspondence with measurements in normal operation and non-normal operations like no-load, inrush current and DC-magnetization.
QC20100708

Hydropower maintains its position as the most important source of renewable electric energy in the world. The efficiency of large hydropower plants is unsurpassed, and after more than hundred years of development, the technology is mature and highly reliable. While new hydro resources are currently being developed in Asia and South America, most European countries go through a phase of intense refurbishment and upgrading of existing plants. Challenges faced by the hydropower industry include a knowledge transfer to new generations and the adaptation of unit designs to meet new operational requirements. As with all branches of engineering, the use of computerized design tools has revolutionized the art of hydropower plant design and the analysis of its performance. In the present work, modern tools like coupled field-circuit models and semi-analytic permeance models are used to address different aspects of electromagnetic analysis of generators in large hydropower plants. The results include the presentation of a mathematical model that uses concepts from rotating field theory to determine the air-gap flux density waveform in a hydroelectric generator. The model was succesfully used to evaluate armature voltage harmonics and damper bar currents at no-load and load conditions. A second study is concerned with the importance of losses due to rotational fields in core loss calculations. It is found that dynamic and rotational effects typically increase the total core loss estimates with about 28% in large hydroelectric generators. In a third study, linear models for the calculation of salient pole shoe form factors at an arbitrary level of magnetic loading are presented. The effect of the damper winding configuration on the damping capability of salient-pole generators is then evaluated in a separate study. The predicted impact of the coupling between damper cages on adjacent poles on the damping torque production is verified in a set of experiments.

A computationally efficient, discrete model is presented for transmission line analysis and passive model order reduction of high-speed interconnect systems. The development of this model was motivated by the on-going efforts in chip/package co-design to route a major portion of the on-chip clock and high-speed data buses through the package in order to overcome the bandwidth reduction and delay caused by the high ohmic loss of on-chip wiring. The geometric complexity of the resulting interconnections is such that model order reduction is essential for rapid and accurate signal integrity assessment to support pre-layout design iteration and optimization. The modal network theory of the skin effect in conjunction with the theory of compact differences is used for the development of discrete models for dispersive, multi-conductor interconnects compatible with passive model order reduction algorithms. The passive reduced-order interconnect modeling algorithm, PRIMA, is then used on the resulting discrete model to generate a low-order, multi-port macromodel for interconnect networks. Numerical examples are used to demonstrate the validity and efficiency of the proposed model.

Efficient design of high-voltage power cables is important to achieve an economical delivery of electric power from wind farms and power plants over the very long distances as well as the overseas electric power. The main focus of this thesis is the investigation of electromagnetic losses in components of high-voltage power cables. The objective of the ongoing research is to develop the theory and optimization techniques as tools to make material choices and geometry designs to minimize the high-frequency attenuation and dispersion for HVDC power cables and the power losses associated with HVAC cables. Physical limitations, dispersion relationships and the application of sum rules as well as convex optimization will be investigated to obtain adequate physical insight and a priori modeling information for these problems. For HVAC power cables, the objectives are addressed by performing measurements and estimation of complex valued permeability of cable armour steel in Papers I and II. Efficient analytical solutions for the electromagnetic field generated by helical structures with applications for HVAC power cables have been obtained in Paper III. For HVDC power cables, estimation of insulation characteristics from dielectric spectroscopy data using Herglotz functions, convex optimization and B-splines, has been investigated in Papers V and VI. The unique solution requirements in waveguide problems have been reviewed in Paper IV.

Axial flux permanent magnet (AFPM) machines have recently attracted significant attention due to several reasons, such as their specific form factor, potentially higher torque density and lower losses, feasibility of increasing the number of poles, and facilitating innovative machine structures for emerging applications. One such machine design, which has promising, high efficiency particularly at higher speeds, is of the coreless AFPM type and has been studied in the dissertation together with more conventional AFPM topologies that employ a ferromagnetic core. A challenge in designing coreless AFPM machines is estimating the eddy current losses. This work proposes a new hybrid analytical and numerical finite element (FE) based method for calculating ac eddy current losses in windings and demonstrates its applicability for axial flux electric machines. The method takes into account 3D field effects in order to achieve accurate results and yet greatly reduce computational efforts. It is also shown that hybrid methods based on 2D FE models, which require semi-empirical correction factors, may over-estimate the eddy current losses. The new 3D FE-based method is advantageous as it employs minimum simplifications and considers the end turns in the eddy current path, the magnetic flux density variation along the effective length of coils, and the field fringing and leakage, which ultimately increases the accuracy of simulations. After exemplifying the practice and benefits of employing a combined design of experiments and response surface methodology for the comparative design of coreless and conventional AFPM machines with cores, an innovative approach is proposed for integrated design, prototyping, and testing efforts. It is shown that extensive sensitivity analysis can be utilized to systematically study the manufacturing tolerances and identify whether the causes for out of specification performance are detectable. The electromagnetic flux path in AFPM machines is substantially 3D and cannot be satisfactorily analyzed through simplified 2D simulations, requiring laborious 3D models for performance prediction. The use of computationally expensive 3D models becomes even more challenging for optimal design studies, in which case, thousands of candidate design evaluations are required, making the conventional approaches impractical. In this dissertation a new two-level surrogate assisted differential evolution multi-objective optimization algorithm (SAMODE) is developed in order to optimally and accurately design the electric machine with a minimum number of expensive 3D design evaluations. The developed surrogate assisted optimization algorithm is used to comparatively and systematically design several AFPM machines. The studies include exploring the effects of pole count on the machine performance and cost limits, and the systematic comparison of optimally designed single-sided and double-sided AFPM machines. For the case studies, the new optimization algorithm reduced the required number of FEA design evaluations from thousands to less than two hundred. The new methods, developed and presented in the dissertation, maybe directly applicable or extended to a wide class of electrical machines and in particular to those of the PM-excited synchronous type. The benefits of the new eddy current loss calculation and of the optimization method are mostly relevant and significant for electrical machines with a rather complicated magnetic flux path, such is the case of axial flux and of transvers flux topologies, which are a main subject of current research in the field worldwide.

Cette thèse est une étude sur la caractérisation, la modélisation et l’optimisation des effets substrat dans les circuits intégrés, dédies à des applications WLAN.L’objectif de ces travaux de recherche est de développer une nouvelle méthodologie d’extraction qui prenne en compte tous les parasites ; à savoir les modèles RLCK distribués, les effets électromagnétiques, ainsi que le couplage substrat.Les effets substrat ont été optimisés grâce au développement de nouvelles structures d’isolation utilisant des tranches profondes d’isolation (DTI).La prédictibilité des simulations circuits a été améliorée grace à l’introduction d’une nouvelle méthodologie d’extraction, basée sur une approche quasi-statique prenant en compte avec précision la description exacte et complète du procédé BiCMOS ainsi que les pertes dans le substrat, aussi bien diélectriques que résistives.La validité de cette méthodologie a été évaluée en comparant les résultats de simulation avec les mesures sur silicium. La bonne corrélation des résultats démontre la pertinence de cette nouvelle méthodologie. Cette méthode permet de plus, de réduire le « time to maket » grâce à l’optimisation des temps de simulations
This thesis is about characterization, modelling and optimization of substrate effects in integrated circuits, dedicated to WLAN applications.The objective of this thesis is to develop a new extraction methodology that takes into account all parasites; distributed RLCK models, electromagnetic effects, as well as substrate coupling.Substrate effects have been optimized through the development of a new insulation strategies using deep isolation isolation (DTIs).The circuit predictability has been improved thanks to the development of a new extraction methodology, based on a quasi-static approach taking into account the complete description of the BiCMOS process as well as the substrate loss, both capacitive and resistive effects.The validation of this methodology was evaluated by comparing simulation results with silicon measurements. The good correlation of the obtained results demonstrates the accuracy of this new methodology. This method also makes it possible to reduce the time to market thanks to the optimization of the simulation times

Thesis (Ph. D.)--Ohio State University, 2003.
Title from first page of PDF file. Document formatted into pages; contains xxiii, 152 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Benedikt Munk, Dept. of Electrical Engineering. Includes bibliographical references (p. 250-252).

Дисертація на здобуття наукового ступеня доктора технічних наук за спеціальністю 05.09.03 – Електротехнічні комплекси та системи. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019. У роботі міститься вирішення актуальної наукової проблеми аналізу якості електропостачання та електромагнітної сумісності електротехнічних комплексів та систем. Ця проблема полягає у відсутності математичної бази та, відповідно, нормативної бази оцінювання впливу окремого електротехнічного комплексу або системи споживача на якість електроенергії. Діючи норми покладають усю відповідальність за низьку якість електропостачання на безпосередньо постачальну організацію у вигляді штрафів, що, як показує досвід, не сприяє побудові оптимальних систем електропостачання. В роботі запропоновано оцінку якості електропостачання шляхом порівняння режиму електроспоживання діючого електротехнічного комплексу з еталонним споживачем у вигляді числових коефіцієнтів потужності та втрат. Отримані розрахункові формули для однофазних, трифазних трипровідних та чотирьохпровідних систем електропостачання. Запропоновано розподіл загальних втрат на втрати від несиметрії, не лінійності, реактивності та нестаціонарності. Запропоновано та досліджено концепції еталонного реактивного споживача та усередненого реактивного споживача. Запропоновано методику врахування якості електроспоживання при розрахунках за спожиту електроенергію, яка створює економічний стимул для підвищення ефективності енергорежимів споживача. Запропоновано методику оцінки порушення споживачем норм споживання за величиною потужності і гармонійних складових, що потенційно здатні викликати вихід показників якості електричної енергії за допустимі межі. Надано основи методики побудови штрафних санкцій щодо споживача у разі перевищення допустимих параметрів електроспоживання, а також штрафних санкцій щодо постачальника електричної енергії у разі низької якості електричної енергії та відсутності порушень з боку споживача.
The dissertation on achieving the scientific degree Doctor of Technical Sciences by specialty 05.09.03 – "Electrotechnical complexes and systems" - National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2020. The paper contains the solution of the actual scientific problem of the analysis of quality of power supply and electromagnetic compatibility of electrotechnical complexes and systems. This problem is the lack of a mathematical basis and, accordingly, a regulatory framework for assessing the impact of a particular electrical complex or consumer system on the quality of electricity. The current regulations place all responsibility for the low quality of electricity supply directly on the supply organization in the form of fines, which, as experience shows, does not contribute to the construction of optimal power supply systems. The paper analyzes the compatibility of the existing regulatory framework (including IEEE519, EN50160) and evaluates the effectiveness of the proposed methods of determining responsibility using computer simulations. The analysis showed that the existing methods have significant limitations, as a result of which they are not suitable for practical application. The paper proposes an assessment of the quality of power supply by comparing the mode of power consumption of the existing electrical complex with the reference consumer in the form of numerical coefficients of power and losses. Calculation formulas for single-phase, three-phase three-wire and four-wire power supply systems are obtained. Three-phase three-wire system the reference consumer, regardless of the voltage parameters, is a symmetrical triangle of constant active resistance is shown. Three-phase four-wire system the reference consumer, regardless of voltage parameters, is a combination of a symmetric triangle of constant active resistances and a symmetrical star, the resistance in the branches of which is as many times more than the resistance of the triangle is shown. It is noted that the general assessment of the loss ratio is not informative enough about the reasons for the deterioration of electricity quality. To solve this problem, the division of total losses into losses from asymmetry, nonlinearity, reactivity and nonstationarity is proposed. The concept of the reference reactive consumer is offered, and conclusions concerning possibility and expediency of its use are made. A method for determining the reactivity coefficient by volumes of energy flowing in the forward and reverse directions is proposed. The concept of the average reactive consumer is offered. The paper proposes to build an assessment of the contribution of a separate electrical complex or consumer system in the deterioration of power supply on the basis of power values specified in the contract and the establishment of normalized resistance of the power supply system. Based on these values, a mathematical apparatus is proposed, which allows not only to determine the fact of violation of the limits of electromagnetic compatibility but also to quantify the amount of electricity that has been damaged. It is proposed to determine the coefficient of losses from asymmetry using a reference consumer. This coefficient is calculated as the ratio between the power loss of three independent single-phase reference consumers to the losses of the reference three-phase consumer. This solution avoids the influence of such factors as nonlinearity and reactivity. In addition, the device of symmetrical components is not used, which is inconvenient in the case of non-sinusoidal voltages and currents. It is proposed to select individual coefficients of losses from reactivity and nonlinearity, which are calculated by dividing the harmonic components of the distortion current by the power direction. The method of calculation of losses from nonstationarity is calculated, which is calculated as the ratio of total losses of reference consumers on several "short" intervals, and losses of the reference consumer on a long interval that includes all "short". The analysis of character of complex resistance of an electric network depending on parameters of its elements for typical cases of connection of consumers of various character on voltage of 10 KV is carried out. The obtained dependence allows us to talk about the possible use of normalized values to estimate network bandwidth. An empirical method for calculating the normalized resistance is proposed. A method for measuring the parameters of the electrical network mode is proposed, which allows to implement algorithms for assessing the quality of power consumption, the advantages of which are self-synchronization, calculation of values strictly for one period of the main voltage harmonic, absence of gaps and overlays of observation intervals. A method for measuring the current values of currents and voltages on their discrete images is proposed, taking into account the discrepancy between the moments of the initial and final readings of the digital image of the signal with the moments of the beginning and end of the measurement period. A method of taking into account the quality of electricity consumption in the calculations for the consumed electricity is proposed, which creates an economic incentive to increase the efficiency of energy regimes of the consumer. The method of estimation of infringement by the consumer of norms of consumption on size of power and harmonic components which are potentially capable to cause an exit of indicators of quality of electric energy beyond admissible limits is offered. The basics of the method of construction of penalties against the consumer in case of exceeding the allowable parameters of electricity consumption, as well as penalties against the supplier of electricity in case of low quality of electricity and the absence of violations by the consumer. In the experimental part of the work the application of the offered mathematical devices on the examples of test mathematical models and oscillograms obtained on real objects is tested. The experiment allowed to confirm the effectiveness of the proposed methods, in addition to the method of comparison with the reference medium-reactive consumer, which has not proved to be an effective tool for analysis and does not seem promising. Also in the work the hardware realization in the form of the electric energy meter taking into account its quality is offered.

Lors de la phase de dimensionnement d’un générateur électrique, des choix préliminaires imposent généralement la topologie. Cette thèse a pour objectif d’apporter une aide décisionnelle au choix des structures de générateurs de fortes puissances. L’intérêt des machines à haute efficacité énergétique est porté par des objectifs environnementaux forts. En conséquence, maîtriser et comprendre l’origine des pertes dans les machines de production d’électricité est un enjeu capital. Ainsi, une méthodologie de calculs de pertes fer est développée pour des générateurs de fortes puissances.Dans les secteurs de la production et conversion d’énergie, les Machines Synchrones à Double Excitation présentent un fort potentiel pour répondre aux défis de la transition énergétique. Dès lors, il est important de quantifier l’impact de ces nouvelles structures par rapport aux solutions existantes. Cette thèse propose une modélisation par méthodes analytiques et semi-analytiques dans l’objectif de concevoir un ensemble de structures de générateurs. La modélisation est également comparée à deux prototypes de fortes puissances, dont un pour une application éolienne à attaque directe.Ensuite, cette modélisation est employée dans un processus de conception par optimisation. Les structures Pareto optimales sont comparées suivant différents cahiers des charges. Ces optimisations permettent de mettre en avant des gains significatifs par rapport aux solutions existantes notamment sur des données statistiques de fonctionnement éolien
During the design phase of an electrical generator, the topology is generally imposed by preliminary criteria. This thesis aims at providing a decision support for the choice of high power generator structures. The interest for high efficiency machines is driven by strong environmental objectives. Consequently, understanding the origin of losses in power generation machines is a major issue. Thus, a methodology for iron loss calculation is developed for high power generators.In the energy production and conversion sectors, Hybrid Excitation Synchronous Machines have a great potential to respond to the challenges of energy transition. It is important to quantify the impact of these new structures compared with existing solutions. This thesis proposes analytical and lumped models to design a set of generator structures. The modeling approach is also compared with two high power generators, including one for a direct drive wind turbine. Then, this modeling is used in an optimization design process. The optimal Pareto structures are compared according to different specifications. These optimized designs show significant gains compared to the existing solutions, especially on wind profile from a Weibull probability density function

L'emploi de matériaux composites dans le domaine du Génie Electrique est actuellement un sujet de recherche en plein essor, notamment pour des considérations d’économie d'énergie. Les composites magnétiques doux (SMC - Soft Magnetic Composites) intègrent les propriétés de leurs différents constituants. Ils sont conçus pour présenter une perméabilité élevée et avoir une faible densité de pertes par courants de Foucault (EC - Eddy Current) par comparaison aux structures plus classiques comme l'acier laminé. Néanmoins, la détermination des propriétés électromagnétiques des SMC n’est pas aisée. Une approche classique est d’appliquer les outils numériques tels que la méthode des éléments finis (FEM - Finite Element Method) pour obtenir une description complète du SMC. Cependant, la microstructure doit être finement maillée, ce qui représente un fardeau numérique significatif et des instabilités dans l'approche par FEM. Pour surmonter cette restriction, les méthodes d'homogénéisation semi-analytiques sont appliquées. Ce travail consiste d'abord à développer un modèle de perméabilité complexe pour SMC. La perméabilité magnétique et les pertes EC sont intégrées respectivement comme les parties réelle et imaginaire de la perméabilité complexe. La perméabilité magnétique effective macroscopique peut s’obtenir par des estimations classiques en homogénéisation. Une détermination correcte de la perméabilité effective, i.e. la partie réelle de la perméabilité complexe, est cruciale pour une estimation précise de pertes EC. Les formules de pertes EC sont dérivées pour des SMC à microstructure périodique dans les cas 2D et 3D. En outre, différentes approches s’appuyant sur différentes moyennes du champ magnétique permettent d’obtenir des limites inférieures et supérieures pour l’estimation des pertes EC dans les SMC. La perméabilité complexe ainsi obtenue est ensuite appliquée à une structure de transformateur. Le champ magnétique et la répartition des pertes EC peuvent être obtenus sur le transformateur équivalent (homogénéisé). Les résultats sont comparés aux calculs en champ complet du transformateur hétérogène. Un bon accord est observé. Enfin, on étudie l'effet des contraintes mécaniques sur la perméabilité magnétique et les pertes EC des SMC, ce qui conduit à une formule couplée de la densité de pertes EC en fonction de la contrainte macroscopique et du champ magnétique
Composite materials have been widely used in Electrical Engineering, and they have stimulated a growing number of scientific research, especially when it comes to energy savings. Soft Magnetic Composites (SMC) incorporate the attributes of different constituents. They can be designed to exhibit high permeability and to dissipate low Eddy Current (EC) losses compared to more conventional structures such as laminated steel. Nevertheless, electromagnetic properties of SMC are not easily determined. Numerical tools such as finite element method (FEM) are usually employed to provide a full-field description of SMC. As the microstructure has to be finely meshed, it brings significant numerical burden and instabilities. To overcome this restriction, semi-analytical homogenization methods are adapted and applied here. They consist in developing a complex permeability model. In the complex permeability model for SMC, the static magnetic permeability and EC losses are integrated respectively as the real and imaginary part of the complex permeability. Classical estimates are applied to determine the macroscopic effective magnetic permeability. A correct determination of the effective permeability, i.e. the real part of the complex permeability, is crucial for the estimate of EC losses. EC losses formulas are derived for SMC with periodic microstructure in 2D and 3D cases. Furthermore, different approaches of field averaging are employed to obtain lower and upper bounds on the EC losses in SMC. The complex permeability model is then applied to analyze a transformer structure. The magnetic field and EC losses distribution can be obtained on the equivalent homogenized transformer. The results are compared to the full-field calculations on the heterogeneous transformer. A good consistency is observed. Finally, the effect of mechanical stress on the magnetic permeability and loss property of SMC is studied, which leads to a coupled formula of EC loss density as a function of macroscopic stress and magnetic field

This thesis presents a study on core loss calculations in rotating electrical machines. The basic concepts concerning magnetic moments, ferromagnetism, magnetic domains and magnetic hysteresis are introduced. The three-term models for alternating and rotational core losses in electrical steel sheets are presented. Several core loss measurement techniques are reviewed and an experiment is carried out to measure the total core losses in an electrical sheet steel sample under alternating and rotational magnetic fields of various frequencies and amplitudes. The coefficients in the loss models for alternating and rotational core losses are obtained through curve fitting process. The theory of electromagnetic fields is presented through the Maxwell equations and field scalar equations. A detailed review on core loss models for rotating electrical machines is presented. A rotational core loss model is adopted to calculate the core losses in a PM motor. The total core loss in the PM motor is obtained by summing the element losses using a MATLAB program. An experiment is conducted to measure the total core loss in the PM motor. The calculated total core loss in the PM motor is compared with the experimental results. The calculated total core losses are about 19% lower than the tested results. Various possible causes for this discrepancy are discussed
Master of Engineering (Hons)

Дисертація на здобуття наукового ступеня доктора технічних наук за спеціальністю 05.09.03 – "Електротехнічні комплекси та системи". – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019. У дисертаційній роботі вирішується важлива науково-технічна проблема підвищення якості електропостачання електротехнічних об'єктів, комплексів та систем і забезпечення їх електромагнітної сумісності шляхом розвитку математичного та апаратного забезпечення систем обліку електроенергії з урахуванням енергетичної ефективності режимів електроспоживання і виявлених порушень меж електромагнітної сумісності з боку постачальника електричної енергії або її споживача. У вступі визначено існуючу проблему і обґрунтовано актуальність теми дисертації, наведено зв'язок роботи з науковими програмами, планами, темами, сформульовано мету і завдання наукового дослідження, розглянуто об'єкт та предмет досліджень, наведено перелік методів дослідження, що застосовувалися для досягнення поставленої мети роботи. Викладено наукову новизну й практичну значущість отриманих результатів, наведено дані про публікації й апробацію результатів роботи, охарактеризовано особистий внесок здобувача, надано відомості про впровадження результатів роботи. У першому розділі на підставі вивчення та систематизації результатів аналізу матеріалів з відкритих джерел сформульовані основні недоліки існуючих методів оцінки якості електропостачання та нормативної бази, яка не дозволяє у повному обсязі вирішувати конфліктні ситуації при виникненні порушень меж електромагнітної сумісності у розрізі електропостачальник-споживач. Також розглянуті методи визначення відповідальності за погіршення якості електричної енергії та окремих її показників. У другому розділі проведено аналіз типової схеми електропостачання, що дозволило зробити висновки та отримати основні числові характеристики системи електропостачання трифазного електротехнічного об'єкту з напругою живлення 10 кВ. За допомогою комп’ютерної моделі показано взаємний вплив декількох споживачів на показники якості напруги у точці приєднання та проаналізовано вплив параметрів системи електропостачання ці показники. Показано, що визначення джерела вищих гармонік за напрямком складової потужності вищої гармоніки не дозволяє гарантовано виділити споживача з нелінійним навантаженням у разі якщо кількість таких споживачів більша за одного. Також проаналізовано сумісність стандартів EN 50160 та IEEE 519 з точки зору норми рівнів гармонійних складових у складі струму та напруги. Отримані результати дозволяють говорити про наявність окремих моментів в яких вищи гармонійні складові струму, що генерує споживач не порушуючи меж стандарту IEEE 519, можуть викликати наявність гармонік напруги що перевищують норми установлені EN 50160. Також зроблено висновки щодо встановлення обмежень генерації вищих гармонійних складових за допомогою нормованих значень опору системи. У третьому розділі запропоновано подальший розвиток математичного апарату визначення коефіцієнтів потужності та втрат, як показників якості електроспоживання, зокрема обґрунтовані визначення інтегральних коефіцієнтів втрат для трифазних трипровідних та чотирьохпровідних мереж. Отримала подальший розвиток теорія "еталонного" споживача. Показано, що в трифазній трипровідній мережі еталонним споживачем незалежно від параметрів напруги є симетричний трикутник постійних активних опорів. Показано, що в трифазній чьотирьохпровідній системі еталонним споживачем незалежно від параметрів напруги є поєднання симетричного трикутника постійних активних опорів і симетричної зірки, опір в гілках якої в стільки ж разів більше опорів трикутника, у скільки разів активний опір провіднику нейтралі більше опору фазних провідників. Вперше запропоновано математичний апарат виділення окремих складових із загальних коефіцієнтів потужностей та втрат за такими типами спотворень як несиметрія, нелінійність, реактивність та нестаціонарність. Запропоновано концепцію еталонного реактивного споживача з умов максимуму потужності або мінімуму втрат при рівності співвідношень перетоків потужності від і до споживача, що дозволяє реалізувати обчислення коефіцієнту реактивності та потужності при довільній формі напруги у однофазних та трифазних мережах. Показано, що при такій постановці еталонний реактивний споживач тяжіє до генерації вищих гармонік і не має зручного аналітичного або чисельного рішення для порівняння з поточним споживачем. Запропоновано концепцію середньореактивного споживача, у якого усі гармоніки мають рівне співвідношення перетікань потужності до і від споживача, що дозволяє реалізувати порівняння режиму електроспоживання поточного споживача з таким середньореактивним. Запропоновано методику оцінки коефіцієнтів втрат і потужності від несиметрії для трифазного споживача при довільній напрузі. Запропоновано методику оцінки співвідношення коефіцієнтів втрат від реактивності і нелінійності споживача шляхом поділу відповідних гармонік струму Фризе у напрямку активної складової. Запропоновано методику оцінки коефіцієнтів втрат і потужності від нестаціонарності споживання. У четвертому розділі проведено аналіз характеру комплексного опору електричної мережі в залежності від параметрів її елементів для типових випадків підключення споживачів на напрузі 10 КВ. Отримана залежність дозволяє говорити про можливе застосування нормованих значень для оцінки пропускної здатності мережі. Набув подальшого розвитку метод вимірювання електричних параметрів трифазної мережі заснований на апроксимації вхідного сигналу сумою гармонійних складових. Особливостями методу є автоматичне підстроювання по частоті і тривалості інтервалу спостереження у заданому діапазоні, використання повного набору напруг фаз (або лінійних) при визначенні частоти з урахуванням їх вагових значень, що дозволяє зменшити похибки вимірювання у складних умовах – при наявності несиметрії, вищих гармонік, аперіодичної складової або при відсутності напруги у окремій фазі. Крім того, метод вимірювання використовує постійну частоту квантування вхідних цифрових даних, що дозволяє спростити апаратну частину приладу. Запропоновано метод обчислення діючих значень з точною прив'язкою до періоду напруги, одержуваного попереднім методом, що дозволяє виключити частотну похибку при вимірюванні незалежно від розташування початку та закінчення інтервалу спостереження відносно відліків вхідного цифрового сигналу. Запропоновано систему обліку електричної енергії з використанням показників якості електричної енергії та ефективності електроспоживання. Особливістю системи є додатковий облік втрат на передачу електричної енергії шляхом порівняння характеристик електроспоживання поточного споживача з такими для еталонного споживача, тобто використання коефіцієнтів втрат або потужності. Такий метод обліку дозволяє коректно тарифікувати всі відхилення в режимах роботи навантаження, такі як реактивність, нелінійність і нестаціонарність. Запропоновано систему штрафних санкцій за погіршення якості електричної енергії, заснована на підрахунку "штрафної" енергії в разі, якщо споживач порушує норми електроспоживання і "нетарифікованої" енергії, в разі коли порушень з боку споживача немає, але якість електроенергії не відповідає нормам. Запропоновано основи тарифікації на базі даної системи обліку електроенергії. У п'ятому розділі експериментально отримані дані, що підтверджують теоретичні положення розділів 3 та 4. Зокрема були реалізовані оцінки якості електроспоживання шляхом порівняння з набором еталонних споживачів. Експеримент показав можливість успішного застосування виділення струму Фрізе і його подальшого аналізу з метою оцінки якості електроспоживання. При цьому можливе паралельне використання його трифазної і однофазної реалізацій для оцінки несиметрії, нелінійності і реактивності відповідно. Запропонована в розділі 3 методика порівняння з еталонним среднереактівним споживачем не виявила себе в якості ефективного інструменту аналізу і не представляється перспективною. У той же час поділ гармонійних складових струму Фрізе у напрямку їх активної складової дозволяє ефективно відстежувати джерело походження струмів вищих гармонік. Визначені вище методи з використанням моделі фрагменту енергосистеми з різними типами навантаження підтвердили коректність розроблених методів оцінки якості електроспоживання. Випробування за допомогою осцилограм, отриманих на реальних трифазних навантаженнях (тягової підстанції) також підтвердило працездатність та ефективність розроблених методів оцінки. В моделях з перевищенням допустимих режимів, використання математичного апарату розробленого в розділі 4 дозволило виявити джерело спотворень, навіть за умови коли одночасно декілька споживачів виступають в якості джерел цих спотворень.
The dissertation on competition of a scientific degree of the doctor of technical sciences on a specialty 05.09.03 - "Electrotechnical complexes and systems". - National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2019. In the dissertation the important scientific and technical problem of increase of quality of power supply of electrotechnical objects, complexes and systems and maintenance of their electromagnetic compatibility by development of mathematical and hardware of systems of the account of the electric power taking into account energy efficiency of modes of power consumption and the revealed infringements of electromagnetic compatibility energy or its consumer. In the introduction the existing problem is defined and the urgency of the dissertation topic is substantiated, the connection of work with scientific programs, plans, themes is given, the purpose and tasks of scientific research are formulated, the object and subject of researches are considered, the list of research methods applied for achievement of the set purpose is given work. The scientific no velty and practical significance of the obtained results are stated, the data on publications and approbation of the results of the work are given, the personal contribution of the applicant is characterized, the information on the implementation of the results of the work is given. In the first section, based on the study and systematization of the results of analysis of materials from open sources, the main shortcomings of existing methods of assessing the quality of electricity supply and regulatory framework, which does not fully resolve conflict situations in violation of electromagnetic compatibility in terms of electricity supplier - consumer. Methods for determining the responsibility for the deterioration of electricity quality and its individual indicators are also considered. The second section analyzes the typical power supply scheme, which allowed to draw conclusions and obtain the main numerical characteristics of the power supply system of a three-phase electrical facility with a supply voltage of 10 kV. The computer model shows the mutual influence of several consumers on the quality indicators of the voltage at the point of connection and analyzes the influence of the parameters of the power supply system, these indicators. It is shown that the definition of the source of higher harmonics in the direction of the component power of the higher harmonic does not guarantee to allocate a consumer with a nonlinear load if the number of such consumers is greater than one. The compatibility of EN 50160 and IEEE 519 standards in terms of the norm of levels of harmonic components in the composition of current and voltage is also analyzed. The obtained results allow to speak about the presence of certain moments in which the higher harmonic components of the current generated by the consumer without violating the IEEE 519 standard can cause the presence of voltage harmonics exceeding the norms set by EN 50160. It is also concluded that the generation of higher harmonic components system resistance values. The third section proposes further development of the mathematical apparatus for determining power and loss coefficients as indicators of power consumption quality, in particular, the determination of integrated loss coefficients for three-phase three-wire and four-wire networks is substantiated. The theory of the "reference" consumer was further developed. It is shown that in a three-phase three-wire network the reference consumer, regardless of the voltage parameters, is a symmetrical triangle of constant active resistances. It is shown that in a three-phase four-wire system the reference consumer, regardless of voltage parameters, is a combination of a symmetric triangle of constant active resistances and a symmetric star, the resistance in the branches of which is as many times the resistance of the triangle as the active resistance of the neutral conductor. For the first time, a mathematical apparatus for selecting individual components from the total power and loss coefficients for such types of distortions as asymmetry, nonlinearity, reactivity and nonstationarity has been proposed. The concept of the reference reactive consumer from the conditions of maximum power or minimum losses at equality of ratios of power flows from and to the consumer is offered, that allows to realize calculation of coefficient of reactivity and power at any form of voltage in single-phase and three-phase networks. It is shown that in such a statement the reference reactive consumer tends to generate higher harmonics and does not have a convenient analytical or numerical solution for comparison with the current consumer. The concept of the average reactive consumer is proposed, in which all harmonics have an equal ratio of power flows to and from the consumer, which allows to compare the current consumption mode of the current consumer with such an average reactive one. A method for estimating the coefficients of loss and power from asymmetry for a three-phase consumer at arbitrary voltage is proposed. A method for estimating the ratio of the coefficients of losses from reactivity and nonlinearity of the consumer by dividing the corresponding harmonics of the Frieze current in the direction of the active component is proposed. A method for estimating the coefficients of losses and power from non-stationary consumption is proposed. In the fourth section the analysis of character of complex resistance of an electric network depending on parameters of its elements for typical cases of connection of consumers on voltage of 10 KV is carried out. The obtained dependence allows us to talk about the possible use of normalized values to estimate network bandwidth. The method of measuring the electrical parameters of a three-phase network based on the approximation of the input signal by the sum of harmonic components has been further developed. Features of the method are automatic adjustment of the frequency and duration of the observation interval in a given range, the use of a complete set of phase voltages (or linear) in determining the frequency taking into account their weight values, which reduces measurement errors in difficult conditions - in the presence of asymmetry, higher harmonics, aperiodic component or in the absence of voltage in a separate phase. In addition, the measurement method uses a constant quantization frequency of the input digital data, which simplifies the hardware of the device. A method of calculating the current values with a precise reference to the voltage period obtained by the previous method is proposed, which eliminates the frequency error in the measurement regardless of the location of the beginning and end of the observation interval relative to the input digital signal. The system of the account of electric energy with use of indicators of quality of electric energy and efficiency of electric consumption is offered. A feature of the system is the additional accounting of losses for the transmission of electricity by comparing the characteristics of electricity consumption of the current consumer with those for the reference consumer, ie the use of loss factors or power. This method of accounting allows you to correctly rate all deviations in the modes of load, such as reactivity, nonlinearity and nonstationarity. A system of penalties for deterioration of electricity quality is proposed, based on the calculation of "penalty" energy if the consumer violates the norms of electricity consumption and "non-tariffed" energy, if there are no violations by the consumer, but the quality of electricity does not meet the norms. The basics of billing on the basis of this electricity metering system are proposed. In the fifth section, the data confirming the theoretical provisions of sections 3 and 4 were experimentally obtained. In particular, estimates of the quality of electricity consumption were implemented by comparison with a set of reference consumers. The experiment showed the possibility of successful application of Frieze current generation and its subsequent analysis to assess the quality of electricity consumption. At the same time parallel use of its three-phase and single-phase implementations for an estimation of asymmetry, nonlinearity and reactivity accordingly is possible. The method of comparison with the reference average reactive consumer proposed in section 3 has not proved to be an effective tool of analysis and does not seem promising. At the same time, the separation of the harmonic components of the Frieze current in the direction of their active component allows you to effectively track the source of currents of higher harmonics. The above methods using the model of a fragment of the power system with different types of load confirmed the correctness of the developed methods for assessing the quality of electricity consumption. Tests using oscillograms obtained on real three-phase loads (traction substation) also confirmed the efficiency and effectiveness of the developed assessment methods. In models with exceeding the permissible modes, the use of the mathematical apparatus developed in Section 4 allowed to identify the source of distortion, even if several consumers act as sources of these distortions at the same time.

The dissertation documents research work carried out on Pulse Width Modulation (PWM) strategies for hard switched Voltage Source Inverters (VSI) for variable speed electric drives. This research is aimed at Hybrid Electric Vehicles (HEV). PWM is at the heart of all variable speed electric drives; they have a huge influence on the overall performance of the system and may also help eventually give us an extra degree of freedom in the possibility to rethink the inverter design including the re-dimensioning of the inverter components.HEVs tend to cost more than conventional internal combustion engine (ICE) vehicles as they have to incorporate two traction systems, which is the major discouraging factor for consumers and in turn for manufacturers. The two traction system increases the maintenance cost of the car as well. In addition the electric drives not only cost extra money but space too, which is already scarce with an ICE under the hood. An all-electric car is not yet a viable idea as the batteries have very low energy density compared with petrol or diesel and take considerable time to charge. One solution could be to use bigger battery packs but these add substantially to the price and weight of the vehicle and are not economically viable. To avoid raising the cost of such vehicles to unreasonably high amounts, autonomy has to be compromised. However hybrid vehicles are an important step forward in the transition toward all-electric cars while research on better batteries evolves. The objective of this research is to make electric drives suitable for HEVs i.e. lighter, more compact and more efficient -- requiring less maintenance and eventually at lower cost so that the advantages, such as low emissions and better fuel efficiency, would out-weigh a little extra cost for these cars. The electrical energy source in a vehicle is a battery, a DC Voltage source, and the traction motor is generally an AC motor owing to the various advantages it offers over a DC motor. Hence the need for a VSI, which is used to transform the DC voltage into AC voltage of desired amplitude and frequency. Pulse width modulation techniques are used to control VSI to ensure that the required/calculated voltage is fed to the machine, to produce the desired torque/speed. PWM techniques are essentially open loop systems where no feedback is used and the instantaneous values differ from the required voltage, however the same average values are obtained. Pulse width modulated techniques produce a low frequency signal (desired average value of the switched voltage) also called the fundamental component, along with unwanted high frequency harmonics linked to the carrier signal frequency or the PWM period. In modern cars we see more and more mechanical loads driven by electricity through digital processors. It is very important to eliminate the risk of electromagnetic interference between these systems to avoid failure or malfunction. Hence these unwanted harmonics have to be filtered so that they do not affect the electronic control unit or other susceptible components placed in the vicinity. Randomised modulation techniques (RPWM) are used to dither these harmonics at the switching frequency and its multiple. In this thesis a random modulator based on space vector modulation is presented which has additional advantages of SVM. Another EMI problem linked to PWM techniques is that they produce common mode voltages in the load. For electric machines, common mode voltage produces shaft voltage which in turn provokes dielectric stress on the motor bearings, its lubricant and hence the possibility of generating bearing currents in the machine that can be fatal for the machine. To reduce the common mode voltage a space vector modulation strategy is developed based on intelligent placement of zero vectors. (...)

This thesis presents a study on core loss calculations in rotating electrical machines. The basic concepts concerning magnetic moments, ferromagnetism, magnetic domains and magnetic hysteresis are introduced. The three-term models for alternating and rotational core losses in electrical steel sheets are presented. Several core loss measurement techniques are reviewed and an experiment is carried out to measure the total core losses in an electrical sheet steel sample under alternating and rotational magnetic fields of various frequencies and amplitudes. The coefficients in the loss models for alternating and rotational core losses are obtained through curve fitting process. The theory of electromagnetic fields is presented through the Maxwell equations and field scalar equations. A detailed review on core loss models for rotating electrical machines is presented. A rotational core loss model is adopted to calculate the core losses in a PM motor. The total core loss in the PM motor is obtained by summing the element losses using a MATLAB program. An experiment is conducted to measure the total core loss in the PM motor. The calculated total core loss in the PM motor is compared with the experimental results. The calculated total core losses are about 19% lower than the tested results. Various possible causes for this discrepancy are discussed

Le nombre d’appareils électroniques et de systèmes de communication sans fil a considérablement augmenté au cours des 20 dernières années. Les boîtiers de blindage utilisés pour protéger les appareils électroniques contre les radiations externes, mais aussi pour limiter leurs émissions sont généralement conçus en alliages d’aluminium. Mais la nécessité de réduire le poids des aéronefs incite l’industrie aéronautique à l’utilisation de matériaux composites.La modélisation de boîtiers de blindage composés de matériaux homogènes est possible par l’utilisation d’outils numériques tels que la méthode des éléments finis. Mais la discrétisation de boîtiers constitués de matériaux composites impliquerait un nombre d’éléments trop important rendant impossible toute modélisation numérique. Le recours à l’homogénéisation semi-analytique est une possibilité pour s’affranchir de cette restriction. Les milieux homogènes équivalents obtenus avec ces méthodes peuvent être insérés dans des outils numériques pour simuler le comportement électromagnétique de boîtiers de blindage complexes. Les modèles d’homogénéisation existants, tel que le modèle de Maxwell-Garnett, sont toutefois limités a des applications quasi-statiques.La définition des propriétés effectives de matériaux composites illuminés par des ondes électromagnétiques est l’objectif principal de ce travail. Il en résulte deux méthodes d’homogénéisation dynamiques. La première introduit un effet de taille entre les fibres et la longueur d'onde. Elle permet ainsi d’étendre une méthode basée sur des problèmes d'inclusion aux micro-ondes. Mais elle reste limitée par l’apparition de l’effet de peau dans les renforts conducteurs. La seconde est basée sur la définition des pertes par effet Joule dans les fibres, permettant ainsi d’étendre la première méthode après l’apparition de l’effet de peau. Cette dernière est enfin utilisée pour modéliser le comportement électromagnétique d’un boîtier de blindage réaliste
The number of electronic devices and wireless communication systems has significantly increased over the past 20 years. Shielding enclosures used to protect electronic devices against radiated waves and to limit their emissions are usually designed in aluminum alloys. But the need to reduce the weight of aircraft incites the aerospace industry to the use of composite materials.Modeling shielding enclosures composed of homogeneous materials is possible by the use of numerical tools such as the finite element method. But considering every details of the microstructure would involve a excessive number of unknowns preventing numerical modelings. The use of semi-analytical homogenization methods is a possibility to overcome this restriction. The equivalent homogeneous mediums obtained with these methods can be inserted into numerical tools to simulate the electromagnetic behavior of complex shielding enclosures. But classical homogenization models such as Maxwell-Garnett model, are limited to quasi-static applications.Calculating the effective properties of composite materials illuminated by electromagnetic waves is the main objective of this work. This leads to two dynamic homogenization methods. The first one introduces a size effect between the fibers and the wavelength. It allows to extend a method based on inclusion problems to microwave frequencies. However it is limited by the occurrence of the skin effect in conductive inclusions. The second consider Joule losses and extends the first method after the occurrence of the skin effect. This second homogenization method is finally used to model the behavior of a realistic shielding enclosure

Thesis (M.Sc (Hons)) -- University of Western Sydney, Nepean, 2000.
"Submitted for the degree of Master of Engineering (Hons), School of Mechatronic, Computer & Electrical Engineering, University of Western Sydney, Nepean" Includes bibliographical references (leaves 107-114).

Cette thèse se concentre sur la conception de moteurs à aimants permanents à haute vitesse et faible puissance, spécifiquement destinés à l'entraînement d'un compresseur contrarotatif. L'objectif principal est de garantir une intégration directe et compacte du moteur, tant en termes de longueur que de volume, dans les roues du compresseur. Pour répondre à ces exigences, plusieurs topologies de moteurs à flux axial, à flux radial, ainsi qu'une structure novatrice à entrefer conique, ont été modélisées et évaluées. Ces évaluations incluent une analyse approfondie des performances électromagnétiques et thermiques, visant à maximiser le rendement des moteurs à haute vitesse. Une attention particulière a été portée à l'étude des pertes électromagnétiques, qui deviennent significatives à ces vitesses élevées, pour chacune des topologies considérées. En parallèle, des analyses mécaniques détaillées ont été réalisées sur des rotors discoïdes, peu documentés dans la littérature, ainsi que sur des rotors cylindriques, afin de caractériser leur comportement mécanique à une vitesse de rotation de 90 000 tr/min. Les contraintes liées à la fabrication ont orienté le choix final vers une topologie à flux radial, dont le prototypage est actuellement en cours
This thesis focuses on the design of high-speed, low-power permanent magnet motors specifically intended for driving a counter-rotating compressor. The primary objective is to ensure direct and compact integration of the motor, both in terms of length and volume, within the compressor wheels. To meet these requirements, several motor topologies—axial flux, radial 268 flux, and an innovative conical airgap structure—were modeled and evaluated. These evaluations included an in-depth analysis of electromagnetic and thermal performance, aimed at maximizing motor efficiency at high speeds. Particular attention was given to the study of electromagnetic losses, which become significant at these high speeds, for each of the considered topologies. In parallel, detailed mechanical analyses were conducted on disc-shaped rotors, which are sparsely documented in the literature, as well as on cylindrical rotors, to characterize their mechanical behavior at a rotational speed of 90,000 rpm. Manufacturing constraints ultimately led to the selection of the radial flux topology, which is currently under prototyping

We present Bessel function and Gaussian beam models for a study of microwave power deposition in bounded and inhomogeneous lossy media. The aim is to develop methods that can accurately simulate practical results commonly found in electromagnetic hyperthermic treatment, which is a noninvasive method. The Bessel function method has a closed form solution and can be used to compute accurate results of electromagnetic fields emanating from applicators with cosinusoidal aperture fields. On the other hand, the Gaussian beam method is approximate but has the capability to simplify boundary value problems and to compute fields in three-dimensions with extremely low CPU time (less than 30 sec). Although the Gaussian beam method is derived from geometrical optics theory, it performs very well in domains outside the realm of geometrical optics which stipulates that aperture dimension/λ ≥ 5 in the design of microwave systems. This condition has no relevance to the Gaussian beam method since the method shows that a limit of aperture dimension/ λ ≥ 0.9 is possible, which is a very important achievement in the design and application of microwave systems. Experimental verifications of the two theoretical models are integral parts of the presentation and show the viability of the methods.

The demand for high power density keeps driving the development of electromagnetic integration technologies in the field of power electronics. Based on planar homogeneous integrated structures, the mechanism of the electromagnetic integration of passives has been investigated with distributed-parameter models. High order modeling of integrated passives has been developed to investigate the electromagnetic performance. The design algorithm combining electromagnetic design and loss models has been developed to optimize and evaluate the spiral winding structure. High power density of 480 W/in3 has been obtained on the prototype. Due to the structural limitation, the currently applied planar spiral winding structure does not sufficiently utilize the space, and the structure is mechanically vulnerable. The improvement on structures is necessary for further application of integrated passives. The goal of this research is to investigate and evaluate alternative structures for high-power-density integrated passives. The research covers electromagnetic modeling, constructional study, design algorithm, loss modeling, thermal management and implementation technology The symmetric single layer structure and the stacked structure are proposed to overcome the disadvantages of the currently applied planar spiral winding structure. Because of the potential of high power density and low power loss, the stacked structure is selected for further research. The structural characteristics and the processing technologies are addressed. By taking an integrated LLCT module as the study case, the general design algorithm is developed to find out a set of feasible designs. The obtained design maps are used to evaluate the constraints from spatial, materials and processing technologies for the stacked structure. Based on the assumption of one-dimensional magnetic filed on the cross-section and linear current distribution along the longitudinal direction of the stacked structure, the electromagnetic field distribution is analyzed and the loss modeling is made. The experimental method is proposed to measure the loss and to verify the calculation. The power loss in the module leads to thermal issues, which limit the processed power of power electronics modules and thus limit the power density. To further improve the power handling ability of the module, the thermal management is made based on loss estimation. The heat extraction technology is developed to improve the heat removal ability and further improve the power density of integrated passives. The experimental results verify the power density improvement from the proposed stacked structure and the applied heat extraction technology. The power density of 1147 W/in3 (70 W/cm3) is achieved in the implemented LLCT module with the efficiency of 97.8% at output power of 1008W.
Ph. D.

A three dimensional finite element method software package has been developed for solving electromagnetic vector fields in conducting, magnetic materials and has been applied in two dimensions to ferromagnetic filaments and in three dimensions to a sphere. The bulk of this dissertation describes the approach to formulating the problem, choosing a solution routine, developing a method of discretization, verifying the accuracy and characterizing the computational efficiency of the package. Spurious vector solutions, which arise in numerical approximations to three dimensional electromagnetic problems, were eliminated by using a node-based formulation, with modified vector wave equation to ensure that divergence free conditions are satisfied. Conjugate gradient, iterative quasi-minimal residual solver (QMR) with a non-zero matrix element storage scheme expedited computation and reduced memory requirements. An automatic mesh generator for hexahedral elements was developed for discretization. The two dimensional study continued earlier analytical and experimental work on induction heating of multi-filament ferromagnetic strands. The present results demonstrate that coupling between filaments does not occur in two dimensions and is, in fact, a three dimensional effect provided the filaments are not in electrical contact. Furthermore, the accuracy of the solution can be established quantitatively by a single parameter, the ratio of one side of the finite element to the electromagnetic skin (or penetration) depth. The three dimensional parametric study investigates the effects on power absorption patterns in the sphere as a function of conductivity and permeability. Primarily, this research demonstrates that these types of problems can be solved accurately. Finally, it is shown that while the discretization must extend completely throughout the sphere for non-magnetic, moderately lossy media (conductivity, σ∼ 1 S/m, relative permeability, μᵣ ∼1), it need only consist of a thin shell of about three skin depths thick for highly conducting magnetic materials. The core of this sphere can be replaced by a field free inner perfectly conducting sphere. While the problem of computing power absorption in ferromagnetic implants for hyperthermia, the motivation for this study, was not solved completely, the foundations have been laid. Dependence of power absorption upon size, shape, permeability and conductivity as well as interactions between filaments of finite length can be addressed with this beginning.

The problem of electromagnetic field penetration in the finite-resistivity conductors of a uniform, multiple, coupled transmission line system (MTL) is considered. Under the assumption of quasi-transverse electric and magnetic (quasi-TEM) mode of propagation, the problem of determining the per-unit-length resistance and inductance matrices for such MTL systems reduces to solving a quasi-magnetostatic problem. An integral equation for the current density distribution inside the conductors is formulated and solved numerically using the method of moments. From straightforward energy considerations and the current density distribution, the per-unit-length resistance and inductance matrices are calculated. Several microstrip configurations are then analysed and the effects of the geometrical characteristics of the structures on the per-unit-length inductance and resistance matrices, as well as their frequency dependence are investigated.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Electrical and Computer Engineering, Thomas J. Watson School of Engineering and Applied Science, 2008.
Includes bibliographical references.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.12 "Напівпровідникові перетворювачі електроенергії" – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019. Дисертацію присвячено вирішенню важливої наукової задачі – створенню трифазних напівпровідникових перетворювачів з покращеними енергетичними та масовими характеристиками. Проведено аналіз характеристик існуючих типів трифазних випрямлячів з електронним зсувом фаз та показано, що трифазний випрямляч з електронним зсувом фаз пульсністю більш ніж 12 має містити узгоджувальний пристрій для балансування рівня вихідних напруг. Запропоновано використання низькочастотної широтно-імпульсної модуляції для балансування вихідної напруги модулів трифазного випрямляча, що дає можливість відмовитися від застосування автотрансформаторів на вході перетворювача. Проаналізовано електромагнітні процеси в перетворювачі на основі багатопульсних випрямлячів з електронним зсувом фаз та показано, що для розглянутого класу перетворювачів доцільно використовувати випрямлячі з пульсністю від 18 до 24 для мереж малої потужності. Запропоновані схемотехнічні рішення багатопульсних випрямлячів з електронним зсувом фаз, можуть бути використані в розробці та проектуванні перспективних джерел постійного струму, що вимагають покращених масових показників, відповідності вимогам по електромагнітній сумісності. Наприклад:– при розробці та проектуванні перспективних джерел постійного струму електрифікованих залізниць. – в наземному електрообладнанні аеропортів, як складова частина комплексу наземного живлення 3х115 В 400 Гц 30-90 кВт та ін.
thesis is devoted to the solution of an important scientific problem - the creation of three-phase semiconductor converters of alternating current to constant current with improved energy and mass characteristics. The characteristics of existing types of three-phase rectifiers with electronic phase shift are analyzed and it is shown that a three-phase rectifier with electronic phase shift with a pulse frequency of more than 12 should contain a matching device for balancing the output voltage level. The use of low-frequency pulse-width modulation for balancing the output voltage of three-phase rectifier modules is proposed, which eliminates the use of autotransformers at the input of the converter. Electromagnetic processes in the converter based on multipulse rectifiers with electronic phase shift are analyzed and it is shown that for the considered class of converters it is advisable to use rectifiers with a pulse range from 18 to 24. The proposed circuit solutions of multi-pulse rectifiers with electronic phase shift can be used in the development and design of promising sources of direct current, requiring improved mass performance and compliance with the requirements for electromagnetic compatibility. For example: - In the development and design of promising sources of direct current electrified railways. - In the ground electrical equipment of airports, as an integral part of the ground supply complex 3x115 V 400 Hz 30-90 kW, etc.

This thesis presents a novel study on Second Generation High Temperature Superconductors, which covers their electromagnetic characteristics and AC loss analysis. Lorentz Force Electrical Impedance Tomography (LFEIT) is one of the most promising hybrid diagnostic scanners with burgeoning potential for biological imaging, particularly in the detection of cancer and internal haemorrhages. The author tried a novel combination of superconducting magnets together with the LFEIT system. The reason is that superconducting magnets can generate a magnetic field with high intensity and homogeneity, which could significantly enhance the electrical signal induced from a sample, thus improving the Signal-to-Noise Ratio (SNR). The author developed four magnet designs for the LEFIT system using the Finite Element Method (FEM) package, COMSOL Multiphysics, and found that a Superconducting Halbach Array magnet can achieve all the requirements (magnetic field properties, geometry, portability, etc.) for the LFEIT system. The optimization study of the superconducting Halbach Array magnet has been carried out on the FEM platform of COMSOL Multiphysics, with 2D models using H-formulation based on B-dependent critical current density and bulk approximation. Optimization focused on the location of the coils, as well as the geometry and number of coils on the premise of maintaining the total amount of superconducting material used in the design. The optimization results showed that the Halbach Array configuration based superconducting magnet is able to generate a magnetic field with an intensity of over 1 Tesla and improved homogeneity. In order to efficiently predict the optimization performance, mathematical formulas were developed for these optimization parameters to determine the intensity and homogeneity of the magnetic field. The mathematical model for the LFEIT system was built based on the theory of the magneto-acousto-electric effect. Then the basic imaging of the electrical signal was developed using Matlab. The magnetic field properties of the magnet design were imported into the LFEIT model. The LFEIT model simulated two samples located in three different magnetic fields with varying magnetic strength and homogeneity. Even if there are no actual alternating currents involved in the DC superconducting magnets mentioned above, they have power dissipation during normal operation (e.g. magnet ramping) and under different background fields. This problem generally goes under the category of “AC loss”. Therefore, the AC loss characteristics of HTS tapes and coils are still fundamentally important for HTS magnet designs, even if they are normally operating in DC conditions. This thesis starts with the AC loss study of HTS tapes. The investigation and comparison of AC losses on Surround Copper Stabilizer (SCS) Tape and Stabilizer-free (SF) Tape have been carried out, which includes AC loss measurement using the electrical method, as well as the real geometry and multi-layer HTS tape simulation using the 2D H formulation by COMSOL Multiphysics. Hysteresis AC losses in the superconducting layer, and eddy current AC losses in the copper stabilizer, silver overlayer and substrate were concerned in this investigation. The measured AC losses were compared to the AC losses from the simulation, using 3 cases of different AC frequency: 10 Hz, 100 Hz, and 1000 Hz. The frequency dependence of AC losses from Stabilizer free Tape and Copper Stabilizer Tape were compared and analysed. A comprehensive AC loss study of a circular HTS coil has been fulfilled. The AC losses from a circular double pancake coil were measured using the electrical method. A 2D axisymmetric H-formulation model using FEM package COMSOL has been established, which was able to make consistency with the real circular coil used in the experiment. To model a circular HTS coil, a 2D axisymmetric model provided better accuracy than a general 2D model, and was also more efficient than a 3D model. Three scenarios were analysed: (1) AC transport current and DC magnetic field, (2) DC transport current and AC magnetic field, (3) AC transport current and AC magnetic field. The angular dependence analysis on the coil under the magnetic field with the different orientation angle  was carried out for all three scenarios. For scenario (3), the effect of the relative phase difference ∆ between the AC current and the AC field on the total AC loss of the coil was investigated. To summarise, a current/field/angle/phase dependent AC loss (I, B, , ∆) study of circular HTS coil has been carried out, which could potentially benefit the future design and research of HTS AC systems. The AC losses of horizontally parallel HTS tapes have been investigated. The AC losses of the middle and end tape of three parallel tapes have been measured using the electrical method, and compared to those of an individual isolated tape. The effect of the interaction between tapes on AC losses has been analysed, and compared with finite element method (FEM) simulations using the 2D H formulation implemented in COMSOL Multiphysics. The electromagnetic induction around the three parallel tapes was monitored using COMSOL simulation. The electromagnetic induction and AC losses generated by a conventional three turn coil were simulated as well, and then compared to the case of three parallel tapes with the same AC transport current. The analysis demonstrated that HTS parallel tapes could be potentially used in wireless power transfer systems, which could have lower total AC losses than conventional HTS coils. By using FEM simulations, cases of increasing number of parallel tapes was considered, and the normalised ratio between the total average AC losses per tape and the AC losses of an individual single tape have been calculated for different gap distances. A new parameter is proposed, Ns, a turning point the for number of tapes, to divide Stage 1 and Stage 2 for the AC loss study of horizontally parallel tapes. For Stage 1, N < Ns, the total average losses per tape increased with the increasing number of tapes. For Stage 2, N > Ns, the total average losses per tape started to decrease with the increasing number of tapes. The analysis demonstrates that horizontally parallel HTS tapes could be potentially used in superconducting devices like HTS transformers, which could retain or even reduce the total average AC losses per tape with large numbers of parallel tapes.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.12 "Напівпровідникові перетворювачі електроенергії" – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019. Дисертацію присвячено вирішенню важливої наукової задачі – створенню трифазних напівпровідникових перетворювачів з покращеними енергетичними та масовими характеристиками. У багатьох електричних мережах і системах напівпровідникові перетворювачі є одним з основних видів навантаження. Напівпровідникові перетворювачі є для мережі живлення нелінійним навантаженням, і його робота впливає на режими роботи мережі, особливо якщо потужність перетворювача і мережі співрозмірні. Тому при проектуванні як електричних мереж, так і напівпровідникових перетворювачів необхідно враховувати вплив роботи перетворювачів на мережу живлення. В силовій електроніці одним з найпоширеніших перетворювачів є трифазний випрямляч. Схеми випрямлячів трифазного живлення застосовуються в основному для живлення споживачів середньої й великої потужності. Покращення електромагнітної сумісності в цих системах можливе з використанням схем трифазних випрямлячів зі збільшеною пульсністю. Для роботи таких випрямлячів необхідним є використання фазозсувних трансформаторів або автотрансформаторів. Використання фазозсувних магнітних елементів погіршує масові характеристики перетворювача, а при збільшенні пульсності випрямляча ускладняється їх конструкція. Покращення масових характеристик та електромагнітної сумісності можливе з використанням електронного зсуву фаз в трифазних випрямлячах зі збільшеною пульсністю. В дисертаційній роботі запропоновано структуру багатопульсних випрямлячів з електронним зсувом фаз пульсністю більше 12-ти, що дозволяє поліпшити гармонійний склад споживаного струму за рахунок підвищення пульсності випрямляча, отримання високого коефіцієнту потужності за рахунок використання «відстаючих» і «випереджаючих» кутів керування. Обґрунтовано доцільність використання повністю керованих напівпровідникових ключів з зворотною блокуючою здібністю в трифазних випрямлячах з електронним зсувом фаз, що дозволяє отримати високий коефіцієнт зсуву між вживаним струмом і напругою джерела живлення за рахунок уніфікації використовуваних напівпровідникових ключів. Запропоновано використання низькочастотної широтно-імпульсної модуляції для балансування вихідних напруг модулів трифазного випрямляча, що дозволяє реалізувати схему перетворювача без використання вхідних узгоджувальних електромагнітних елементів. Досліджені електромагнітні процеси в трифазних багатопульсних випрямлячах з електронним зсувом фаз при використанні повністю керованих напівпровідникових ключів зі зворотною блокуючою здатністю, що дозволило отримати основні вирази для оцінки комутаційних втрат. Запропоновані схемотехнічні рішення багатопульсних випрямлячів з електронним зсувом фаз, можуть бути використані в розробці та проектуванні перспективних джерел постійного струму, що вимагають покращених масових показників, відповідності вимогам по електромагнітній сумісності. Наприклад: – в наземному електрообладнанні аеропортів, як складова частина комплексу наземного живлення літаків 3х115 В 400 Гц 30-90 кВт; – в перетворювачах частоти з ланкою постійного струму при підключенні AC/AC перетворювача безпосередньо до мережі живлення, тобто без використання масштабуючих трансформаторів.
Thesis for the degree of candidate of technical sciences in the specialty 05.09.12 "Semiconductor power converters" – National Technical University "Kharkiv Polytechnic Institute", Kharkov, 2019. The thesis is devoted to the solution of an important scientific problem - the creation of three-phase semiconductor converters of alternating current to constant current with improved energy and mass characteristics. In many electrical networks and systems, semiconductor transducers are one of the main types of load. Semiconductor transducers are nonlinear for the power supply, and its operation affects the network operating modes, especially if the power of the converter and the network are dimensional. Therefore, when designing both electrical networks and semiconductor converters, it is necessary to take into account the effect of converters on the power supply. In power electronics, one of the most common converters is a three-phase rectifier. Schemes of three-phase power rectifiers mainly used for power supply to consumers of medium and high power. Improvement of electromagnetic compatibility in these systems is possible using schemes of three-phase rectifiers with increased pulsativeness. The use of phase-shift transformers or autotransformers is necessary for such rectifiers. The use of phase-shift magnetic elements, worsens the mass characteristics of the converter, and when the rectifier pulsity increases, their design becomes more complicated. Improvement of mass characteristics and electromagnetic compatibility is possible with the use of electronic phase shift in three-phase rectifiers with increased pulsatility. In the dissertation work the structure of multipulse rectifiers with electron phase shift of pulses more than 12 is proposed, which allows to improve the harmonic composition of consumed current by increasing the rectifier pulsity, obtaining a high power factor by using the "lagging" and "outgoing" angles of control. The expediency of using fully controlled semiconductor keys with reverse blocking capability in three phase rectifiers with electron phase shift is substantiated. The use of low-frequency pulse-width modulation for balancing the output voltages of three-phase rectifier modules is proposed. The proposed circuitry solutions of multi-pulse rectifiers with electron phase shift can be used in the design of advanced DC sources requiring improved mass performance, compliance with electromagnetic compatibility requirements.

It is important to investigate the threat posed to commercial aircraft by on board electronic transmitters in the passenger cabin and the cargo holds of large transport aircraft. These transmitters may be in the form of unintentional use of portable electronic devices or even intentional radio frequency (RF) threat sources from terrorists. Thus, it is of interest to determine the "interference path loss" (IPL) from a transmitting device inside the cabin of such aircraft to the antenna terminals of a potential victim system of the aircraft. Past studies have concentrated on measurements. These efforts to measure IPL directly have demonstrated that accurate and repeatible measurements are difficult to obtain. Very little modeling work has been done successfully to understand the IPL on aircraft. In this thesis, we propose a 3-step methodology to quantify the interference path loss (IPL). We then apply this methodology to a broad class of aircraft and show results. To validate our results, we compare our findings to known measurements and discuss possible sources of errors. Finally we suggest areas of improvement to our analysis and propose future work.
Master of Science

Efectes de Geometria en les Propietats Electromagnètiques de Materials Lineals i de Superconductors en l'Estat Crític
El comportament electromagnètic d'un cert material no només depèn de les seves propietats intrínseques sinó també de la geometria de la mostra estudiada. De fet, algunes magnituds magnètiques en mostres del mateix material però geometria diferent poden diferir en varis ordres de magnitud.
La tesi està dividida en dues parts. La primera part està dedicada a l'estudi dels efectes de geometria, també denominats efectes desimantadors, en mostres de materials lineals, homogenis i isòtrops (LHI) sota l'aplicació d'un camp magnètic uniforme. Per quantificar els efectes desimantadors en les magnituds magnètiques més rellevants en materials LHI s'utilitzen els factors de desimantació fluxmètric i magnetomètric (Nf i Nm); el seu càlcul teòric és necessari per poder determinar algunes propietats intrínseques dels materials a partir d'experiments. Després de detectar grans mancances en els resultats teòrics previs dels factors de desimantació per prismes rectangulars, presentem nombrosos càlculs originals de Nf i Nm. Pels casos de prismes infinitament llargs i prismes quadrats finits Nf i Nm es calculen per un rang ampli de relació gruix-amplada i susceptibilitat magnètica. Pel cas d'un prisma finit perfectament diamagnètic es presenta un estudi sistemàtic dels factors de desimantació en funció de les dimensions relatives del prisma a partir de càlculs precisos. També es calculen resultats numèrics per cilindres amb camp aplicat en la direcció radial, situació per la que existien molt poques dades.
L'altra part de la tesi consisteix en un estudi de superconductors durs, que són materials molt interessants per aplicacions pràctiques. En aquest cas, l'estudi es centra en algunes geometries infinitament llargues immerses en un camp magnètic altern i uniforme aplicat en direcció transversal o bé que transporten un corrent elèctric altern. Concretament, s'estudien amb detall les geometries de prisma infinit de secció rectangular, el·líptica i varis casos de conjunts de múltiples prismes rectangulars. L'estudi d'aquestes geometries és de gran importància pràctica a l'hora de dissenyar cintes i cables superconductors per treballar en dispositius elèctrics en corrent altern, pels que és fonamental la reducció de les pèrdues energètiques per la viabilitat de la tecnologia basada en cables superconductors. Per fer l'estudi esmentat es desenvolupa un mètode numèric basat en el model d'estat crític per superconductors i la minimització de l'energia magnètica. Pels casos de camp magnètic aplicat, el mètode permet descriure dos tipus de connexió entre filaments, elèctricament aïllats un a un o interconnectats entre sí al extrems dels prismes. Malgrat que el primer tipus de connexió és la que presenta pèrdues energètiques més baixes, no havia estat possible simular-lo fins ara. Els resultats numèrics obtinguts a partir d'aquest mètode són originals i de gran precisió. A més, la descripció sistemàtica del problema permet realitzar un estudi en profunditat de les propietats electromagnètiques per aquestes geometries, gràcies al que s'obtenen unes tendències bàsiques per reduir les pèrdues energètiques.
The electromagnetic behaviour of a certain material do not only depends on its internal properties but also on the geometry of the studied sample. Actually, some magnetic quantities in samples of the same material but different geometry can vary in several orders of magnitude.
The thesis is divided into two parts. In the first part we study the geometry effects, also called demagnetizing effects, in samples made of linear homogenous isotropic materials (LHI) subjected to a uniform applied magnetic field. In order to quantify the demagnetizing effects on the most relevant magnetic quantities of the samples, we carry out accurate calculations for the fluxmetric and magnetometric demagnetizing factors (Nf and Nm); the calculation of these factors is needed to determine some internal magnetic properties of materials from experiments. After detecting some important lacks in the already existing theoretical results for rectangular prisms, we present a complete set of original calculated data of Nf and Nm. For the cases of infinitely long rectangular prisms and finite square bars we calculate Nf and Nm for a wide range of thickness-to-width aspect ratio and magnetic susceptibility. For the case of a perfectly shielding rectangular prism, we present a systematic study of the demagnetizing factors as a function of the relative dimensions of the prism by means of accurate numerical calculations. Numerical results are also presented for cylinders under radial applied field, situation for which there existed very few data.
The other part of the thesis consists in a study of hard superconductors, which are materials very interesting for applications. For this case, we have focused on some infinitely long geometries subjected to either a transverse AC applied field or a transport alternating current. Specifically, there have been studied in detail the geometries of an infinitely long prism with rectangular cross-section, elliptical one and some arrangements of several rectangular prisms. The study of these geometries is of great practical importance for the design of superconducting tapes and cables for devices operating in AC conditions, for which the reduction of the AC loss is of vital importance for the viability of the technology based on superconducting wires. In order to do such an study, we develop a numerical method based on the critical-state model for superconductors and magnetic energy minimization. For the cases considering an applied magnetic field, the method allows the description of two different kinds of filament connexion, mutually electrically isolated or interconnected at the ends of the prisms. Although the first kind of connection presents lower AC loss, this situation has not been simulated until now by any author. The numerical results obtained from this method are original and very accurate. Furthermore, the systematic study of the problem provides a deep understanding of the electromagnetic properties for these geometries, thanks to which we obtain some general trends to reduce the AC loss.

Microwave heating is an emerging but still underutilized tool in modern industrial applications. The task of designing microwave applicators for heating industrial materials with temperature-dependent properties is challenging, and trial-and-error system prototyping is an expensive and wasteful means to accomplish this goal. The purpose of this work is to combine existing heat transfer and electromagnetic models to provide a complete simulation for heating dielectric materials in a resonant microwave cavity. The numerical simulation is validated by comparison to several independent sets of experimental data. The ultimate goal is to provide a research tool that will facilitate the industrial microwave applicator design process. With a complete, accurate, and user-friendly numerical simulation, parameters affecting the temperature distribution in stationary and moving process materials can be studied to optimize the results before the first prototype is made. This work also explores the sources of power loss in a microwave system and develops means for quantifying these power losses.
Master of Science

Wearable wireless sensors are a part of human life in the future for applications such as healthcare, sports, navigating, security etc. The number of wearable wireless sensors for fitness and healthcare applications will reach 90 million shipments by 2017 base on ABI research report [1]. The IEEE Standard 802.15.6 for local and metropolitan area networks, part 15.6, “Wireless Body Area Networks” was published on February 2012 to specify the short range wireless communication in the vicinity or inside of the human body [2]. This shows the importance of research needed to maximize the quality of wireless communications around the body. The human body is a lossy medium that absorbs the radio frequency (RF) energy and this affects the propagation of electromagnetic waves used in wireless communication. The specific absorption rate (SAR) is defined by the Federal Communications Commission (FCC) to identify criteria for measuring the rate of absorption and amount of interaction between the body and a source of RF energy [3].
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith school of Engineering
Science, Environment, Engineering and Technology
Full Text

The proper functioning of the auditory processing needs an integration of many types of information, and a synchronised action between auditory cortex and other cortical and subcortical centres. The normal development of connectivity between the auditory system and the higher neurocognitive functions depends on sensory experience, and congenital hearing loss makes it essentially impossible. The aim of this work was to perform an electrophysiological analysis of auditory cortical areas in patients with cochlear implant (CI). Thirty implanted patients were included in the study. Twenty-four of them were prelingual patients and they were divided into three groups, according to the age at time of CI surgery and to the duration of CI use: group A - early implant and lengthy CI use, group B - late implant and lengthy CI use, group C - late implant and short CI use. The remaining six patients were affected by postlingual deafness, and they were included in the group D. Each patient group was compared with a normal hearing age matched control group. Each subject underwent an Event-related potentials (ERPs) evaluation and electroencephalographic registration. All data analysis were performed by using Loreta software (Low Resolution Electromagnetic Tomography). ERPs latencies were for the most part significantly longer in patients than in controls. Concerning the Event-related cortical activity, all the control groups showed a high and well-defined activation in frontals areas and the cingulate cortex, in the N200 and P300 time windows. A comparable activation in strength and timing, between patients and controls, was only found in the first prelingual patient group (A), and to a lesser extent in the second group (B), while patients belonging to the third prelingual group (C) showed a very low cortical activation, with no cyclic pattern. Postlingual patients (D) showed no difference in activation compared to controls. ln a second step of the study, functional connectivity was analysed from EEG data, in two different conditions: resting state and activation state. Default mode network, left and right Precuneus and associative visual cortex were examined. No difference between prelingual patients and controls was found in the first group (A). Functional connectivity showed a significant increase in the second (B) and third (C) prelingual patient group, especially in the activation state, and specifically between visual areas and Precuneus and posterior cingulate cortex, while postlingual patients (D) showed no difference compared to controls. Cochlear implant adds a new auditory modality in prelingual patients, allowing the creation of a functional network. This involves the areas implicated in sensory and cognitive modalities, and needs some time to form. The duration of CI use is crucial: prolonged CI use, in addiction to an early time of implant, can restore auditory network, allowing a normalization process, from both an audiological and a neurophysiological point of view. However, in the case of patients with postlingual hearing loss, cochlear implant seems to restore and reinforce a cortical network that has already been formed, before the onset of the hearing impairment.
Un corretto funzionamento del processamento uditivo necessità di una sincronizzazione tra corteccia uditiva ed altre unità corticali e subcorticali, e di elaborare molti tipi di informazioni differenti. Il normale sviluppo della connettività tra sistema uditivo a altre funzioni neurocognitive è strettaemente legato all’esperienza uditiva del soggetto. In questo senso la deprivazione uditiva rende impossibile un corretto sviluppo. Scopo del lavoro è stato valutare da un punto di vista elettrofisiologico l’attività corticale in pazienti con impianto cocleare. Il campione dello studio è costituito da trenta pazienti portatori di impianto cocleare (IC), dei quali 24 con un’ipoacusia preverbale e 6 postverbale. I soggetti preverbali sono stati suddivisi in tre gruppi, sulla base di due parametri, età di impianto e tempo di utilizzo del dispositivo: gruppo A – impianto precoce e lungo utilizzo; gruppo B – impianto tardivo e lungo utilizzo; gruppo C – impianto tardivo e breve periodo di utilizzo. I pazienti postverbali costituiscono il gruppo D. Ciascun gruppo di pazienti è stato confrontato con un gruppo di soggetti normoacusici, comparabile per età. Ogni soggetto è stato sottoposto a registrazione dei potenziali evento-correlati e a registrazione elettroencefalografica. Tutti i dati sono stati analizzati mediante l’utilizzo del software Loreta (Low Resolution Electromagnetic Tomography). Le latenze dei potenziali registrati sono risultati complessivamente maggiori nei pazienti rispetto ai controlli. Per quanto riguarda l’attivazione delle sorgenti corticali durante l’elicitazione dei potenziali, tutti i controlli hanno mostrato un’attivazione corticale definita e rilevante, in corrispondenza delle aree frontali e del cingolato, sia per quanto riguarda la N200 che per la P300. Un’attivazione corticale simile si è riscontrata solo nei pazienti appartenenti al gruppo A, e in misura minore a quelli del gruppo B, mentre i pazienti del gruppo C hanno mostrato un’attivazione corticale molto bassa, e senza un pattern ciclico. Nei pazienti postverbali del gruppo D invece non sono state riscontrate differenze di attivazione rispetto ai relativi controlli. In una seconda fase dello studio è stata valutata la connettività funzionale, mediante analisi dei dati EEG, in due differenti condizioni: stato di veglia rilassata e stato di attivazione. Sono stati analizzati il Default mode network, il precuneo, la corteccia visiva. Anche in questo caso il gruppo A di pazienti non ha mostrato differenze con i controlli, in termini di connettività. I pazienti del gruppo B, e ancora di più quelli del gruppo C, hanno mostrato valori più alti di connettività, specialmente per quanto riguarda lo stato di attivazione. Anche in questa analisi i pazienti del gruppo D non hanno mostrato differenze rispetto ai controlli. L’impianto cocleare crea una nuova modalità uditiva nei pazienti preverbali, permettendo la creazione di un network funzionale che richiede del tempo per formarsi, e che coinvolge aree implicate in attività di tipo sensoriale e cognitivo. Fondamentale per un miglioramento in termini audiologici e neurofisiologici è risultato il parametro di durata di utilizzo dell’impianto cocleare. Nei pazienti postverbali invece l’impianto cocleare va a ripristinare un network corticale già formato prima dell’insorgenza dell’ipoacusia.

The rapid development of second generation (2G) high temperature superconducting (HTS) wires in the last decade has made it possible to wind high quality 2G HTS coils. These 2G HTS coils show promise for future applications such as magnetic resonance imaging (MRI) magnets, electrical machines, magnetic levitation trains, energy storage, etc. 2G HTS coils can be operated using either dc current or ac current. Several important issues have yet to be resolved, such as how to properly magnetise an HTS coil under dc conditions, or how to minimise losses under ac conditions. These problems should be carefully studied before the 2G HTS coils can be widely applied in scientific and industrial applications. This thesis focuses on emerging HTS flux pump technology for HTS coils operating in a dc environment. HTS flux pump technology applies a travelling magnetic wave to fully magnetise an HTS coil, which is both efficient and economical, and has in recent years been proven feasible. However, the underlying physics of this technology are so far poorly understood. In order to study the influence of a travelling magnetic wave on HTS films such as YBa2Cu3O7-δ, two types of circular-type magnetic flux pump (CTMFP) devices were proposed and built. These novel devices generate an annular-shape travelling magnetic wave. The first type was the original CTMFP magnet, which produces the longest wavelength of travelling wave. The second type was the updated CTMFP magnet, which can produce a shorter wavelength of travelling wave (1/2 of the original CTMFP magnet in the six phase connection and 1/4 in the three phase connection). A 2 inch diameter round shape YBCO thin film (200 nm thick of the YBCO layer) and a 46 mm× 46 mm square shape YBCO tape (1.0 µm thick of the YBCO layer, with a hole of Φ26 mm in the centre) were tested. When using a round shape YBCO thin film and the original CTMFP magnet, it was found that the travelling wave tends to decrease the existing critical magnetic gradient inside the YBCO film. The experiment was repeated under different conditions, such as zero-field cooling (ZFC), field cooling (FC), delta-shape trapped field, etc. A simulation based on the H-formulation using FEM software revealed that, after application of the travelling wave, the current density distribution inside the round shape YBCO sample was disturbed, becoming much lower than its critical current density JC. This discovery is interesting because the Bean model suggests that the current density inside a type-II superconductor should be equal to either +JC or - JC (the critical state model). It was found that a round shape YBCO sample follows the Bean model prediction for the homogeneous oscillating field (homogeneous in space), which suggests that the travelling wave is more efficient for transporting the magnetic flux inside YBCO film, compared to a homogeneous oscillating field. An updated CTMFP magnet was designed and built to investigate the influence of the degree of field inhomogeneity on the change of an existing critical magnetic gradient. The results were compared between the six phase connection (1/2 wavelength of the original CTMFP magnet) and the three phase connection (1/4 wavelength of the original CTMFP magnet). It was found that with a travelling wave of consistent amplitude, by shortening the wavelength, the change of magnetic gradient is made stronger. The result supports the assumption that the field inhomogeneity in space may have an important influence on the magnetisation of a YBCO sample. Additionally, in the case of a three phase connection (1/4 wavelength), by reversing the direction of the travelling wave, a different magnetisation profile was obtained, which suggests that the experiment may have detected a macroscopic “magnetic coupling” phenomenon. However, this result needs further study before it can be confirmed. The square shape YBCO sample was tested by applying a travelling wave in a dc background field under FC conditions. The square shape YBCO sample has a centre hole (Φ26 mm), which is closest to the condition of an HTS coil (single layer instead of multi-layer). However, in the experiment there was no clear change of magnetic flux inside the superconducting loop after application of the travelling wave. This might be attributed to the fact that, the field inhomogeneity is not strong enough to cause flux migration in the experiments, and the YBCO layer is relatively thicker which increases the difficulties. Moreover, the width of the superconducting region is relatively small (10 mm), in order to help magnetic flux migrate into the superconducting loop, the field inhomogeneity must be strong enough in the superconducting region, which increases the technical difficulties. However, this might be able to be accomplished by increase the amplitude of the travelling waves. Some experiments will be carried out in the future. The experimental findings in this thesis can not only aid in understanding the mechanism of HTS flux pump technology for an HTS coil, but also can help in understanding ac loss from a coil exposed to a travelling wave. As was suggested by the experimental results, the magnetisation of the YBCO film due to the travelling wave is very different from the magnetisation induced by a homogeneous oscillating field. Under operational conditions, such as inside an HTS motor, the HTS coils experience a travelling wave rather than a homogeneous oscillating field. This thesis discusses the difference in resultant ac loss from a travelling wave and a homogeneous oscillating field of the same amplitude. It was found that, for the round shape YBCO sample, the ac loss from a travelling wave is about 1/3 of the loss from a homogeneous oscillating field. The regions in which the ac loss occurred are also different between a travelling wave and a homogeneous oscillating field. These results suggest that the travelling wave cannot be equated to a homogeneous oscillating field when calculating ac loss. In conclusion, this thesis studies two novel experimental devices, built to study the magnetisation of YBCO films under the influence of a travelling wave. Several novel electromagnetic behaviours were observed in the YBCO films under the influence of a travelling wave, which may help improve understanding of HTS flux pump technology for an HTS coil, and the ac loss induced by a travelling wave.