Les gains sur la vitesse de commutation des composants actifs actuels offrent la possibilité de faire fonctionner les convertisseurs de puissance à des fréquences de découpage supérieures à 1 MHz. Le principal verrou à la montée en fréquence des convertisseurs provient des matériaux magnétiques des composants passifs qui sont le siège de dissipations thermiques. Les matériaux magnétiques utilisés, présentant un niveau de pertes acceptable entre 1 et 5 MHz, sont des ferrites de structure spinelle de type (Ni,Zn,Cu)Fe2O4. L’objectif de cette thèse est d’apporter une contribution expérimentale à la compréhension des liens entre la microstructure et les propriétés magnétiques statiques et dynamiques.Nous avons étudié deux procédés de synthèse des ferrites spinelles Ni-Zn-Cu (Ni,Zn,Cu)Fe2O4, d’une part par voie solide classique et, d’autre part, par la méthode sol-gel Pechini. Les propriétés structurales et magnétiques des échantillons produits ont été caractérisées de manière systématique et corrélées. Nous avons réussi à maîtriser l’élaboration et la mise en ordre et à obtenir une microstructure contrôlée de grains de l’ordre du µm et de forte densité (d>92%dth). Les résultats suggèrent que les ferrites synthétisés par la méthode Pechini peuvent être une alternative à la voie classique céramique pour la réalisation de composants magnétiques à faibles pertes.L’analyse des pertes magnétiques en fréquence a permis de montrer que l’ensemble des résultats obtenus était compatible avec un mécanisme de dissipation lié à l’amortissement des spins dans les parois. Ces résultats justifient la réalisation de pièces massives denses composées de petits grains avec du cobalt pour obtenir de faibles pertes sur une large plage d’induction (jusqu’à environ 25mT). / The high commutation rate of the wide gap semiconductor (GaN) allows operating with switching frequency above 1MHz in power converters. However, current magnetic materials comprising passive components in power converters cannot sustain the rise in the operating frequency, especially above 1 MHz. The main limitation comes from the sharp increase in power losses creating thermal dissipation inside the magnetic core. The core-losses are due to dynamic magnetization process (including domain wall movement and spin rotation) and they increase with the frequency. (Ni,Zn,Cu)Fe2O4 spinel ferrite is currently the best magnetic material with limited core-losses. The objective of the Ph.D. is to experimentally contribute to the understanding of the link between the microstructure and the static and dynamic magnetic properties.Synthesis process of (Ni,Zn,Cu)Fe2O4 spinel ferrite such as sold-state reaction and Pechini method were studied. The structural and magnetic properties were systematically measured and correlated together. We managed to master the elaboration and produce high density ferrite with controlled grain size (about few µm) and high density (d>92% dth). Results suggest that ferrites synthesized by Pechini method can be considered as an interesting basis for the design of low-loss magnetic components alternatively to the conventional route.The analysis on core-loss showed that the results are compatible with a dissipation mechanism linked to spin damping inside domain walls. It justifies the production of well-densified massive pieces composed of small grains and cobalt to obtain low core-loss for large amplitude excitation (up to 25mT).

The main objects of this doctoral thesis are analysis of a small induction motor losses and research of ways how to reduce losses and increase efficiency of this motor. The ways how to reduce losses and increase efficiency under study are as follow: reduction of stator winding’s resistance, lengthening of magnetic circuit, modification of turn number, cooper squirrel cage, slots shape optimization, sheets annealing and use of sheets with lower specific losses. The losses analysis and the research of ways how to reduce losses are done due to laboratory work. For this laboratory work, eleven different samples of the motor with above mentioned modifications were manufactured. Results of their measurements and losses analysis are presented in this thesis. There were also simulations by finite elements method used to help solve objects of this thesis. Due to the simulations, analysis of loses of the induction motor under study was done. Results of this analysis include some details that are not included in the results from measurement, for example separation of core losses between rotor and stator. The simulations were also used for analysis of manufacturing technology impact onto the motor’s performance. During this analysis, following impacts were considered: actual shape of magnetic circuit, stator’s sheets riveting, influence of cutting onto material’s properties and placement of the stator into conductive frame. Results of this analysis are presented in this thesis.

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

This thesis deals with the possibility of using the finite elements method for the analysing of synchronous permanent magnets machines. The aim of this work is to discuss the possibility of the machine design more effectively with using the finite elements method and Maxwell software for the simulations. On the created parametric model, simulations were performed according to master thesis assignment. The aim of this work is to determine induced voltage, iron losses, machine inductances and make a permanent magnets demagnetization analysis. From simulations results the machine efficiency is calculated. The parametric model was used for the optimization of selected parameters. From results of optimization new dimensions of permanent magnets was obtained. Machine efficiency was increased by new permanent magnet material and optimized design.

The main purpose of the thesis Automatic measurement of induction machine using LabVIEW was to develope an automated measuring system, which is used to perform tests of induction motors. The algorithm of the system is programmed in LabVIEW. In the practical part of this thesis, a measurement of the motor Atas Elektromotory Náchod a.s. T22VT512 is carried out, in order to verificate functions of the algorithm, and to perform tests of the motor to analyse losses. Another part of the work is dedicated to the electromagnetic calculation of the motor T22VT512. For this purpose, two softwares with different principles of calculation have been used. Firstly, the calculation is solved by an analytical based software called RMxprt. Secondly, the software Maxwell 2D is used to make the calculation of electric and magnetic fields by the finite element method.

The aim of this master´s thesis is to analyze core losses of a small induction motor. Analyzed values are obtained from laboratory measurements, software analysis and 2D finite element method simulation. The theoretical part of this thesis consists of two parts. The analysis of the higher spatial harmonics presents in the induction motor and the analysis of core losses of the motor. Practical part consists of laboratory measurements according to ČSN. Measured values are used to calculate individual losses. The next part consists of creating a model for software analysis (Maxwell RMxprt). The generated model is converted into a 2D simulation environment (Maxwell 2D), where it is adapted to obtain values from the examined parts (rotor and stator teeth and rotor cage). Results of simulations at different loads are compared and analyzed from the point of view of higher harmonics.