Método de estimación de las pérdidas de los conductores y del núcleo de componentes inductivos asimétricos mediante la técnica de análisis por método de elementos finitos en 3D

Tesis doctoral con la Mención de "Doctor Internacional"Dentro del campo de la ingeniería eléctrica, los convertidores electrónicos de potencia, que permiten generar una tensión y corriente de unas determinadas características a partir de una fuente de energía, juegan un papel crítico en las energías renovables, vehículos eléctricos o la ingeniería aeroespacial. Los componentes magnéticos constituyen uno de los elementos esenciales en los convertidores de potencia determinando el filtrado de corriente, la operación y la eficiencia del convertidor. Uno de los parámetros más críticos que influyen en la eficiencia de los convertidores son las pérdidas de los componentes magnéticos que dependen de determinados efectos electromagnéticos como el efecto pelicular, de proximidad, de entre-hierros y de borde. Estos efectos son aún más relevantes en rangos de alta frecuencia, a la que suelen operar habitualmente los convertidores electrónicos de potencia. La optimización del convertidor de potencia requiere un análisis detallado de los componentes magnéticos y de los efectos de frecuencia producidos en función de cada aplicación particular, y sus requisitos específicos, principalmente en los rangos de media y alta frecuencia. La trasmisión, almacenamiento y pérdidas de energía eléctrica y magnética son relevantes en este contexto y están determinadas por las ecuaciones de Maxwell, cuya resolución es compleja. Existen tres importantes enfoques para la resolución de estas ecuaciones: métodos analíticos, análisis utilizando herramienta de elementos finitos y por realización de ensayos. El primero de ellos consiste en la resolución analítica de las ecuaciones, con las necesarias simplificaciones, siendo la más habitual el asumir simetrías en las distribuciones de los campos magnéticos para poder resolver las ecuaciones de Maxwell en una o dos dimensiones. Como desventaja, dicha simplificación no permite determinar la distribución del campo magnético dentro de los conductores. El segundo enfoque utiliza un método de elementos finitos, resolviendo las ecuaciones de Maxwell en cada elemento finito, no siendo posible simular algunos componentes magnéticos complejos por precisar un tiempo de simulación sea muy elevado, haciendo que esta solución no resulte práctica para los ingenieros de desarrollo. El tercer enfoque, basado en la realización de ensayos de laboratorio, permite obtener los parámetros eléctrico de cualquier componente magnético. No obstante, el tiempo necesario es también alto y sólo es usado para los ajustes finales. La mayoría de los ingenieros electrónicos y científicos usan los análisis basados en elementos finitos de los componentes magnéticos realizando las posibles simplificaciones teniendo en cuenta la distribución de campo magnético y la simétrica del componente. Cuando el componente magnético no presenta ninguna simetría, deben utilizarse modelos 3D para la determinación de sus parámetros del circuito eléctrico equivalente y la optimización magnética del componente, así como un detallado estudio de los efectos pelicular y de proximidad, que son especialmente relevantes cuando el componente trabaja en alta frecuencia. En este trabajo, se proponer una metodología basada en elementos finitos en 3D con un bajo tiempo de simulación que permite obtener los parámetros que del modelo eléctrico equivalente para componentes magnéticos asimétricos a partir de la estimación de las pérdidas del bobinado y del núcleo.In electrical engineering, power converters, as devices that are able to transform a defined current and voltage from an energy source, have a critical role in different fields as renewable energy, electric vehicles or aerospace engineering. The magnetic components are relevant elements in power converters because determines the current filtering and conversion functions and converter efficiency and performance. One of the critical parameters that influence in the efficiency of converters are the losses in the magnetic components that depends on particular effects as they are the skin, proximity, airgap and edge effects. These effects are more relevant in the high frequency ranges where the power converters are usually operated. The optimization of the power converter requires of the detailed analysis of the magnetic component and the involved frequency effects according to the application when particular requirements are needed, mostly in the medium and high frequency. Transmission, storage and losses of magnetic and electric energy analysis is relevant in this context and are determined by the Maxwell´s equations whose resolution is a complex task. There are three main methods to solve this equation system: analytical method, finite element method analysis and experimental methodology. The first method consists on the analytical resolution of the equations with the necessary simplifications, being the most common approach the assumption of the magnetic field distribution in one or two dimensions to solve the equations system, however this simplification does not allow determining the magnetic field into the conductors. The second approach uses the Finite Element Method, solving the Maxwell equations in very finite element of the component, but is not possible to simulate some complex magnetic components because it requires a high computational time, being not useful for power electronics designers. The third method, based on experimental lab tests, allows to obtain the electrical parameters for any magnetic component. Nevertheless, the time cost is also huge and it is only used for adjustments in the final stage. Most of the power electronics designers and scientists use the analysis of the magnetic components based on Finite Element Method doing the available simplification taking into account the magnetic field distribution and the symmetry of the magnetic component. If the magnetic component has not any symmetric, a 3D model is necessary to determine the electromagnetic or thermal parameters for the electrical equivalent circuit and the magnetic component optimization, as well as a detailed study for skin effect and proximity effect, even more if the magnetic components work at high frequency. In this work, it is proposed a new method based in 3D Finite Element Analysis with a low computational time that allows obtaining the electrical equivalent model parameters for asymmetric magnetic components from the estimation of winding and core power losses

Ferrite-based micro-inductors for power systems on chip : from material elaboration to inductor optimisation

Les composants passifs intégrés sont des éléments clés pour les futures alimentations sur puce, compactes et présentant des performances améliorées: haut rendement et forte densité de puissance. L'objectif de ce travail de thèse est d'étudier les matériaux et la technologie pour réaliser de bobines à base de ferrite, intégrées sur silicium, avec des faibles empreintes (<4 mm ²) et de faible épaisseur (<250 µm). Ces bobines, dédiées à la conversion de puissance (˜ 1 W) doivent présenter une forte inductance spécifique et un facteur de qualité élevé dans la gamme de fréquence visée (5-10 MHz). Des ferrites de NiZn ont été sélectionnées comme matériaux magnétiques pour le noyau des bobines en raison de leur forte résistivité et de leur perméabilité stable dans la gamme de fréquence visée. Deux techniques sont développées pour les noyaux de ferrite: la sérigraphie d'une poudre synthétisée au laboratoire et la découpe automatique de films de ferrite commerciaux, suivi dans chaque cas du frittage et le placement sur les conducteurs pour former une bobine rectangulaire. Des bobines tests ont été réalisées dans un premier temps afin que la caractérisation puisse être effectuée : les propriétés magnétiques du noyau de ferrite notamment les pertes volumiques dans le noyau sont ainsi extraites. L'équation de Steinmetz a permis de corréler les courbes de pertes mesurées avec des expressions analytiques en fonction de la fréquence et de l'induction. La deuxième phase de la thèse est l'optimisation de la conception de la micro-bobine à base de ferrite, en tenant compte des pertes attendues. L'algorithme générique est utilisé pour optimiser les dimensions de la bobine avec pour objectif ; la minimisation des pertes et l'obtention de la valeur d'inductance spécifique souhaitée, sous faible polarisation en courant. La méthode des éléments finis pour le magnétisme FEMM est utilisée pour modéliser le comportement électromagnétique du composant. La deuxième série de prototypes a été réalisée afin de valider la méthode d'optimisation. En perspective, les procédés de photolithographie de résine épaisse et le dépôt électrolytique sont en cours de développement pour réaliser les enroulements de cuivre épais autour des noyaux de ferrite optimisés et ainsi former le composant complet.On-chip inductors are key passive elements for future power supplies on chip (PwrSoC), which are expected to be compact and show enhanced performance: high efficiency and high power density. The objective of this thesis work is to study the material and technology to realize small size (<4 mm²) and low profile (< 250 µm) ferrite-based on-chip inductor. This component is dedicated to low power conversion (˜ 1 W) and should provide high inductance density and high quality factor at medium frequency range (5-10 MHz). Fully sintered NiZn ferrites are selected as soft magnetic materials for the inductor core because of their high resistivity and moderate permeability stable in the frequencies range of interest. Two techniques are developed for the ferrite cores: screen printing of in-house made ferrite powder and cutting of commercial ferrite films, followed in each case by sintering and pick-and place assembling to form the rectangular toroid inductor. Test inductors were realized first so that the characterization could be carried out to study the magnetic properties of the ferrite core and the volumetric core losses. The core losses were fit from the measured curve with Steinmetz equation to obtain analytical expressions of losses versus frequency and induction. The second phase of the thesis is the design optimization for the on-chip ferrite based inductor, taking into account the expected losses. Genetic algorithm is employed to optimize the inductor design with the objective function as minimum losses and satisfying the specification on the inductance values under weak current-bias condition. Finite element method for magnetics FEMM is used as a tool to calculate inductance and losses. The second run of prototypes was done to validate the optimization method. In perspective, processes of thick-photoresist photolithography and electroplating are being developed to realize the completed thick copper windings surrounding ferrite cores

Modeling of directional solidification of multicrystalline silicon in a traveling magnetic field

Melt flow plays an important role in directional solidification of multicrystalline silicon influencing the temperature field and the crystallization interface as well as the transport of impurities. This work investigates the potential of a traveling magnetic field (TMF) for an active control of the melt flow. A system of 3D numerical models was developed and adapted based on open-source software for calculations of Lorentz force, melt flow, and related phenomena. Isothermal and non-isothermal model experiments with a square GaInSn melt were used to validate the numerical models by direct velocity measurements. Several new 3D flow structures of turbulent TMF flows were observed for different melt heights. Further numerical parameter studies carried out for silicon melts showed that already a weak TMF-induced Lorentz force can stir impurities near to the complete mixing limit. Simultaneously, the deformed temperature field leads to an increase of the deflection of crystallization interface, which may exhibit a distinct asymmetry. The numerical results of this work were implemented in a research-scale silicon crystallization furnace. Scaling laws for various phenomena were derived allowing a limited transfer of the results to the industrial scale

Impedance Transformers

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Analysis and Design of Low-Cost Waveguide Filters for Wireless Communications

The area of research of this thesis is built around advanced waveguide filter structures. Waveguide filters and the waveguide technology in general are renowned for high power capacity, low losses and excellent electromagnetic shielding. Waveguide filters are important components in fixed wireless communications as well as in satellite and radar systems. Furthermore, their advantages and utilization become even greater with increase in frequency, which is a trend in modern communication systems because upper frequency bands offer larger channel capacities. However, waveguide filters are relatively bulky and expensive. To comply with more and more demanding miniaturization and cost-cutting requirements, compactness and economical design represent some of the main contemporary focuses of interest. Approaches that are used to achieve this include use of planar inserts to build waveguide discontinuities, additive manufacturing and substrate integration. At the same time, waveguide filters still need to satisfy opposed stringent requirements like small insertion loss, high selectivity and multiband operation. Another difficulty that metal waveguide components face is integration with other circuitry, especially important when solid-state active devices are included. Thus, improvements of interconnections between waveguide and other transmission interfaces are addressed too. The thesis elaborates the following aspects of work: Further analysis and improved explanations regarding advanced waveguide filters with E-plane inserts developed by the Wireless Communications Research Group, using both cross coupled resonators and extracted pole sections (Experiments with higher filter orders, use of tuning screws, degrees of freedom in design, etc. Thorough performance comparison with competing filter technologies) - Proposing novel E-plane filter sections with I-shaped insets - Extension of the E-plane filtering structures with metal fins to new compact dual band filters with high frequency selectivity and miniaturized diplexers. - Introduction of easy-to-build waveguide filters with polymer insert frames and high-performance low-profile cavity filters, taking advantage of enhanced fabrication capabilities when using additive manufacturing - Developing new substrate integrated filters, as well as circuits used to transfer signals between different interfaces Namely, these are substrate integrated waveguide to metal waveguide planar transitions that do not require any modifications of the metal waveguides. Such novel transitions have been designed both for single and orthogonal signal polarizations

A Novel Power-Efficient Wireless Multi-channel Recording System for the Telemonitoring of Electroencephalography (EEG)

This research introduces the development of a novel EEG recording system that is modular, batteryless, and wireless (untethered) with the supporting theoretical foundation in wireless communications and related design elements and circuitry. Its modular construct overcomes the EEG scaling problem and makes it easier for reconfiguring the hardware design in terms of the number and placement of electrodes and type of standard EEG system contemplated for use. In this development, portability, lightweight, and applicability to other clinical applications that rely on EEG data are sought. Due to printer tolerance, the 3D printed cap consists of 61 electrode placements. This recording capacity can however extend from 21 (as in the international 10-20 systems) up to 61 EEG channels at sample rates ranging from 250 to 1000 Hz and the transfer of the raw EEG signal using a standard allocated frequency as a data carrier. The main objectives of this dissertation are to (1) eliminate the need for heavy mounted batteries, (2) overcome the requirement for bulky power systems, and (3) avoid the use of data cables to untether the EEG system from the subject for a more practical and less restrictive setting. Unpredictability and temporal variations of the EEG input make developing a battery-free and cable-free EEG reading device challenging. Professional high-quality and high-resolution analog front ends are required to capture non-stationary EEG signals at microvolt levels. The primary components of the proposed setup are the wireless power transmission unit, which consists of a power amplifier, highly efficient resonant-inductive link, rectification, regulation, and power management units, as well as the analog front end, which consists of an analog to digital converter, pre-amplification unit, filtering unit, host microprocessor, and the wireless communication unit. These must all be compatible with the rest of the system and must use the least amount of power possible while minimizing the presence of noise and the attenuation of the recorded signal A highly efficient resonant-inductive coupling link is developed to decrease power transmission dissipation. Magnetized materials were utilized to steer electromagnetic flux and decrease route and medium loss while transmitting the required energy with low dissipation. Signal pre-amplification is handled by the front-end active electrodes. Standard bio-amplifier design approaches are combined to accomplish this purpose, and a thorough investigation of the optimum ADC, microcontroller, and transceiver units has been carried out. We can minimize overall system weight and power consumption by employing battery-less and cable-free EEG readout system designs, consequently giving patients more comfort and freedom of movement. Similarly, the solutions are designed to match the performance of medical-grade equipment. The captured electrical impulses using the proposed setup can be stored for various uses, including classification, prediction, 3D source localization, and for monitoring and diagnosing different brain disorders. All the proposed designs and supporting mathematical derivations were validated through empirical and software-simulated experiments. Many of the proposed designs, including the 3D head cap, the wireless power transmission unit, and the pre-amplification unit, are already fabricated, and the schematic circuits and simulation results were based on Spice, Altium, and high-frequency structure simulator (HFSS) software. The fully integrated head cap to be fabricated would require embedding the active electrodes into the 3D headset and applying current technological advances to miniaturize some of the design elements developed in this dissertation

The Effect of Winding Curvature and Core Permeability on the Power Losses and Leakage Inductance of High-Frequency Transformers

At the frequencies used in switching dc-dc converters, the skin and proximity effects have a significant effect on both the losses and leakage inductance of the transformers used in these circuits. Analytical expressions that have been derived to calculate ac resistance and leakage inductance have primarily used a 1-D approximation. They also have used Cartesian coordinates or approximations that are equivalent to Cartesian coordinates, as well as usually assuming an ideal core of infinite permeability. The classical result in the case of the resistance/losses is Dowell’s equation, and there are analogous results for leakage inductance. This dissertation derives new equations that take the effect of winding curvature into account by using cylindrical coordinates. These equations are also more general in that they permit any interleaving pattern as well as variable layer thicknesses and gaps between layers. Additionally, new equations for the magnetic field coefficients are derived that take the core permeability into account, which requires a full 2-D model and the method of images applied in two dimensions. These coefficients then allow calculations of resistance/losses and leakage inductance that also take the core permeability and winding width into account. The accuracy of all of these equations is assessed by comparing their results with those of finite-element analysis (FEA) simulations. Due to the large number of parameters involved with the fully general equations, a statistical approach is used in which a large number of randomly generated devices are simulated. Finally, for a special class of more specific transformers, the effects of a reduced number of independent parameters on the resistance/losses and leakage inductance is determined empirically. The relative sensitivity of these quantities on these parameters is also determined