Rozprawy doktorskie: „High frequency transformers”

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Shen, Wei. "Design of High-density Transformers for High-frequency High-power Converters". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/28280.

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Moore's Law has been used to describe and predict the blossom of IC industries, so increasing the data density is clearly the ultimate goal of all technological development. If the power density of power electronics converters can be analogized to the data density of IC's, then power density is a critical indicator and inherent driving force to the development of power electronics. Increasing the power density while reducing or keeping the cost would allow power electronics to be used in more applications. One of the design challenges of the high-density power converter design is to have high-density magnetic components which are usually the most bulky parts in a converter. Increasing the switching frequency to shrink the passive component size is the biggest contribution towards increasing power density. However, two factors, losses and parasitics, loom and compromise the effect. Losses of high-frequency magnetic components are complicated due to the eddy current effect in magnetic cores and copper windings. Parasitics of magnetic components, including leakage inductances and winding capacitances, can significantly change converter behavior. Therefore, modeling loss and parasitic mechanism and control them for certain design are major challenges and need to be explored extensively. In this dissertation, the abovementioned issues of high-frequency transformers are explored, particularly in regards to high-power converter applications. Loss calculations accommodating resonant operating waveform and Litz wire windings are explored. Leakage inductance modeling for large-number-of-stand Litz wire windings is proposed. The optimal design procedure based on the models is developed.
Ph. D.

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Imdad, Kashif. "High frequency modeling of power transformers under transients". Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/457774.

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This thesis presents the results related to high frequency modeling of power transformers. First, a 25kVA distribution transformer under lightning surges is tested in the laboratory and its high frequency model is proposed. The transfer function method is used to estimate its parameters. In the second part, an advanced high frequency model of a distribution transformer is introduced. In this research, the dual resonant frequency distribution transformer model introduced by Sabiha and the single resonant frequency distribution transformer model under lightning proposed by Piantini at unloaded conditions are investigated and a modified model is proposed that is capable to work on both single and dual resonant frequencies. The simulated results of the model are validated with the results of Sabiha and Piantini that have been taken as reference. Simulations have shown that the results of the modified model such as, secondary effective transfer voltages, transferred impedances and transformer loading agree well with the previous models in both time and frequency domains. The obtained objectives of this research are: * Methodology for determining the parameters of a power transformer. * High frequency modeling of a transformer in order to simulate its transient behavior under surges. * Modification of high frequency model for single and dual resonance frequency. The originality and methodology of this research are: * High frequency transformer model is derived by means of the transfer function method. In the literature, the transfer function method has been used in many applications such as the determination of the mechanical deformations or insulation failure of interturn windings of transformers. In this thesis, the parameters of the proposed model are estimated using the transfer function method. * Modification of high frequency model for single/dual resonance frequency using the transfer function method. The transfer function can also be used to determine the state of the transformer. The modification in the developed model using the proposed technique has been validated. The high frequency transformer model was presented by Sabiha at two resonance frequency under both condition loading and unloading was used as reference model for modification and further enhancement. A transformer with 25kVA capacity was tested in UPC Terrassa Spain in High voltage lab under the effect of impulse voltage and the digital data was stored via oscilloscope in computer. An algorithm was developed to estimate the transformer parameters by transfer function method using fast Fourier transform analysis. In this scheme the two port network theory concept was taken for black box analysis of transformer. The series of transient¿s frequencies of experimental digital data was noted. The transformer parameters such as Z11, Z12, Z21, and Z22 calculated on all these frequencies in order to generate a narrow band of correct frequency at which the transients was developed experimentally and therefore it has to be developed on that specific frequencies. Earlier the transfer function method was used for the mechanical deformation analysis in the transformer, now similar method of modeling used to estimate the parameters of transformer and propose accurate transformer model for two resonance frequencies only and the parameters estimation was based simply placing RLC elements. The proposed model also tested and validated for accuracy and reliability. In the second phase of research high frequency models of transformer for protection from the transients based on experimental data are presented. Which were tested and validated for unloading and loading for Single and Two resonant frequencies, and modeled using transfer function method. The proposed single model leads to others two models which are verified by two port network theory, unloaded transfer under time domain and frequency domain analysis, transformer loading under different loads and transfer function
Esta tesis presenta los resultados relacionados con el modelado en alta frecuencia de transformadores de potencia. Primero, un transformador de distribución de 25 kVA es ensayado a perturbaciones tipo rayo y se propone un modelo de alta frecuencia. El método de la función de transferencia es utilizado para estimar sus parámetros. En segundo lugar, se introduce un modelo avanzado de alta frecuencia. El modelo resulta de la investigación y modificación de los modelos de resonancia dual introducido por Sabiha y el de resonancia única introducido por Piantini con condiciones sin carga. El modelo propuesto es capaz de representar tanto la resonancia única como dual. El modelo es validado a partir de los resultados de referencia de Sabiha y Piantini. Los resultados de simulación indican que el modelo representa las sobretensiones transferidas al secundario, las impedancias de transferencia y el trabajo en carga del transformados coinciden con los modelos anteriores tanto en el dominio temporal y de la frecuencia. Los objetivos obtenidos en esta tesis son: * Metodología para determinar los parámetros de un transformador de potencia. * Modelo de alta frecuencia para simular el comportamiento transitorio frente a perturbaciones. * Modificación del modelo de alta frecuencia para representar una y dos resonancias. La originalidad y metodología de la tesis son: * El modelo de alta frecuencia del transformador ha sido obtenido a partir de la metodología de la función de transferencia. En la literatura, esta metodología ha sido usada en muchas aplicaciones como en la determinación de deformaciones mecánicas o fallo de aislamiento en espiras de transformadores. En esta tesis, los parámetros del modelo propuesto son obtenidos mediante esta metodología. * Modificación del modelo de alta frecuencia con resonancia única o dual utilizando el método de la función de transferencia. La metodología propuesta puede ser utilizada para determinar el estado del transformador. Sabiha propuso un modelo de alta frecuencia representado dos resonancias en condiciones de carga y de vacío. Este modelo ha sido utilizado como referencia para la modificación y mejora. En la tesis, el transformador de distribución 25 kVA disponible en el Departamento de Ingeniería Eléctrica de la UPC en la ESEIAAT ha sido ensayado a impulsos tipo rayo. Un algoritmo ha sido desarrollado para estimar los parámetros del transformador mediante el método de la función de transferencia utilizando la transformada de Fourier. En este esquema, una red de dos puertos ha sido adoptada para el análisis del transformador. Los parámetros del transformador como la Z11, Z12., Z21 y Z22 son calculadas para representar las frecuencias consideradas. Mediante el método de la función de transferencia los parámetros del transformador son determinados. El modelo propuesto se basa en elementos simples RLC capaces de representar con precisión dos frecuencias de resonancia. En la segunda parte de la tesis, un nuevo modelo es introducido capaz de representar ambos modelos de resonancia única y dual en uno solo. Se analiza el caso de carga y vacío.

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Augla, Kader Hmood. "Losses in high frequency power inductors and transformers". Thesis, University of Bath, 1985. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354726.

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This thesis is concerned with some aspects of losses produced in the inductors and transformers of switched-mode power supplies (SMPS). The main subject of study is the eddy-current losses due to non-uniform current distribution across foil windings. These are calculated and measured for the cases when the foil constitutes an air-cored inductor, and when it is used as the secondary of a ferrite cored transformer. A coupled circuit model is used in which the foil inductor is subdivided into sets of mutually coupled filament coils. A formal method of solution of the resulting sets of equations is presented, and alternative mathematical methods of calculating self and mutual inductances are also compared. In addition to this work two other topics are addressed briefly. First, the magnetic fields in and around magnetic cores are measured, and compared with computed results using a 3D magnetostatic package, TOSCA. Secondly, core losses in ferrite cores due to sinusoidal and non-sinusoidal excitation are measured and calculated.

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Water, Wayne. "Modelling and Design of Advanced High Frequency Transformers". Thesis, Griffith University, 2014. http://hdl.handle.net/10072/367584.

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Carbon dioxide emission reduction has been a popular topic in recent years because it alleviates the current global warming crisis. Hence, there is an urgent need to adapt current technologies to help reduce carbon dioxide emissions before the global warming situation worsens. Amongst carbon dioxide reduction technologies, Electric Vehicle (EV) and renewable energy technologies are most likely to assist in improving this current status of the environmental issue in coming years. Due to increased interest in energy storage systems, such as EV and renewable energy, there is a pending need to improve the existing DC-DC converters used. The DC-DC converter systems used at present are usually bulky, costly and inefficient due to their low operating frequency. Hence, by increasing the operating frequency of the DC-DC converter, the size of the passive elements can be greatly reduced. Among these passive elements, the transformer occupies the most important role indisputably. A High Frequency Coaxial Transformer (HFCT), with a range of 1 kW to 20 kW was designed and introduced in this dissertation. The operating frequency was raised to between 100 kHz and 300 kHz in order to achieve high power densities and high performance efficiency. However, the coupling capacitance accompanied by an increased operating frequency (which couples high frequency noise between the primary and secondary windings) can cause serious common mode problems. Hence, the Faraday shield was placed between the windings of introduced transformers. This reduces the coupling capacitance and consequently the electromagnetic interference. The shielding effect analysis has been conducted to verify the HFCT performance with the insertion of the Faraday shield.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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5

Xue, Jing. "Single-phase vs. Three-phase High Power High Frequency Transformers". Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/32919.

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This thesis proposes one comparison methodology for single and three-phase high power high frequency transformers in power conversion systems. The objective is to compare the volume of the transformers. And single and three-phase Dual Active Bridge Converter (DAB1 and DAB3) topologies with single and three-phase isolating transformers are selected for the transformer comparison. Design optimization of power transformer has been studied and simplified models have been built for the single and three-phase transformer design optimization in this work, including assumptions for core shapes, materials, winding structures and thermal model. Two design methods have been proposed according to different design constraints, named T â B Method and J â B Method separately. T â B Method is based on feature of the core, which has the major limits of maximum flux density and temperature rise. The flux density should not reach the saturation value of the core, and temperature rise should meet specifications in different applications to assure the performance of the core (permeability, saturation flux density, and core loss) and the insulation of the wire. And J â B Method starts from the comparison of area product in conventional design method. The relationship between area product of transformer cores and the flux and current of the transformer in design is analyzed. There is specified relationship between area product of single and three-phase transformers if flux and current densities are specified for both. Thus J â B Method is proposed with the design constraints of specified current and flux density. Both design methods include both single and three-phase transformer design. One example case for single and three-phase transformer comparison is selected as high power high frequency DAB conversion system. Operation principles are studied for both DAB1 and DAB3 based on previous work. And transformer design based on the T â B and J â B Methods are carried out and transformer volumes are compared. And results show that three-phase transformer has little benefit in volume or thermal than single-phase transformer, when they are utilized in single-phase DAB and three-phase DAB converters separately. Scaled-down single and three-phase DAB systems have been built and volume and thermal tests have been carried out.
Master of Science

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6

Abou-Fakher, Yehia. "Implementing and simulating low frequency inverters using high frequency transformers and devices". Thesis, University of Bath, 1997. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362147.

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Bjerkan, Eilert. "High frequency modeling of power transformers : Stresses and Diagnostics". Doctoral thesis, Norwegian University of Science and Technology, Department of Electrical Power Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-622.

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In this thesis a reliable, versatile and rigorous method for high frequency power transformer modeling is searched and established. The purpose is to apply this model to sensitivity analysis of FRA (Frequency Response Analysis) which is a quite new diagnostic method for assessing the mechanical integrity of power transformer windings on-site. The method should be versatile in terms of being able to estimate internal and external overvoltages and resonances. Another important aspect is that the method chosen is suitable for real transformer geometries. In order to verify the suitability of the model for real transformers, a specific test-object is used. This is a 20MVA transformer, and details are given in chapter 1.4.

The high frequency power transformer model is established from geometrical and constructional information from the manufacturer, together with available material characteristics. All circuit parameters in the lumped circuit representation is calculated based on these data. No empirical modifications need to be performed. Comparison shows capability of reasonable accuracy in the range from 10 kHz to 1 MHz utilizing a disc-to-disc representation. A compromise between accuracy of model due to discretisation and complexity of the model in a turn-to-turn representation is inevitable.

The importance of the iron core is emphasized through a comparison of representations with/without the core included. Frequency-dependent phenomena are accurately represented using an isotropic equivalent for windings and core, even with a coarse mesh for the FEM-model. This is achieved through a frequency-dependent complex permeability representation of the materials. This permeability is deduced from an analytical solution of the frequency-dependent magnetic field inside the conductors and the core.

The importance of dielectric losses in a transformer model is also assessed. Since published data on the high frequency properties of pressboard are limited, some initial measurements are done on impregnated pressboard at different temperatures and moisture-levels. Tanδ is found to be twice the corresponding value for impregnated paper at frequencies from 50 kHz to 1MHz. Moisture has a minor effect on the losses when frequency approaches 1MHz. Service-aged paper (impregnated) is also tested in order to investigate other ageing-effects than produced water, but the test show the same decreasing influence at higher frequencies as impregnated pressboard with moisture added. The following main conclusions were drawn from this work:

• A simple, analytical approach cannot be used to build a versatile high frequency power transformer model. The reason being mainly the lack of a proper representation of the iron core, since a FEM-representation without the core did not increase coherence to measurements significantly.

• A proper representation of the iron core is very important for the calculation of inductances. Losses mainly originate from the core at intermediate frequencies (10-200 kHz), and not only from eddy currents in the windings as traditionally assumed. The permeability seem to be of less importance as long as it is well above permeability for oil, since the internal resonances mainly depends on the leakage inductances. The core leg equivalent is important for the leakage field and determines the leakage inductances and winding losses.

• Using a frequency-dependent complex permeability in a FEM-simulation makes possible an accurate representation of core and windings using a coarse mesh. If coating resistivity is sufficiently low to create interlaminar currents/ losses, the iron laminates should be represented by a 2-dimensional complex permeability. Coating parameters are seldom available.

• Dielectric properties of power transformer insulating materials depend on frequency, temperature, moisture, ageing and pressure. Temperature has minor influence on FRA-signatures, other parameters have practically no influence.

• Impulse- and resonant overvoltages both internally and on terminals can be analysed using this method with sufficient accuracy, provided the discretisation of the winding is sufficiently refined regarding the frequencies involved. Since terminal behaviour is given by the internal geometry and material parameters, it is assumed that internal behaviour is related to the accuracy of the terminal behaviour.

• FRA sensitivity to axial displacement is 1.2% of total axial height. The sensitivity to radial deformation (forced buckling) is found to be a buckling depth of 9% of the radius of the winding. Turn-to-turn short-circuits could not be modeled correctly since the lumped elements includes several turns. Disc-todisc short circuits are easily detected. Axial bending is not detectable. Detection of loose windings and aged insulation is improbable and will be dependent on the available sensitivity (mainly related to the repeatability of the measurements and the reference utilized for comparison).

The contributions in this work relates to different topics such as; Frequency-dependent iron core representation in FEM, study of interlaminar currents and its effect on the internal magnetic field, characterization of high frequency dielectric properties of impregnated pressboard and service-aged impregnated paper, procedure for evaluation of internal/external overvoltages, and finally sensitivity guidelines for the application of FRA to mechanical deformations.

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Bolborici, Valentin. "Design of low-profile transformers for high-frequency operation". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/MQ45982.pdf.

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9

Jessee, J. Patrick. "A coupled thermal-magnetic finite element model for high frequency transformers". Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-12172008-063409/.

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10

Williams, Richard. "High frequency multi-element transformers for switched-mode power supplies". Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283625.

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Wong, Fu Keung, i n/a. "High Frequency Transformer for Switching Mode Power Supplies". Griffith University. School of Microelectronic Engineering, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20050211.110915.

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A power supply is an essential part of all electronic devices. A switching mode power supply is a light weight power solution for most modern electronic equipment. The high frequency transformer is the backbone of modern switched mode power supplies. The skin effect and proximity effects are major problems in high frequency transformer design, because of induced eddy currents. These effects can result in transformers being destroyed and losing their power transferring function at high frequencies. Therefore, eddy currents are unwanted currents in high frequency transformers. Leakage inductance and the unbalanced magnetic flux distribution are two further obstacles for the development of high frequency transformers. Winding structures of power transformers are also a critical part of transformer design and manufacture, especially for high frequency applications. A new planar transformer with a helical winding structure has been designed and can maintain the advantages of existing planar transformers and significantly reduce the eddy currents in the windings. The maximum eddy current density can be reduced to 27% of the density of the planar transformer with meander type winding structure and 33% of the density of the transformer with circular spiral winding structure at an operating frequency of 1MHz. The voltage ratio of the transformer with helical winding structure is effectively improved to 150% of the voltage ratio of the planar transformer with circular spiral coils. With the evenly distributed magnetic flux around the winding, the planar transformer with helical winding structure is excellent for high frequency switching mode power supplies in the 21st Century.

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Wong, Fu Keung. "High Frequency Transformer for Switching Mode Power Supplies". Thesis, Griffith University, 2004. http://hdl.handle.net/10072/367650.

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A power supply is an essential part of all electronic devices. A switching mode power supply is a light weight power solution for most modern electronic equipment. The high frequency transformer is the backbone of modern switched mode power supplies. The skin effect and proximity effects are major problems in high frequency transformer design, because of induced eddy currents. These effects can result in transformers being destroyed and losing their power transferring function at high frequencies. Therefore, eddy currents are unwanted currents in high frequency transformers. Leakage inductance and the unbalanced magnetic flux distribution are two further obstacles for the development of high frequency transformers. Winding structures of power transformers are also a critical part of transformer design and manufacture, especially for high frequency applications. A new planar transformer with a helical winding structure has been designed and can maintain the advantages of existing planar transformers and significantly reduce the eddy currents in the windings. The maximum eddy current density can be reduced to 27% of the density of the planar transformer with meander type winding structure and 33% of the density of the transformer with circular spiral winding structure at an operating frequency of 1MHz. The voltage ratio of the transformer with helical winding structure is effectively improved to 150% of the voltage ratio of the planar transformer with circular spiral coils. With the evenly distributed magnetic flux around the winding, the planar transformer with helical winding structure is excellent for high frequency switching mode power supplies in the 21st Century.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Microelectronic Engineering
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13

Dai, Ning. "Modeling, analysis, and design of high-frequency high-density low-profile power transformers". Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-151512/.

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14

Zhang, Ziwei. "High frequency finite element modeling and condition assessment of power transformers". Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2052862/.

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Due to the reforming and deregulation of electric power industry, investments in transmission equipment have drastically decreased to meet the economic needs of the competitive market. The electrical utility sector was forced to cut the costs in maintenance and operation without endangering steady supply of electrical power. With this trend, the maintenance strategy desires advanced methods for condition monitoring and assessment of in-service power transformers. Among the common condition assessment techniques, Frequency Response Analysis (FRA) is considered as an efficient off-line diagnostic technique for fault detection in transformer windings. Precise interpretation of the FRA output has proven a great challenge and attracted much effort in recent years. There is also a strong need in this research field to develop an intelligent interpretation procedure for automatic assessment of power transformer conditions. This thesis focuses on two main aspects of power transformer condition assessment: developing an accurate transformer model for the interpretation of transformer FRA responses, and establishing FRA-based novel algorithms to automatically identify transformer failure modes. Reviewing existing transformer modeling methods, this thesis explicitly introduces a simplified distributed parameter model (hybrid winding model) for FRA. The hybrid winding model has the advantage of less computational complexity and high accuracy in simulation results, even in the frequency range above 1 MHz. Analytical expressions for calculating key electrical parameters of winding models are presented. The electrical parameters of transformer windings with a complex or deformed structure are difficult to calculate using analytical formulations. Therefore, computational models based on Finite Element Method (FEM) are developed in this thesis to calculate the frequency-dependent parameters of transformer windings especially with deformed structures. These parameters are then applied to the transformer winding model for frequency response analysis. By applying the electrical parameters obtained from the FEM models, the accuracy of the hybrid winding model has been improved for cases with incipient winding faults. This methodology is implemented in simulation studies of radial winding deformation and minor axial winding movement to reveal the characteristic features of these two types of winding fault. Results show that: (1) frequency-dependent inductances and structure-dependent shunt capacitance derived from FEM models can be used in FRA analysis, (2) by using the proposed methodology, characteristics of frequency response above 1 MHz can be analyzed, (3) regarding radial winding deformation and minor axial winding movement, the changes in the electrical parameters also affect the frequency response in the high frequency range ( > 1 MHz). A Hierarchical Dimension Reduction (HDR) classifier built on FRA results is proposed in this thesis for condition assessment of power transformers. The algorithms of this classifier make advantageous use of advanced image processing technologies including image binalization and binary erosion in the first step of the procedure. This preprocessing procedure optimizes the measured FRA data by filtering the frequency sections with minor deviations which can effect the calculating results of the indices. Also in this step, FRA diagrams are re-scaled in a linear coordinate system for the convenience of calculating the indices in later step. Subsequently, based on the correlation between electrical properties and features of FRA responses, a division approach is proposed to dynamically divide the frequency range into 5 sub-bands. This division method of frequency range is more reasonable than the conventional methods of fixed frequency sub-bands and more applicable than other existing methods. Then the proposed algorithms of hybrid quantitative indices which include four indices are employed. The dimension reduction for the FRA data is processed by these algorithms in the 5 dynamic frequency sub-bands. It is the first time to establish the algorithms of the hybrid quantitative indices, which include two classical indices and two novel indices, for reducing the dimensions of the FRA data. Two new algorithms of indices, Area Ratio Index (ARI) and Angle Difference (AD), are proposed based on knowledge of FRA interpretation with respect to typical transformer failure modes. They are able to improve the classification performance in terms of the ability to identify electrical failures and the condition of residual magnetization. Based on these advantageous processes, the HDR classifier can aggregate related expertise and approved statistical indices in furtherance of automatic decision analysis on identifying transformer failure modes or conditions. The performance of this classifier has been verified by 32 sets of experimental FRA data, in which 20 sets are primarily used for determination of threshold values of the related algorithms and the rest 12 are purely used for the verification. Results of this implementation of the HDR classifier are 100% accuracy with using the 20 sets of training data and 95.83% accuracy with using the rest 12 sets.

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Skutt, Glenn R. "High-Frequency Dimensional Effects in Ferrite-Core Magnetic Devices". Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30596.

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MnZn ferrites are widely used in power electronics applications where the switching frequency is in the range of several tens of kilohertz to a megahertz. In this range of frequencies the combination of relatively high permeability and relatively low conductivity found in MnZn ferrite helps to minimize the size of magnetic devices while maintaining high efficiency. The continuing improvement in semiconductor switches and circuit topologies has led to use of high-frequency switching circuits at ever increasing power levels. The magnetic devices for these high-power, high-frequency circuits require magnetic CORES that are significantly larger than standard ferrite-core devices used at lower power levels. Often such large ferrite cores must be custom designed, and at present this custom design is based on available material information without regard for the physical size of the structure. This thesis examines the issues encountered in the use of larger MnZn ferrite cores for high-frequency, high-power applications. The two main issues of concern are the increased power dissipation due to induced currents in the structure and the change in inductance that results as the flux within the core is redistributed at higher frequencies. In order to model these problems using either numerical or analytical methods requires a reliable and complete set of material information. A significant portion of this work is devoted to methods for acquiring such material information since such information is not generally available from the manufacturers. Once the material constants required for the analysis are determined, they are used in both closed-form and numerical model to illustrate that large ferrite cores suffer significant increases in loss and significant decreases in inductance for frequencies as low as several hundred kilohertz. The separate impacts of the electrical and magnetic losses in the core are illustrated through the use of linear finite element analyses of several example core structures. The device impedances calculated using the FEA tools show fair agreement with measurement. An analysis of gapped structures and segmented cross-sections shows that these design options can reduce the severity of the dimensional problems for some designs.
Ph. D.

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16

Ambatipudi, Radhika. "High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies". Doctoral thesis, Mittuniversitetet, Avdelningen för elektronikkonstruktion, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-20270.

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Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend inrelation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the convertercircuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses whichare functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequencyband width with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8,15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is lessthan that of the two layered transformer because of the decreased radius for thesame amount of inductance.The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50Wand possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer fordriving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuitvitogether with the designed signal transformer is 0.37W. Both these signal andpower transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significanceof the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformerfor the given power transfer application have been proposed. The designed corebased planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency ofthe converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in thefrequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.In conclusion, the research in this dissertation proposed a solution for obtaining high power density converters by designing the highly integrated, high frequency(1 - 10MHz) coreless and core based planar magnetics with energy efficiencies inthe range of 92 - 97%. This solution together with the latest semiconductor GaN/SiC switching devices provides an excellent choice to meet the requirements of the next generation ultra flat low profile switch mode power supplies (SMPS).

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Lesser, Beverly Brown. "Thermal-magnetic finite element model of a high frequency transformer". Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/44121.

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In high-frequency power transformers, magnetic material properties cannot be assumed to be constant. These properties vary with frequency, temperature, and magnetic flux density. Heat generation is, in turn, a function of the magnetic permeability, magnetic flux density, and frequency. Current design methods are either empirical or based on linear, uncoupled models. To better understand the relationship between heat transfer, magnetic flux density, material properties, and core geometry in a miniature, high-frequency transformer, a finite-element program has been developed to solve the coupled thermal-magnetic equations for an axisymmetric transformer. The program accounts for nonlinear temperature and magnetic field dependent material properties, geometry, and driving frequency.

The program, HT-MAG, is based on a series of derived magnetic field equations. The Ritz method is applied to the magnetic and thermal equations in the development of the program. The program alternately solves the finite element approximations to the thermal and magnetic governing equations until the magnetic properties match within a specified fraction or a maximum number of iterations are performed. In addition, the program can be linked with existing pre- and post-processors or can accept manual pre- and post-processing.

Six test cases were run to test the validity of the program. The first two cases tested the uncoupled heat transfer calculations. One of these tested the thermal conduction calculations while the other tested the heat generation calculations. The next two cases tested the uncoupled magnetic equations. The first was a direct current (DC) case, while the second was an alternating current (AC) case. The final two cases tested the thermal magnetic coupling. Solutions to these cases are presented and discussed.

Master of Science

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Murthy, Bellur Dakshina S. "Hard-Switching and Soft-Switching Two-Switch Flyback PWM DC-DC Converters and Winding Loss due to Harmonics in High-Frequency Transformers". Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1278704361.

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Ambatipudi, Radhika. "Multilayered Coreless Printed Circuit Board (PCB) Step-down Transformers for High Frequency Switch Mode Power Supplies (SMPS)". Licentiate thesis, Mittuniversitetet, Institutionen för informationsteknologi och medier, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-13967.

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The Power Supply Unit (PSU) plays a vital role in almost all electronic equipment. The continuous efforts applied to the improvement of semiconductor devices such as MOSFETS, diodes, controllers and MOSFET drivers have led to the increased switching speeds of power supplies. By increasing the switching frequency of the converter, the size of passive elements such as inductors, transformers and capacitors can be reduced. Hence, the high frequency transformer has become the backbone in isolated AC/DC and DC/DC converters. The main features of transformers are to provide isolation for safety purpose, multiple outputs such as in telecom applications, to build step down/step up converters and so on. The core based transformers, when operated at higher frequencies, do have limitations such as core losses which are proportional to the operating frequency. Even though the core materials are available in a few MHz frequency regions, because of the copper losses in the windings of the transformers those which are commercially available were limited from a few hundred kHz to 1MHz. The skin and proximity effects because of induced eddy currents act as major drawbacks while operating these transformers at higher frequencies. Therefore, it is necessary to mitigate these core losses, skin and proximity effects while operating the transformers at very high frequencies. This can be achieved by eliminating the magnetic cores of transformers and by introducing a proper winding structure. A new multi-layered coreless printed circuit board (PCB) step down transformer for power transfer applications has been designed and this maintains the advantages offered by existing core based transformers such as, high voltage gain, high coupling coefficient, sufficient input impedance and high energy efficiency with the assistance of a resonant technique. In addition, different winding structures have been studied and analysed for higher step down ratios in order to reduce copper losses in the windings and to achieve a higher coupling coefficient. The advantage of increasing the layer for the given power transfer application in terms of the coupling coefficient, resistance and energy efficiency has been reported. The maximum energy efficiency of the designed three layered transformers was found to be within the range of 90%-97% for power transfer applications operated in a few MHz frequency regions. The designed multi-layered coreless PCB transformers for given power applications of 8, 15 and 30W show that the volume reduction of approximately 40-90% is possible when compared to its existing core based counterparts. The estimation of EMI emissions from the designed transformers proves that the amount of radiated EMI from a three layered transformer is less than that of the two layered transformer because of the decreased radius for the same amount of inductance. Multi-layered coreless PCB gate drive transformers were designed for signal transfer applications and have successfully driven the double ended topologies such as the half bridge, the two switch flyback converter and resonant converters with low gate drive power consumption of about half a watt. The performance characteristics of these transformers have also been evaluated using the high frequency magnetic material made up of NiZn and operated in the 2-4MHz frequency region. These multi-layered coreless PCB power and signal transformers together with the latest semiconductor switching devices such as SiC and GaN MOSFETs and the SiC schottky diode are an excellent choice for the next generation compact SMPS.

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Whitman, Daniel J. "The Effect of Winding Curvature and Core Permeability on the Power Losses and Leakage Inductance of High-Frequency Transformers". Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1624286375555269.

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Gradzki, Pawel Miroslaw. "Core loss characterization and design optimization of high-frequency power ferrite devices in power electronics applications". Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-165934/.

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Kotte, Hari Babu. "High Speed (MHz) Switch Mode Power Supplies (SMPS) using Coreless PCB Transformer Technology". Licentiate thesis, Mittuniversitetet, Institutionen för informationsteknologi och medier, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-13964.

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The most essential unit required for all the electronic devices is the Power Supply Unit (PSU). The main objective of power supply designers is to reduce the size, cost and weight, and to increase the power density of the converter. There is also a requirement to have a lower loss in the circuit and hence in the improvement of energy efficiency of the converter circuit. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. At present the switching frequency of the converter circuit is limited due to the increased switching losses in the existing semiconductor devices and in the magnetic area, because of increased hysteresis and eddy current loss in the core based transformer. Based on continuous efforts to improve the new semi conductor materials such as GaN/SiC and with recently developed high frequency multi-layered coreless PCB step down power transformers, it is now feasible to design ultra-low profile, high power density isolated DC/DC and AC/DC power converters. This thesis is focussed on the design, analysis and evaluation of the converters operating in the MHz frequency region with the latest semi conductor devices and multi-layered coreless PCB step-down power and signal transformers. An isolated flyback DC-DC converter operated in the MHz frequency with multi-layered coreless PCB step down 2:1 power transformer has been designed and evaluated. Soft switching techniques have been incorporated in order to reduce the switching loss of the circuit. The flyback converter has been successfully tested up to a power level of 10W, in the switching frequency range of 2.7-4 MHz. The energy efficiency of the quasi resonant flyback converter was found to be in the range of 72-84% under zero voltage switching conditions (ZVS). The output voltage of the converter was regulated by implementing the constant off-time frequency modulation technique. Because of the theoretical limitations of the Si material MOSFETs, new materials such as GaN and SiC are being introduced into the market and these are showing promising results in the converter circuits as described in this thesis. Comparative parameters of the semi conductor materials such as the vi energy band gap, field strengths and figure of merit have been discussed. In this case, the comparison of an existing Si MOSFET with that of a GaN MOSFET has been evaluated using a multi-layered coreless PCB step-down power transformer for the given input/output specifications of the flyback converter circuit. It has been determined that the energy efficiency of the 45 to 15V regulated converter using GaN was improved by 8-10% compared to the converter using the Si MOSFET due to the gate drive power consumption, lower conduction losses and improved rise/fall times of the switch. For some of the AC/DC and DC/DC applications such as laptop adapters, set-top-box, and telecom applications, high voltage power MOSFETs used in converter circuits possess higher gate charges as compared to that of the low voltage rating MOSFETs. In addition, by operating them at higher switching frequencies, the gate drive power consumption, which is a function of frequency, increases. The switching speeds are also reduced due to the increased capacitance. In order to minimize this gate drive power consumption and to increase the frequency of the converter, a cascode flyback converter was built up using a multi-layered coreless PCB transformer and this was then evaluated. Both simulation and experimental results have shown that with the assistance of the cascode flyback converter the switching speeds of the converter were increased including the significant improvement in the energy efficiency compared to that of the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the power converter, double ended topologies were chosen. For this purpose, a gate drive circuitry utilising the multi-layered coreless PCB gate drive transformer was designed and evaluated in both a Half-bridge and a Series resonant converter. It was found that the gate drive power consumption using this transformer was less than 0.8W for the frequency range of 1.5-3.5MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the series resonant converter was found to be 86.5% with an output power of 36.5W.

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Goksu, Omer. "Shaft Transducerless Vector Control Of The Interior Permanent Magnet Motor With Speed And Position Estimation Using High Frequency Signal Injection And Flux Observer Methods". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609617/index.pdf.

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In this thesis, shaft transducerless vector control of Interior Permanent Magnet (IPM) motor with speed and position estimation using saliency based high frequency signal injection and fundamental model based flux observer methods will be investigated. The magnetic saliency characteristic of a 2.2-kW IPM motor will be experimentally extracted by means of high frequency signal injection. High frequency signal injection method will be used to estimate the speed and position at zero and low speed based on the magnetic saliency of the IPM motor. At high speed, fundamental model based flux observer method will be utilized for speed and position estimation. Seamless transition between the two estimation methods will be provided. Using the estimated speed and position information, the motor will be closed loop vector controlled and the drive motion performance over wide speed and load range will be investigated. The IPM motor drive and the estimation/control algorithms will be modeled and their performance will be demonstrated by detailed computer simulations. A three-phase voltage source inverter and a motor test bench will be built, and the estimation/control algorithms will be implemented on a DSP based motor control platform. The IPM motor drive system will be tested in the laboratory and the theory and simulation results will be verified by the experiments.

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Jansson, Vincent, David Bergman i Niklas Hermansson. "High Frequency Transformer : Implementation of prototype". Thesis, Uppsala universitet, Elektricitetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-387307.

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Since its invention in 1885 by Otto Bláthy, Miksa Déri and KárolyZipernowsky, transformers have become an important cornerstone of theelectrical infrastructure we have today. They are found mostprominently in any machinery or device that requires a differentlevel of voltage or current than a general grid can supply, such ascomputers, motors or even cars. In the case of this project, thetransformer was originally intended to be connected to a resonatingH-bridge which supplies the primary coil with high frequency voltagepulses to be converted into a higher voltage transferred to arectifier unit. Because of the level of frequency supplied, thetransformer was required to be constructed with a different type ofcore and cable for the winding. When it became clear that the cablecouldn't be supplied in time, the focus shifted towards constructinga prototype instead. The prototype was designed to generate a certainamount of leakage inductance while subjected to a short circuit test.After a couple of attempts, the group managed to construct atransformer whose leakage inductance was well within range of thespecifications. The finished transformer prototype was delivered andthe group had thus successfully constructed what is to be used as atemplate for further transformers of the same type.A special thanks to ScandiNova Systems AB for initiating this projectand giving us the opportunity to participate, and to Per Nilsson, PerBenkowski and Klas Elmqvist for mentoring us along the way.

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Al-Alawi, Hamed. "High frequency modeling of a transformer winding". Thesis, Al-Alawi, Hamed (2012) High frequency modeling of a transformer winding. Other thesis, Murdoch University, 2012. https://researchrepository.murdoch.edu.au/id/eprint/13092/.

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Major faults in power transformer windings usually originate from small charges called partial discharges (PD). These discharges could lead to a breakdown in insulation and ultimate failure in the power transformers if they are allowed to develop. Therefore, this thesis will present and develop a high-frequency model of power transformer winding, which can detect the propagation of high-frequency partial discharges in a continuous disc type of high-voltage transformer winding. The lumped parameter model will be used to simulate the windings of the power transformer. This model represents the transformer winding with two discs of the winding represented by a single circuit. PD will be injected at different locations along the model. Using the knowledge of the frequency response of the winding within the faulty transformer, will help locating the partial discharges on the windings. Locating PDs in high-voltage power transformers, is useful for those who maintain the equipment.

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Li, Jeffrey. "Integrated High Frequency Transformer Design Virtual Laboratory". Thesis, Griffith University, 2015. http://hdl.handle.net/10072/380060.

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The High Frequency Coaxial Transformer (HFCT) has been successfully used in many areas. It has many benefits and advantages compared with other transformer products. Thus, demand for HFCT design and device development is increasing. Conventionally, all the related design procedures for the HFCT rely on the implementation of electromagnetic equations on paper. The device model needs to be manually drawn by an engineer and simulated with software. There is no existing software that can help the engineer to design the device and automatically build the model. On the other hand, the simulation and optimization for the device requires hardware resources, and a personal computer is limited in this regard. Even if the device is developed and the prototype is made, the device still needs to pass EMC testing in order to be labelled. However, many research groups and companies cannot afford to build an EMC lab. A solution is proposed to solve the above issues. The HF transformer design virtual laboratory is developed and tested. It is a computer-based system, which provides the following: 1. Computer software, which can be used to design, model, simulate and optimize a HF transformer device. It is based on computational electromagnetics and numerical geometric techniques. The engineer can use the software to adjust the device structure and obtain a FEM simulation result. 2. A cluster system, which can provide a high performance and high availability computing environment to support the transformer design software. It provides convenient services to the end-user, such as remote access, shared resources, collaborative work and parallel computing. 3. A 3D scanning system, which can pre-test the device before sending it to the EMC lab. It is a much cheaper system compared to building an EMC testing lab. Many case studies have been used to test the design virtual laboratory. The system successfully proves its capability in device design, simulation and testing. By using the system, the engineer can develop a reliable HF transformer device in a short development time period, compared with the conventional HF transformer device design method. Although, an experienced engineer can deliver a well-designed HF transformer as well. The advantage of the integrated HF transformer design laboratory is that, the system is not only provide design function, but also the modelling, simulation, optimization and measurement functions as well. It provides a convenient method to design a HF device from the sketch to the prototype.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text

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Li, Jie. "High frequency power transformer modelling for frequency response analysis (FRA) diagnosis". Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538489.

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Transformer fault diagnosis through Frequency Response Analysis (FRA) has been receiving a great deal of attention in recent years. As a comparative technique, FRA has good capability and sensitivity in detecting mechanical faults that are difficult to identify by conventional condition assessment techniques. Power transformers are among the most expensive equipment owned by electric utilities, and it is not reasonable to produce deformation on actual transformers and carry out measurement sensitivity studies. On the other hand, simulation models, which can accurately reproduce transformer high frequency behaviours, are flexible tools for performing FRA deformation type sensitivity studies for deriving FRA interpretation rules. The main objective of this thesis is to develop appropriate simulation models for use in FRA diagnosis and to improve the interpretation of FRA responses through simulation studies. The transformer models developed at the University of Manchester (then UMIST) were by far the best representation of state-of-art modelling techniques; the inductance and the capacitance of the basic model unit were calculated using winding geometry and material properties, the frequency dependent conductive and dielectric losses were also included. In addition, mutual capacitive and inductive couplings between units were carefully considered to ensure the accuracy of the model. However, there is still some room for improvement on these models and during this PhD research, major contributions are made on as. follows: firstly take core effect into consideration to reproduce valid FRA characteristic representation in the low frequencies, secondly status of network terminal nodes are uniformed represented by externally connecting an impedance so that during FRA deformation sensitivity study, it is flexible to change the terminal condition, thirdly reconfigure the network node and unit relationship so that tap winding connection are precisely represented as the design, finally convert the single-phase model to a three-phase model and by developing a reduced matrix model, keep the simulation accuracy intact for a three-phase transformer up to 2 MHz, at the same time reduce computational time significantly. In detail, this PhD thesis describes the following three parts of my research: Firstly a transformer model incorporating a magnetic core based on the Principle of Duality is established to interpret low frequency characteristics of FRA responses (from 10Hz to up to 1 kHz). This model includes leakage inductances and capacitances of windings and can explain FRA low frequency differences caused by asymmetry of magnetic paths in three-limb and five-limb core transformers. Secondly, FRA characteristics were studied systematically using a component-system approach through building models for single windings, a one-phase winding set and finally the three-phase transformer. In this way the effects of winding structure, inductive and capacitive coupling among windings, among phases and terminal connection effect on FRA characteristics were studied. FinaUya complete three-phase transformer reduced matrix model is built, that can flexibly represent winding terminal connection and precisely describe tap positions. Using this modelling strategy, transmission power transformers at 2751132 kVand 275/33 kV voltage levels are simulated and numerous deformation sensitivity studies are performed, in order to gain better understanding on their FRA characteristics and to identify FRA features of different winding deformation types on these transformers. The research indicates that the overall approach used to develop these simulation models has helped in improving interpretation of FRA responses. The transformer modelling techniques being developed, with further refinement, can be a useful tool for FRA diagnosis and benefit the test engineers from the industry.

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LI, QUAN, i q. li@cqu edu au. "HIGH FREQUENCY TRANSFORMER LINKED CONVERTERS FOR PHOTOVOLTAIC APPLICATIONS". Central Queensland University. N/A, 2006. http://library-resources.cqu.edu.au./thesis/adt-QCQU/public/adt-QCQU20060830.110106.

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This thesis examines converter topologies suitable for Module Integrated Converters (MICs) in grid interactive photovoltaic (PV) systems, and makes a contribution to the development of the MIC topologies based on the two-inductor boost converter, which has received less research interest than other well known converters. The thesis provides a detailed analysis of the resonant two-inductor boost converter in the MIC implementations with intermediate constant DC links. Under variable frequency control, this converter is able to operate with a variable DC gain while maintaining the resonant condition. A similar study is also provided for the resonant two-inductor boost converter with the voltage clamp, which aims to increase the output voltage range while reducing the switch voltage stress. An operating point with minimized power loss can be also established under the fixed load condition. Both the hard-switched and the soft-switched current fed two-inductor boost converters are developed for the MIC implementations with unfolding stages. Nondissipative snubbers and a resonant transition gate drive circuit are respectively employed in the two converters to minimize the power loss. The simulation study of a frequency-changer-based two-inductor boost converter is also provided. This converter features a small non-polarised capacitor in a second phase output to provide the power balance in single phase inverter applications. Four magnetic integration solutions for the two-inductor boost converter have also been presented and they are promising in reducing the converter size and power loss.

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Tavakoli, Hanif. "A High Frequency Transformer Winding Model for FRA Applications". Licentiate thesis, Stockholm : Skolan för elektro- och systemteknik, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11178.

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Ng, Wing Lun. "Low-voltage high-frequency CMOS transformer-feedback voltage-controlled oscillators /". View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ECED%202006%20NG.

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Muhammed, Adil Hussein. "High frequency transformer design and modelling using finite element technique". Thesis, University of Newcastle Upon Tyne, 2000. http://hdl.handle.net/10443/747.

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The field of high power density power supplies has received much attention in recent years. The area of the most concern is to increase the switching frequency so as to achieve a reduction in the power supply size. Such concern in high frequency power conversion units has led to many resonant structures (quasi, multi, and pseudo). In all resonant types, the power transfer from the source to the load is controlled by varying the ratio of operating to resonant frequencies. Every effort has been made to reduce the switching losses using zero voltage and/or zero current techniques. In contrast, little attention has been given to the area of the design of the magnetic components at high frequency operation. It is usually accepted that the weak point in further high frequency power supply design is in the magnetic devices ( transformer and inductor ). No accurate model of the transformer taking into account the high frequency range has been performed yet. It is well known that as the frequency increasess o the transformerm odel becomesm ore complicated,d ue to the complexity of the transformer element distribution, and the nature of frequency dependence of some of these elements. Indeed, work of this kind can take many directions, and the attempt here is to introduce a number of mathematics, analytical, numerical, and practical directions to model the transformer. The main factors affecting the high frequency performance are the eddy current losses, leakage flux and the effects due to the transformer elements, where the transformer is part of the resonant converter. Two dimensional transformer finite element modelling is used to examine different cases, including open and short circuit conditions. The frequency dependency of the winding resistance and leakage inductance is fully explained. The practical design of the transformer and testing is used to valididate the simulation results. These results are supported by the results obtained from the mathematical formulation. Special attention is given to reducing both copper losses and leakage in the windings. Three dimensional modelling of the high frequency transformer and the solution using a program solving the full set of Maxwell's equations is the original part of the present work. Frequency response characteristics are found and compared to that obtained from the test. Curves of these characteristics are used to predict a simplified transformer equivalent circuit. This circuit is used with the simulation of a full bridge series resonant converter, where all units ( switches, control, isolation, feedback, and transformer ) are represented by an equivalent circuit. The power supply operation and its behaviour in respect to the change with frequency of each of the transformer elements are examined. Two cases are considered through the simulation, when the operating frequency is above and when it is below the resonant tank frequency. The simulated results are validated by building a practical power supply. In addition, the numerical solution of modelling the transformer by an equivalent network is also introduced. The highest possible number of elements (R, L, and Q) are used, where all the elements are found using 2D FEM solution of both magnetostatic and electrostatic fields. This network is solved using the trapezoidal rule of integration and electric network theory. The examination of the influences of the distribution capacitances on the internal winding frequency response characteristic is carefully examined. The last work in the present research is focussed on finding a general model of an exact transformer equivalent circuit to cover the wide frequency range. The thesis is completed with a conclusion.

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Sagaale, Mohamoud. "High frequency modelling of a transformer winding for partial discharge localization". Thesis, Sagaale, Mohamoud (2013) High frequency modelling of a transformer winding for partial discharge localization. Other thesis, Murdoch University, 2013. https://researchrepository.murdoch.edu.au/id/eprint/22265/.

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The IEEE defines Partial Discharge (PD) as an electric discharge that only partially bridges the insulation between two conductors. In high voltage equipment such as transformers, floating components or defects in transformers can be the cause of partial discharge. Over periods of time the transformer ages and will result in faults. The materials in the transformer such as the windings can be damaged due to mechanical and electrical stresses. For this reason study of PDs is important for the prevention of faults and in maintenance of transformers. In this thesis a 3-phase 6.6kV, 1MVA high voltage transformer winding is modelled using the lumped parameter model. The transformer winding is then simulated using MATLAB/ SIMULINK along with SimPowerSystems toolbox. A simulated current pulse is injected at different positions along the winding, to simulate PDs in the winding. The responses due to the PD injection at various positions are measured from the line-end and analysed. The voltage response results indicated that PD’s along the winding have more oscillations moving away from the line-end, hence PD at disc pair 10 is the most oscillatory. It was also evident that as the PD moves away from the line-end the waveforms have a greater distortion. The frequency spectra results showed that the poles (crests) always occurred at fixed frequencies no matter the location of the PD, thus the frequency of the poles are independent of the PD location. However the zeros (troughs) altered in frequency depending on the PD location, and as the PD source moved away from the line-end, the zeros increased in frequencies.

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Tavakoli, Hanif. "An FRA Transformer Model with Application on Time Domain Reflectometry". Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48568.

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Frequency response analysis (FRA) is a frequency-domain method which is used to detect mechanical faults in transformers. The frequency response of a transformer is determined by its geometry and material properties, and it can be considered as the transformer’s fingerprint. If there are any mechanical changes in the transformer, for example if the windings are moved or distorted, its fingerprint will also be changed so, theoretically, mechanical changes in the transformer can be detected with FRA. A problem with FRA is the fact that there is no general agreement about how to interpret the measurement results for detection of winding damages. For instance, the interpretation of measurement results has still not been standardized.The overall goal of this thesis is to try to enhance the understanding of the information contained in FRA measurements. This has been done in two ways: (1) by examining the FRA method for (much) higher frequencies than what is usual, and (2) by developing a new method in which FRA is combined with the ideas of Time Domain Reflectometry (TDR). As tools for carrying out the above mentioned steps, models for the magnetic core and the winding have been developed and verified by comparison to measurements.The usual upper frequency limit for FRA is around 2 MHz, which in this thesis has been extended by an order of magnitude in order to detect and interpret new phenomena that emerge at high frequencies and to investigate the potential of this high-frequency region for detection of winding deteriorations.Further, in the above-mentioned new method developed in this thesis, FRA and TDR are combined as a step towards an easier and more intuitive detection and localization of faults in transformer windings, where frequency response measurements are visualized in the time domain in order to facilitate their interpretation.
QC 20111122

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Kotte, Hari Babu. "High Frequency (MHz) Resonant Converters using GaN HEMTs and Novel Planar Transformer Technology". Doctoral thesis, Mittuniversitetet, Avdelningen för elektronikkonstruktion, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-20894.

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The increased power consumption and power density demands of modern technologies have increased the technical requirements of DC/DC and AC/DC power supplies. In this regard, the primary objective of the power supply researcher/engineer is to build energy efficient, high power density converters by reducing the losses and increasing the switching frequency of converters respectively. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. Therefore, the thesis work is focussed on the design, analysis and evaluation of isolated converters operating in the 1 - 5MHz frequency region with the assistance of the latest semi conductor devices, both coreless and core based planar power transformers designed in Mid Sweden University and which are suitable for consumer applications of varying power levels ranging from 1 – 60W. In high frequency converter circuits, since the MOSFET gate driver plays a prominent role, different commercially available MOSFET gate drivers were evaluated in the frequency range of 1 - 5MHz in terms of gate drive power consumption, rise/fall times and electromagnetic interference (EMI) and a suitable driver was proposed. Initially, the research was focused on the design and evaluation of a quasi resonant flyback converter using a multilayered coreless PCB step down transformer in the frequency range of 2.7 – 4MHz up to the power level of 10W. The energy efficiency of this converter is found to be 72 - 84% under zero voltage switching conditions (ZVS). In order to further improve the energy efficiency of the converter in the MHz frequency region, the new material device GaN HEMT was considered. The comparisons were made on a quasi resonant flyback DC-DC converter using both the Si and GaN technology and it was found that an energy efficiency improvement of 8 – 10% was obtained with the GaN device in the frequency range of 3.2 – 5MHz. In order to minimize the gate drive power consumption, switching losses and to increase the frequency of the converter in some applications such as laptop adapters, set top box (STB) etc., a cascode flyback converter using a low voltage GaN HEMT and a high voltage Si MOSFET was designed and evaluated using a multi-layered coreless PCB transformer in the MHz frequency region. Both the simulation and experimental results have shown that, with the assistance of the cascode flyback converter, the switching speeds of the converter can be increased with the benefit of obtaining a significant improvement in the energy efficiency as compared to that for the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the converter circuit, double ended topologies were considered. Due to the lack of high voltage high side gate drivers in the MHz frequency region, a gate drive circuitry utilizing the multi-layered coreless PCB signal transformer was designed and evaluated in both a half-bridge and series resonant converter (SRC). It was found that the gate drive power consumption using this transformer was around 0.66W for the frequency range of 1.5 - v 3.75 MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the SRC using multilayered coreless PCB power transformer was found to be 86.5% with an output power of 36.5W in the switching frequency range of 2 – 3MHz. In order to further enhance the energy efficiency of the converter to more than 90%, investigations were carried out by using the multiresonant converter topology (LCC and LLC), novel hybrid core high frequency planar power transformer and the GaN HEMTs. The simulated and experimental results of the designed LCC resonant converter show that it is feasible to obtain higher energy efficiency isolated DC/DC converters in the MHz frequency region. The peak energy efficiency of the LCC converter at 3.5MHz is reported to be 92% using synchronous rectification. Different modulation techniques were implemented to regulate the converter for both line and load variations using a digital controller. In order to realize an AC/DC converter suitable for a laptop adapter application, consideration was given to the low line of the universal input voltage range due to the GaN switch limitation. The energy efficiency of the regulated converter operating in the frequency range of 2.8 – 3.5MHz is reported to be more than 90% with a load power of 45W and an output voltage of 22V dc. In order to determine an efficient power processing method on the secondary side of the converter, a comparison was made between diode rectification and synchronous rectification and optimal rectification was proposed for the converters operating in the MHz frequency range for a given power transfer application. In order to maintain high energy efficiency for a wide load range and to maintain the narrow switching frequency range for the given input voltage specifications, the LLC resonant converter has been designed and evaluated for the adapter application. From the observed results, the energy efficiency of the LLC resonant converter is maintained at a high level for a wide load range as compared to that for the LCC resonant converter. Investigations were also carried out on isolated class E resonant DC-DC converter with the assistance of GaN HEMT and a high performance planar power transformer at the switching frequency of 5MHz. The simulated energy efficiency of the converter for the output power level of 16W is obtained as 88.5% which makes it feasible to utilize the designed isolated converter for various applications that require light weight and low profile converters. In conclusion, the research in this dissertation has addressed various issues related to high frequency isolated converters and has proposed solution by designing highly energy efficient converters to meet the current industrial trends by using coreless and core based planar transformer technologies along with the assistance of GaN HEMTs. With the provided solution, in the near future, it is feasible to realize low profile, high power density DC/DC and AC/DC converters operating in MHz frequency region suitable for various applications.
High Frequency Switch Mode Power Supplies

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Zhao, Sen Peng. "Design and implementation of a frequency response test system for instrument voltage transformer performance studies". Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/design-and-implementation-of-a-frequency-response-test-system-for-instrument-voltage-transformer-performance-studies(3e65a4d8-937e-4a3d-8308-734e03f29255).html.

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Power system harmonics are always an important issue in power networks as they can cause many negative impacts, such as equipment thermal stress, on installations within power networks. Recently, with the increasing connections of power electronic devices based Renewable Energy Source (RES) and High Voltage Direct Current (HVDC) transmission applications, harmonics in power networks, especially high frequency harmonics (>50th order or 2.5 kHz) are on the rise. Currently, the majority of conventional VTs, such as Wound-type Voltage Transformers (WVT) and Capacitor Voltage Transformers (CVT), are widely installed and used in High Voltage (HV) and Extra High Voltage (EHV) power networks for voltage measurement. Since most of them were mainly designed to measure voltage with the required accuracy at the fundamental frequency (i.e. 50Hz in the UK), they are limited to measuring high frequency harmonics due to the coupling of their internal inductive and capacitive elements. To achieve high frequency harmonic measurements, voltage measurement devices with wide frequency bandwidths are required. Recently, non-conventional VTs, such as optical voltage transducers, are commercially available, which could provide accurate voltage measurements over a wide range of frequency. However, before they can be considered by any power utilities, their frequency response performances must be tested at a rated fundamental voltage with required minimum harmonic injections from 100Hz to 5 kHz. This must require a test system which should be capable of providing a rated fundamental voltage up to 400kV with controllable harmonic injections at required levels from 100Hz to 5 kHz. Therefore, the objective of this project is to design and implement such a test system in the National Grid (NG) HV laboratory at the University of Manchester. However, the design and the implementation of such a test system bring many challenges; for instance, a lack of adequate equipment and considerable power to provide the required harmonic injections above 0.5% to the test object.In this thesis, an Instrument Voltage Transformer Frequency Response (VTFR) test system with three different voltage power source designs is presented; The voltage power source designs are: (i) Design 1 is based on a single power source inductive coupling method to provide both a rated fundamental voltage and controllable harmonics; (ii) Design 2 is based on two separate voltage power sources inductive coupling method to provide both a rated fundamental voltage and controllable harmonics; and (iii) Design 3 is based on two separate voltage power sources capacitive coupling method to provide both the rated fundamental voltage and controllable harmonics. A hybrid approach, which combines the VTFR test system with both the voltage power sources Design 2 and 3, is proposed for testing the frequency response of any type of VTs at their rated fundamental voltages with 1% harmonic injections from 100Hz to 5 kHz. The proposed VTFR test system with voltage power source designs were firstly validated at a relatively low voltage of 33kV in the HV laboratory. Then three different VTFR test systems were constructed based on available equipment for testing VTs from 11kV to 400kV. An 11kV, a 33kV WVT and a 400kV WVT and a 275kV CVT were tested. The test results were analyzed, compared and discussed. The models of the test systems were also established and simulated. Simulation results were analysed, compared and discussed.

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Iuravin, Egor. "Transformer Design For Dual Active Bridge Converter". Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami1532601248778308.

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Karamat, Asghar. "High frequency inverter-transformer-cycloconverter system for DC to AC (3-phase) power conversion". Thesis, Brunel University, 1991. http://bura.brunel.ac.uk/handle/2438/5195.

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This thesis is concerned with a 3-phase multistage high frequency link DC to AC power conversion with a novel inverter-cycloconverter circuitry. The conversion system is composed of a high frequency PWM inverter, step-up high frequency transformer and cycloconverter with bidirectional switching devices. In first stage the DC voltage of the power source , say a submarine battery, is inverted to a system of 3-phase sinusoidally modulated I kHz alternative wave forms. For this purpose a suggested optimized PWM technique for 3-phase inverter operation is adopted, in which harmonic components up to 17 th ( 17 kHz) are eliminated from the inverter output voltages. In the second stage, for DC input isolation from AC output and also for a voltage transformation ( here stepping-up )a high frequency ( size reduced ) transformer is employed. Generalized high frequency operation, influence and side effects of the transformer on overall system design & performance is investigated. In the final stage the 1 kHz -to- 50 Hz conversion process is accomplished by a 3-phase cycloconverter. The proposed "nonlinear modulation strategy" for cycloconverter output voltage and associated harmonic analysis is demonstrated, in which the harmonic components up to 38th (1.9 kHz ) are eliminated from the conversion system output voltage. To assess the suggested functioning principles for the inverter & cycloconverter , the prototype conversion system was developed. Some design criteria and switching device selection are presented, together with different voltage & current wave forms of the prototype system under resistive & inductive load (induction motor) and their respective spectra.

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Sterk, Douglas Richard. "Compact Isolated High Frequency DC/DC Converters Using Self-Driven Synchronous Rectification". Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/9648.

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In the early 1990's, with the boom of the Internet and the advancements in telecommunications, the demand for high-speed communications systems has reached every corner of the world in forms such as, phone exchanges, the internet servers, routers, and all other types of telecommunication systems. These communication systems demand more data computing, storage, and retrieval capabilities at higher speeds, these demands place a great strain on the power system. To lessen this strain, the existing power architecture must be optimized. With the arrival of the age of high speed and power hungry microprocessors, the point of load converter has become a necessity. The power delivery architecture has changed from a centralized distribution box delivering an entire system's power to a distributed architecture, in which a common DC bus voltage is distributed and further converted down at the point of load. Two common distributed bus voltages are 12 V for desktop computers and 48 V for telecommunications server applications. As industry strives to design more functionality into each circuit or motherboard, the area available for the point of load converter is continually decreasing. To meet industries demands of more power in smaller sizes power supply designers must increase the converter's switching frequencies. Unfortunately, as the converter switching frequency increases the efficiency is compromised. In particular, the switching, gate drive and body diode related losses proportionally increase with the switching frequency. This thesis introduces a loss saving self-driven method to drive the secondary side synchronous rectifiers. The loss saving self-driven method introduces two additional transformers that increase the overall footprint of the converter. Also, this thesis proposes a new magnetic integration method to eliminate the need for the two additional gate driver magnetic cores by allowing three discrete power signals to pass through one single magnetic structure. The magnetic integration reduces the overall converter footprint.
Master of Science

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Yan, Ning. "High-frequency Current-transformer Based Auxiliary Power Supply for SiC-based Medium Voltage Converter Systems". Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/101507.

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Auxiliary power supply (APS) plays a key role in ensuring the safe operation of the main circuit elements including gate drivers, sensors, controllers, etc. in medium voltage (MV) silicon carbide (SiC)-based converter systems. Such a converter requires APS to have high insulation capability, low common-mode coupling capacitance (Ccm ), and high-power density. Furthermore, considering the lifetime and simplicity of the auxiliary power supply system design in the MV converter, partial discharge (PD) free and multi-load driving ability are the additional two factors that need to be addressed in the design. However, today’s state-of-the-art products have either low power rating or bulky designs, which does not satisfy the demands. To improve the current designs, this thesis presents a 1 MHz isolated APS design using gallium nitride (GaN) devices with MV insulation reinforcement. By adopting LCCL-LC resonant topology, the proposed APS is able to supply multiple loads simultaneously and realize zero voltage switching (ZVS) at any load conditions. Since high reliability under faulty load conditions is also an important feature for APS in MV converter, the secondary side circuit of APS is designed as a regulated stage. To achieve MV insulation (> 20 kV) as well as low Ccm value (< 5 pF), a current-based transformer with a single turn structure using MV insulation wire is designed. Furthermore, by introducing different insulated materials and shielding structures, the APS is capable to achieve different partial discharge inception voltages (PDIV). In this thesis, the transformer design, resonant converter design, and insulation strategies will be detailly explained and verified by experiment results. Overall, this proposed APS is capable to supply multiple loads simultaneously with a maximum power of 120 W for the sending side and 20 W for each receiving side in a compact form factor. ZVS can be realized regardless of load conditions. Based on different insulation materials, two different receiving sides were built. Both of them can achieve a breakdown voltage of over 20 kV. The air-insulated solution can achieve a PDIV of 6 kV with Ccm of 1.2 pF. The silicone-insulated solution can achieve a PDIV of 17 kV with Ccm of 3.9 pF.
M.S.
Recently, 10 kV silicon carbide (SiC) MOSFET receives strong attention for medium voltage applications. Asit can switch at very high speed, e.g. > 50 V/ns, the converter system can operate at higher switching frequency condition with very small switching losses compared to silicon (Si) IGBT [8]. However, the fast dv/dt noise also creates the common mode current via coupling capacitors distributed inside the converter system, thereby introducing lots of electromagnetic interference (EMI) issues. Such issues typically occur within the gate driver power supplies due to the high dv/dt noises across the input and output of the supply. Therefore, the ultra-small coupling capacitor (<5 pF) of a gate driver power supply is strongly desired.[37] To satisfy the APS demands for high power modular converter system, a solution is proposed in this thesis. This work investigates the design of 1 MHz isolated APS using gallium nitride (GaN) devices with medium voltage insulation reinforcement. By increasing switching frequency, the overall converter size could be reduced dramatically. To achieve a low Ccm value and medium voltage insulation of the system, a current-based transformer with a single turn on the sending side is designed. By adopting LCCL-LC resonant topology, a current source is formed as the output of sending side circuity, so it can drive multiple loads importantly with a maximum of 120 W. At the same time, ZVS can use realized with different load conditions. The receiving side is a regulated stage, so the output voltage can be easily adjusted and it can operate in a load fault condition. Different insulation solutions will be introduced and their effect on Ccm will be discussed. To further reduce Ccm, shielding will be introduced. Overall, this proposed APS can achieve a breakdown voltage of over 20 kV and PDIV up to 16.6 kV with Ccm<5 pF. Besides, multi-load driving ability is able to achieve with a maximum of 120 W. ZVS can be realized. In the end, the experiment results will be provided.

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Ammanambakkam, Nagarajan Dhivya. "Design of HF Forward Transformer Including Harmonic Eddy Current Losses". Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1292874300.

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Zhao, Shishuo. "High Frequency Isolated Power Conversion from Medium Voltage AC to Low Voltage DC". Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/74969.

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Modern data center power architecture developing trend is analyzed, efficiency improvement method is also discussed. Literature survey of high frequency isolated power conversion system which is also called solid state transformer is given including application, topology, device and magnetic transformer. Then developing trend of this research area is clearly shown following by research target. State of art wide band gap device including silicon carbide (SiC) and gallium nitride (GaN) devices are characterized and compared, final selection is made based on comparison result. Mostly used high frequency high power DC/DC converter topology dual active bridge (DAB) is introduced and compared with novel CLLC resonant converter in terms of switching loss and conduction loss point of view. CLLC holds ZVS capability over all load range and smaller turn off current value. This is beneficial for high frequency operation and taken as our candidate. Device loss breakdown of CLLC converter is also given in the end. Medium voltage high frequency transformer is the key element in terms of insulation safety, power density and efficiency. Firstly, two mostly used transformer structures are compared. Then transformer insulation requirement is referred for 4160 V application according to IEEE standard. Solid insulation material are also compared and selected. Material thickness and insulation distance are also determined. Insulation capability is preliminary verified in FEA electric field simulation. Thirdly two transformer magnetic loss model are introduced including core loss model and litz wire winding loss model. Transformer turn number is determined based on core loss and winding loss trade-off. Different core loss density and working frequency impact is carefully analyzed. Different materials show their best performance among different frequency range. Transformer prototype is developed following designed parameter. We test the developed 15 kW 500 kHz transformer under 4160 V dry type transformer IEEE Std. C57.12.01 standard, including basic lightning test, applied voltage test, partial discharge test. 500 kHz 15 kW CLLC converter gate drive is our design challenge in terms of symmetry propagation delay, cross talk phenomenon elimination and shoot through protection. Gate drive IC is carefully selected to achieve symmetrical propagation delay and high common mode dv/dt immunity. Zero turn off resistor is achieved with minimized gate loop inductance to prevent cross talk phenomenon. Desaturation protection is also employed to provide shoot through protection. Finally 15 kW 500 kHz CLLC resonant converter is developed based on 4160V 500 kHz transformer and tested up to full power level with 98% peak efficiency.
Master of Science

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Li, Quan, i q. li@cqu edu au. "DEVELOPMENT OF HIGH FREQUENCY POWER CONVERSION TECHNOLOGIES FOR GRID INTERACTIVE PV SYSTEMS". Central Queensland University. School of Advanced Technologies & Processes, 2002. http://library-resources.cqu.edu.au./thesis/adt-QCQU/public/adt-QCQU20020807.152750.

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This thesis examines the development of DC-DC converters that are suitable for Module Integrated Converters, (MICs), in grid interactive photovoltaic (PV) systems, and especially concentrates on the study of the half bridge dual converter, which was previously developed from the conventional half bridge converter. Both hard-switched and soft-switched half bridge dual converters are constructed, which are rated at 88W each and transform a nominal 17.6Vdc input to an output in the range from 340V to 360Vdc. An initial prototype converter operated at 100kHz and is used as a base line device to establish the operational behaviours of the converter. The second hard-switched converter operated at 250kHz and included a coaxial matrix transformer that significantly reduced the power losses related to the transformer leakage inductance. The soft-switched converter operated at 1MHz and is capable of absorbing the parasitic elements into the resonant tank. Extensive theoretical analysis, simulation and experimental results are provided for each converter. All three converters achieved conversion efficiencies around 90%. The progressive increases in the operation frequency, while maintaining the conversion efficiency, will translate into the reduced converter size and weight. Finally different operation modes for the soft-switched converter are established and the techniques for predicting the occurrence of those modes are developed. The analysis of the effects of the transformer winding capacitance also shows that soft switching condition applies for both the primary side mosfets and the output rectifier diodes.

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Hashimoto, Kazuki. "Analysis and Design of Air-Core Transformer Based on Internal Magnetic Flux Density Distribution for High-Frequency Power Converter". Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263662.

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Ahmed, Mohamed Hassan Abouelella. "Power Architectures and Design for Next Generation Microprocessors". Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/103175.

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With the rapid increase of cloud computing and the high demand for digital content, it is estimated that the power consumption of the IT industry will reach 10 % of the total electric power in the USA by 2020. Multi-core processors (CPUs) and graphics processing units (GPUs) are the key elements in fulfilling all of the digital content requirements, but come with a price of more power-hungry processors, driving the power per server rack to 20 KW levels. The need for more efficient power management solutions on the architecture level, down to the converter level, is inevitable. Recently, data centers have replaced the 12V DC server rack distribution with a 48V DC distribution, producing a significant overall system efficiency improvement. However, 48V rack architecture raises significant challenges for the voltage regulator modules (VRMs) required for powering the processor. The 48V VRM in the vicinity of the CPU needs to be designed with very high efficiency, high power density, high light-load efficiency, as well as meet all transient requirements by the CPU and GPU. Transferring the well-developed multi-phase buck converter used in the 12V VRM to the 48V distribution platform is not that simple. The buck converter operating with 48V, stepping down to sub 2V, will be subjected to significant switching related loss, resulting in lower overall system efficiency. These challenges drive the need to look for more efficient architectures for 48V VRM solutions. Two-stage conversions can help solve the design challenges for 48V VRMs. A first-stage unregulated converter is used to step-down the 48V to a specific intermediate bus voltage. This voltage will feed a multi-phase buck converter that powers the CPU. An unregulated LLC converter is used for the first-stage converter, with zero voltage switching (ZVS) operation for the primary side switches, and zero current switching (ZCS) along with ZVS operation, for the secondary side synchronous rectifiers (SRs). The LLC converter can operate at high frequency, in order to reduce the magnetic components size, while achieving high-efficiency. The high-efficiency first-stage, along with the scalability and high bandwidth control of the second-stage, allows this architecture to achieve high-efficiency and power density. This architecture is simpler to adopt by industry, by plugging the unregulated converter before the existing multi-phase buck converters on today's platforms. The first challenge for this architecture is the transformer design of the first-stage LLC converter. It must avoid all of the loss associated with high frequency operations, and still achieve high power density without scarifying efficiency. In this thesis, the integrated matrix transformer structure is optimized by SR integration with windings, interleaved primary side termination, and a better PCB winding arrangement to achieve high-efficiency and power density, and minimize the losses associated with high-frequency operations. The second challenge is the light load efficiency improvement. In this thesis a light load efficiency improvement is proposed by a dynamic change of the intermediate bus voltage, resulting in more than 8 % light load efficiency improvements. The third challenge is the selection of the optimal bus voltage for the two-stage architecture. The impact of different bus voltages was analyzed in order to maximize the overall conversion efficiency. Multiple 48V unregulated converters were designed with maximum efficiency >98 %, and power densities >1000 W/in3, with different output voltages, to select the optimal bus voltage for the two-stage VRM. Although the two-stage VRM is more scalable and simpler to design and adopt by current industry, the efficiency will reduce as full power flows in two cascaded DC/DC converters. Single-stage conversion can achieve higher-efficiency and power-density. In this thesis, a quasi-parallel Sigma converter is proposed for the 48V VRM application. In this structure, the power is shared between two converters, resulting in higher conversion efficiency. With the aid of an optimized integrated magnetic design, a Sigma converter suitable for narrow voltage range applications was designed with 420 W/in3 and a maximum efficiency of 94 %. Later, another Sigma converter suitable for wide voltage range applications was designed with 700W/in3 and a maximum efficiency of 95 %. Both designs can achieve higher efficiency than the two-stage VRM and all other state-of-art solutions. The challenges associated with the Sigma converter, such as startup and closed loop control were addressed, in order to make it a viable solution for the VRM application. The 48V rack architecture requires regulated 12V output converters for various loads. In this thesis, a regulated LLC is used to design a high-efficiency and power-density 48V bus converter. A novel integration method of the inductor and transformer helps the LLC achieve the required regulation capability with minimum losses, resulting in a converter that can provide 1KW of continuous power with efficiency of 97.8 % and 700 W/in3 power density. This dissertation discusses new power architectures with an optimized design for the 48V rack architectures. With the academic contributions in this dissertation, different conversion architectures can be utilized for 48V VRM solutions that solve all of the challenges associated with it, such as scalability, high-efficiency, high density, and high BW control.
Doctor of Philosophy
With the rapid increase of cloud computing and the high demand for digital content, it is estimated that the power consumption of the IT industry will reach 10 % of the total electric power in the USA by 2020. Multi-core processors (CPUs) and graphics processing units (GPUs) are the key elements in fulfilling all of the digital content requirements but come with a price of more power-hungry processors, driving the power per server rack to 20 KW levels. The need for more efficient power management solutions on the architecture level, down to the converter level, is inevitable. The data center manufacturers have recently adopted a more efficient architecture that supplies a 48V DC server rack distribution instead of a 12V DC distribution to the server motherboard. This helped reduce costs and losses, but as a consequence, raised a challenge in the design of the DC/DC voltage regulator modules (VRM) supplied by the 48V, in order to power the CPU and GPU. In this work, different architectures will be explored for the 48V VRM, and the trade-off between them will be evaluated. The main target is to design the VRM with very high-efficiency and high-power density to reduce the cost and size of the CPU/GPU motherboards. First, a two-stage power conversion structure will be used. The benefit of this structure is that it relies on existing technology using the 12V VRM for powering the CPU. The only modification required is the addition of another converter to step the 48V to the 12V level. This architecture can be easily adopted by industry, with only small modifications required on the system design level. Secondly, a single-stage power conversion structure is proposed that achieves higher efficiency and power density compared to the two-stage approach; however, the structure is very challenging to design and to meet all requirements by the CPU/GPU applications. All of these challenges will be addressed and solved in this work. The proposed architectures will be designed using an optimized magnetic structure. These structures achieve very high efficiency and power density in their designed architectures, compared to state-of-art solutions. In addition, they can be easily manufactured using automated manufacturing processes.

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Capellán, Villacián Cándido. "Aportaciones al modelado del transformador en AF". Doctoral thesis, Universidad de Cantabria, 2012. http://hdl.handle.net/10803/81555.

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El diseño de modelos equivalentes es una técnica utilizada para llegar a entender el comportamiento de dispositivos trabajando a AAFF. La presente tesis aborda este tema aplicado al transformador. Se han recopilado y analizado los trabajos más relevantes referidos al modelado del transformador en alta frecuencia. Tomando como base experimental un transformador trifásico de 4 kVA, se han planteado los montajes y metodologías asociadas para conseguir los modelos de baja y alta frecuencia. Los modelos obtenidos pueden ser sintetizados a circuitos RLC y su precisión evaluada mediante sencillos montajes. Inicialmente, se somete a prueba al modelo clásico de BF para determinar la frecuencia máxima hasta la que puede ser utilizado. A continuación, se propone un nuevo modelo en AF y su respuesta es evaluada y validada mediante medidas.
Modelling is a useful technique able to provide a suitable knowledge about the behaviour of all the devices operated at high frequencies. This thesis approaches this topic to the case of the transformer. A state of the art about high-frequency modelling is summarized and the most relevant research works are analysed. By using a 4 kVA three-phase power transformer, a set-up facility and the associated methodology has been proposed in order to develop a method able to obtain both the low and high-frequency models. The obtained model can be synthesized using passive LCR circuits. The accuracy of the model is then evaluated using the set-up facility. In initial experiments, the classic low-frequency model is put to the test in order know the maximum frequency at which the model can be used. After that, a new high-frequency model is proposed and its response is evaluated and validated with measurements.

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Danekar, Abhishek V. "Analysis and Design of High-Frequency Soft-Switching DC-DC Converter for Wireless Power Charging Applications". Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1493990400812363.

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Fei, Chao. "Optimization of LLC Resonant Converters: State-trajectory Control and PCB based Magnetics". Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/83206.

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With the fast development of information technology (IT) industry, the demand and market volume for off-line power supplies keeps increasing, especially those for desktop, flat-panel TV, telecommunication, computer server and datacenter. An off-line power supply normally consists of electromagnetic interference (EMI) filter, power factor correction (PFC) circuit and isolated DC/DC converter. Isolated DC/DC converter occupies more than half of the volume in an off-line power supply and takes the most control responsibilities, so isolated DC/DC converter is the key aspect to improve the overall performance and reduce the total cost for off-line power supply. On the other hand, of all the power supplies for industrial applications, those for the data center servers are the most performance driven, energy and cost conscious due to the large electricity consumption. The total power consumption of today's data centers is becoming noticeable. Moreover, with the increase in cloud computing and big data, energy use of data centers is expected to continue rapidly increasing in the near future. It is very challenging to design isolated DC/DC converters for datacenters since they are required to provide low-voltage high-current output and fast transient response. The LLC resonant converters have been widely used as the DC-DC converter in off-line power supplies and datacenters due to its high efficiency and hold-up capability. Using LLC converters can minimize switching losses and reduce electromagnetic interference. Almost all the high-end offline power supplies employs LLC converters as the DC/DC converter. But there are three major challenges in LLC converters. Firstly, the control characteristics of the LLC resonant converters are very complex due to the dynamics of the resonant tank. This dissertation proposes to implement a special LLC control method, state-trajectory control, with a low-cost microcontroller (MCU). And further efforts have been made to integrate all the state-trajectory control function into one MCU for high-frequency LLC converters, including start-up and short-circuit protection, fast transient response, light load efficiency improvement and SR driving. Secondly, the transformer in power supplies for IT industry is very bulky and it is very challenging to design. By pushing switching frequency up to MHz with gallium nitride (GaN) devices, the magnetics can be integrated into printed circuit board (PCB) windings. This dissertation proposes a novel matrix transformer structure and its design methodology. On the other hand, shielding technique can be employed to suppress the CM noise for PCB winding transformer. This dissertation proposes a novel shielding technique, which not only suppresses CM noise, but also improves the efficiency. The proposed transformer design and shielding technique is applied to an 800W 400V/12V LLC converter design. Thirdly, the LLC converters have sinusoidal current shape due to the nature of resonance, which has larger root mean square (RMS) of current, as well as larger conduction loss, compared to pulse width modulation (PWM) converter. This dissertation employs three-phase interleaved LLC converters to reduce the circulating energy by inter-connecting the three phases in certain way, and proposed a novel magnetic structure to integrated three inductors and three transformers into one magnetic core. By pushing switching frequency up to 1MHz, all the magnetics can be implemented with 4-layer PCB winding. Additional 2-layer shielding can be integrated to reduce CM noise. The proposed magnetic structure is applied to a 3kW 400V/12V LLC converter. This dissertation solves the challenges in analysis, digital control, magnetic design and EMI in high-frequency DC/DC converters in off-line power supplies. With the academic contribution in this dissertation, GaN devices can be successfully applied to high-frequency DC/DC converters with MHz switching frequency to achieve high efficiency, high power density, simplified but high-performance digital control and automatic manufacturing. The cost will be reduced and the performance will be improved significantly.
Ph. D.

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48

Barbosa, Giancarlos Costa. "Projeto de um Transformador utilizado em uma Planta de Plasma". Universidade Federal do Rio Grande do Norte, 2012. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15453.

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Made available in DSpace on 2014-12-17T14:56:08Z (GMT). No. of bitstreams: 1 GiancarlosCB_DISSERT.pdf: 5458787 bytes, checksum: 8900cf5f95194fd230853ddd24b869cd (MD5) Previous issue date: 2012-08-13
Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
This work discusses the design of a transformer used in a plant plasma. This plant, which is being developed in UFRN, will be used in the treatment of waste. It consists basically of a radio frequency power supply and a inductive plasma torch. The transformer operates at the nominal frequency of 400 kHz, with 50 kW, allowing the adaptation of impedance between the power supply and torch. To develop the project, a study was done on the fabrication technologies and physical effects on the frequency of operation. This was followed by the modeling of this transformer. Finally, simulations and tests were conducted to validate the design
Este trabalho aborda o projeto de um transformador utilizado em uma planta de plasma. Esta planta, que est? sendo desenvolvida na UFRN, ser? utilizada no tratamento de res?duos. Ela ? composta, basicamente, por uma fonte de alimenta??o de radiofrequ?ncia e uma tocha indutiva de plasma. O transformador opera na frequ?ncia nominal de 400 kHz, com pot?ncia de 50 kW, permitindo a adapta??o de imped?ncias entre a fonte de alimenta??o e a tocha. Para o desenvolvimento do projeto, foi feito um estudo sobre as tecnologias de fabrica??o e efeitos f?sicos na frequ?ncia de opera??o. Posteriormente, foi realizada a modelagem deste transformador. Por fim, foram realizados simula??es e testes de forma a validar o projeto

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49

Bacega, Felippe. "Avaliação do estado dos equipamentos do sistema de transporte de energia elétrica através de técnicas de medição de descargas parciais em campo". Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/106/106131/tde-05112014-150019/.

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Neste trabalho é apresentado um novo método de medição de descargas parciais, através de transformadores de corrente de alta frequência, instalados no condutor de aterramento dos equipamentos do sistema elétrico de potência e acoplados a um osciloscópio. Esse novo método de medição tem como grande ganho o fato dos equipamentos não precisarem ser retirados de operação para realização de medição. Pelo fato das transmissoras serem remuneradas pela disponibilidade das funções transmissão, o diagnóstico dos equipamentos em serviço faz com que os custos sejam reduzidos. Foi realizado um levantamento teórico onde foi definida a curva característica esperada como resposta do transformador de corrente a um sinal impulsivo. Foram levantadas curvas características, em laboratório, através de oscilogramas no domínio do tempo, das assinaturas de descargas parciais em equipamentos com isolação a óleo e a gás SF6, de modo a validar o sinal esperado na fundamentação teórica. Essas assinaturas foram utilizadas em medições em campo, que comprovaram a viabilidade da fundamentação teórica e das assinaturas obtidas em laboratório. Adicionalmente foram levantados fatores que podem influenciar nas medições e mostrados sinais que possuam características diferentes daquelas das descargas parciais, de modo a diferencia-los.
This work presents a new method of measuring partial discharges, through high frequency current transformers, installed in the equipment grounding conductor of the electrical power system and coupled to an oscilloscope. This new measurement method has as great gain, the fact that the equipment doesnt need to be removed from service to perform measurement. Because of the transmission being remunerated by the availability of the transmission functions, diagnosis of equipment in service makes the costs been reduced. A theoretical survey where the characteristic curve expected response from the current transformer to an impulsive signal was set has been done. Characteristic curves were raised in the laboratory through oscillograms in the time domain, of signatures of partial discharges in equipment with SF6 gas and oil isolation, in order to validate expected signal discharges in the theoretical foundation. These signatures were used in field measurements, which proved the feasibility of the theoretical foundation and signatures obtained in the laboratory. Further factors were raised that may influence the measurements and shown signs that have different characteristics from those of partial discharges in order to differentiate them.

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50

Amrhein, Andrew Aloysius. "Induction Heating of Aluminum Cookware". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/77400.

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Induction heating has become a popular alternative to other heat sources for stovetop cooking applications due to performance, efficiency, control response, and safety. The main drawback is that extreme difficulty is encountered when trying to head low-resistivity, non-ferromagnetic metals such as aluminum and copper, which are commonly used for cookware in several societies. The lack of ferromagnetic properties, resulting in no hysteresis dissipation, and low resistivity of such metals results in an impractically low resistance reflected through the work coil. The resultant impedance complicates inverter design, as it is too low to be efficiently driven with conventional inverter topologies. The magnitudes of current involved in exciting this impedance also severely impact the efficiency of the coil and resonant components, requiring extreme care in coil design. This work explores various techniques that have been proposed and/or applied to efficiently heat low-resistivity cookware and the associated limitations. A transformer-coupled series-load-resonant topology driven by a full-bridge inverter is proposed as a means of efficiently heating aluminum cookware within practical design constraints. The experimental circuit is built and successfully tested at an output power of 1.66kW. The procedure of optimizing the work coil for improved efficiency is also presented along with the procedure of measuring coil efficiency. An improved circuit incorporating switch voltage detection to guarantee zero-voltage switching is then built in order to overcome limitations of this design.
Master of Science

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