Design Of Coreless Pcb Transformer For A Fullbridge Dc-Dc Converter Application

This thesis present acoreless Printed Circuit Board (PCB) transformer developed for a full-bridge direct current (DC) to DC converter application. During the last decade, the coreless PCB transformer was used in high frequency applications. It was found that these transformers have good features in high frequency range and not useful at frequencies smaller than 300-400 kHz.After one decade of utilizing coreless PCB transformers due to some problems such as low coupling factor, high leakage inductance and low voltage gain, the performance of these transformers reduced. The most important objectives of this thesis are modification of the design, improve performance and increase energy efficiency of both coreless PCB transformer and full-bridge DC-DC converter. Based on these objectives, a three layer coreless PCB transformer is chosen to be designed and simulated by using CST Studio 3D software. This transformer can be employed for both signal and power transfer at low power level. In this case, there are two primary and two secondary windings that they are connected in series. In addition, this research also improves a high frequency fullbridge DC to DC converter using high speed switching devices. The designed converter operates in MHz frequency region. By increasing the switching frequency, the size of bulky magnetic components and parts of the converter is reduced. The input voltage region of converter is varied from 10-30V DC with a nominal supply voltage of 30V. In order to improve energy efficiency and reduce losses, the zero voltage switching (ZVS) technique was used in this converter. The maximum energy efficiency of the designed converter is identified to be 82% at a frequency of 1 MHz and it is also shown that the efficiency is more than 75% in the voltage range of 10- 30V

Past, Present and Future Trends of Non-Radiative Wireless Power Transfer

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Circuits and passive components for radio-frequency power conversion

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 141-149).This thesis focuses on developing technology for high efficiency power converters operating at very high frequencies. The work in the thesis involves two aspects of such converters: rf (radio-frequency) power circuit design techniques and magnetic material characterization and application. In the aspect of circuit design techniques, the thesis investigates a new class of matching networks that overcomes a major limitation of rf converter circuits - their high sensitivity to loading condition. These networks, which are termed resistance compression networks, serve to substantially decrease the variation in effective resistance seen by a tuned rf inverter as loading conditions change. The thesis explores the operation, performance characteristics, and design of these networks, and present experimental results demonstrating their performance. The thesis also presents analysis and design considerations for lumped (inductor and capacitor) matching networks operating at high efficiency (> 95%). Formulas for calculating matching network efficiency are given and used to evaluate the optimum number of matching stages as a function of conversion ratio. Both simulation and experimental results are presented that validate the analytical formulation. In the aspect of magnetic materials and applications, the thesis investigates the loss characteristics of several commercial rf magnetic materials for power conversion applications in the 10 MHz to 100 MHz range.(cont.) A measurement method is proposed to identify loss characteristics of different commercial rf magnetic core materials. The loss characteristics of these materials, which have not previously been available, are illustrated and compared in tables and figures. Based on results in characterization of magnetic materials, the thesis describes a procedure for magnetic components design with low permeability magnetic materials that is for very high frequency power conversion applications. This procedure provides a method to compare and evaluate different magnetic materials for given specifications of a magnetic-core inductor. Some important information, e.g. quality factor and size of the inductor can be predicted before the final design. The thesis also investigates some problems such as optimization of a magnetic-core inductor.by Yehui Han.Ph.D

Modeling of Inductive Contactless Energy Transfer Systems

In the domain of electronic devices and especially desktop peripherals, there is an industrial trend which consists in removing the cables that pollute our domestic and professional environments. In this sense, wireless communication protocols are already massively widespread while the power supplies still use wires or batteries. To address this problem, alternative solutions must be investigated such as contactless energy transfer (CET). In a broad sense, CET is a process that allows to bring electrical energy from one point to another through a given medium (generally air or vacuum) and at a certain distance. Inductive CET means that the intermediate form of energy is the magnetic induction, generated from primary coils excited by high-frequency alternating currents and collected in secondary coils by induced voltages. Most of existing approaches to design CET systems are applicable to only single applications and do not include an optimization method. For this reason, the present thesis focuses on the modeling, design and optimization of inductive CET systems. Using the coreless transformer as the central part of CET systems, an equivalent electric model is derived from the theory of conventional transformers. The absence of ferrite core gives rise to a specific characteristic, which is to have large leakage inductances compared to the main one. In order to circumvent this issue, using a high frequency together with a resonant circuit allow to enhance the effect of the mutual inductance and to transfer power with an excellent efficiency. Different parts of the coreless transformer are addressed separately. First, an accurate modeling of DC resistances, self and mutual inductances is proposed. Then, the equivalent electric circuit is resolved and the different compensation topologies for the resonant circuit are discussed. Finally, the AC resistance is computed using a 2D finite element modeling that takes into account the skin and proximity effects in the conductors. So as to exploit optimally FEM simulations, a complete output mapping together with a specific interpolation strategy are implemented, giving access to the AC resistance evaluation in a very short time. As a result, all the models are implemented in a way that makes them highly adaptable and low-consuming in term of computing resources. Then a sensitivity analyzis is performed in order to restrict the variation range of different parameters and to provide a general and intuitive understanding of inductive CET. After that, an optimization method using genetic algorithms (GAs) is presented. The main advantage of GAs is that the number of free parameters does not change the complexity of the algorithm. They are very efficient when a lot of free parameters are involved and for optimizations where the computing time is a key factor. As existing GAs failed to converge properly for different tested CET problems, a new one is developed, that allows to optimize two objective functions in the same time. It is thus a multiobjective genetic algorithm (MOGA) and has been successfully applied to the design of different CET systems. Finally, in order to validate the models and optimization methods proposed along the thesis, several prototypes are built, measured and tested. Notably, a CET table that allows to supply simultaneously different peripherals is fabricated. By analyzing in real time the current amplitude in the primary coils, an efficient sensorless detection of the peripherals is implemented. Digital control techniques have enabled the autonomous management of the detection and the local activation of the table. These results contribute to the future development of robust and efficient CET tables

Electric Power Systems and Components for Electric Aircraft

Electric aircraft have gained increasing attention in recent years due to their potential for environmental and economic benefits over conventional airplanes. In order to offer competitive flight times and payload capabilities, electric aircraft power systems (EAPS) must exhibit extremely high efficiencies and power densities. While advancements in enabling technologies have progressed the development of high performance EAPS, further research is required. One challenge in the design of EAPS is determining the best topology to be employed. This work proposes a new graph theory based method for the optimal design of EAPS. This method takes into account data surveyed from a large set of references on commonly seen components including electric machines, power electronics and jet engines. Thousands of design candidates are analyzed based on performance metrics such as end-to-end system efficiency, overall mass, and survivability. It is also shown that sensitivity analysis may be used to systematically evaluate the impact of components and their parameters on various aspects of the architecture design. Once an EAPS architecture has been selected, further, detailed, validation of the power system is required. In these EAPS, many subsystems exist with timescales varying from minutes to hours when considering the aerodynamics, to nanosecond dynamics in the power electronics. This dissertation presents a multiphysics co-simulation framework for the evaluation of EAPS with a unique decoupling method to reduce simulation time without sacrificing detail. The framework has been exemplified on a case study of a 500kW all-electric aircraft, including models for aerodynamics, energy storage, electric motors and power electronics. Electric machines for aviation propulsion must meet several performance requirements, including a constant power speed range (CPSR) of approximately thirty percent above rated speed. This operation is traditionally achieved through the flux weakening technique with an injection of negative d-axis current. However, the degree of CPSR achievable through flux weakening is a strong function of the back emf and d-axis inductance. This dissertation reviews alternative methods for CPSR operation in machines with low inductance. A new method of current weakening has been proposed to address this challenge, involving reducing the machine\u27s current inversely proportional to the operating speed, maintaining constant power through the extended speed range. One benefit of the proposed method is that all current is maintained in the q-axis, maintaining maximum torque per ampere operation. Coreless axial flux permanent magnet (AFPM) machines have recently gained significant attention due to their specific form factor, potentially higher power density and lower losses. Coreless machine designs promise high efficiency particularly at higher speeds, due to the absence of a ferromagnetic core. In this dissertation, coreless AFPM machines with PCB stators are investigated as candidates for propulsion in electric aircraft applications. Two PCB stator design variations are presented with both simulation and experimental results

Single-Chip Isolated DC-DC Converter with Self-Tuned Maximum Power Transfer Frequency

abstract: There is an increasing demand for fully integrated point-of-load (POL) isolated DC-DC converters that can provide an isolation barrier between the primary and the secondary side, while delivering a low ripple, low noise regulated voltage at their isolated sides to a high dynamic range, sensitive mixed signal devices, such as sensors, current-shunt-monitors and ADCs. For these applications, smaller system size and integration level is important because the whole system may need to fit to limited space. Traditional methods for providing isolated power are discrete solutions using bulky transformers. Miniaturization of isolated POL regulators is becoming highly desirable for low power applications. A fully integrated, low noise isolated point-of-load DC-DC converter for supply regulation of high dynamic range analog and mixed signal sensor signal-chains is presented. The isolated DC-DC converter utilizes an integrated planar air-core micro-transformer as a coupled resonator and isolation barrier and enables direct connection of low-voltage mixed signal circuits to higher supply rails. The air core transformer is driven at its primary resonant frequency of 100 MHz to achieve maximum power transfer. A mixed-signal perturb-and-observe based frequency search algorithm is developed to improve maximum power transfer efficiency by 60% across the isolation barrier compared to fixed driving frequency method. The isolated converter’s output ripple is reduced by utilizing spread spectrum clocking in the driver. An isolated PMOS LDO in the secondary side is used to suppress switching noise and ripple by 21dB. Conducted and radiated EMI distribution on the IC is measured by a set of integrated ring oscillator based noise sensors with -68dBm noise sensitivity. The proposed isolated converter achieves highest level of integration with respect to earlier reported integrated isolated converters, while providing 50V on-chip junction isolation without the need for extra silicon post-processing steps.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

A Comprehensive Review on Planar Magnetics and the Structures to Reduce the Parasitic Elements and Improve Efficiency

Due to the need for highly efficient and compact power electronic converters to operate at higher frequencies, traditional wire-wound magnetics are not suitable. This paper provides a comprehensive review of planar magnetic technologies, discussing their advantages as well as associated disadvantages. An extensive review of the research literature is presented with the aim of suggesting models for planar magnetics. Several strategies are proposed to overcome the limitations of planar magnetics, including winding conduction loss, leakage inductance, and winding capacitance. The goal of this study is to provide engineers and researchers with a clear roadmap for designing planar magnetic devices