Planar Magnetics Research Articles

A Systematic Approach to Modeling Impedances and Current Distribution in Planar Magnetics

Planar magnetic components using printed circuit board (pcb) windings are attractive due to their high repeatability, good thermal performance, and usefulness for realizing intricate winding patterns. To enable higher system integration at high switching frequency, more sophisticated methods that can rapidly and accurately model planar magnetics are needed. This paper develops a systematic approach to modeling impedances and current distribution in planar magnetics based on a lumped circuit model named as the modular layer model (MLM). Stacked pcb layers are modeled as repeating modular impedance networks, with additional modular impedances representing the magnetic core, air gaps, and vias. The model captures skin and proximity effects, and enables accurate predictions of impedances, losses, stored reactive energy, and current sharing among windings. The MLM can be used to simulate circuits incorporating planar magnetics, to visualize the electromagnetic fields, and to extract parameters for magnetic models by simulations, among many other applications. The modeling results are checked with results of previous theories and finite-element-modeling approaches, with good matching presented. A group of planar magnetic devices, including transformers and inductors with various winding patterns, are prototyped, and measured to validate the proposed approach and clarify the boundaries of its applicability.

Overview of Planar Magnetic Technology—Fundamental Properties

The momentum toward high efficiency, high frequency, and high power density in power supplies limits wide use of conventional wire-wound magnetic components. This paper gives an overview of planar magnetic technologies with respect to the development of modern power electronics. The major advantages and disadvantages in the use of planar magnetics for high-frequency power converters are covered, and publications on planar magnetics are reviewed. A detailed survey of winding conduction loss, leakage inductance, and winding capacitance for planar magnetics is presented so power electronics engineers and researchers can have a clear understanding of the intrinsic properties of planar magnetics.

Catheter Position Tracking System Using Planar Magnetics and Closed Loop Current Control

This paper presents an electromagnetic system for five degrees of freedom position and orientation sensing with application in a virtual bronchoscopy system. Planar magnetic source coils were manufactured on printed circuit boards for reproducibility and low-cost manufacturing. The exact magnetic field of each coil is calculated using a filament-based approach. A constant ac current amplifier is used to drive each coil at an independent frequency and a synchronous demodulator calculates each associated magnetic field component using the current waveform as a reference signal. Commercially available search coil sensors are used and a comparison between shielded and unshielded probes is presented. Extensive testing with two separate methods has shown the accuracy of the system to be between 1 and 2 mm. The use of a novel closed loop coil driver has been found to offer excellent magnetic field stability and significant reduction in crosstalk interference.

Applying Response Surface Methodology to Small Planar Transformer Winding Design

Planar transformers provide a light-weight and low-profile solution for power electronic converters with highly reproducible parameters and simple manufacturability. Parasitic inductances, capacitances, and resistances in planar magnetics are difficult to model due to the complex interactions between the physical winding arrangement of each layer and the core geometry (track width, air gap, clearance, etc.). These nonlinear and multivariate magnetic devices play a key role in defining the performance of traditional, soft-switching, and resonant converters by ruling behaviors such as ringing, self-resonant frequency, conduction losses, and the current rate of change in these converters. In this paper, a methodology for determining parametric models for leakage and magnetizing inductance, inter- and intrawinding capacitances, and the winding resistance of small planar transformers is presented using a variety of winding arrangements. The models are employed to shape the winding design to control parasitic elements in order to optimize soft-switching and resonant converters. A central composite design based on the design of experiment methodology is employed on finite element simulations to provide the comprehensive models. Results from physical verification on a planar Ferroxcube ER18/3.2/10-3F3 core set are provided and show excellent correlation between models and verification tests. The method is later employed to effectively design an LLC resonant converter, which is also experimentally verified to illustrate the benefits of the proposed method. The methodology can be employed to characterize and design planar transformers and to predict their performances as part of a variety of power electronic converters.

Analysis and Design of Fully Integrated Planar Magnetics for Primary–Parallel Isolated Boost Converter

A highly efficient planar integrated magnetic (PIM) design approach for primary–parallel isolated boost converters is presented. All magnetic components in the converter, including two input inductors and two transformers with primary–parallel and secondary–series windings, are integrated into an E–I–E-core geometry, reducing the total ferrite volume and core loss. The transformer windings are symmetrically distributed into the outer legs of E-cores, and the inductor windings are wound on the center legs of E-cores with air gaps. Therefore, the inductor and the transformer can be operated independently. Due to the low-reluctance path provided by the shared I-core, the two input inductors can be integrated independently, and also, the two transformers can be partially coupled to each other. Detailed characteristics of the integrated structure have been studied in this paper. AC losses in the windings and the leakage inductance of the transformer are kept low by interleaving the primary and secondary turns of the transformers substantially. Because of the combination of inductors and transformers, the maximum output power capability of the fully integrated module needs to be investigated. Winding loss, core loss, and switching loss of MOSFETs are analyzed in-depth in this work as well. To verify the validity of the design approach, a 2-kW prototype converter with two primary power stages is implemented for fuel-cell-fed traction applications with 20–50-V input and 400-V output. An efficiency of 95.9% can be achieved during 1.5-kW nominal operating conditions. Experimental comparisons between the PIM module and three separated cases have illustrated that the PIM module has advantages of lower footprint and higher efficiencies.

Planar-Integrated Magnetics (PIM) Module in Hybrid Bidirectional DC–DC Converter for Fuel Cell Application

In most power electronics converters, the overall volume is mainly determined by the number of parts and the size of passive components. Integrated magnetics and planar magnetics techniques, therefore, have been an excellent option in order to reduce the counts and the size of magnetic components, hereby increasing the power density of converters. In this paper, a new planar-integrated magnetics (PIM) module for a phase-shift plus duty-cycle-controlled hybrid bidirectional dc-dc converter is proposed, which assembles one boost inductor and two transformers into an E-I-E core geometry, reducing the number of parts, the total volume of converter, as well as the total core loss of the magnetic components. AC losses in the windings and leakage inductance of the transformers are kept low by interleaving the primary and secondary turns of the transformers. To verify the validity of the design approach and theoretical analysis, a laboratory prototype employing the PIM module is implemented for a fuel cell application with 20-40-V input voltage and 400-V output voltage. Detailed results from the experimental comparisons demonstrate that the PIM module is fully functional and electromagnetically equivalent to the discrete magnetics and a significant reduction of size can be achieved by using the PIM module.

Printed Spiral Winding Inductor With Wide Frequency Bandwidth

Winding parasitic capacitance is a major factor limiting the bandwidth of an inductor. In this paper, 1) the traditional, 2) the alternating, and 3) the partial alternating winding methods are evaluated for the multilayer printed spiral winding inductors for megahertz operations. The self-capacitances of various winding structures are estimated by the summation of parasitic capacitance among the turns of a winding. The electric field energy distributions in the inductors are derived from the voltage profiles to illustrate the relative magnitudes of winding parasitic capacitances. The results show that parasitic capacitance reduction can be achieved by reducing stored electric field energy. The partial alternating winding method is found to have the widest frequency bandwidth with reduced number of through-hole vias for multilayer printed spiral winding design. The theoretical analysis has been confirmed with practical measurements. The results provide useful information for the optimal design of coreless or core-based high-frequency planar magnetics.

Volumetric Optimal Design of Passive Integrated Power Electronics Module (IPEM) for Distributed Power System (DPS) Front-End DC/DC Converter

In most power electronics converters, the overall footprint and profile of the whole system are in large part determined by the footprint and profile of the passive components and the interconnections between them. Planar magnetics, integrated magnetics, and passive integration have been topics of research for the past few years to reduce the count, footprint, and profile of the passive components and, hence, increase the power density of the whole converter. This becomes especially prominent in distributed power system (DPS) front-end converters, as the trend is moving from the 2U (1U=1.75 in) standard toward the 1U standard. Chen, Strydom, and van Wyk presented an integration technology, which combines the planar magnetics, integrated magnetics, and passive integration techniques, to integrate all the high-frequency passive components in a DPS front-end dc/dc converter into a single passive integrated power electronics module (IPEM) to reduce the size and volume of the overall system. To optimally design the passive IPEM, an ac loss model and a thermal model are needed. Based on these models, the volumetric optimal design algorithm is presented. To evaluate the performance of the optimally designed passive IPEM, a passive IPEM prototype is constructed and tested. Comparisons are made between the passive IPEM and the discrete components from viewpoints of volume, profile, efficiency, and thermal management. The optimal design is verified by experimental results.

Recent Developments of Planar Printed Circuit Board (PCB) Transformer Technology

Rapid developments of planar magnetics in recent years have prompted new applications of planar transformers in electronic industry. The low-profi’e features of planar magentics make them attractive in many electronic systems that have stringent thickness requirements. In this article, some recent progress of planar PCB transformers and their applications are described. Comparisons of canventional and pianar transformers are reviewed. New trend of integrated electronic packaging in power electronic systems is briefly discussed.

Analysis of the characteristics of planar power magnetics for high‐frequency DC/DC converters

AbstractAlthough magnetic components combining planar construction windings and flat cores have begun to be applied to planar‐type dc/dc converters, there are many unclear points regarding action of the leakage magnetic flux when the core is made extremely thin.In this paper, combining the analysis by finite element method and experiment, the quantization of the influence on excitation inductance and winding loss by the leakage magnetic flux is attempted. Also, the flatter the core is, the more the leakage magnetic flux linking and the winding increase. Also, although there is the advantage that the excitation inductance increases, it was clarified that, on the one hand, it is accompanied by the disadvantage of increase of winding loss by the leakage magnetic flux.Winding losses in various winding constructions are compared, and it is shown that the sandwich construction is the best from the viewpoint of decrease of loss. the suitability of this result was verified by a 1.2‐MHz, 126‐W prototype voltage resonant dc/dc converter.

Planar magnetic component technology-a review

The materials and the fabrication of planar magnetic components for switch mode power supplies (SMPSs) and other applications are reviewed. The advantages and the disadvantages of such devices are introduced. The magnetic materials used in the devices, such as ferrite, amorphous metallic glass, and thin and thick magnetic films, are detailed. The devices have varying degrees of planarization-partially planar devices with magnetic cores and planar windings and truly planar devices for integrated magnetic circuits with planar windings and planar magnetics. Devices of both types reported in the literature since 1979 are reviewed. The design of the planar magnetic components must be optimized with respect to losses, and design issues which relate to electrical, thermal, and mechanical performance are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>