Single Magnetic Core Research Articles

Lagrangian dynamics model and practical implementation of an integrated transformer in multi‐phase LLC resonant converter

In conventional arrangements of three-phase LLC converters, there are at least three magnetic components that occupy a considerable volume and mass of the power converter. Although, the three-phase LLC topology has many advantages over the single-phase one, circuit designers tend to select the single-phase topology because it has the minimal number of magnetic components. The purpose of this study is to reduce the number of the magnetic components of the three-phase topology, by integrating the three-discrete transformers into a single magnetic core, based on a theoretical framework. Lagrangian dynamics is applied to theoretically prove that it is possible to replace the three-discrete transformers by a single integrated transformer. The Lagrangian dynamics theory allowed us to derive a physically motivated model for the integrated transformer, in which each component of the integrated transformer has its own Lagrangian parameter. The Lagrangian model reveals that in a symmetrical design, there is no interphase coupling, and as a result the magnetic components can be downsized owing to the ac flux cancellation. Along with the theoretical discussion, the practical merits of implementing the integrated transformer is reported. Furthermore, the experimental tests are conducted utilizing a 500 W-390 V/12 V-200 kHz prototype.

Modeling and design of single ring core DC sensor based on a new readout method for DC power system protection

We proposed a new readout method for single ring core direct current (DC) sensor to protect the DC power system.The principle of this readout method is based on the linear relationship between the permeability of magnetic ring core and the DC value when the DC value changes within a small range. We built a Pspice model of single magnetic ring core DC sensor based on the proposed method to prove its correctness. We performed simulations using this model under different conditions, including reference voltage, size of core, turns per coil, excitation period, and sampling frequency. The value of the tested DC can be fitted by one linear equation multiplied by a certain coefficient, and this result was consistent with the principle of the proposed readout method. Several trial manufactures of this sensor participated in a leakage detection test. The sensitivity and noise immunity of physical sensors can be enhanced by using a micro control unit (MCU) embedded system. The correctness of this method can be confirmed using measured data.

Saturated Core Fault Current Limiters in a Live Grid

With two recent successful installations in a U.K. live grid, the saturated core fault current limiter (SCFCL) has become one of the leading candidates for commercial fault current limiting devices. In this work, we review the concept developed at Bar-Ilan University, which was later adapted by GridON, for a novel compact SCFCL. This SCFCL utilizes a superposition of a closed dc magnetic circuit and an open ac magnetic circuit to overcome the intrinsic problem of transformer coupling found in traditional SCFCL designs. It also allows the use of a single magnetic core for a full ac current cycle limiting. In addition, the relatively short path for the dc magnetic circuit supports copper coils as an alternative to superconducting bias coils, allowing easier market penetration. The performances of the SFCL devices installed in live grids are described.

A universal mathematical model of a three-phase transformer with a single magnetic core

A universal mathematical model of a three-phase transformer with a single magnetic core for different variants of primary and secondary winding connections using wye and delta schemes at each of 12 phase shifts using clock notation is described. Such a model design is necessitated by the requirements of GOST (State Standard) 30830-2002 (IEC 60076-1-93) and by the wide use of phase-shifting transformers as elements of schemes for feeding power semiconductor converters. Examples of simulation results for cases of three-phase transformers of Y/Y-8 and Y/Y-4 schemes and vector groups are shown. The proposed model allows the working regimes to be investigated of a three-phase transformer with unbalanced sets of parameters for its phases or phases of load, as well as in cases of feeding from a source with an asymmetrical voltage, including a nonsinusoidal one. Taking into into account nonlinearity of magnetization curve at each phase separately allows one to correctly simulate the harmonic composition of currents and voltages.

A Dual-Channel Current Source Driver for Complementary Switches

In this paper, a dual-channel current source driver is presented as an efficient means of driving complementary switches. The driver transfers charge between the gates of the power devices through a single magnetic core with a discontinuous current. This promotes lower conduction loss than continuous current resonant gate drivers (RGDs), and lower component count or conduction loss than existing discontinuous current RGD applied to complementary switches. In addition, controlled switching speed is achieved through nonzero inductor current resulting in lower current stress, and faster switching compared to some pulse RGD circuits. There is good correlation between the analysis and experimental results of a 1.8-MHz prototype.

Frequency dependent impedance model for heteropolar magnetic bearings

Accurate analytical models are fundamental to design and optimise high performance magnetic bearings. Understanding the bearing’s dynamic behaviour over its operational envelope is essential to this task and is performed through frequency response analyses. This work formulates an integrated frequency dependent model of a radial heteropolar active magnetic bearing (AMB) in which terms for the stray capacitance, winding resistance, and winding leakage inductance are included. The model is based on a lumped parameter model frequently used for high frequency laminated inductor applications. Two magnetic core models are evaluated. The first comprises a reluctance network approach and incorporates eddy-current, fringing, and leakage correction terms, while the second constitutes a single gapless magnetic core of equivalent length and effective permeability. The accuracy of the latter is improved by intuitively adjusting two parameters in the analytical model. The magnetic bearing parameters calculated as functions of frequency are compared with practical measurements. The integrated single core model demonstrates superior correlation with experimental results for frequencies up to 1MHz.

Homogeneity of Magnetic Properties Within a Single Soft Magnetic Core, Especially in Huge Cores

Soft magnetic cores made of nanocrystalline FINEMET-type <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$({\rm Fe}_{73,5}{\rm Cu}_{1}{\rm Nb}_{3}{\rm Si}_{15,5}{\rm B}_{7})$ </tex-math></inline-formula> ribbon have never been studied whether they are homogenous regarding their magnetic and mechanical properties. For small cores (i.e., cores with thin wall thickness), this is not so much in doubt as for heavy cores (e.g., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">${\sim}{\rm 2}~{\rm kg}$ </tex-math></inline-formula> with 46 mm wall thickness). As it is well known, during the annealing process, this mass cannot be heated uniformly in normal industrial conditions, which causes differences regarding the magnetic and mechanical properties between the samples taken from various parts of the core. In this paper, we demonstrate that high inhomogeneity exists within a single toroidal core in terms of its magnetic properties. The measurement method and the experimental results are described in detail.

Multifunctional hybrid silica nanoparticles based on [Mo6Br14]2− phosphorescent nanosized clusters, magnetic γ-Fe2O3 and plasmonic gold nanoparticles

We report on the synthesis, characterization and photophysical study of new luminescent and magnetic hybrid silica nanoparticles. Our method is based on the co-encapsulation of single maghemite γ-Fe2O3 nanoparticles and luminescent molybdenum cluster units [Mo6Bri8Bra6]2− through a water-in-oil (W/O) microemulsion technique. The as-prepared core–shell [Cs2Mo6Br14-γFe2O3]@SiO2 nanoparticles (45–53nm) possess a single magnetic core (6, 10.5 or 15nm) and the cluster units are dispersed in the entire volume of the silica sphere. The [Cs2Mo6Br14-γFe2O3]@SiO2 nanoparticles have a perfect spherical shape with a good monodispersity and they display red and near-infrared (NIR) emission in water under UV excitation, whose intensity depends on the magnetic core size. The hybrid nanoparticles have been characterized by transmission electron microscopy (TEM), high annular angular dark field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDX), UV–Vis–NIR spectroscopy and magnetometer SQUID analysis. Small gold nanoparticles were successfully nucleated at the surface of the hybrid silica nanoparticles in order to add plasmonic properties.

Development of a magnetic nanoparticle susceptibility magnitude imaging array

There are several emerging diagnostic and therapeutic applications of magnetic nanoparticles (mNPs) in medicine. This study examines the potential for developing an mNP imager that meets these emerging clinical needs with a low cost imaging solution that uses arrays of digitally controlled drive coils in a multiple-frequency, continuous-wave operating mode and compensated fluxgate magnetometers. The design approach is described and a mathematical model is developed to support measurement and imaging. A prototype is used to demonstrate active compensation of up to 185 times the primary applied magnetic field, depth sensitivity up to 2.5 cm (p < 0.01), and linearity over five dilutions (R2 > 0.98, p < 0.001). System frequency responses show distinguishable readouts for iron oxide mNPs with single magnetic domain core diameters of 10 and 40 nm, and multi-domain mNPs with a hydrodynamic diameter of 100 nm. Tomographic images show a contrast-to-noise ratio of 23 for 0.5 ml of 12.5 mg Fe ml−1 mNPs at 1 cm depth. A demonstration involving the injection of mNPs into pork sausage shows the potential for use in biological systems. These results indicate that the proposed mNP imaging approach can potentially be extended to a larger array system with higher-resolution.

Single-Ended High-Efficiency Step-up Converter Using the Isolated Switched-Capacitor Cell

The depletion of natural resources and renewable energy sources, such as photovoltaic (PV) energy, has been highlighted for global energy solution. The PV power control unit in the PV power-generation technology requires a high step-up DC-DC converter. The conventional step-up DC-DC converter has low efficiency and limited step-up ratio. To overcome these problems, a novel high step-up DC-DC converter using an isolated switched capacitor cell is proposed. The step-up converter uses the proposed transformer and employs the switched-capacitor cell to enable integration with the boost inductor. The output of the boost converter and isolated switched-capacitor cell are connected in series to obtain high step-up with low turn-on ratio. A hardware prototype with 30 V to 40 V input voltage and 340 V output voltage is implemented to verify the performance of the proposed converter. As an extended version, another novel high step-up isolated switched-capacitor single-ended DC-DC converter integrated with a tapped-inductor (TI) boost converter is proposed. The TI boost converter and isolated-switched-capacitor outputs are connected in series to achieve high step-up. All magnetic components are integrated in a single magnetic core to lower costs. A prototype hardware with 20 V to 40 V input voltage, 340 V output voltage, and 100 W output power is implemented to verify the performance of the proposed converter.

Energy Harvesting Based on Magnetic Dispersion for Three-Phase Power System

This paper presents a comparative study on Magnetic-Dispersion based Energy Harvesting Systems (MD-EHS) on electrical conductors that supply power for a three-phase AC motor. It introduces two MD-EHS which are based on magnetic cores of different material, named, nanocrystalline, ferrite and iron powder. The first one consists of harvesting energy from magnetic flux through three symmetrical magnetic cores installed on each power conductors of a three-phase AC motor. The second one consists of a single magnetic core for harvesting energy from magnetic flux of only one of these conductors. Both ones have an AC/DC converter and a variable resistor based load. Experimental results have agreed with the theoretical analysis and show that the first proposed MD-EHS is capable of supplying 14 times more energy than the second MD-EHS, considering nanocrystalline cores and phase current of 3 A, and 7.5 times more energy, considering ferrite cores and phase current of 9 A. Such energy can be applied to various low-power devices, especially in wireless sensor network.

Analysis, design and implementation of a new zero-voltage-switching interleaved asymmetrical half-bridge converter using an integrated transformer

This study proposes an interleaved asymmetrical half-bridge zero-voltage-switching (ZVS) forward-flyback converter (AHBFFC), which uses a single magnetic core. The presented topology is composed of an asymmetrical half-bridge forward converter in parallel with an asymmetrical half-bridge flyback converter. The two converters, which are paralleled in AHBFFC use common switches with ZVS operation. Moreover, two switches of the converter have low-voltage stresses in comparison with the switches used in active-clamping converters. The interleaved operation of the converter reduces the input and output current ripples and hence the size of the output choke and capacitor. The transformer copper loss is decreased because of sharing the input and output currents between two transformers. In this topology, the two transformers are integrated into one magnetic core including gapped legs. Owing to the coupling between two transformers, input current ripple and crossing area of the magnetic core are reduced. The proposed converter has some advantages like high-efficiency, high-power density, small size and simple control. A prototype converter has been implemented and experimental results have been recorded with an ac input voltage of 85-135 Vrms, an output voltage 12 V and output current 15 A.

Synthesis and characterization of amino-functionalized single magnetic core–silica shell composites

The thermal decomposition approach, reverse micro-emulsion system and surface modification technique had been successfully used to synthesis single magnetic core Fe3O4@Organic Layer@SiO2–NH2 complex microspheres. The magnetization of the magnetic microspheres core could be easily tuned between 28 and 56emu/g by adjusting the amount of 2-mercaptobarbituric acid. It was found that the Organic Layer to some extent had a protective effect on avoiding Fe3O4 being oxidized into Fe2O3. Each Fe3O4@Organic Layer microsphere could be coated uniformly by about 30nm of silica shell. The average diameter of the Fe3O4@Organic Layer@SiO2 composites was about 538nm. The saturation magnetization of the Fe3O4@Organic Layer@SiO2 complex microspheres was 12.5% less than magnetic microspheres cores. The Fe3O4@Organic Layer@SiO2–NH2 composites possessed a huge application potentiality in specificity enriching and separating biological samples.

Bridgeless Boost Rectifier With Low Conduction Losses and Reduced Diode Reverse-Recovery Problems

A bridgeless boost rectifier with low conduction losses and reduced diode reverse-recovery problems is proposed for power-factor correction. The proposed boost rectifier can reduce the conduction losses and alleviate the diode reverse-recovery problems by using a coupled inductor and two additional diodes. Zero-current turn-off of the output diodes is achieved, and the reverse-recovery currents of the additional diodes are slowed down to reduce the diode reverse-recovery losses. All inductive components are realized on a single magnetic core by utilizing the leakage inductance of the coupled inductor. Furthermore, for the use of this topology in the practical design, the linear peak current mode control is employed for the proposed boost rectifier. A detailed analysis and a control strategy are presented. Experimental results for a 300-W prototype are also discussed to show the performance of the proposed boost rectifier

Interleaved Three-Phase Forward Converter Using Integrated Transformer

An interleaved three-phase forward converter using an integrated transformer is proposed in this paper. This type of converter has the attractive features of flexible voltage conversion ratio, high output current (due to the parallel connection of outputs), near-zero output-current ripple (due to the output-current-ripple cancellation), fast transient response (due to the small effective output-filtering inductance), and is particularly suitable for high-output-current and low-output-voltage applications such as telecommunication and computer systems. The integrated transformer of the proposed converter consists of three step-down transformers on a single magnetic core. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated transformer are derived. Based on the equivalent-circuit model, the principle of operation of the proposed converter is explained. The analysis and design criteria of the basic circuit, the operation of the regenerative LC snubber circuit, the simulation, and experimental verification are also described.

A Leakage-Inductance-Based ZVS Two-Inductor Boost Converter With Integrated Magnetics

A two-inductor boost converter topology has conduction loss and transformer utilization advantages in converting low-voltage higher current inputs to high output voltages. In this letter, a new zero-voltage switching (ZVS) two-inductor boost converter with integrated magnetics is proposed. In the new topology, the two current source inductors, a resonant inductor and a two-winding transformer, are integrated into one single magnetic core with three windings. Two windings simultaneously perform the functions of the current source inductors and the transformer primary. The transformer leakage inductance forms the resonant inductance. This leads to a much more compact converter design with a significant reduction in the number of core and winding components. A theoretical analysis establishes the operating point of the ZVS converter. Both of the theoretical and experimental waveforms, including flux waveforms for the legs of the integrated core structure, are presented at the end of the letter.

Two-phase forward converter using an integrated magnetic component

An interleaved two-phase forward converter using an integrated magnetic component is proposed for telecommunication and computer applications. The integrated magnetic component consists of two step-down transformers and two output-filtering inductors on a single magnetic core. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated magnetic component are presented. The circuit operation and design criteria of the proposed converter are described. All theoretical analyses are verified by simulated and experimental results.

New active input current shapers to allow AC-to-DC converters with asymmetrically driven transformers to comply with the IEC-1000-3-2

Four new topologies of active input current shapers (AICSs) for converters with symmetrically driven transformers (such as half-bridge, full-bridge and push-pull) have been proposed. This paper analyzes the extension of the use of these new AICSs topologies to converters with asymmetrically driven transformers. Using some of these topologies, the size of AICS inductors can be reduced and even integrated in a single magnetic core. As in the case of other converters with AICS circuit, the new topologies allow line current harmonics to be reduced and thereby to comply with the IEC 1000-3-2 specifications, whilst maintaining all the features of standard DC-to-DC converters (e.g., fast transient response). Finally, the proposed topologies have been experimentally tested.

A novel soft-switched PWM inverter for AC motor drives

A novel soft-switched inverter topology is derived from the passively clamped quasi-resonant link (PCQRL) circuit. By introducing magnetic coupling between the two resonant inductors, the number of auxiliary switches can be reduced from two to one, and only a single magnetic core is required for the resonant DC link. An analysis of this novel PCQRL topology with coupled inductors is presented to reveal the various soft-switching characteristics. In comparison with the conventional passively clamped, continuously resonant DC link inverter, this soft-switched inverter can reduce voltage stresses from more than 2 per unit (pu) to 1.1-1.3 pu. It can also provide soft-switched pulse-width modulated (PWM) operation. Simulations and experiments are performed to backup the analysis.

Accurate AC measurements of standard resistors between 1 and 20 Hz

A new version of an AC bridge for low-frequency (1-20-Hz) measurements of resistance ratios is designed. The bridge is based on an alternating current comparator operating at room temperature. The current comparator uses a single magnetic core of high permeability provided with a tuned detection winding enclosed in electrostatic and magnetic shields. Comparators with ratios equal to 1/1, 100/1, 64.53/1, and 129.06/1 were built, allowing the calibration of 1- and 100- Omega resistance standards in terms of the quantized Hall resistance. Ratio windings are formed by the series connection of strands from a set of individually guarded cables, a technique which provides low ratio error, not exceeding a few parts in 10/sup 9/ at 1 Hz. The AC behavior of 1- Omega DC standard resistors from different manufacturers is studied using this bridge. The time constant of these resistors is on the order of 1 mu s. If the frequency does not exceed 1 Hz, the AC/DC resistance difference due to eddy currents in the metallic can enclosing the resistors is lower than one part in 10/sup 9/. At 1 Hz, the AC-DC difference due to the Peltier effect is found to be less than a few parts in 10/sup 9/, with the exception of two particular resistors for which the difference was on the order of one part in 10/sup 8/. >