Tape Wound Cores Research Articles

Three-Dimensional Numerical Field Analysis in Transformers to Identify Losses in Tape Wound Cores.

To find the total core losses in 1-phase medium-frequency transformers, a 3D numerical field analysis was carried out. The proposed numerical modeling was based on the extended iterative homogenization method (IHM) developed by the authors. The achieved calculation results were validated by the corresponding values obtained experimentally, and a reasonably close agreement was obtained.

A rapid heat treatment for nanocrystallization of amorphous Fe75.1Cu1Nb1.5Si15.5B6.9 and Fe83Cu1Nb4B12 tape wound cores

A rapid annealing technique for soft magnetic Fe75.1Cu1Nb1.5Si15.5B6.9 and Fe83Cu1Nb4B12 tape wound cores is presented. Its effectiveness for creating a fine-grained nanocrystalline structure is demonstrated by measurements of the magnetic hysteresis loops as well as by structural investigations done by X-ray diffraction. The results show that the technique reduces the average crystallite sizes from about 27 nm to 17 nm for Fe75.1Cu1Nb1.5Si15.5B6.9, and from about 52 nm to 15 nm for Fe83Cu1Nb4B12. The coercivity after the rapid annealing is about three times lower for the Fe75.1Cu1Nb1.5Si15.5B6.9 alloy and up to one order of magnitude lower for the Fe83Cu1Nb4B12 alloy compared to the coercivity after the standardized long-time heat treatment. The improved heat treatment is outstanding in the way that it produces better soft magnetic properties in high-performance alloy cores within much shorter time than the standard core heat treatments.

Coupled 2-D FEM and 1-D Micromagnetic Model for Transverse Anisotropy Tape-Wound Magnetic Cores

We present a new approach for modeling high-frequency losses in transverse anisotropy magnetic tapes by solving a 1-D eddy-current problem coupled to a micromagnetic constitutive law. Contrary to earlier models, the model is derived using a magnetic flux-density conforming formulation. The model allows coupling the tape-level magnetization process to a 2-D finite element model for analyzing larger cores by homogenizing the tape layers. The developed model predicts the high-frequency losses in a good agreement with previously presented measured results and models, demonstrating potential for increased accuracy in the calculation of losses in tape-wound cores.

Strength distributions of laminated FeNi-based metal amorphous nanocomposite ribbons

Metal Amorphous Nanocomposite (MANC) materials offer low losses at high magnetic switching frequency, enabling high power density motors with increased rotational speed. While MANCs have high strength, they are brittle. The use of motor components such as a rotor consisting of brittle material presents a reliability concern. Here, a promising MANC alloy is subjected to tensile tests and failure is observed with high-speed photography. A method is developed to prepare tensile specimens of laminated MANC and epoxy layers, simulating the stacking of an epoxy-impregnated tape-wound core. Tensile tests are conducted for single layer ribbon and for five- and ten-layer stacks of laminated material with thin layers of thermosetting epoxy. Failure distributions are shown to have increasing Weibull modulus with increasing layer count. The composite MANC material system is modeled using chain-of-bundles models. Using a k-failure model, we show that single ribbon strength distribution data can be used to predict well the failure distribution of laminated stacks. The agreement occurs when the assumed ineffective length, over which load is recovered in a failed layer, is comparable to the observed interlaminar separation length.

Behavioral Modeling of Complex Magnetic Permeability With High-Order Debye Model and Equivalent Circuits

In this article, a systematic procedure to derive equivalent circuit networks accurately reproducing the frequency response of the input impedance of magnetic cores in a broad frequency range is presented. The proposed procedure foresees to represent the effective complex permeability spectra of a magnetic core (i.e., the permeability resulting from the superposition of intrinsic material properties and effects due to structural features of the core) by a high-order Debye series expansion, which is subsequently synthesized into suitable Foster and Cauer networks. Such networks can be implemented in any circuit simulator, and are particularly favorable for time-domain transient simulation since they can be easily combined with hysteresis models. Two nanocrystalline tape-wound cores and a commercial bulk current injection probe are used as test cases to prove the effectiveness of the proposed method both in terms of accuracy and ease of implementation.

Magnetic Properties in Finemet-Type Soft Magnetic Toroidal Cores Annealed under Radial Stresses

Applying tensile stresses on straight soft magnetic ribbons before core fabrication is a routine method of inducing magnetic anisotropy, while methods of stress annealing of ribbons after core winding are seldom explored. In this study, we utilize a novel approach to induce magnetic anisotropy by applying radial stresses on tape-wound cores of Fe73.5Si13.5B9Cu3Nb1 (at. %) ribbon during crystallization heat treatment. The results show that while stress annealing does not change the structural characteristics of annealed samples, the magnetic anisotropies induced can increase to values ~3–5 times larger than the sample annealed in the absence of external stress. This increase in magnetic anisotropy energy is associated with ~25–50% decrease of magnetic inductance in the treated cores. These results suggest that the magnetic properties of nanocrystalline soft magnetic alloys can be effectively tuned by applying radial stresses.

Rapid Thermal Analysis of Nanocrystalline Inductors for Converter Optimization

To capitalize fully on modern component technologies such as nanocrystalline cores and wide bandgap devices, multi-objective converter design optimization is essential, requiring simple and accurate component models. In this article, a lumped parameter (LP) thermal model is presented for nanocrystalline inductors with ceramic heat spreaders. The key challenge is the nonuniform loss distribution in gapped, tape-wound cores, particularly the high loss densities adjacent to the gaps. However, uneven loss distributions are not handled easily by the LP techniques. It is shown that by treating the ceramic heat spreaders as “passive” heat sources, a simple thermal model of the inductor can be derived to estimate the hot-spot temperature of the core. The model is validated through comparison to 3-D finite element analysis (FEA) and experimental measurements on a 60-kW dc–dc converter. The proposed model offers a comparable level of accuracy to the FEA with a fraction of the running time, executing in $99~\mu \text{s}$ in MATLAB.

A comprehensive study of microstructures and soft magnetic properties of amorphous Co66Fe4Mo2Si16B12 tape wound core

Abstract The microstructures and soft magnetic properties of Co66Fe4Mo2Si16B12 amorphous tape wound core were systematically investigated. The phase composition and corresponding structure evaluation of Co66Fe4Mo2Si16B12 amorphous ribbon after annealing at various temperatures were identified firstly. In particular, at 758 K the microstructure of the ribbon is primarily composed of Co2B, Fe2B and β-Co phases. With the temperature approaching to 768 K, the new phases α-Co and CoSi appears. When the temperature increases to 778 K, the mixed phase combination of α(Co) + β(Co) + Co2B + Fe2B + CoSi exists along with an apparent nano-crystallization. The soft magnetic properties of tape wound core assembled by Co66Fe4Mo2Si16B12 amorphous ribbon were then studied at annealed temperature from 713 K to 753 K. At 723 K, we found the permeability is highest with a maximum value of μm = 1.675 × 103, and the coercive force is lowest with a minimum value of 0.134 Oe. The magnetization curve and the hysteresis loop of established tape would core annealed at 713–753 K remain almost unchanged. Finally, the relation between frequency and magnetic permeability and quality factor were carefully examined at different annealing temperatures.

Mitigation of Gap Losses in Nanocrystalline Tape-Wound Cores

A split-core technique is proposed to mitigate the gap losses in high-frequency nanocrystalline cores, which enables significant size reductions in thermally limited designs. Finite element analysis is used to examine the gap loss dependence on core width D revealing a nonlinear relationship of the form loss ∝ $D^{\alpha }$ . α is approximately constant for frequencies of 10–200 kHz over the range of core widths typically used in power electronics, but α increases with gap length. Splitting the core into a number of subcores can therefore provide significant reductions in gap loss, especially with larger gap lengths. The results from a 300-A (peak), 200-A (continuous) inductor show that with three subcores and a gap length of 4 mm, the gap losses are reduced by 50%, and the hot-spot temperature is reduced by 24.5 °C. Using the technique it is estimated that the original inductor weight could be reduced by 40% with four split cores, making a significant impact on converter power density.

Nonlinear Model of Tape Wound Core Transformers

Recently, tape wound cores due to their excellent magnetic properties, are widely used in different types of transformers. Performance prediction of these transformers needs an accurate model with ability to determine flux distribution within the core and magnetic loss. Spiral structure of tape wound cores affects the flux distribution and always cause complication of analysis. In this paper, a model based on reluctance networks method is presented for analysis of magnetic flux in wound cores. Using this model, distribution of longitudinal and transverse fluxes within the core can be determined. To consider the nonlinearity of the core, a dynamic hysteresis model is included in the presented model. Having flux density in different points of the core, magnetic losses can be calculated. To evaluate the validity of the model, results are compared with 2-D FEM simulations. In addition, a transformer designed for series-resonant converter and simulation results are compared with experimental measurements. Comparisons show accuracy of the model besides simplicity and fast convergence.

Determination of Wound Core Transformer Losses and Temperature Rise

Recently tape wound cores are widely used in transformers for power electronics applications. The spiral structure of theses cores affects the flux distribution inside the core and causes complication of magnetic analysis. In this paper, a model based on reluctance networks method is used for analysis of magnetic flux in toroidal wound cores and losses calculation. A Preisach based hysteresis model is included in the model to consider the nonlinear characteristic of the core. Magnetic losses are calculated by having the flux density in different points of the core and using hysteresis model. Additionally a thermal equivalent circuit is applied to determine the temperature rise in transformer due to the magnetic and electric losses. A transformer for using in a series resonant converter is modeled and the results are compared with experimental measurements to evaluate the validity of the model. Comparisons show accuracy of the model besides simplicity and fast convergence.

New Methods of Damping Very Fast Transient Overvoltages in Gas-Insulated Switchgear

Very fast transient overvoltages (VFTO) are a well-known phenomenon in gas-insulated switchgear. They are mainly generated due to several pre- or restrikes during disconnector switching operations. Since VFTOs may cause complications in substations, a reliable method for damping these transient voltages is of great interest, especially in ultra-high voltage applications. Two new approaches are presented in this paper and compared with a matched radio-frequency resonator, which is an already existing theory. The new methods are an inductive arrangement with surge arrestors and rings of nanocrystalline tape-wound cores. All methods were investigated inside a high-voltage experimental test setup. Therefore, VFTOs with amplitudes of 600 kV and more were generated. The first VFTO amplitude was damped by up to 20%. Even higher damping is possible depending on the damping method and the test conditions. In addition to high-voltage tests and their results, this paper illustrates the theoretical background of all damping methods.

Development of a Permanent Magnet Motor Utilizing Amorphous Wound Cores

An axial-gap permanent-magnet motor that utilized tape wound amorphous cores was designed, manufactured and tested. The motor employs two 8-pole rotors and one 12-slot amorphous cores stator. In order to reduce iron loss, the magnetic and iron loss properties of ring-shaped amorphous cores with different lamination direction are investigated determine a suitable core structure for motor application. Tape wound core was chosen because of its simple manufacture process. In the motor design, lamination direction of AMM core was designed perpendicular to field produced by rotors to decrease eddy current loss. Three-dimensional finite element analysis (3D FEA) was used to model and analyze the motor performance. No-load tests and load tests of the trial motor were conducted to demonstrate the feasibility of the motor design and verify the 3-D FEA calculation. This paper presents the details of amorphous cores' properties, motor design and test results.

Dynamic magnetization process of nanocrystalline tape wound cores with transverse field-induced anisotropy

The correlation between dynamic magnetic domain formation and dynamic magnetization loss is studied in nanocrystalline FeCuNbSiB tape wound cores with different strengths of transverse field-induced anisotropy. A significant excess loss component is measured, in particular for high induction levels. The excess loss cannot be explained by homogeneous magnetization rotation, the ideal magnetization process for a transverse field-induced anisotropy. In fact, dynamic domain observation reveals inhomogeneous rotation of magnetization, wall displacement processes, and domain nucleation besides homogeneous rotation. Domain refinement is accordingly observed with increasing frequency. The domain width is smallest for cores with weak induced anisotropy, where excess loss is the lowest. In these cores, surface roughness yields residual domains, which persist at field strengths above the inductively measured saturation field.

Magnetization loss and domain refinement in nanocrystalline tape wound cores

Stroboscopic Kerr microscopy observations of the dynamic magnetization process on nanocrystalline Fe 73Cu 1Nb 3Si 16B 7 tape wound cores with different induced longitudinal anisotropy K u are presented. As the frequency of the magnetic field increases from the quasi-static case up to 10 kHz, domain refinement is distinctive. The domain wall multiplication depends on the strength of K u which influences excess losses. The original wide domains of the core with the weakest induced anisotropy even decay into a patchy domain pattern at 1 kHz. The occurrence of the patchy domains is discussed in terms of induction rate, amplitude, and the influence of residual anisotropies.

Soft magnetic powder-core composites of Fe90Zr7B3 and Fe49Co21Al5Ga2P9.65C5.75B4.6Si3 alloys

Amorphous and nanocrystalline alloys in ribbon form exhibit excellent soft magnetic properties, but their forms are limited to tape wound cores. Complex shapes require the implementation of a powder metallurgical approach resulting in reduced permeabilities. The present study investigates Fe-based Fe90Zr7B3 (C1) and Fe49Co21Al5Ga2P9.65C5.75B4.6Si3 (C2) melt-spun ribbons as precursors for compacted powder cores. Single-roller melt spinning of C1 produced partially crystallized structures while C2 resulted in amorphous ribbons. Annealing studies were carried out based on the crystallization temperatures of various phases extracted from M(T) measurements. In ribbon form and under optimum annealing conditions, C1 revealed a 1.88T saturation flux density (Bs) and 44A∕m coercivity (Hc), while C2 exhibited a Bs of 0.78T and Hc of 2.4A∕m.

Nickel‐Iron Alloys with Special Soft Magnetic Properties for Specific Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

Stress annealing process suitable for the production of low permeable nanocrystalline tape wound cores

A possible large-scale fabrication process of nanocrystalline tape wound cores with stress-induced anisotropy is investigated. The common method to pass the tape through a furnace under stress prior to core winding is not suitable due to brittleness of the nanocrystalline tape. We introduce a new method to anneal and apply the stress after core winding. Additionally, magnetoelastic effect is used to achieve cores with defined hysteresis loop and reasonable soft magnetic properties.

Nickel–iron alloys with special soft magnetic properties for specific applications

The magnetic properties of the initial permeability and the saturation induction characterize mainly the different available soft magnetic nickel–iron alloys. The nickel–iron alloys Magnifer 75, Magnifer 7904 and Magnifer 8105 with nickel contents between appr. 75 and 82% achieve a saturation induction of appr. 0.8 T. The initial permeability of these alloys can reach values up to a few 100,000 depending on thickness of the material and the frequency of the applied magnetic field. On the other hand, nickel–iron alloys are also available with a higher saturation up to appr. 1.6 T, but then in general with a lower initial permeability around 10,000. These are the alloys Magnifer 36 and Magnifer 50 with nickel contents of appr. 36% and 48%, respectively. In the case of Magnifer 50 different grades can be produced by different processing routes having the different grain and texture structures resulting in different magnetic behaviours. An exception is the alloy Magnifer 53 that combines both properties—high saturation induction and a relative high initial permeability—by applying a magnetic field annealing after the standard high-temperature heat treatment using tape wound cores processed from thin foil of the material. A description of the soft magnetic characteristics of nickel–iron alloys produced by ThyssenKrupp VDM GmbH and some of their applications will be presented.

Comparison of the dynamic response of radial and tangential magnetic flux thrust bearings

Theoretical predictions were made for the dynamic performance of a tangential flux magnetic thrust bearing. A prototype bearing was built with the stators and rotors made from tape wound strip. The performance of this bearing was measured and compared to the theoretical predictions and also to the performance of a radial flux thrust bearing. Tangential flux bearings are intrinsically amenable to construction from tape wound cores. Tape wound cores come in high saturation alloys like supermenduer which can give the bearing a high force to size ratio. The thin tape laminates give the bearing a broad frequency bandwidth. By comparison the paper shows that it is difficult to make a laminated rotor magnetically efficient for radial flux bearings. A test rig is described that was built to measure the performance of the tangential flux bearing. A power amplifier with current feedback provides DC and harmonic currents to the coils. A load cell was built into the test rig to measure the axial thrust, an inductive/Hall sensor was included to measure the coil current, and a Hall probe was used to measure the gap flux.