High Saturation Flux Research Articles

Review of coupled inductors in power electronics: From concept to practice

With the increasing complexity of power electronics converters, magnetic components like inductors, transformers in different configurations, etc., play important roles in shaping a power controller to meet its desired performance effectively and efficiently. Now, coupled inductors have emerged as one important category of magnetic components that can improve the performance of several types of power controllers used in different domains. They are used to improve the control response, reduce ripple content of output control variables, improve efficiency, enhance power density, etc. This review paper deals with coupled inductors in two ways. Firstly, it details the application prospects as well as design requirements for different applications of coupled inductors. Later, it deals with the design and practical validation of one coupled inductor essentially required for one complex application where the leakage inductance of each winding should be minimal. This review has analyzed that the magnetic circuit design would play a dominant role where both the soft magnetic material and winding layout would be extremely important. While designing a practical coupled inductor, this review article has further analyzed that a core material with low loss density, high saturation flux density and interleaved winding would make the ideal magnetic circuit. The proposed magnetic circuit has been thoroughly validated in a parametric-sensitive power controller for alternating current tungsten inert gas (AC TIG) welding.

A Review of Fe‐Based Amorphous and Nanocrystalline Alloys: Preparations, Applications, and Effects of Alloying Elements

Fe‐based amorphous and nanocrystalline alloys are widely used in transformers, electronic information, and aerospace applications due to their high saturation flux density (Bs), high permeability, low iron loss, and low coercivity (Hc). This article briefly introduces soft magnetic materials, gives an overview of the classification, preparation methods, soft magnetic properties, and applications of Fe‐based amorphous and nanocrystalline alloys, and reviews the effects of elements such as Fe, Co, Ni, Si, B, P, and Nb in the alloys on the properties of Fe‐based amorphous and nanocrystalline alloys such as amorphous forming ability, Bs and Hc. The challenges and development directions of Fe‐based amorphous and nanocrystalline alloys in research are pointed out.

Power density improvement of axial flux permanent magnet synchronous motor by using different magnetic materials

PurposeThe purpose of this paper is to exploit the optimal performances of each magnetic material in terms of low iron losses and high saturation flux density to improve the efficiency and the power density of the selected motor.Design/methodology/approachThis paper presents a study to improve the power density and efficiency of e-motors for electric traction applications with high operating speed. The studied machine is a yokeless-stator axial flux permanent magnet synchronous motor with a dual rotor. The methodology consists in using different magnetic materials for an optimal design of the stator and rotor magnetic circuits to improve the motor performance. The candidate magnetic materials, adapted to the constraints of e-mobility, are made of thin laminations of Si-Fe nonoriented grain electrical steel, Si-Fe grain-oriented electrical steel (GOES) and iron-cobalt Permendur electrical steel (Co-Fe).FindingsThe mixed GOES-Co-Fe structure allows to reach 10 kW/kg in rated power density and a high efficiency in city driving conditions. This structure allows to make the powertrain less energy consuming in the battery electric vehicles and to reduce CO2 emissions in hybrid electric vehicles.Originality/valueThe originality of this study lies in the improvement of both power density and efficiency of the electric motor in automotive application by using different magnetic materials through a multiobjective optimization.

Effect of Magnetic Properties of Magnetic Composite Tapes on Motor Losses

Alternating current (AC) copper losses in motors increase with carrier frequency of the pulse width modulation (PWM) and are further increased by leakage flux of the permanent magnet. Therefore, AC copper losses increase with motor speed. Conventional techniques for reducing AC copper losses tend to increase other losses. In this paper, AC copper loss was reduced by wrapping a magnetic tape made of a magnetic composite material around the winding. This method controlled the flux path through the winding. Magnetic composite materials are mixtures of magnetic powders and liquid resins whose magnetic properties can be manipulated by changing the combination and other factors. When Fe–Si–Al magnetic tape was wrapped around the winding, the AC copper loss was reduced by 40%. The loss was further reduced by optimizing the magnetic properties of the magnetic composite material. The AC copper loss was maximally reduced when the specific permeability was 100 and the saturation flux density was 1.6. Magnetic tapes composed of magnetic composite materials with high saturation flux density and specific permeability reduce the AC copper losses without increasing other losses in the motor.

Improving the Soft Magnetic Properties of Fe-Co-B-Zr-Nb Alloy by Tuning the Fe/Co Ratio

Amorphous (FeSUBx/SUBCoSUB1-x/SUB)SUB85/SUBBSUB5/SUBZrSUBy/SUBNbSUB10-y/SUB (x = 0.6, 0.7, 0.8, or 0.9 and y = 7 or 8 at.%) ribbons were fabricated by the melt-spinning technique, and their thermal and magnetic properties were investigated. The results showed that all alloys had a fully amorphous structure, and the substitution of Zr for Nb resulted in high thermal stability and high saturation flux density (BSUBs/SUB) with fairly low coercivity (HSUBc/SUB 21 A/m). Moreover, by varying the Fe/Co ratio, the optimum ratio with the highest BSUBs/SUB and low HSUBc/SUB was determined. As the Fe/Co ratio changed from 6:4 to 9:1, HSUBc/SUB decreased from approximately 20 to 9 A/m, and BSUBs/SUB also decreased gradually. A saturation flux density of 1.33 T was achieved with a coercivity of 9 A/m after optimization.

Composition engineering of ultra-soft-magnetic Co-based alloys

In the present study, the liquidus temperature, mixing enthalpy, and atomic mismatch factor are used to predict and empirically evaluate the amorphisation capability of Co-Fe-B alloys fabricated by melt spinning. Based on this approach, five out of seven alloys have an amorphous structure, confirming the capability of the proposed model in predicting the alloy compositions with higher amorphisation ability in a ternary alloy system in the absence of any costly elements, such as Nb, Mo and Zr. X-ray diffraction, TEM and Mössbauer results show that the other two alloys exhibit different in-situ crystallisation behaviour. In one case, only the free-side crystallises, whereas the crystallisation occurs through the entire thickness of the ribbon in the other alloy. The lower amorphisation ability exhibited by these alloys in relation to the predictive parameters has been evaluated. Additionally, there is a strong correlation between amorphisation ability and crystallisation behaviour of alloys. Alloys, which crystallise through eutectic mode, are more likely to exhibit high amorphisation capability, whereas crystallisation via the primary mechanism can be the sign of lower amorphisation ability. The output of the alloy design process is five amorphous compositions, among which one is magnetically ultra-soft, Hc = 2.9 A/m; a surface crystalline alloy, with a low coercivity and higher value of anisotropy field compared to amorphous samples; and a nanocrystalline sample with a very high saturation flux density, Bs = 1.57 T. The surface crystallisation can eliminate the need for inducing transverse anisotropy by magnetic annealing. Therefore, optimising the alloy composition through this method can be a universal strategy of composition design for the fabrication of alloys with excellent properties, to be utilised in both high-Bs and low-Hc applications.

Synthesis and magnetic properties of low-temperature sintered, LMZBS glass-doped dense NiCuZn ferrites

Doping has been used to control the microstructure and optimize the magnetic properties of low-temperature co-fired ceramics. In this study, the growth mechanism of (Ni0.2Cu0.2Zn0.6O)1.03(Fe2O3)0.97 ferrites doped with Li2CO3–MgO–ZnO–B2O3–SiO2 (LMZBS) glass and sintered at 920 °C was investigated. X-ray diffraction showed that all the samples had a single-crystalline phase structure, with no secondary phases generated. Scanning electron microscopy showed that LMZBS glass exhibited a dense microstructure with a reduced number of pores. The glass promoted a compact ferrite crystal structure formation under low-temperature conditions. The magnetic properties of the ferrites were also improved considerably. Specifically, the permeability of the NiCuZn samples was improved from 320.75 to 547.01 at 0.001 GHz. The sample with 0.25 wt% LMZBS exhibited a saturation magnetization of 4066.973 Gauss and high saturation flux density (Bs = 278.2 mT) and remanence (Br = 151.2 mT). Overall, the LMZBS glass promoted NiCuZn ferrites with uniform and compact microstructure and excellent magnetic properties.

Impact of Stator Segmentation on the Performance of Aerospace Propulsion Machines

<div class="section abstract"><div class="htmlview paragraph">Electric machines offering a high power density are required for aerospace applications. Soft magnetic material with a high saturation flux density is one of the key component which is required to realize these power density targets. The need for a high saturation flux density necessitates the use of cobalt iron lamination over the conventional silicon steel. However, cobalt iron is very expensive i.e. order of 10 in comparison to silicon steel. Stator segmentation is identified as an appropriate method to reduce the wastage and cost associated with lamination. Consequently, in this paper, stator segmentation is analyzed on a 1.35 MW, 16-pole 48-slot propulsion machine. The impact of manufacturing is accounted by controlling the resulting airgap between the segmented structures. Electromagnetic performance for various segmented topologies are compared in terms of torque, torque ripple, and iron loss. Average torque is found to degrade by nearly 10% with an increase in the number of stator segments and the thickness of resulting airgap. Therefore, a tight tolerance is required between the segmented parts to retain the electromagnetic performance. On the other hand, this increases the cost of fabrication and nullifies the benefits offered by stator segmentation.</div></div>

Improving DC superimposition characteristics of powder cores by applying coupled inductors in multi‐phase boost converter

In applications where DC current is superimposed, such as inductors for non-isolated DC-DC converters, powder core can be considered as an attractive solution owing to its superior features such as: high saturation flux density, high Curie temperature, and soft-saturation property. However, in powder cores, a drop of inductance appears prominently due to DC superimposition characteristics. This feature is not a desirable characteristic because it leads to an increase in the inductor ripple current under heavy load, which complicates the thermal design of power semiconductors and capacitors. This paper verifies the improvement of DC superimposition characteristics of powder cores by applying coupled inductors. First, the effect of coupled inductors on the improvement of DC superimposition characteristics is experimentally verified. Second, a measurement method for the DC superimposition characteristics of coupled inductor is proposed. Then, a magnetic circuit model is built using the measurement results. Finally, a coupled analysis of magnetic and electric circuits is performed, and it is confirmed that lower magnetic field operation can be realized by coupled inductors even under heavy load conditions. It has been proven that coupled inductors are effective in improving the DC superposition characteristics of the powder cores.

Highly Efficient 11.1-kW Wireless Power Transfer Utilizing Nanocrystalline Ribbon Cores

Nanocrystalline alloys have been recently considered as an alternative to ferrite as the magnetic cores in inductive power transfer systems due to their superior properties such as higher saturation flux density and permeability. They are also less brittle, more stable to temperature variations, and have a higher thermal conductivity. To take advantage of these properties, a dedicated design approach is required, different from the one used for ferrite cores. In this article, special considerations and methods for the design of nanocrystalline ribbon cores are presented. An 11.1-kW pad is designed and compared with one with identical ferrite cores. Results show that IPT pads with nanocrystalline ribbon cores yield superior magnetic performance in terms of inductances and coupling factors. Higher efficiency and power density were also achieved with the proposed design. Furthermore, compared to ferrite-based pads, they showed lower leakage flux and a superior stability to temperature variations.

The effects of post-processing on longitudinal magnetostriction and core losses of high saturation flux density FeSiBC amorphous alloy ribbons and cores

Fe-based amorphous soft magnetic materials play an attractive role in energy saving and emission reduction due to low core losses. One of the problems is the acoustic noise resulting from magnetostriction during AC magnetization process. In this work, amorphous ribbons with a nominal composition of Fe81.5Si4B14C0.5 (at. %) were produced by planar flow casting and subjected to various postprocessing treatments. The influences of annealing conditions on the longitudinal magnetostriction, acoustic noise and core losses of the ribbons measured at low-field were studied. The effects of bending stress and epoxy impregnation and curing on medium frequency core losses of the alloy cores with different shapes were also investigated. It is shown that larger longitudinal magnetostriction of amorphous ribbons leads to higher acoustic noise emission from amorphous cores. Although the longitudinal magnetostriction was found to be reduced by applying a longitudinal magnetic field during annealing, the core loss was increased. The minimum longitudinal magnetostriction value at 1000 A/m is 7 ppm for ribbon annealed at 350 °C for 90 min. under an applied longitudinal magnetic field, while the lowest core losses at 1.4 T and 50 Hz is 0.213 W/kg for toroidal core annealed at 350 °C for 90 min. under an applied transverse magnetic field. The coupling between longitudinal magnetostriction and bending stress of amorphous ribbon results in an increase in core losses. Furthermore, extra stress was introduced after epoxy impregnation and curing, which also results in an increase in core losses. Thus, low longitudinal magnetostriction is important for stress insensitivity and soft magnetic properties.

Investigation on growth mechanism and gyromagnetic properties of low-sintered Li0.43Zn0.27Ti0.13Fe2.17O4 ferrite doped with Nb2O5 and glass sintering additives

Interest in improving the magnetic properties by co-doping has thrived since it is demonstrated that such co-doping can be used to control the microstructure of ferrites at a low sintering temperature. Usually this process involves grain growth and densification by liquid phase sintering or, in some cases, abnormal growth of grain. Here, we study the growth mechanism of the low-sintered LiZnTi ferrites doped with additions of Nb2O5 and Li2CO3-MgO-ZnO-B2O3-SiO2 (LMZBS) glass through characterization of microstructure and magnetic properties. SEM results show that along with the increase of LMZBS glass contents, the change of ferrite grain presents three different stages. At the initial stage, densification of grain is dominant and grain growth is unconspicuous. Due to the increase of LMZBS glass content, the main process at the second stage is grain growth. At the last stage, however, grain growth starts to be suppressed and pores appear again because of competition between the two additives. Corresponding to each stage, the magnetic parameters of the LiZnTi ferrites, including 4πMs, Hci, Bs, Br/Bs and ΔH, have different trends. Moreover, XRD patterns show that all samples have a pure spinel phase, which means influence of the two additives on crystal structure is negligible. All in all, we obtain a LiZnTi ferrite with uniform and compact microstructure, high saturation flux density (Bs=294.2mT), remanence ratio (Br/Bs=0.87), saturation magnetization (4πMs=3700.1 G) and low ferromagnetic resonance linewidth (ΔH=253) at 900 °C.

High winding ratio, high frequency, ultracompact step-up transformers with laminated metallic magnetic cores

The development and characterization of step-up transformers with high winding ratios and laminated metallic magnetic cores for MHz-range step-up transformers used in DC-DC power converters is presented. The use of metallic magnetic cores with higher saturation flux density than traditional ferrites offers the possibility of reducing the physical size of the transformers. Core eddy currents are suppressed by forming the magnetic cores in a sequential electrodeposition process through toroidal lithographic molds, followed by self-assembly. This approach results in relatively thick magnetic cores (in the hundreds of microns range), comprised of many individual laminations with micron-scale thicknesses. Transformers were formed by manual winding of primary and secondary coils on these cores. The resultant transformers, with typical dimensions in the cubic millimeter range, exhibited primary and secondary inductances in the microhenry and hundreds of microhenry ranges, respectively. Typical transformer coupling coefficients were in the range 0.85–0.95. The transformers exhibited expected voltage step-up ratios as high as 10:1 at typical operation frequencies of 1–2 MHz. These ultracompact devices exhibit up to seven times higher inductance per unit volume and five times higher inductance per weight than typical commercial coupled inductors, and show promise for use in space-constrained electronic systems.

Study on the influence of armature on the efficiency of reluctance accelerator

The armature is an important part affecting the energy conversion efficiency of a reluctance accelerator. In this paper, six kinds of soft magnetic materials are chosen and four structures are designed for the armature. At first, the circuit and magnetic force are theoretically analyzed. Then the armatures with different materials and structures are used in the simulation, and the performances are compared and analyzed. At last, the experiment verifies the theory analysis and simulation design. It is concluded that the saturation flux density and conductivity of the material are the key factors affecting the armature force, and the optimization of armature structure can effectively restrain the eddy current, reduce negative force and improve efficiency. Compared with cutting slits in solid armatures, laminating the sheets radially can reduce the eddy current more efficiently. Although slitting can prevent the eddy current to a certain extent, meanwhile, it will decrease the magnetic force because of the losing of magnetized volume and the surface area. Hence, choosing the high saturation flux density material and making out the armature with radially_laminated sheets will improve the efficiency of the reluctance accelerator. In this paper, the silicon steel radially_laminated armature is a better choice for the armature design of the reluctance accelerator.

The complementary effects of Fe and metalloids on the saturation magnetization of Fe-based amorphous alloys

Developing Fe-based amorphous alloys with high saturation flux density (Bs) have been challenging topics for a long time. Metalloid elements like B, Si, C, and P are key elements for Fe-based amorphous alloys, but the addition of multiple metalloids would significantly complicate the effects of each metalloid on saturation flux density. Herein, Fe83-85(B, C, Si)14–16P1 amorphous alloys with high Bs of 1.61–1.71 T and low coercivity (Hc) of 2.2–8.7 A/m were successfully developed. Fe and metalloids were found to have strong interrelated effects on the total magnetic moment and the strength of magnetic exchange interaction, which largely determine the Bs of Fe-based amorphous alloys. It was revealed that for Fe-rich amorphous alloys, the effects of metalloids on Bs are much more significant than that of Fe, and the effects are largely dependent on Fe content. The complementary effects of metalloids on Bs and the Fe-sensitive behavior of these effects, as well as the underlying mechanisms, have been revealed. These results pave a new way to understand the composition-property relationship, and would help design and develop high-performance Fe-based soft magnetic amorphous alloys.

A new pulse measurement method for magnetisation characteristics of small loss angle core

It is difficult to measure the magnetisation characteristics of magnetic powder cores with small loss angle and high saturation flux density. Here, a new pulse measurement method is proposed, in which the capacitance with preset bias voltage applies pulse excitation voltage to the measured magnetic component through RLC oscillation discharge, and the air core inductor whose permeability is vacuum permeability is used as the standard magnetic component to eliminate the numerical differential error of the traditional pulse measurement method. Based on the detailed analysis of the measurement principle and error source of the new pulse measurement method, the measurement system is established. The impedance analyser method is used to verify that it can accurately measure the magnetisation characteristics of the magnetic powder core with small loss angle.

Improving the glass formation ability and magnetic properties by Nb in Fe-Si-B-P-Cu-Nb nanocrystalline alloys

Fe-based nanocrystalline alloys with high saturation flux density (Bs) are highly desired for the miniaturization of electronic devices. However, the glass forming ability (GFA) and the temperature window of annealing processing of the high Fe content nanocrystalline alloys need to be improved to satisfy the industrial production. In this work, the influence of Nb on the GFA, crystalline behavior, soft magnetic properties of melt-spun Fe86.3-xSi1.3B8.9P3Cu0.5Nbx (0 ≤ x ≤ 4) alloys have been comprehensively investigated. It has been found that full amorphous structure can be obtained when the content of Nb is more than 3 at. %, and Nb may play a critical role in the optimization of crystalline processing. It has been also demonstrated that α-Fe (Si) grains were obviously refined by Nb so as to result in the decease of coercivity (Hc). In this work, Fe82.3Si1.3B8.9P3Cu0.5Nb4 ribbon exhibits an Hc of 4.2 A/m after relaxation, and a Bs of 1.54 T after annealed at 500℃, respectively, which are comparable to those of NANOPERM alloys.

Synergy effects between Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and CuO-Bi2O3 mixtures in low-temperature sintered LiZnTi ferrites with enhanced gyromagnetic and microwave dielectric properties

Promoting grain growth and optimizing microstructure are valid strategies for enhancing gyromagnetic and microwave dielectric properties of low-temperature sintered ferrite materials. Here, a modified low-temperature sintering technique was attempted for the synthesis of LiZnTi ferrites that have compact microstructure and improved performances. Trace amounts of CuO-Bi2O3 mixtures (0.50 wt%) were adopted as sintering additives to promote grain growth and to reduce the sintering temperature. Meanwhile, Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles (∼21.9 nm) were synthesized using a sol-gel auto-combustion method and were used to optimize the microstructure and to restrain abnormal grain growth. XRD Rietveld refinement and SEM images revealed that uniform and dense LiZnTi ferrites with single-phase spinel structure were obtained. Results demonstrated that co-doping of Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and CuO-Bi2O3 mixtures allows low-temperature sintering (900 °C) to be achieved and also promotes grain growth and densification. In particular, LiZnTi ferrites that were modified with 5.00 wt% Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and 0.50 wt% CuO-Bi2O3 sintering additives exhibited narrow ferromagnetic resonance linewidth (ΔH, ∼145 Oe) and low dielectric loss tangent (tanδε, ∼2.45 × 10−4) at ∼9.50 GHz, high saturation flux density (Bs, ∼364 mT), and high squareness ratio (Br/Bs, ∼0.89). Such a modified sintering technique at a low sintering temperature, as reported in this work, provides a reference for other advanced ferrites.

Effects of Bi2O3–MnO2 additives on tunable microstructure and magnetic properties of low temperature co-fired NiCuZn ferrite ceramics

The development of miniaturized high frequency ferrite ceramics is attracting widely interest for next generation MLCI (multi-layer chip inductors). However, there exist short comings in the microstructure adversely affecting magnetic properties. In this study, 0.5 wt% MnO2-x wt% Bi2O3 (x = 0.1, 0.5, 1.0, 1.5, 2.0, and 3.0) were introduced into NiCuZn ferrites to adjust the microstructure at low temperatures. Also, the microstructure changes and high frequency magnetic properties of NiCuZn ferrites were investigated via controlling the addition of MnO2–Bi2O3 and sintering temperatures. SEM results indicated that quantitative MnO2 can suppress abnormal grain growth when optimized amount of Bi2O3 was added. In addition, various amounts of Bi2O3 were added to adjust the magnetic properties by controlling grain growth. Results revealed that 0.5 wt% MnO2-1.5 wt% Bi2O3 composite addition is a critical point to enhance the homogeneity of the samples. Also, interestingly, the dominant contribution to dynamic magnetization mechanism changes from spin rotation to domain wall motion when the content of Bi2O3 is greater than 1.0 wt%. Finally, fine microstructure of NiCuZn ferrites with high permeability (μ′ ≈ 291), high saturation magnetization (Ms ≈ 58.83 emu/g), high saturation flux density (Bs ≈ 290.04), high Q factor (~ 75) and enhanced cutoff frequency (~ 60 MHz) can be obtained sintered at 925 °C. Thus, this work may provide new guidance for developing RF frequency LTCC NiCuZn ferrite ceramics.

Investigation of grain growth and magnetic properties of low-sintered LiZnTi ferrite-ceramic

LiZnTi ferrite-ceramics with good magnetic properties and high Curie temperature have been widely studied and utilized in microwave devices. However, it is necessary to further lower sintering temperature and enhance magnetic properties of the ferrites to meet the requirements of practical application. Here, fully dense LiZnTi ferrite-ceramic with high saturation magnetization (4πMs) and high saturation flux density (Bs) is synthesized through solid phase reaction, using low-melting V2O5 additive. Results indicate that the LiZnTi ferrite-ceramic sintered at 925 °C has dense microstructure. Also, average grain size, Bs and 4πMs of the sample increase to 6.38 μm, 324.4 mT and 4277 Gs when the amount of V2O5 increases from 0.00 wt% to 0.40 wt%, respectively. Interestingly, second grain growth occurs when the amount of V2O5 additive increases to 0.60 wt%. Although the competitive second grain growth results in many small grains, the LiZnTi ferrite still has acceptable magnetic properties (Bs=316.3 mT; 4πMs=4072 Gs). The characteristic of second grain growth can allow the development of V2O5-based composite additive for fabricating uniform and dense ceramic materials with enhanced properties, especially for ferrite materials.