Soft Magnetic Core Research Articles

Direct Digital Control of Single-Phase Grid-Connected Inverters With <italic>LCL</italic> Filter Based on Inductance Estimation Model

Soft magnetic powder cores with their high saturation flux density and low core loss are excellent alternatives for filter inductors in inverter-based applications. However, their nonlinear current-dependent inductance characteristics pose a challenge for control of grid-connected inverter with LCL filter. In this paper, the variable inductance conundrum is discussed and a modified direct digital control method based on a variable-structure inductance estimation model that takes into consideration wide nonlinear variation in both inverter- and grid-side inductances is proposed. The proposed method is shown to have better grid-voltage harmonic rejection and improved stability margins. However, investigation of stability which is conventionally based on nominal values of filter inductors cannot predict instabilities over the entire range of inductance variation. Hence, a parametric approach to conventional stability methods with a parameter space defined by variation in actual and estimated inductance is explored in this paper. The effect of line impedance on stability is also investigated with impedance-based stability criterion by considering line inductance as an additional dimension in the parameter space. A pattern in stability margins is observed due to inductance variation, with inductance at its minimum being most vulnerable to instability. Experimental results measured from a 5 kW single-phase grid-connected inverter with various LCL filters have verified the feasibility of the proposed control method. The experimental results also match the analytical results with reasonable accuracy.

Soft Magnetic Multilayered FeSiCrB–Fe$_{x}$N Metallic Glass Composites Fabricated by Spark Plasma Sintering

Novel multilayered FeSiCrB-Fe x N (1 = 2-4) metallic glass composites were fabricated using spark plasma sintering of FeSiCrB amorphous ribbons (Metglas 2605SA3 alloy) and Fe x N (1 = 2-4) powder. Crystalline Fe x N can serve as a high magnetic moment, high electrical resistance binder, and lamination material in the consolidation of amorphous and nanocrystalline ribbons, mitigating eddy currents while boosting magnetic performance and stacking factor in both wound and stacked soft magnetic cores. Stacking factors of nearly 100% can be achieved in an amorphous ribbon/iron nitride composite. FeSiCrB-Fe x N multilayered metallic glass composites prepared by spark plasma sintering have the potential to serve as a next-generation soft magnetic material in power electronics and electrical machines.

Magnetic Anisotropy and Switching Behavior of Fe3O4/CoFe2O4 Core/Shell Nanoparticles

A uniform core/shell nanoparticle system composed of a soft magnetic core (Fe3O4) and a hard magnetic shell (CoFe2O4) was synthesized and characterized to understand how the shell influences the magnetism and exchange coupling of the system. In the case of Fe3O4(8 nm)/CoFe2O4(2 nm) core/shell nanoparticles, DC and AC susceptibility measurements revealed three features associated with the blocking temperatures of the core/shell system (TB-cs ∼ 300 K), the CoFe2O4 shell (TB-s ∼ 200 K), and the Fe3O4 core (TB-c ∼ 50 K). Radio-frequency transverse susceptibility gave a direct probe of the effective magnetic anisotropy field (HK) and switching field (HS), as well as their temperature evolutions. Interestingly, we found that HK of the core/shell structure increased with decreasing temperature. HS was observed only below TB-s, which first decreased drastically with lowering temperature and then increased sharply below TB-c. This is attributed to the effect of a coercive field of CoFe2O4 on the spin flipping of Fe3O4 in the superparamagnetic state (TB-c < T < TB-s) and the blocked state (T < TB-c), respectively. Our study sheds light on the magnetic exchange coupling mechanism in core/shell nanoparticle systems and demonstrates the possibility of controlling the nanomagnetism of a soft magnetic core to which the hard magnetic shell is coupled in such systems.

Analysis and Optimization of Cogging Torque in Yokeless and Segmented Armature Axial-Flux Permanent-Magnet Machine With Soft Magnetic Composite Core

Analysis and Optimization of Cogging Torque in Yokeless and Segmented Armature Axial-Flux Permanent-Magnet Machine With Soft Magnetic Composite Core

Fe3Si-core/amorphous-C-shell nanocapsules with enhanced microwave absorption

Abstract Nanoscale heterostructures, like core-shell structures, show attractive microwave-absorption characteristics because of the synergetic effects of their dielectric shells and soft-magnetic cores. A new type of nanocapsules with amorphous C shell encapsulating Heusler soft-magnetic Fe3Si alloy has been designed and synthesized in which Si atoms were doped in the C shell to effectively produce a large amount of Si-C bonds to induce the formation of an amorphous C shell. This further significantly improves the dielectric properties of C shells by enhanced dielectric polarization. These tailored Fe3Si/C nanocapsules, exhibit enhanced microwave-absorption properties because of the desirable impedance match between the amorphous C shell and the soft-magnetic Fe3Si. The optimal Fe3Si/C nanocapsules exhibit a highest absorption intensity of −68.3 dB at 13 GHz and an absorption bandwidth of 4.6 GHz (for RL lower than −10 dB) for absorber thicknesses of 2.1 mm and 1.4 mm, respectively. This new type of nanocapsules is of potential interest for application as novel microwave-absorption material.

Robust Design of a Low-Cost Permanent Magnet Motor with Soft Magnetic Composite Cores Considering the Manufacturing Process and Tolerances

This paper uses the Taguchi method to optimize the manufacturing process and robust design of a low-cost permanent magnet motor with soft magnetic composite (SMC) cores. For the manufacturing process, SMC cores are produced by using the molding technology without any wire cutting costs. To maximize the relative permeability and minimize the core loss, the Taguchi method is employed to identify the best control factor values for the heat treatment of SMC cores based on a series of experimental results. Due to the manufacturing tolerances, there are significant uncertainties in the core densities and motor dimensions, which will result in big performance variations for the SMC motors in the batch production. To obtain a robust design less sensitive to these tolerances, the conventional Taguchi parameter design method and a sequential Taguchi optimization method are presented to maximize the average torque and minimize the core loss of a low-cost PM motor. Through comparison, it is found that the proposed optimization method is efficient. It can provide an optimal design with better motor performance and manufacturing quality. The proposed method will benefit the industrial production of cost-effective PM-SMC motors with robust and compact designs.

A Soft Magnetic Core can Enhance Navigation Performance of Magnetic Nanoparticles in Targeted Drug Delivery

Magnetic nanoparticles (MNPs) are a promising candidate for use as carriers in drug delivery systems. A navigation system with real-time actuation and monitoring of MNPs is inevitably required for more precise targeting and diagnosis. In this paper, we propose a novel electromagnetic navigation system with a coil combined with a soft magnetic core. This system can be used for magnetic particle imaging (MPI) and electromagnetic actuator functions with a higher steering force and enhanced monitoring resolution. A soft magnetic core with coils can increase the magnetic gradient field. However, this also generates harmonic noise, which makes it difficult to acquire MNP monitoring signals with MPI. Therefore, the use of amplitude modulation magnetic particle imaging (AM MPI) is suggested. AM MPI uses a low-amplitude excitation field combined with a low-frequency drive field. Using this system, the measured signal becomes less sensitive to the soft magnetic core. Based on the new MPI scheme and the combination of the coil with the magnetic cores, the proposed navigation system can implement one-dimensional (1-D) MNP navigation and 2-D MPI. The proposed navigation system can shorten the 1-D guidance time by about 25% for MNPs in the size range of 45–60 nm and give an improved 2-D imaging resolution of 43%, compared with an air-coil structure.

Design Issues for Claw Pole Machines with Soft Magnetic Composite Cores

By using global ring winding, the torque coefficient of the transverse flux machine (TFM) is proportional to its number of pole pairs, and thus the TFM possesses high torque density ability when compared with other electrical machines. As a special kind of TFM, the claw pole machine (CPM) can have more torque due to its special claw pole teeth. The manufacturing of CPM or TFM with silicon steels was very difficult in the past, and is a handicap for the progress of this kind of machine. Thanks to the advent of soft magnetic composite (SMC) materials, the manufacturing process of CPM has become more and more simple. More attention has been paid to this kind of technology, and some mass production CPMs with SMC cores have appeared. However, there are few works that discuss the key design issues for this kind of machine. In this paper, a small CPM with SMC is used as as a research benchmark. Various design methods that can be adopted to improve its performance have been studied, including unequal stator claw pole teeth, a skewing magnet design, consequent pole design, and etc. The 3D finite element method (FEM) is used for the machine analysis, and it is verified by the experimental results of a CPM with SMC cores.

Low core loss combined with high permeability for Fe-based amorphous powder cores produced by gas atomization powders

Toroid-shaped Fe-based soft magnetic amorphous powder cores were prepared from Fe76Si9B10P5 (at.%) amorphous powder by gas atomization and subsequent cold pressing with epoxy resin as a binder and insulation. The influence of epoxy resin content and annealing temperature on the magnetic properties of the amorphous soft magnetic powder cores were analyzed. The core loss at a frequency of 100 kHz for the samples with 2 wt% epoxy resin and annealed at 480 °C for 1 h is evaluated to be less than 800 mW/cm3 under a maximum induction of 100 mT. Meanwhile, the cores also exhibit high permeability of 86 at a frequency up to 20 MHz. These results suggest that Fe-based amorphous powder cores provide great potential for expanding the application of high frequency electronic elements used in rectifiers, inverters, transformers and inductance, which requires soft magnetic cores with high saturation magnetization, high permeability, and low core loss.

Robust Tolerance Design Optimization of a PM Claw Pole Motor With Soft Magnetic Composite Cores

In the past decades, various methods have been investigated for assessing performance variation and robust optimization for electromagnetic device design under uncertainties and/or tolerances. However, in actual production, the manufacturing tolerances are variable to a certain extent, which can be optimized for integrating the performance, manufacturing cost, and production quality. This paper proposes a tolerance design optimization approach by optimizing the design parameters and tolerances simultaneously based on design for six sigma technique. A permanent magnet claw pole motor with soft magnetic composite cores is optimized by using the proposed approach. For this high-dimensional optimization problem involving electromagnetic and thermal performance, Kriging model and 3-D thermal network model are employed under the multilevel framework for increasing the optimization efficiency. Finally, through the analysis, the proposed robust tolerance optimization method shows good performance with improved motor performance as well as the diversity controlling without cost increasing.

Design Optimization of a Permanent Magnet Claw Pole Motor With Soft Magnetic Composite Cores

In our previous study, the claw pole motor (CPM) shows promising magnetic concentrating performance for permanent magnet motors with soft magnetic composite cores. Meanwhile, its relatively complex structure also increases the core loss and cogging torque. To conduct the high dimensional optimization of the CPM with comprehensive analysis models, this paper presents an improved multilevel strategy of high efficiency. Since the holistic performances, including output torque, efficiency, cogging torque, and back electromotive force, are considered, an orthogonal design is utilized for the surrogate model building for increasing the optimization efficiency. A full factor sample method for the surrogate model is also conducted for comparison. The similar optimization results with the two kinds of models prove the effectiveness of the proposed method and optimal design.

직류자장이 중첩된 분말코어의 철손측정

직류자장이 중첩된 Fe-Si-Al, Ni-Fe 분말코어의 코어손실을 측정하였다. 교류자화곡선의 형상, 교류자장 진폭 및 투자율 변화는 직류이력곡선의 형상과 증분 투자율 변화에 기인하였다. 투자율이 높은 코어에서 직류자장이 증가하면 주파수에 관계없이 최소값을 나타낸 후 급격히 증가하였다. 코어손실이 감소하는 것은 직류자장이 증가함에 따른 이력손실의 감소에 기인하며, 코어손실이 증가하는 것은 과도한 투자율의 감소로 인한 교류자장의 진폭의 증가에 기인하는 것으로 판단되었다.

Application-Oriented Robust Design Optimization Method for Batch Production of Permanent-Magnet Motors

From the perspective of industrial production, the design and optimization of electrical machines are application oriented, including maximizing production quality and minimizing production cost in terms of different manufacturing conditions. To achieve these goals, this study presents an efficient application-oriented robust design optimization method for permanent-magnet (PM) motors. The method consists of two main contributions. The first one is the development of an overall optimization strategy, including qualitative and quantitative analyses to provide possible options for an application. Multiphysics analysis, uncertainty analysis, production cost, and optimization models need to be investigated. The second one proposes a multilevel optimization method for the high-dimensional robust design problem of each option. To illustrate the advantages of the proposed method, PM motors with soft magnetic composite cores are investigated for domestic applications. The design optimization is conducted in terms of three motor options and three batch production volumes for both conventional deterministic and robust approaches, and it consists of 18 high-dimensional multiphysics optimization problems in total. Main optimization results are presented and discussed. Experimental and simulation results are presented to validate the effectiveness of the proposed models and methods.

Temperature dependent and applied field strength dependent magnetic study of cobalt nickel ferrite nano particles: Synthesized by an environmentally benign method

Spinel ferrites have come a long way in their versatile applications. The ever growing applications of these materials demand detailed study of material properties and environmental considerations in their synthesis. In this article, we report the effect of temperature and applied magnetic field strength on the magnetic behavior of the cobalt nickel ferrite nano powder samples. Basic structural properties of spinel ferrite nano particles, that are synthesized by an environmentally benign method of auto combustion, are characterized through XRD, TEM, RAMAN spectroscopy. Diffuse Reflectance Spectroscopy (DRS) is done to understand the nickel substitution effect on the optical properties of cobalt ferrite nano particles. Thermo magnetic studies using SQUID in the temperature range 5 K to 400 K and room temperature (300 K) VSM studies are performed on these samples. Fields of 0Oe (no applied field: ZF), 1 kOe (for ZFC and FC curves), 5 kOe (0.5 T), 50 kOe (5T) (for M-H loop study) are used to study the magnetic behavior of these nano particles. The XRD,TEM analysis suggest 40 nm crystallites that show changes in the cation distribution and phase changes in the spinel structure with nickel substitution. Raman micrographs support phase purity changes and cation redistributions with nickel substitution. Diffuse reflectance study on powder samples suggests two band gap values for nickel rich compounds. The Magnetic study of these sample nano particles show varied magnetic properties from that of hard magnetic, positive multi axial anisotropy and single-magnetic-domain structures at 5 K temperature to soft magnetic core shell like structures at 300 K temperature. Nickel substitution effect is non monotonous. Blocking temperature of all the samples is found to be higher than the values suggested in the literature.

3D-Printed Detector Band for Magnetic Off-Plane Flux Measurements in Laminated Machine Cores.

Laminated soft magnetic cores of transformers, rotating machines etc. may exhibit complex 3D flux distributions with pronounced normal fluxes (off-plane fluxes), perpendicular to the plane of magnetization. As recent research activities have shown, detections of off-plane fluxes tend to be essential for the optimization of core performances aiming at a reduction of core losses and of audible noise. Conventional sensors for off-plane flux measurements tend to be either of high thickness, influencing the measured fluxes significantly, or require laborious preparations. In the current work, thin novel detector bands for effective and simple off-plane flux detections in laminated machine cores were manufactured. They are printed in an automatic way by an in-house developed 3D/2D assembler. The latter enables a unique combination of conductive and non-conductive materials. The detector bands were effectively tested in the interior of a two-package, three-phase model transformer core. They proved to be mechanically resilient, even for strong clamping of the core.

Development of a New Low-Cost 3-D Flux Transverse Flux FSPMM With Soft Magnetic Composite Cores and Ferrite Magnets

In this paper, a new 3-D flux transverse flux flux switching permanent magnet machine (3-DFTFFSPMM) is proposed. The cost of this machine is very low since both the soft magnetic composite (SMC) cores and ferrite magnets are very cheap, and the performance of this machine is good due to the special designed topology. For the qualitative analysis and initial design, the simplified power equation is developed to find the optimal design, and the 3-D finite-element method is applied for the quantitative analysis. Considering it is very difficult to obtain a special ferrite magnet in the current market, the 3-DFTFFSPMM for prototyping in the workshop is improved with a new design. For the prototyping, the SMC cores are made by using the manual die compacting technology. Last, the efficiency map of these two machines is obtained to judge the operational performance.

Exchange biased spin valve-based gating flux sensor

A hybrid type of magnetic sensor, combining the advantages of both fluxgate sensors and giant magnetoresistance sensors (GMR), was developed in this work by applying the fluxgate principle into the GMR sensors. The well-known measuring principle of the fluxgate sensor is based on the offset of the hysteresis curve and the second harmonic characteristic using the phase sensitive detection technique. The GMR spin valve was used as the soft magnetic core and the pickup coil of the fluxgate. Based on the harmonic analysis using Fourier series, the second harmonic component of the hybrid GMR-fluxgate sensor output was found to be dominated. The sensitivity of the device was maximized by turning the amplitude and the phase of the sinusoidal excitation current. The obtained sensitivity was 1.52 mV/mT and the field noise was found to be 5.7 nT/√Hz@1Hz. The non-hysteresis of the transfer V-B curve was achieved, and the nonlinearity was about 2.5% within the operation range of ±0.2 mT. The proposed sensor is an appropriate design for low field measurements and geomagnetic applications.

Pure-iron/iron-based-alloy hybrid soft magnetic powder cores compacted at ultra-high pressure

We developed Fe/FeSiAl soft magnetic powder cores (SMCs) for realizing the miniaturization and high efficiency of an electromagnetic conversion coil in the high-frequency range (∼20 kHz). We found that Fe/FeSiAl SMCs can be formed with a higher density under higher compaction pressure than pure-iron SMCs. These SMCs delivered a saturation magnetic flux density of 1.7 T and iron loss (W1/20k) of 158 kW/m3. The proposed SMCs exhibited similar excellent characteristics even in block shapes, which are closer to the product shapes.

Effects of Annealing Temperature and Compaction Pressure on Magnetic Properties of Fe–Si Powder Cores Fabricated by an Improved Bluing Method

Fe-6.5wt%Si soft magnetic powder cores were prepared by using an improved bluing insulation method. A high-quality oxide insulation layer with good temperature stability was found to distribute continuously in the intervals between the Fe–Si particles. The effects of the annealing temperature and the compaction pressure on the core’s magnetic properties were investigated in detail. It was found that high temperature and low compaction pressure are beneficial to decrease the core’s inner stress and high compaction pressure is helpful to reduce the air gap. All the variations of the magnetic performance for the powder cores discussed in this paper were explained reasonably by considering these two factors. From the point of view of low loss, 760 °C and 2090 MPa were confirmed to be the relatively best annealing temperature and compaction pressure, respectively. The μ e , the % μ e at 100 Oe, and the loss at 50 kHz/1000 Gs for the core prepared under these two conditions are 63.57, 72.82%, and 547.66 mW/cm3, respectively.

An Improved DAQ-Based Method for Ferrite Characterization

In this paper, we propose an improved version of the classical volt-amperometric measurement method for the characterization of magnetic hysteresis and losses in soft magnetic cores. Using an appropriate circuital solution for the automatic cancellation of the measurement offset and a synchronous data-acquisition-based scheme for both generation and acquisition of signals, we are able to implement a high performance and low error fully automatic test system. This reduces the testing time, while allowing the use of new segmentation algorithms for the study of both major and minor hysteresis loops and the extraction of all the desired properties. We tested the system on a ferrite core, reproducing results already known from the literature with a higher degree of accuracy and reliability, and propose a test to assess the limits of applicability of the method. Energetic magnetic behavior during the formation of asymmetric minor loops is shown and discussed throughout this paper.