Low Coercive Force Research Articles

Design and Performance Analysis of a Novel Hybrid PM Five-Phase Fault- Tolerant Switched-Flux Memory Motor

Background: The existing literature depicts that since the advent of the hybrid permanent magnet switched-flux memory motor (HPMSF-MM), comprehensive research is focused on the design of three (3)-phase HPMSF-MM topologies, which limits their practical safety crucial design application range or scope, namely, in electric vehicle (EV). Objective: This research work aims to design a novel five (5)-phase fault-tolerant HPMFS-MM using the synergy of two key PMs, namely, a neodymium magnet (NdFeB) and Alnico magnet, also known as low coercive force (LCF) with an intrinsic overload fault detection capacity and excellent flux-regulation capacity to extend it practical application scope. Methods: This research paper employs finite element analysis (FEA) via ANSYS Maxwell electromagnetic software in designing, simulation, and analyzing the proposed fault-tolerant HPMSF-MM. Results: The key merit of the Proposed HPMSF-MM is the exhibition of an overload fault protection mechanism via an injection of a reversed temporary control pulse current into the field winding (FW) in the event of an overload fault condition to demagnetize the Alnico PM configuration to ensure that, almost all the generated flux are short-circuited via the design stator-core without linking the designed rotor as in the case of normal operation is effectively verified via the flux-linkage analysis in this paper. Conclusion: The proposed HPMFS-MM can effectively demonstrate its intrinsic overload fault detection mechanism, due to its tremendous flux-regulating or weakening capacity, in addition to its fault-tolerant teeth implementation merit of ensuring physical motor winding phase isolation in an event of a fault.

Bipolar Pulse Current Magnetizer for Driving a Magnetization Reversal Motor

Magnetization reversal motors (MRMs) have been proposed as motors with lower power losses. MRMs comprise the same configuration as interior permanent magnet synchronous motors; however, a low coercive force core is applied to the stator. Driving an MRM requires a pulse current for magnetizing the stator core. In this paper, a bipolar pulse current magnetizer is proposed for driving MRMs Moreover, the relationship between passive components is reported in terms of voltage, current, and circuit constant. Finally, this paper presents experimental verification of the proposed magnetizer using an inductive load to simulate a single phase of an MRM.

MICROEMULSION-BASED METHOD OF SYNTHESIS OF ZINC-NICKEL FERRITE AND THEIR MAGNETIC PROPERTIES

Solid solutions of nickel-zinc ferrites ZnxNi1-xFe2O4 were synthesized by two different methods: synthesis in microemulsions and by stepwise precipitation. The properties of the resulted nano-sized particles synthesized by two different methods were compared. It was found that the increase in zinc content leads to an increase in the lattice parameters. During the synthesis by the method of microemulsions, the temperature of a single-phase product formation is 400 °C, while by the method of precipitation, a single-phase product formation begins at 600 °C. It was shown that the materials synthesized by both methods have similar unit cell parameters. The average size of ferrite nanoparticles synthesized in microemulsions is smaller, lattice strain is higher compared to ferrites synthesized by stepwise precipitation. Also, lower treatment temperatures provide higher stoichiometry, and homogeneity of materials while magnetization difference is negligible. The particles of the obtained powders have high saturation magnetization Ms = 45.6 Am2/kg for synthesis from microemulsions and Ms = 44.8 Am2/kg for co-precipitated samples, the low coercive force Hc = 1.3 kA/m and Hc = 3 kA/m, respectively. Changes made make synthesized particles more applicable in film deposition, and manufacturing of high-quality magnetic coatings.

A Novel Slot PM-Assisted Hybrid Magnet Memory Machine

This article presents a novel slot permanent-magnet-assisted hybrid-magnet memory machine (SPMA-HMMM) with hybrid permanent magnets (PMs) in both stator yoke and slot opening. The key is each pair of yoke PMs is composed of one pole of high coercive force (HCF) PM and one pole of low coercive force (LCF) PM with flexible flux regulation. LCF PMs can be freely magnetized and demagnetized through dc current pulses, which are supplied by dc excitation coils wound on LCF PMs. This design leads to high efficiency of machine due to negligible field excitation loss. In this article, the machine configuration and operation principle are illustrated in detail. An equivalent magnetic circuit is modeled to unveil flux regulation and parallel excitation effect. Then, the electromagnetic performances of SPMA-HMMM under different magnetization states (MSs) are investigated, which verify flux regulation ability of the proposed machine with changeable MSs of LCF yoke PMs.

Influence of Low-Coercive-Force Magnet Property on Electromagnetic Performance of Variable Flux Memory Machine

The magnetization properties of low-coercive-force (LCF) permanent magnets (PMs), i.e., remanent flux density, coercivity, and hysteresis curve slopes, are closely related to the magnetization characteristics of variable flux memory machine (VFMM). Therefore, this article investigates the inherent relationship between the properties of LCF PMs and electromagnetic characteristics of VFMM using a combined solution integrated with magnetic equivalent circuit (MEC) and graphical methods. First, the hysteresis curve of the LCF PM is analytically modeled by a simplified piecewise linear hysteresis model to characterize the mathematical relationships among the key parameters of the hysteresis model. Then, a simplified MEC method is used to obtain the permeability curves of VFMM, thereby further determining the intrinsic relationship between the dimensional parameters of the LCF PM and the electromagnetic characteristics of VFMM. Afterward, the flux regulation characteristics and on-load magnetization state (MS) stabilization capability of VFMM are qualitatively analyzed using a newly developed coupled approach. Furthermore, the electromagnetic characteristics of three VFMMs equipped with different version LCF PM materials are comprehensively compared using the finite-element (FE) method. Finally, a VFMM prototype using the selected AlNiCo magnet is manufactured and tested to verify the correctness of the theoretical and FE analyses.

Investigation of Axial Field Switched Flux Memory Machine by a Combined Analytical Method

This article proposes a novel axial field switched flux memory machine (AF-SFMM) which is analyzed by a combined analytical method. Compared with conventional axial field (AF) permanent magnet (PM) machines having magnets in the rotor side, the AF-SFMM benefits from good heat dissipation, high rotor robustness, and improved power density. Meanwhile, because of the utilization of low coercive force PM materials, the proposed machine can flexibly regulate air-gap flux. This analytical method is characterized by the combination of a quasi-3-D (quasi-3D) finite element method, a magnetomotive force–permeance-based method, and a virtual linear hysteresis model of low coercive force PM. In addition, compared with conventional time-consuming 3-D finite element analysis (FEA), the proposed method can improve the computational efficiency significantly with satisfactory accuracy. This makes the proposed combined analytical method suitable for preliminary sizing determination of AF-SFMM. Meanwhile, the effectiveness of the proposed analytical method is validated by FEA results.

Swiveling Magnetization for Anisotropic Magnets for Variable Flux Spoke-Type Permanent Magnet Motor Applied to Electric Vehicles

This paper investigates the application of anisotropic low-coercive force (LCF) magnets to a novel variable-flux spoke-type permanent magnet synchronous motor (VFS-PMSM) for electrical vehicles with a wide speed range. In the VFS-PMSM, flux is regulated by swiveling the magnetization of the anisotropic LCF magnets instead of directly magnetizing or demagnetizing them. The previously proposed VFS-PMSM uses only isotropic LCF magnets for easily swiveling the magnetic pole direction, resulting in lower torque density. The challenge thus lies in the feasibility to swivel the magnetic pole direction of the anisotropic LCF magnet, and the impact of the different magnetization strengths of the anisotropic magnets on the motor performance. This paper first studies the feasibility to swivel the magnetization direction of anisotropic LCF magnets through experiments. It is confirmed that the magnetization direction can be successfully swiveled by 90 degrees with a reduced external magnetizing field. Then, two VFS-PMSM topologies and various rotor configurations are compared in terms of key performance indices to determine critical sizing factors for performance enhancement. Finite element analysis is used for simulations. In comparison with the VFS-PMSM equipped with isotropic LCF magnets, the maximum torque of the proposed topology can be improved for the same flux adjustment ability. Alternatively, the flux adjustment ability can also be enhanced by 37.43% for the same maximum torque.

A Novel Asymmetric-PM Hybrid-Magnetic-Circuit Variable Flux Memory Machine for Traction Applications

In this paper, a novel asymmetric-permanent- magnet hybrid-magnetic-circuit variable flux memory machine (AH-VFMM) is proposed. The low coercive force (LCF) permanent magnets (PMs) are located on one biased side of the hybrid magnetic circuit branch, forming an AH configuration. Compared to its conventional symmetric-PM hybrid-magnetic-circuit (SH) counterpart, the proposed design benefits from the reduced usage of high coercive force (HCF) rare-earth magnet, alleviating the magnetic saturation to improve the flux regulation (FR) range, while the excellent load demagnetization withstand (LDW) capability can be still maintained. The topology evolution and operating principle of the proposed machine are introduced and described, respectively. Then, based on the combination of the magnetic equivalent circuit (MEC) method and Schwarz-Christoffel (SC) transformation, a hybrid analytical model is established to quantitatively reveal the mechanism of FR range extension, and facilitate the initial design of the machine. The electromagnetic characteristics of the proposed machine under different magnetization states (MSs) are investigated and compared with those of the conventional SH counterpart. Finally, an AH-VFMM prototype is manufactured, and the experimental measurements are carried out to verify the validity of the proposed design.

On Unintentional Demagnetization Effect of Switched Flux Hybrid Magnet Memory Machine

This paper investigates the unintentional demagnetization (UD) characteristics of low-coercive-force (LCF) permanent magnets (PMs), in switched flux hybrid magnet memory machines (SF-HMMMs). Although the LCF PM field is magnetically in parallel to the magnetic fields produced by the NdFeB PM, as well as the armature reaction in the investigated machines, the UD phenomenon of LCF PMs still possibly occurs, particularly, under on-load operation due to the magnetic saturation effect. First, the UD effect is revealed by the frozen permeability method (FPM), and analytically explained via a magnetic circuit model. Various UD types are then identified with the finite-element (FE) method, coupled with a virtual linear hysteresis curve (VLHC) of LCF PM and FPM. In addition, the dimension and grade of the LCF PM are designed with the aid of VLHC, in order to prevent the UD effect. Finally, a fabricated SF-HMMM prototype is tested to verify the theoretical analyses.

Effect of Bi2O3 contents on magnetic and electromagnetic properties of LiZnMn ferrite ceramics

Soft LiZnMn ferrites with low coercive force values and small grain sizes were developed by the solution combustion synthesis and low temperature sintering technique for microwave applications at a high frequencies. Bismuth oxide was used as an additive to lower the sintering temperature. The examination covered the influence of Bi2O3 on the crystal structure, microstructure, primary magnetic and dielectric characteristics of lithium-zinc-manganese ferrites. The most promising sample designed for using in microwave devices was produced by sintering at 1075 ℃ temperature for 8 h with added 1.5 wt% Bi2O3. These production conditions have yielded 2.98 µm average grain size in a ceramic product, the density is 4.84 cu cm/g, and the coercive force, residual induction, and saturation induction are 58 A/m, 2078.4 G, and 3439.1 G, respectively. In addition, this sample demonstrates a high initial magnetic permeability (μi = 168), Curie temperature (Tc = 437.5 ℃), high values of the dielectric loss tangent (tan δɛ = 6.32⸱10−3), ferromagnetic resonance line width (ΔH = 280 Oe) and the resonance line of spin waves (ΔHk = 1.87 Oe). Further increase in the bismuth oxide content allows observing a change in the ceramics microstructure, accompanied by a deterioration in the magnetic and electromagnetic characteristics. Here, the discussion covers the mechanism of change in the functional properties of lithium-zinc-manganese ferrites produced in the conditions of solution combustion with added bismuth oxide. Thus, synthesizing of initial pre-ceramic powder by glycine-nitrate combustion and subsequent low-temperature sintering with added bismuth oxide is a novel efficient technique of producing advanced soft high-frequency LiZnMn ferrites.

Development of a variable‐magnet switched reluctance motor drive

This paper introduces a variable magnet switched reluctance motor (VM‐SRM) drive that can be characterized with adjustable performance. It consists of a switched reluctance (SR) motor with low coercive force (LCF) magnets buried on stator yoke and a modified asymmetric half bridge (AHB) converter. Magnetization level of the LCF magnets is adjusted by injecting a current pulse to a phase winding of the VM‐SRM. The magnetization process does not need any extra coil and provides a simplicity owing to modified AHM converter. Possible magnetic saturation that limits the magnetization level is overcome by injecting current pulses to two phase windings at the same time. Thus, LCF magnets can be used with their full capacity. The presented analysis results demonstrate that proposed VM‐SRM drive provides a variable performance and might be a candidate for future variable speed applications. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Investigation of Balanced Bidirectional-Magnetization Effect of a Novel Hybrid-Magnet-Circuit Variable-Flux Memory Machine

In this article, the balanced bidirectional-magnetization effect of a newly developed hybrid-magnet-circuit variable-flux memory machine (HMC-VFMM) is revealed and investigated. First, the machine topology and variable-flux principle of the HMC-VFMM are described. In addition, the balanced bidirectional-magnetization effect is analytically unveiled by using a Fourier-series-based hysteresis model of low coercive force (LCF) magnet. The PM magnetization characteristics are then investigated by a coupled solution, which is employed to identify the mismatch between the LCF magnet movement trajectories subject to either continuous one-way or bidirectional alternate current pulses. Finally, a prototype is manufactured and tested to verify the theoretical analyses.

Unusual symmetry breaking in high-temperature enantiomeric ferroelectrics with large spontaneous polarization.

Chiral organic-inorganic hybrid perovskites have gained extensive research interest due to their combination of chirality and the excellent optical, electrical and spin properties of perovskite materials, especially in two-dimensional hybrid perovskites. Herein, we report two-dimensional organic-inorganic perovskite enantiomeric ferroelectric [(R)-β-MPA]2CdCl4 (1) and [(S)-β-MPA]2CdCl4 (2) (MPA+ =methylphenethylammonium). Their mirror relationships are verified by both circular dichroism (CD) and crystal structures. At the same time, the two exhibit very similar ferroelectricity and related properties, including high Curie temperature (343 K), large spontaneous polarization (4.65 μC cm-2), and low coercive force field (13 kV cm-1). Unusually, at room temperature the crystal phase is monoclinic with the space group C2 and above the phase transition temperature it is triclinic with the space group P1, which means that the symmetry decreases with the increase of temperature. In addition, it exhibits a flexible switchable SHG response, while [(R)-β-MPA]2CdCl4 and [(S)-β-MPA]2CdCl4 have wide band gaps of 4.21 and 4.26 eV, respectively, mainly contributed by inorganic CdCl6 octahedra. This discovery opens a new way for the construction of two-dimensional enantiomeric molecular ferroelectrics.

A Hybrid Field Analytical Method of Hybrid-Magnetic-Circuit Variable Flux Memory Machine Considering Magnet Hysteresis Nonlinearity

Variable flux memory machine (VFMM) is considered a promising solution for traction drives due to their distinctive merits of globally high efficiency over an extended operating range. However, the variable flux property of the low-coercive-force (LCF) permanent magnet (PM) together with an interior hybrid magnet rotor structure brings great challenges for the magnetic field modeling of VFMM. To address the above issues, this article proposes a new hybrid field analytical method for a recently developed hybrid-magnetic-circuit VFMM (HMC-VFMM), which combines the magnetic equivalent circuit (MEC) solution, the Schwarz–Christoffel (SC) transformation, and the subdomain model. First, the remanences of LCF PMs subject to different <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> -axis magnetizing currents are determined by the MEC model, in which the nonlinear magnetic reluctances are calculated by the finite element (FE) model. Subsequently, the air-gap flux density distributions of the slotless stator model under different magnetization states (MSs) are predicted by adopting the open-circuit MEC model. Afterward, the relative permeance function is obtained by using SC transformation considering the stator slotting effect. Then, the no-load flux density distributions of the machine under different MSs are predicted by the proposed method. Besides, a subdomain model taking into account the armature reaction is employed to further obtain the torque characteristic of the machine. Finally, the effectiveness of the proposed method is verified by both FE simulations and test results.

Analysis of a Hybrid Permanent Magnet Variable-Flux Machine for Electric Vehicle Tractions Considering Magnetizing and Demagnetizing Current

The overall driving cycle efficiency of conventional permanent magnet synchronous machines (PMSMs) for electric vehicle tractions in a wide speed range is constrained due to the large field weakening current and high iron loss in high speed. The series hybrid permanent magnet variable flux machines (HPM-VFMs) which employ both low coercive force (LCF) magnets and high coercive force magnets are proposed to obtain high torque density and flexible air-gap flux density simultaneously. The key of HPM-VFMs design is the accuracy of hysteresis model of LCF magnets and operating principle analysis. This article contributes to clarify operating principle based on hysteresis model of AlNiCo magnets and propose a novel design consideration to reduce magnetizing and demagnetizing current. Based on the theoretical analysis, this article proposes a novel series HPM-VFM, in which the NdFeB and AlNiCo magnets are arranged separately. Furthermore, flux paths are designed to achieve appropriate interaction between two kinds of magnets. The proposed machine has features of wide magnetization state (MS) variation range, low magnetizing and demagnetizing current, and low risk of unintentional demagnetization. By manipulating the MS of the proposed machine, the losses of a wide speed range operation could be reduced. The comparison of efficiency maps and the worldwide-harmonized light vehicles test cycle driving cycle losses between the proposed machine and a conventional interior PMSM proves that the proposed machine achieves higher efficiency for electric vehicle.

Crystallization and its kinetics of soft magnetic (Fe1−xNix)79B12P5Si3C1 glassy alloy ribbons

A glassy phase is formed over the whole composition range for melt-spun (Fe1−xNix)79B12P5Si3C1 with x = 0; 0.2; 0.4; 0.5; 0.6 alloy ribbons and these glassy ribbons exhibit good bending plasticity. The Ni-containing glassy alloys show glass transition, followed by a supercooled liquid (SCL) region and then multistage crystallization for the alloys with x = 0.5 and 0.6 (hereafter 0.5Ni and 0.6Ni alloys). The 0.5Ni glassy alloy exhibits the largest SCL region of 43 K and good soft magnetic properties even in as-spun state, i.e., low coercive force of 4.8 A/m, effective permeability of 7400 at 1 kHz and saturation magnetization of 0.80 T. The bending plasticity remains unchanged in the wide annealing temperature range below Tg. The crystallization proceeds in the processes of glassy (G) → bcc(α)Fe(Si) + Fe3B for the 0–0.2 Ni alloys, G → fcc(γ)(Fe,Ni) + Fe3(B,C) + Fe3Ni3(B,C) for the 0.4Ni alloy and G → G’ + γ(Fe,Ni) → γ(Fe,Ni) + Ni5P2 + Fe4P + Fe3Ni3(B,C) for the 0.5Ni and 0.6Ni alloys. Analyses of crystallization reaction in isochronal and isothermal conditions were performed via Kissinger and JMAK models and the activation energy for crystallization is much larger for the 0.5Ni glassy alloy. The appearance of the largest SCL region as well as the highest activation energy for the 0.5Ni alloy is due to the necessity of the simultaneous decomposition to the four crystalline phases. The better magnetic softness for the 0.5Ni alloy is presumably due to the development of medium-range ordered atomic configurations which enable the appearances of the largest SCL region as well as the lower internal stress state. The combination of useful properties for the 0.5Ni glassy alloy is promising for useful soft magnetic materials with mass production ability.

Loss-Reduction-Oriented Optimization Methodology of Hybrid-Magnetic-Circuit Variable Flux Memory Machine for Global Efficiency Improvement

Due to the existence of multiple magnetization states (MSs) of the low coercive force (LCF) PMs, the losses minimization of variable flux memory machine (VFMM) under different MSs are unable obtained simultaneously. This article proposes a loss-reduction-oriented (LRO) optimization methodology for overall efficiency improvement in VFMM. Firstly, a recently developed hybrid-magnetic-circuit (HMC) VFMM is selected as a design example to investigate the proposed optimization methodology. Subsequently, the architecture and overall flowchart of the proposed LRO optimization methodology are introduced and given, which includes two rounds of optimization, namely, dual-operating-mode rough optimization (DOM-RO) and multiple-operating-mode elaborate optimization (MOM-EO). Besides, a computationally efficient multimode field-circuit coupled (MMFC) model is established in finite element (FE) software to account for multiple operating modes within two simple case studies. On this basis, the proposed optimization methodology is applied to the HMC-VFMM, in which the LRO objective function is defined in terms of the time proportions of various MSs in an overall driving cycle. According to the optimization results, the electromagnetic characteristics of the machine are investigated, especially the machine loss and its efficiency maps under different MSs are analyzed. Finally, a prototype is manufactured and tested to verify the validity of the proposed optimization strategy.

Modeling the effect of softening in magnetoactive elastomers

Magnetoactive elastomers (MAE) are composites in which a polymer matrix is filled with microparticles of an isotropic ferromagnet with a low coercive force. The functionality of such materials is due to their ability to change the structure under the influence of an external magnetic field and is determined by the interaction of particles and a matrix on mesoscopic (the order of particle size) scales. In MAE, the effect of softening has been experimentally observed. This effect consists in the fact that in the range of deformations from 0,1 to 1%, the effective modulus of elasticity of the material drops sharply. This work looks into the development of a simple numerical model that qualitatively describes this softening effect. The formation of a chain of particles in an applied magnetic field and its destruction under the action of tensile and compressive mechanical forces are considered. The obtained results clarified the mechanisms of softening in MAE.

Effect of lubricant milling aids on the recrystallization behavior and magnetic properties of ball-milled iron powders having (0 0 1) fiber texture for soft magnetic composite

In ball-milled iron particles for soft magnetic composites (SMCs), milling aids with lubricity can induce a (001) fiber texture with superior magnetic properties. Effects of lubricants on the recrystallization behavior of ball-milled iron particles with fiber texture and their magnetic properties of SMCs using the iron particles were investigated. During ball milling, lubricant oil and boron nitride (a solid lubrication particle) were used as lubricants. Both as-milled iron particles have a (001) fiber texture. However, when these iron particles are recrystallized using heat treatment, the iron particles milled using the lubricant oil almost disappeared while the fiber texture in the particles milled using the boron nitride was strongly retained. Therefore, it is concluded that ball milling for iron particles using boron nitride lubricant can retain (001) fiber texture in heat-treated iron particles, and SMC using these iron particles have higher permeability and lower coercive force.

Investigation of the processes of the formation of a nonequilibrium phase-structural state in FeTiB films obtained by magnetron sputtering

The main trends of modern developing magnetic microelectronics are miniaturization and speed, while ensuring efficient operation in the MHz and GHz frequency ranges of magnetic fields. Developing new magnetic materials featured by properties that ensure the implementation of these trends is the key fundamental and applied problem of materials science. In this regard, Fe-Me-X nanocrystalline soft magnetic alloys (Me is one of the metals from Group IVb of the Periodic Table, X is one of the N, C, O, B light elements) obtained in the form of films are of interest. As shown earlier by the authors of this article on Fe-Zr-N films, such films featuring by the Fe/MeX two-phase structure can provide a combination of high saturation induction (Bs), low coercive force (Hc), high hardness, and thermal stability of the structure. The films were produced by magnetron sputtering. The data obtained and published by the authors on the Fe–Ti–B films earlier indicate great prospects for their application in modern microelectronics. There are no any other published results of FeTiB film studies in the context of microelectronics applications. In this paper, we continue the studies of FeTiB films started earlier to identify the chemical and phase composition providing the level of properties required for film application in microelectronics. Nanocrystalline films containing 0 to 14.3 at.% Ti and 0 to 28.9 at.% B were obtained by DC magnetron sputtering. The phase-structural state of the films was studied by X-ray diffraction and transmission electron microscopy. All films are divided into 3 groups according to phase composition: single-phase (supersaturated solid solution of Ti in α-Fe), two-phase (α-Fe(Ti)/α-Ti, α-Fe(Ti)/TiB2, α-Fe (Ti)/FeTi, α-Fe(Ti)/Fe2B) and XRD amorphous. It is shown that XRD amorphous films feature by a mixed structure represented by a solid solution of α-Fe(Ti) with a grain size between 0.7 and 2 nm and an amorphous phase. A reasonable assumption is made on the amorphous phase enrichment by boron. A quantitative assessment of the α-Fe(Ti) phase grain size and its dependence on the chemical and phase composition of the films is given. The mechanisms of solid solution and dispersion hardening determine the grain size of this phase.