Core Loss Reduction Research Articles

The effect of calcination temperature on microstructure and properties of FeNiMo@Al2O3 soft magnetic composites prepared by sol-gel method

The effect of calcination temperature on the coating layer and the phase of the alloy matrix is the main problem to improve the heat treatment process of SMCs and obtain excellent magnetic properties. In this study, FeNiMo@Al2O3 powders which were coated by sol-gel and calcined at 900–1300 °C were prepared and these powders were pressed into SMCs. The results showed that the surface of the powder was uniformly coated with Al2O3. As the heat treatment temperature increases, the phase of the coating changed from AlOOH to γ-Al2O3, δ-Al2O3, θ-Al2O3, and α-Al2O3. Meanwhile, the new phase γ-Fe, Ni appeared in the alloy matrix. The magnetic permeability of the sample is very stable in the frequency range of 10–500 kHz. The magnetic loss decreases first and then increases, with a minimum at 1100 °C. The permeability and magnetic loss of the sample pressed from the powder obtained by calcination at 1100 °C are 321.78 mw/cm3 and 87.61 (50 kHz, 100 mT) at the typical industrial application conditions of Iron–Nickel SMCs. The microstructure and the magnetic properties show that the obtained α-Al2O3 have excellent insulation and heat resistance. This resulted in a significant reduction in core losses of FeNiMo SMCs.

Core loss reduction for Fe-6.5wt%Si soft magnetic composites doped with Co element

Co element was doped in Fe-6.5Si alloy and the corresponding soft magnetic composites were fabricated successfully by conventional powder metallurgy techniques in this work. Saturation magnetization of Co-doped Fe-6.5Si powder increases compared to powders without Co and the coercivity increases because of grain refinement. Co addition is helpful to improve the electrical resistivity of Fe-6.5Si alloy. After doping Co, it shows a significant trend towards a decrease for core loss of Fe-6.5Si SMCs by reducing both eddy current loss and hysteresis loss. The effective permeability of Co-doped Fe-6.5Si SMCs decreases monotony with the Co content changing from 0 to 7.0 wt%. Fe-6.5Si-1.0Co SMCs shows best magnetic performances (100 mT/50 KHz) with core loss of 781.03 mW/cm3 and effective permeability of 103.36.

A Low-loss and Lightweight Magnetic Material for Electrical Machinery.

A low-loss and lightweight core material, with applications in electrical machinery, is made of highly packed and insulated magnetic microwires (MWs). These MWs are aligned in such a way as to guide the flux in the rotor/stator, with the ultimate goal of increasing efficiency and substantially reducing core losses. Commercial FebalNi29Co17-based MWs with a 127 μm diameter and a 33 μm insulation coating are utilized. The magnetic measurements of the fabricated sample demonstrate high permeability and low core loss in a wide range of frequencies. To prove the utility of this type of material, we used it in the rotor core of a prototype 25 Watt three-phase synchronous reluctance machine (SyncRM). The core is lighter, and the losses are significantly lower than in conventional core materials under the same torque density.

Loss Minimization Design of Ferrite Core in a DD-Coil-Based High-Power Wireless Charging System for Electrical Vehicle Application

In this article, a core design and optimization method is proposed for the double-D (DD) coil-based inductive wireless charging system (WCS) to minimize the core loss. Core loss is the most significant loss in a medium to high power wireless charging pad. Conventional approaches assume a uniform distribution of the magnetic field in the core. However, the magnetic field in the core is highly nonuniform, which leads to a localized higher core loss. For investigating the loss behavior thoroughly, the core loss versus the flux density distribution has been studied analytically for varying core geometry. Based on this analysis, an optimal criterion has been derived for geometric design of the core to minimize the core loss. The proposed model is verified through finite element analysis (FEA) and tested through a laboratory prototype of DD coil-based 5.0-kW WCS. Experimental results showed a noticeable core loss reduction up to 25% compared to the conventional block and bar core. 1 1 This article is prepared based on a closely related concept of the authors presented in the IEEE Applied Power Electronics Conference (APEC) in March 2018 [7] .

Combinatorial surface coating and greatly-improved soft magnetic performance of Fe/Fe3O4/resin composites

Structure-reinforced Fe/Fe3O4/resin soft magnetic composites (SMCs) have been fabricated through coating micron-sized Fe powders with high-purity Fe3O4 nanolayers and silicon resin films by combinatorial controlled oxidation and physical coating method. High magnetization Ms of 201 A m2 kg−1 can be reserved in the Fe/Fe3O4/resin SMCs due to high-purity ferrimagnetic Fe3O4 shells and low-content resin layers. The smooth Fe/Fe3O4 interfaces and uniform silicone resin coating layers in the Fe/Fe3O4/resin SMCs also lead to their low coercivity of 11.4 Oe and high compressed density of 7.50 g/cm3. For traditional metal-based SMCs fabricated by various common coating methods, their reduced core loss is usually achieved but accompanying with low magnetic induction and poor mechanical properties. In this work, high transverse rupture strength value of 92 MPa and greatly enhanced soft magnetic performance with both decreased core loss in accompany with high magnetic inductions are achieved for the fully densified Fe/Fe3O4/resin SMCs due to their well-structured composite interfaces, which promise their great latent applications for high-power and low-loss magnetic components.

Selective laser melting vitrification of amorphous soft magnetic alloys with help of double-scanning-induced compositional homogeneity

Recently, selective laser melting (SLM) of Fe-based soft magnetic bulk metallic glass (BMG) is garnering great attention because it can yield both superior magnetic properties such as high permeability and low core loss and near-net shaping of 3-dimensional complex components. However, full vitrification of BMGs with high saturation magnetization above 1.2 T has never been realized because cooling rates are limited and compositional inhomogeneity induced by rapid laser processing causes severe undesirable crystallization. In this work, a double scan strategy has been employed with the aim of amorphous phase fraction enhancement as well as densification. We have shown that double scanning effectively fills voids generated due to partial melting of powders, and leads to relative density of up to 96% and corresponding saturated magnetization of 1.22 T. More importantly, the double scan strategy stimulates reflow in the melt pool, securing compositional uniformity, and eventually enhances amorphous phase fraction to a value as high as 47%. As a consequence, coercivity has been significantly decreased, which in turn reduces core loss and increases permeability.

High-efficiency Bidirectional Buck–Boost Converter for Residential Energy Storage System

This paper proposes a bidirectional dc–dc converter for residential micro-grid applications. The proposed converter can operate over an input voltage range that overlaps the output voltage range. This converter uses two snubber capacitors to reduce the switch turn-off losses, a dc-blocking capacitor to reduce the input/output filter size, and a 1:1 transformer to reduce core loss. The windings of the transformer are connected in parallel and in reverse-coupled configuration to suppress magnetic flux swing in the core. Zero-voltage turn-on of the switch is achieved by operating the converter in discontinuous conduction mode. The experimental converter was designed to operate at a switching frequency of 40–210 kHz, an input voltage of 48 V, an output voltage of 36–60 V, and an output power of 50–500 W. The power conversion efficiency for boost conversion to 60 V was ≥98.3% in the entire power range. The efficiency for buck conversion to 36 V was ≥98.4% in the entire power range. The output voltage ripple at full load was <3.59 Vp.p for boost conversion (60 V) and 1.35 Vp.p for buck conversion (36 V) with the reduced input/output filter. The experimental results indicate that the proposed converter is well-suited to smart-grid energy storage systems that require high efficiency, small size, and overlapping input and output voltage ranges.

Performance Analysis of Non–Oriented Electrical Steel with Optimum Texture for High–Speed Traction Motors

The magnetic properties of non–oriented electrical steel (NOES) vary significantly with respect to the microstructure and crystallographic texture of the final steel sheets, which, in turn, are highly dependent upon the thermomechanical processing parameters used during hot rolling, cold rolling and annealing. This paper performs an exploratory performance analysis of NOES for use in high–speed traction motors, emphasizing the importance of obtaining an appropriate crystallographic texture to achieve the desired magnetic properties by controlling the annealing temperature and holding time. A 3.2% Si NOES annealed at 860°C for 24 hours after hot rolling can result in reduced core losses after cold rolling and final annealing. This material was chosen for the performance analysis of a laboratory scale high–speed, high–power traction motor (45 kW, 10,000 rpm) using finite element analysis (FEA). The motor using the NOES is compared to that using a commercially available grain–oriented electrical steel (GOES) to highlight the feasibility and advantages of NOES for high–speed motor applications. In addition, the motor performance using the NOES is compared to that using commercial NOES to understand the scope of improvement obtained by optimizing the microstructure and texture of the steel sheet.

Finite Element Modeling and Analysis of High Power, Low-loss Flux-Pipe Resonant Coils for Static Bidirectional Wireless Power Transfer

This paper presents the optimal modeling and finite element analysis of strong-coupled, high-power and low-loss flux-pipe resonant coils for bidirectional wireless power transfer (WPT), applicable to electric vehicles (EVs) using series-series compensation topology. The initial design involves the modeling of strong-coupled flux-pipe coils with a fixed number of wire-turns. The ohmic and core loss reduction for the optimized coil model was implemented by creating two separate coils that are electrically parallel but magnetically coupled in order to achieve maximum flux linkage between the secondary and primary coils. Reduction in the magnitude of eddy current losses was realized by design modification of the ferrite core geometry and optimized selection of shielding material. The ferrite core geometry was modified to create a C-shape that enabled the boosting and linkage of useful magnetic flux. In addition, an alternative copper shielding methodology was selected with the advantage of having fewer eddy current power losses per unit mass when compared with aluminum of the same physical dimension. From the simulation results obtained, the proposed flux-pipe model offers higher coil-to-coil efficiency and a significant increase in power level when compared with equivalent circular, rectangular and traditional flux-pipe models over a range of load resistance. The proposed model design is capable of transferring over 11 kW of power across an airgap of 200 mm with a coil-to-coil efficiency of over 99% at a load resistance of 60 Ω.

Chemical coating of crystalline-Fe/amorphous-Fe core-shell structured composites and their enhanced soft magnetic properties

New-type crystalline-Fe/amorphous-Fe core-shell structures with greatly-improved soft magnetic performance have been synthesized from coating micron-sized Fe powders with amorphous micrometer-thick Fe layers using a facile chemical coating method. Surface-oxidized amorphous Fe layers are uniformly coated upon the surfaces of high-purity Fe particles, which results in their high saturated magnetization (204.6 A m2 kg−1) and high compacted density (7.42 g/cm3) in these crystalline-Fe/amorphous-Fe composites. For metal-based soft magnetic composites used in high-power applications, it is always an important goal to accomplish increased magnetic inductions along with reduced core loss. In the present work, excellent soft magnetic performance containing high inductions, reduced core loss and desirable frequency-dependent magnetic characteristics is successfully achieved in fully compressed crystalline-Fe/amorphous-Fe composites due to higher resistivity of amorphous Fe shells, which promises their latent utilization for high-power metal-based magnetic devices.

Study of soft magnetic composites of iron coated with nanoparticles dispersion in liquid glass

Abstract This work presents the study and development of soft magnetic composites of iron coated with alumina nanoparticles dispersed in sodium silicate, also known as liquid glass. It is proposed that the nanoparticles dispersion increases the thermal resistance of the glassy coating, allowing a heat treatment with higher temperatures, reducing the internal stresses generated during the pressing and reducing core losses. Thermogravimetric analysis under an oxidative atmosphere of the powder samples and Scanning electron microscopy and energy-dispersive X-ray diffraction of fractured compacted samples are shown to discuss the coating thermal behavior. Also, electrical resistivity, relative permeability and magnetic losses of samples with and without nanoparticles dispersed in sodium silicate are shown discussing their loss separation.

Magnetic properties of iron-based soft magnetic composites prepared by utilizing polyimide insulating layer

Polyimide (PI) with excellent insulating property and enhanced thermal stability was used as insulating coating material for the preparation of iron-based soft magnetic composites (SMCs), and the effect of insulating coating content and curing temperature on the magnetic properties of iron-polyimide SMCs was investigated. The results demonstrate that the insulating layer of PI shows satisfactory adhesion property on the surface of iron particles, and uniform insulating layer of PI was obtained by imidization of polyamic acid (PAA) at 200 °C. With the increase of PI content, the thickness of insulating layer increases gradually, accompanied by the increase of resistivity and the reduction of core loss. PI shows enhanced heat resistance, the SMCs can be cured at the temperature up to 400 °C, leading to the effectively release of residual internal stress generated during the compaction process. At the optimized PI content of 1.5 wt% and curing temperature of 400 °C, low core loss of 780 W/Kg (measured at 50 mT and 100 kHz) and higher maximum permeability of 305 were achieved.

New Design and Magnetic Field Analysis of Transformer Shape with V-Connection for Core Loss Reduction in Railway System

This paper presents a new design of transformer shape core used in railway system for loss reduction analyzed via the magnetic vector potential in the form of partial differential equation related to magnetic field. Finite element method is used in order to simulate a three-dimensional system. This paper focuses on the core loss reduction which is calculated from magnetic vector potential and magnetic field behavior on core transformer with V-connection, while the transformer has supplied voltage from three-phase system. The unbalanced input voltage is divided into three case studies in this paper: C-A couple phase, A-B couple phase and B-C couple phase from three-phase system. In addition, a design of transformer shape core has occurred on the corner that is the intersection between vertical core and horizontal core with 5 mm radius curves. The simulation results compare core loss of transformer between the original shape of transformer core and the new design of transformer core even though the supplied voltage is unbalanced. However, the results have shown that the new design of transformer core can decrease the core loss and it can lead to develop the shape of transformer core in order to reduce the core loss in term of manufacturing.

A Current-Fed Dual-Active-Bridge DC–DC Converter Using Extended Duty Cycle Control and Magnetic-Integrated Inductors With Optimized Voltage Mismatching Control

For a current-fed dual-active-bridge bidirectional dc–dc converter, an extended duty cycle control is proposed. The low-voltage-side (LVS) bottom switch duty cycle can operate lower than 50%. The conduction loss of switches can be reduced by using low-voltage-rating mosfet s for the LVS. Meanwhile, a voltage mismatching control with adaptive clamp voltage regulation is proposed to achieve zero-voltage switching for all switches throughout full load range. Besides, for LVS dc inductors, a magnetic-integrated technique is used to reduce core loss, and power density can be improved by the use of only one core. The effectiveness of the proposed control is verified by the experimental results of a 1-kW laboratory prototype.

Design and Evaluation of a Reconfigurable Stacked Active Bridge DC–DC Converter for Efficient Wide Load Range Operation

This paper presents the design and implementation of a large-step-down soft-switched dc-dc converter based on the active bridge technique which overcomes some of the limitations of the conventional Dual Active Bridge (DAB) converter. The topology comprises a double stacked-bridge inverter coupled to a reconfigurable rectifier through a special three-winding leakage transformer. This particular combination of stages enable the converter to run in an additional low-power mode that greatly increases light-load efficiency by reducing core loss and extending the zero-voltage switching (ZVS) range. The converter is implemented with a single compact magnetic component, providing power combining, voltage transformation, isolation, and energy transfer inductance. A 175 kHz, 300 W, 380 V to 12 V GaN-based prototype converter achieves 95.9% efficiency at full load, a peak efficiency of 97.0%, an efficiency above 92.7% down to 10% load and an efficiency above 79.8% down to 3.3% load.

Core Loss Calculation in a Variable Flux Permanent Magnet Machine for Electrified Transportation

The paper is focused on the modeling and measurement of core losses in an AlNiCo-based variable flux permanent magnet machine. The application of AlNiCo as a low coercivity magnet provides the ability of the magnet flux control using short-time $d$ -axis current pulses. This allows a reduction in the machine core losses under high-speed conditions, thus improving the machine efficiency. In order to identify the machine efficiency gains, the core losses have to be accurately modeled at different magnetization levels. An advanced core loss model for the variable flux machine (VFM) is first presented. This model is based on the calculation of an equivalent sinusoidal waveform of nonsinusoidal magnetic flux density. The model is then utilized to calculate the core losses in a tangentially magnetized VFM using finite-element simulation. In order to validate the developed model experimentally, a measurement method is developed to segregate the mechanical losses and the no-load core losses at different speeds and magnetization levels for a 5-hp VFM. Finally, the proposed model accuracy is verified through a comparison with the experimentally measured core losses under a no-load condition.

Active-Clamp ZVZCS Resonant Forward DC Transformer (DCX) With Load-Adaptive ON-Time Control

Targeting at low-power high-density bus converter applications, a megahertz active-clamp resonant forward converter with whole-load-range zero-voltage switching and zero-current switching (ZVZCS) characteristics is proposed in this paper, which improves system efficiency performance. Compared with previous resonant forward converters, the proposed converter can effectively reduce the root-mean-square current and the conduction loss. To realize zero-voltage-switching turn on of switch over the entire input voltage range, a dead-time control is adopted to account for the nonlinear capacitors of switches. Besides, given fixed resonant parameters, the ZVZCS feature can be maintained at various combinations of operating frequency and duty cycle, which is a unique advantage over conventional resonant converters. Based on this concept, a load-adaptive on-time control that can significantly reduce core loss is proposed to improve the light-load efficiency. A 66-W 24-V-to-12-V prototype is built up to verify the effectiveness of the proposed converter, which achieves 96% full-load efficiency and 93.5% 10%-load efficiency.

Enhanced magnetic properties and reduced core loss of intergranular insulating Fe-Si soft magnetic composites with three-shell SiO2-Fe2SiO4-SiO2 insulating layer

The intergranular insulating Fe-Si soft magnetic composites (SMCs) with uniform three-shell SiO2-Fe2SiO4-SiO2 insulating layer were prepared successfully via simple water oxidation combined with the spark plasma sintering process (SPS). The formation mechanism of the insulating layer and the magnetic properties of the Fe-Si SMCs have been studied systematically. Note that the simple water oxidation process could well ensure the uniformity of the oxide layer consisting of Si and Fe3O4. And then, the high temperature solid-state reactions during the SPS process would result in the conversion of the oxide layer (Si-Fe3O4) to the insulating layer with special three-shell structure (SiO2-Fe2SiO4-SiO2). As a consequent, the Fe-Si SMCs exhibit excellent performance suah as high saturation magnetization (181.9 emu/g), stable effective permeability (60.5) and very low core loss (7.8 W/kg at 50 kHz). The results indicate that the preparation method in this study is simple and effective to produce high performance Fe-Si SMCs used in the field of electromagnetic conversion equipment.

Reduction of Stator Core Loss in Interior PM Machines for Electric Vehicle Applications

Stator core loss of four interior permanent magnet (IPM) machines is studied for electric vehicle applications in this paper. The no-load air-gap density, core loss density, core loss harmonics, and the segregation of hysteresis and eddy current losses are investigated with finite-element analysis. The results show that the rotor surface shaping of a single-layered IPM machine and increasing the rotor magnet layers can reduce the stator core loss due to the harmonics of the rotor magnetomotive force. The stator core loss reduction effectiveness of rotor surface shaping is similar to a two-layered magnet configuration, but the reduction effectiveness is less than that the magnet layers increased to three numbers. An IPM machine with three-layered magnets rotor is prototyped to verify the analysis.

Effect of cobalt addition on the magneto-crystalline anisotropy parameter of sintered NiZn ferrites evaluated from magnetization curves

Abstract This paper investigates the effect of the cobalt addition on the magneto-crystalline anisotropy parameter of some polycrystalline ferrites. Magnetization curves have been experimentally determined at different temperatures on Ni1−xZnxFe2O4 sintered samples with or without cobalt addition. In each case, a law of approach to saturation has been fitted to the measured data in order to extract the anisotropy parameter K1 representative for the polycrystalline material. Besides, measurement of the complex susceptibility and power core-loss up to 5 MHz has been performed. This approach allows a discussion on the role of cobalt addition on the power core-loss mitigation. It has been found that the substitution with 0.02 mol. of Co leads to a small decrease in the K1 values. This evolution is consistent with the rise in the rotational permeability. However, the change in K1 cannot account for the core-loss reduction with Co. Rather, it is confirmed that Co hinders the domain wall displacement and subsequent dissipation up to an induction level that depends on the grain size.