Core Loss Reduction Research Articles

Recrystallization behaviour and texture of non-oriented electrical steels

Five numbers of Si steels with different alloying elements, viz., 1.35% Si, 2.2% Si, 1.48% Si with 0.11% Sn, 1.44% Si with 0.05% Sb and, 1.52% Si with 0.11% P (all are in wt%), were made in laboratory. Hot bands of 2.2% Si and 1.52% Si with 0.11% P showed recovered grains of very coarse elongated ferrite while that of 1.35% Si steel showed fine ferrite grain of both elongated and fine equiaxed type similar to that of remaining two steels. Grain boundary misorientation and recrystallization study of hot bands before and after annealing indicated nearly complete recrystallization of 1.35% Si and partial recrystallization of Sn and Sb added steels containing low Si. In the case of 2.2% Si and 1.52% Si with 0.11% P steels, the recovered grains were observed mostly containing substructures. The retardation to recrystallization in these two steels has been attributed to the elemental effect of P and high Si. The no-recrystallization temperature (Tnr) of only these two steels were noticed at ≤ 1000 °C. The ϕ2 = 45° and ϕ2 = 90° ODF sections of hot bands indicated that all experimental steels except 1.35% Si steel show magnetically favourable texture components of θ fiber (<001>//ND) and η fiber (<001>//RD) components. The beneficial θ fiber components were also further noticed in cold rolled and final annealed 2.2% Si, 1.44% Si with 0.05% Sb and, 1.52% Si with 0.11% P steels. The presence of the magnetically favourable texture in these steels probably resulted in reduced core loss of these steels while the highest core loss was noticed in 1.35% Si steel. The mechanical properties of final processed steels were also found to be suitable for cold forming and stamping operation during their electrical applications.

Core Structure and Electromagnetic Field Evaluation in WPT Systems for Charging Electric Vehicles

The electromagnetic field (EMF) in a wireless power transfer (WPT) system needs to couple inductively between the primary and the secondary coils through a large air gap, thus giving the system a loosely coupled characteristic. Therefore, magnetically permeable material must be employed to improve the coupling and reduce leakage magnetic flux. However, adding an iron core increases the weight and introduces core loss as a new factor. In this paper, a WPT system model using a lumped circuit model is introduced. Moreover, the relationship between the relative permeability and the coupling coefficient in addition to the core amount (core thickness) and core loss are discussed. Three cores structure named: pot, slotted, and shaped bars cores are investigated using finite element method (FEM) software. Inspired by the investigation results, a new core structure using optimum shaped bars is proposed, the EMF level for reducing core loss in high-power transfer systems and in order to mitigate the EMF exposure to humans is intensively evaluated. The proposed core succeeded in reducing EMF and core loss by about 44% and 30%, respectively. The FEM software and physical prototype were used to validate the proposed optimum core structure. Results showed that 3.5 kW power transferred through a 20 cm air gap with 96% system efficiency(coil–coil).

Fabrication of carbonyl iron powder/SiO2–reduced iron powder/SiO2 soft magnetic composites with a high resistivity and low core loss

Carbonyl iron powder (CIP) and reduced iron powder (RIP) were homogeneously coated with an SiO2 insulating layer by a controlled in-suit chemical deposition procedure and used as raw materials to fabricate CIP/SiO2-RIP/SiO2 (C-R) soft magnetic composites (SMCs) by powder metallurgy techniques. Compared with RIP/SiO2 powders, CIP/SiO2 powders possess a higher SiO2 content and more stable Si-O covalent network. The addition of CIP/SiO2 to the C-R SMCs leads to a significantly increase in the resistivity due to the full electrical isolation of the RIP/SiO2 particles. Transmission electron microscopy analysis confirms that a SiO2 amorphous layer approximately 100–400 nm in thickness grows with a high packing density and adheres tightly to the iron grains, resulting in the effective constraint of electron transfer between the Si and O atoms. Annealed C-R SMCs containing 15–20 wt% CIP/SiO2 have optimum properties with a high resistivity of 4980–6383 μΩ·m and a low core loss of 19.08–23.66 W/kg (50 mT, 100 kHz). The results of this present study provide a significant method to improve resistivity and reduce core loss.

Technical Problems for Core Loss Reduction of High-Speed Motor

This paper describes the technical problems for upgrading efficiency by core loss reduction on high speed motor. These contents are based on the ultra-thin electrical steel sheet for motor core and vector magnetic characteristic technology. It is difficult to get successful results by replace of high performance core materials. Because the utilization technique of these materials is necessary as recipe for research and development of high efficiency high speed motor.

Experimental Evaluation for Core Loss Reduction of a Consequent-Pole Bearingless Disk Motor Using Soft Magnetic Composites

This paper focuses on core loss reduction of a consequent-pole bearingless disk motor using a C-shaped stator core made of soft magnetic composites (SMC). The core loss of the previously built test machine was significantly high, because the C-core has a three-dimensional flux path; therefore, conventional laminated steel cannot be used. In this paper, the solid iron core is replaced by the SMC, and its effectiveness is experimentally demonstrated. The core loss with solid iron, when the bearingless motor is driven at 3000 r/min under no load condition, is 3.8 W, but that with the SMC core is reduced to only 0.6 W. The maximum efficiency with solid iron is 27%, but that with the SMC core is improved to 61%. It is experimentally verified that the SMC core is effective to reduce the core loss and improve the efficiency of the bearingless disk motor with C-shaped stator cores.

SiO2 nanoparticles enhanced silicone resin as the matrix for Fe soft magnetic composites with improved magnetic, mechanical and thermal properties

SiO2 nanoparticles have been introduced into epoxy-modified silicone resin (ESR) via two routes including direct addition (DA) and in-situ growth (ISG). Growth mechanism of the SiO2 nanoparticles has been revealed where chemical bonding forms between the SiO2 and the epoxy, ester and hydroxyl groups of the ESR during ISG. The obtained hybrid resins have been used as the matrix in the fabrication of Fe soft magnetic composites (SMCs). Effects of the SiO2 incorporation method and its content on the magnetic, electrical and mechanical properties of the SMCs have been investigated. Optimized performance of the SMC with large effective permeability (107.9), reduced core loss (1220 mW/cm3) and enhanced mechanical strength (2.95 MPa) can be achieved by introduction of 34 wt% SiO2 nanoparticles into the ESR via ISG. The formation of chemical bonding between the SiO2 nanoparticles and the ESR also gives rise to improved thermal stability for complete stress relaxation of the SMCs.

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.

Incorporation of the Fe3O4 and SiO2 nanoparticles in epoxy-modified silicone resin as the coating for soft magnetic composites with enhanced performance

Three inorganic-organic hybrids have been designed by incorporating epoxy-modified silicone resin (ESR) with SiO2, Fe3O4 and their mixture in the application as the coating of Fe soft magnetic composites (SMCs). The introduced SiO2 nanoparticles are well dispersed in the ESR, while the Fe3O4 tends to agglomerate or even separate from the ESR. Simultaneous addition of the SiO2 and Fe3O4 gives rise to satisfactory distribution of both nanoparticles and optimized magnetic performance of the SMCs with high permeability (124.6) and low loss (807.8 mW/cm3). On one hand, introduction of the ferromagnetic Fe3O4 reduces the magnetic dilution effect, which is beneficial for improved magnetization and permeability. On the other hand, SiO2 incorporation prevents the agglomeration of the Fe3O4 nanoparticles and gives rise to increased electrical resistivity for reduced core loss as well as enhanced mechanical strength of the SMCs.

High-Efficiency High-Power-Density LLC Converter With an Integrated Planar Matrix Transformer for High-Output Current Applications

Isolated high-output current DC/DC converters are critical for future data center power architecture. LLC converters with matrix transformer are suitable for these applications due to its high efficiency and high power density. Different matrix transformer structures are investigated in this paper. To improve the current design practice, a high-frequency transformer loss model is developed and a detailed design methodology is proposed. Moreover, a novel matrix transformer structure is proposed to integrate four elemental transformers into one magnetic core with simple four-layer print circuit board windings implementation and further reduced core loss. By pushing switching frequency up to megahertz with GaN devices, the proposed matrix transformer can achieve high efficiency, high power density, and automatic manufacturing for magnetic components. A 1-MHz 380 V/12 V 800-W LLC converter with GaN devices is demonstrated. The prototype achieves a peak efficiency of 97.6% and a power density of 900 W/in3.

Performance comparison of a spoke‐type PM motor with different permanent magnet shapes and the same magnet volume

This study investigates the characteristics of a spoke-type permanent magnet (PM) motor with one of three magnet shapes, rectangular magnet (RM), trapezoidal magnet (TM), or inverted TM (ITM) in order to compare motor performance for the same magnet volume. The three magnet shapes vary in terms of upper thickness, lower thickness, and width of the magnet. Two-dimensional (2D) finite element method is performed to analyse torque, inductance, core loss, efficiency, and demagnetisation reliability. Advantages and disadvantages of each magnet shape are presented based on the analysis results. The ITM motor shows higher efficiency at its rated load due to the reduced core loss resulting from the decreased armature reaction field coupled with the increased magnetic reluctance circuit of the rotor near the airgap. However, the ITM motor shows lower maximum torque due to the reduced reluctance torque and demagnetisation reliability with a heavy over-current. ITM is thus suitable for applications that require low core loss with small starting torque, e.g. fans, TM is helpful for increasing maximum torque, and RM is appropriate for low-cost applications that require high demagnetisation reliability. Therefore, magnet shape should be carefully considered based on the required specifications of the motor application.

Fuzzy Control of Wind Cage Induction Generator System

A variable speed wind energy conversion system, with squirrel cage induction generator, is reported in this paper. The induction generator is driven by a vertical axis wind turbine and feeds power to utility grid through two double side pulse width modulated converters connected between stator and grid. Fuzzy logic control is used to increase the energy captured from wind, and to increase efficiency by reducing core loss. Transient performance of speed control system is also improved. The generator control system uses three fuzzy controllers. The first fuzzy controller tracks the generator speed with the wind velocity to extract maximum power. The second fuzzy controller programs machine flux for light load efficiency improvement. The third fuzzy controller provides robust speed control against wind vortex and turbine oscillatory torque. The performance of the fuzzy controlled variable speed wind energy conversion system is evaluated through simulation study in MATLAB. Simulation results prove that wind power system with fuzzy control captures more power, has more efficiency and less core loss. Closed loop speed response of the generator with fuzzy controller, shows that fast speed response can be obtained with well designed fuzzy controller.

Two-Stage 48 V-12 V/6 V-1.8 V Voltage Regulator Module With Dynamic Bus Voltage Control for Light-Load Efficiency Improvement

The two-stage 48 V-12 V-1.8 V voltage regulator module (VRM) structure is gaining more and more attention in high-end server applications. The LLC converter is the preferred choice for the first conversion stage because it provides the isolated 12-V output efficiently, which is then converted to 1.8 V by the multiphase Buck converter. Since the CPU works in sleep-mode most of the time, the light-load efficiency is very important for energy saving. This paper proposes to change the primary side of the LLC converter from the full-bridge (FB) configuration into the half-bridge (HB) configuration dynamically in the light-load condition, so that the output of the LLC dc transformer (DCX) can be changed from 12 to 6 V. This will increase the overall light-load efficiency significantly due to the reduced core loss of the LLC DCX and the reduced switching loss of the multiphase Buck converter. To achieve a fast transition of the bus voltage between 12 and 6 V, the capacitance for the intermediate bus is properly selected and the optimal trajectory control for transition between the FB configuration and HB configuration is proposed. A high-efficiency high-density 48–12 /6 V LLC DCX is designed, and experiments on the two-stage VRM demonstrate that there is a fast transient response and a more than 10% light-load efficiency improvement.

Selection of an optimum flux density to offer reduced core loss and its effect on temperature rise of transformers

Commonly used grades for transformer core stampings are Cold Rolled Grain Oriented Steel of grades M3, M4, M5 and M6. As the flux density increases, the magnitude of no load loss and no load current increases. But studies also indicated that, a given magnitude of core loss can be attained with both high and low magnitudes of no load current. This result can be used to ascertain the presence of inferior grade core material. It is essential to operate the transformer in the linear region of BH curve. Operation in saturated state will result in increased no load current which in turn will have a detrimental effect on the temperature rise of transformer as additional I2R losses are generated. With the limits of temperature rise being more stringent in IS standard than in IEC, the choice of flux density is crucial. In this paper an attempt is made to realize the best operational flux density, which gives a benchmark for deciding the magnitude of no load current and the corresponding no load power factor.

Fe-Si/ZrO2 composites with core-shell structure and excellent magnetic properties prepared by mechanical milling and spark plasma sintering

Fe-Si alloy powders were coated with ZrO2 nanopowders via mechanical milling to fabricate Fe-Si (core)/ZrO2 (shell) composite powders. The resultant composite powders were consolidated to magnetic powder cores by spark plasma sintering (SPS). The effects of sintering temperature on microstructure, resistivity and magnetic properties were investigated along with the densification process of the composite compacts. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed that the surfaces of the composite powders were coated with a layer of ZrO2 powders after mechanical milling. Moreover, the polished surface of the sintered composite compacts displayed a micro-morphology of core-shell structure with core of Fe-Si alloy particles and shell of ZrO2 layers indicating that the electric Fe-Si alloy particles were well insulated by the intergranular ZrO2 layers. The Fe-Si/ZrO2 magnetic powder cores with 7.5 wt.% ZrO2 sintered at 825 °C exhibited excellent magnetic properties: 1.43 T for saturation magnetic induction, 220 for maximum permeability and 25.48 Oe for coercivity. The core-shell structured powder cores possessed much higher resistivity and lower core loss (688 μΩ cm and 147 W/kg) than those of the raw Fe-Si powder cores (94 μΩ cm and 471 W/kg). Overall, the preparation process of magnetic powder cores by SPS provides a promising method to reduce core loss and improve magnetic properties of soft magnetic composite materials.

Effect of Al content on magnetic properties of Fe-Al Non-oriented electrical steel

The effects of Al content (0.53≤Al≤9.65wt%) on microstructure, texture, magnetic flux density, permeability, core loss and magnetic domain structure of Fe-Al based electrical steel were measured or observed. Average grain size decreased as Al content increased, but Al contents had no severe effects on texture. Magnetic flux density and permeability tends to decrease as Al content increased. Total core loss Ptot was separated into hysteresis loss Ph, eddy-current loss Pe and anomalous loss Pa. As Al increased, Ph increased, but Pe and Pa decreased, so the optimal grain size increased. To reduce core loss of electrical steel with high resistivity, annealing should be conducted at high temperature and for a long time to increase grain size.

Effect of Aluminium Addition on the Magnetic Properties of a Semi-Processed Electrical Steel

Aluminum is often added to electrical steels since this element causes improvement of the magnetic properties. However the addition of aluminum is usually limited to 0.30 wt%1. Therefore, this work aimed at evaluating the influence of higher levels of aluminum in the magnetic properties of semi-processed steels. To accomplish this, four types of steel were produced in laboratory with different aluminum contents (0.10, 0.30, 0.60 and 1.0 wt%). Carbon, manganese and silicon concentrations were kept constant. It was observed that an increased aluminum content caused reduction of the magnetic core loss, especially of the eddy current component. However, the magnetic permeability virtually wasn't influenced by aluminum concentration.

The Effect of Two- and Three-Level Inverters on the Core Loss of a Synchronous Reluctance Machine (SynRM)

The paper shows the reduction of core losses by using a three-level inverter over a two-level inverter for the same dc-bus voltage and switching frequency. A synchronous reluctance machine stator-core toroid was used in the analysis. Hence, the analysis is realistic as it accounts for mechanical effects through the stator core, and the distorted supply of the line-to-line inverter voltage supplies. The paper also shows the limitations of using finite element-derived excitation; hence, the toroid was directly supplied by the inverter. The reduction of core losses by use of a three-level inverter is significant at very high flux densities and frequencies; approximately 60% lower core losses. Therefore, it can reduce the cooling burden especially in the hard to cool teeth, increase the service life, and allow increased output. The latter is because the output of the three-level fundamental voltage is higher for the same dc-bus and switching frequency at lower machine losses.

Effect of Multilayer Windings With Different Stator Winding Connections on Interior PM Machines for EV Applications

The interior permanent magnet (IPM) machine equipped with a fractional-slot concentrated winding (FSCW) has met an increasing interest in electric vehicle applications due to its higher power density and efficiency. Torque production is due to both PM and reluctance torques. However, one of the main challenges of FSCWs is their inability to produce a high-quality magnetomotive force (MMF) distribution, yielding undesirable rotor core and magnet eddy-current losses. Literature shows that the reduction of low-order space harmonics significantly reduces these loss components. Moreover, it has been previously shown that by employing a higher number of layers, although causing some reduction in the winding factor of the torque-producing MMF component, both machine saliency and reluctance torque components are improved. Recently, a dual three-phase winding connected in a star/delta connection has also shown promise to concurrently enhance machine torque of a surface-mounted PM machine while significantly reducing both rotor core and magnet losses. In this paper, a multilayer winding configuration and a dual three-phase winding connection are combined and applied to the well-known 12-slot/10-pole IPM machine with v-shaped magnets. The proposed winding layout is compared with a conventional double-layer winding, a dual three-phase double-layer winding, and a four-layer winding. The comparison is carried out using 2-D finite-element analysis. The comparison shows that the proposed winding layout, while providing similar output torque to a conventional double-layer three-phase winding, offers a significant reduction in core and magnet losses, correspondingly a higher efficiency, improves the machine saliency ratio, and maximizes the reluctance toque component.

電気機器の高効率化のための低損失化法

電気機器の高効率化のための低損失化法

Loss reduction by combining electrical steels in the core of power transformers

Summary This paper analyzes a practical methodology to assemble/combine commercial electrical steels in a single-phase core-type power transformer. The main advantage of these electrical steel combinations is the reduction of core losses and their associated cost, without compromising the integrity of the transformer. An explanation of the improved performance with a combination of electrical steels in core-type power transformers is presented in this paper. The steel combinations are studied using transient, nonlinear, 3D finite-element simulations, with proper calculation of core losses. Electrical steels in the core are modeled using their magnetization curves. Five commercial electrical steels are considered: four conventional steels (M-6, M-5, M-4, and M-3) and a laser-scribed electrical steel (TRAN-COR H0). From the simulations, the attainable reduction in core losses by means of steel combinations is determined. Results from the simulations are compared with laboratory tests. Finally, 3D finite element static thermal formulations are used to rule out hot spots in the cores made of electrical steel combinations. Copyright © 2015 John Wiley & Sons, Ltd.