Magnet Eddy Current Loss Research Articles

Heat transfer study on a stator-permanent magnet electric motor: A hybrid estimation model for real-time temperature monitoring and predictive maintenance

When electrical machines operate without a specific cooling system, the surrounding environment plays a crucial role in the rise of temperature and the duty cycle of operation. More clearly, a natural convection cooling system with a low value of heat transfer coefficient carries the risk of thermal breakdown, insufficient safety, and reliability. This paper studies the heat transfer aspects of a low-power flux switching permanent magnet (FSPM) motor under natural convection cooling to implement a novel real-time sensor-less temperature monitoring system. Thermal and electromagnetic experiments are carried out to create foundations for transient and steady-state numerical models. A data-driven, deep learning algorithm estimates the core and permanent magnet (PM) eddy current losses in real-time, besides the already available copper and friction losses. Subsequently, a two-node thermal equivalent circuit in a hybrid model with a feed-forward neural network estimates the dynamic temperature profile of windings and PMs. It is indicated that the worst-case estimation error is below 7.5%, and the configuration is applicable under a wide range of operation states and environmental conditions. Lastly, the system, including the power source, FSPM motor, and hybrid temperature estimation unit, will be implemented in MATLAB/Simulink to investigate the fault prediction and operation management capabilities.

Analysis and Efficient Calculation of the Magnet Eddy Current Loss of PMSM

Analysis and Efficient Calculation of the Magnet Eddy Current Loss of PMSM

High-performance CeFeCo/FeSiAl soft magnetic composites for megahertz power devices

Soft magnetic composites (SMCs) play a crucial role in modern electronics and electrical devices, for which challenges remain in maintaining magnetic performance and reducing loss at megahertz (MHz) frequencies. Here, CeFeCo/FeSiAl@ polyurethane (PU) SMCs have been rationally designed with the simultaneous achievement of large relative permeability, high domain-wall resonance frequency, and low power loss. As a rare-earth soft magnetic alloy, the CeFeCo is promising for high-frequency applications due to its easy-plane anisotropy, whereas FeSiAl is advantageous with increased electrical resistivity as well as approaching-zero magnetocrystalline anisotropy and magnetostriction. Hot pressing has been adopted to achieve a dense and homogeneous distribution of CeFeCo and FeSiAl powders in the PU for reduced magnetic dilution and eddy current loss. The resultant SMCs exhibit optional soft magnetic performance with large relative permeability of 21.0, low power loss of 3677.5 kW·m−3 at 5 MHz, and high domain-wall resonance frequency of 386.1 MHz. As such this work provides insights into the design of high-frequency SMCs incorporating novel rare-earth soft magnetic alloys.

Hierarchical etching-assembly engineering of Fe-based composite microspheres with balanced magnetic-dielectric synergy towards ultrahigh electromagnetic wave absorption

Hierarchical engineering of magnetic-dielectric composite microspheres has attracted increasing attention owing to its potential to enhance electromagnetic wave absorption (EMA) through magnetic-dielectric synergy. However, optimizing magnetic-dielectric balance in composite microspheres at the nanoscale remains a formidable task due to their limited component optimization and microstructural regulation. Herein, a novel approach is proposed to modify conventional carbonyl iron powder (CIP) microspheres via synergistic etching-assembly strategy. By applying a polydopamine coating, successive tannic acid (TA) etching-assembly, and pyrolysis, hierarchical iron@carbon-1/N-doped carbon (Fe@C-1/NC) composite microspheres are obtained. This overcomes the drawbacks of CIP microspheres, including their high density and poor impedance matching, which hinder EMA performance. Hierarchical carbon layer engineering can introduce abundant dipole centers, heterogeneous interfaces, and conductive networks to induce dielectric loss, while magnetic components contribute to magnetic resonance and eddy current loss, as demonstrated by the results. Accordingly, Fe@C-1/NC composite microspheres demonstrate a minimum reflection loss (RLmin) of −70.7 dB and an effective absorption bandwidth of 3.75 GHz at a matching thickness of 2.3 mm. Generally, this work paves the way towards CIP engineering to provide guidance to the future exploration of hierarchical magnetic-dielectric EMA materials.

Why state-of-the-art analytical models for eddy current losses in PM of PMSM are insufficient for variable speed motors

This is the third paper in a series on novel methods for calculating eddy current losses in permanent magnets (PM) and the shortcomings of previously conducted analyses. In the first paper, Ruoho’s work on homogeneous materials was discussed. The distribution of fields has been expanded to include the reaction field of the eddy currents within the permanent magnets. This approach was based on the methods of the harmonic complex AC calculation. In the second paper, the models were expanded to enable a harmonic calculation of eddy current losses in permanent magnets for homogeneous fields including the effects of eddy current losses in an adjacent ferromagnetic material, leakage flux factors, and source behavior. In this third and final publication, a look at state-of-the-art analytical models will be taken. With regard to the results of the second publication of this series, it can be shown that established analytical models are insufficient when calculating inverter-related eddy current losses in permanent magnets of permanent magnet synchronous machines (PMSM). Furthermore, a short introduction to eddy current loss mechanics in permanent magnets of PMSM will be given.

Chemical surface modification for the preparation of MgO cladding to enhance magnetic properties of Fe-Si-Nb-B-Cu nanocrystalline soft magnetic composites

This study employed chemical synthesis and decomposition techniques to fabricate MgO insulation coating on the surface of nanocrystalline soft magnetic powder. It was found that this coating effectively suppresses the time lag effect in the magnetization process of soft magnetic materials under high-frequency alternating magnetic fields, consequently reducing the overall losses of soft magnetic composite materials by mitigating the time-dependent effects during magnetization. Specifically, at an MgO content of 0.8 wt%, the power losses of nanocrystalline soft magnetic composite materials decreased from 519.13 kW/m3 and 3665.78 kW/m3 to 277.69 kW/m3 and 2718.3 kW/m3 respectively, under alternating magnetic fields with magnetic induction strengths of 20 mT and frequencies of 1 MHz and 3 MHz. The MgO insulation coating effectively mitigated the relaxation phenomenon in the dynamic hysteresis loops of nanocrystalline soft magnetic composite materials within dynamic magnetic fields, reducing the adverse effects of internal eddy currents in high-frequency alternating magnetic fields, thereby confirming the close relationship between magnetic hysteresis losses and eddy current losses in soft magnetic composite materials. Additionally, with the increase in MgO content, there was a significant improvement in the quality factor of nanocrystalline soft magnetic composite materials, showing a decreasing trend in the imaginary part of the complex permeability, which reflects the magnitude of power losses. Furthermore, the positive response of MgO coating in enhancing DC superimposition performance and reducing inductance impedance values has been validated, underscoring its crucial role in improving the stability of circuit systems.

Fabrication of Fe-Based Nanocrystalline Powder-Pressed Magnetic Core and Application to Planar Reactor for Hundreds of kHz or Beyond

In this study, to decrease coercivity and iron loss for the Fe-Si-B-Nb-Cu-C nanocrystalline powder-pressed magnetic core for hundreds kHz or beyond, a post annealing after pressing the Fe-Si-B-Nb-Cu-C amorphous powder was executed for nanocrytallization and release of the residual strain induced through the pressing the powder. In addition, novel fabrication procedure for obtaining the small coercivity powdered magnetic core was proposed. It was found that the fabricated Fe-Si-B-Nb-Cu-C nanocrystalline powdered magnetic core exhibited a saturation magnetization of 0.91 T, coercvity of 123 A/m, relative permeability of 32.5 and iron losses of 105 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> at 100kHz, 50mT and 2194 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> at 1MHz, 50mT. From the iron loss break-down for the fabricated Fe-Si-B-Nb-Cu-C nanocrystalline powdered magnetic core, its hysteresis and eddy current losses were smaller than those of Fe-Si-B-C-Cr powder-pressed magnetic core. In addition, a planar reactor was fabricated using the powder-pressed magnetic core, which had a size of 47×44×16 mm, DC coil resistance of 7.3mΩ, inductance of 12.1 μH, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor of about 127 at 1MHz and inductance drop of 4.1% at a superimposed DC current of 30A.

PM Eddy-Current Loss Reduction of Axial Flux PM Wheel Motor With Arc Incompletion Segmentation

The high permanent magnet (PM) eddy-current loss will inevitably cause the risk of irreversible demagnetization, and the PM complete segmentation (CS) method is a common method to reduce the PM eddy-current loss. However, PM CS design will increase the cost and difficulty of assembly process, especially for axial flux PM (AFPM) machines. To address this issue, a new arc incompletion segmentation (AIS) method is proposed to reduce the PM eddy current loss and cost, including double-side AIS and single-side AIS designs. Then, some of the key parameters are optimized. In addition, the PM eddy current loss, cost, and torque performance are studied and compared with different segmentation methods under different conditions based on 3-D finite element method (FEM). Finally, two different 25kW prototypes are manufactured and tested to validate the proposed method and analysis.

Lumped model for the calculation of harmonic eddy current losses in permanent magnets for homogeneous flux distributions considering eddy current reaction flux

This is the first of a series of papers on novel methods for the calculation of eddy current losses in permanent magnets (PMs) and the shortcomings of previously conducted analyses. Eddy current losses in PMs and their mitigation are significant factors when designing inverter-fed electric drives. Especially with the need for drives with high power density, a trend toward increased rotational speeds and, therefore, higher fundamental frequencies and inverter switching frequencies are observable. Higher harmonic frequency components of concentrated windings and fractional slot windings are widely taken into account when designing rare sintered earth magnets for permanent magnet synchronous machines (PMSMs). However, inverter-related losses are rarely simulated in Finite Element Method (FEM) co-simulations and can contribute as a major factor to the power losses in PMSMs. In the worst case, this neglection can lead to the thermal demagnetization of the permanent magnets. Segmentation provides an effective measure to limit eddy current losses. However, not every kind of segmentation proves effective in a drive application. Depending on the frequency behavior of the magnetic flux in a permanent magnet, segmentation can increase eddy current losses within the magnet compared to a non-segmented magnet. This behavior is due to the reaction to the flux caused by the eddy currents within the magnet. The reaction of the eddy currents is often neglected [1, 2], and, in other cases, the vicinity of ferromagnetic material is neglected in analytical calculations [3] but proves crucial for the exact calculation of higher frequency losses [4, 5]. In this paper, an analytical solution to calculate harmonic eddy current losses in permanent magnets, including the reaction flux with homogeneous excitation, is given.

Lumped model eddy current analysis of influence factors on PM segmentation effectiveness

This is the second of a series of papers on new methods for the calculation of eddy current losses in permanent magnets (PMs) and the shortcomings of previous analyses. Our first paper extended Ruoho’s work on harmonic field distributions to the reaction field of eddy currents within permanent magnets. The approach was based on the methods of the harmonic complex AC calculation. In this paper, the models presented in our previous paper are further extended to allow a harmonic calculation of eddy current losses in permanent magnets for homogeneous fields, including the effects of eddy current losses in an adjacent ferromagnetic material, leakage flux factors, and non-constant inductance.

Performance Improvement of Flux Switching Permanent Magnet Wind Generator Using Magnetic Flux Barrier Design

Flux-switching permanent magnet (FSPM) machines have attracted significant research attention in the field of wind power generation. In this study, the utilization of a magnetic flux barrier to improve the performance of the nine-phase FSPM generator designed for low-speed wind power applications is conducted. The proposed approach involves introducing magnetic flux barriers of different topologies to the conventional FSPM generator and analyzing their performance using 2D finite element simulations. Results suggested that |-shaped magnetic flux barriers exhibited the highest performance among other topologies, making them the appropriate choice for this generator. The geometry of the |-shaped flux barriers was further optimized using response surface methodology to maximize the generator’s performance. The proposed generator exhibits a significant decrease in cogging torque, achieving a remarkable reduction of up to 23.7%, while maintaining electromotive force. Moreover, it shows a significant decrease in permanent magnet eddy-current loss, with a noteworthy reduction of up to 51%. Additionally, significant improvements were demonstrated in terms of electromagnetic torque, torque ripple, output power, and efficiency. Details on the physical reasoning behind these improvements have been provided. Overall, the proposed FSPM generator with inserted flux barriers has the potential to meet the demands of low-speed wind power generation effectively.

Particular Model for Efficient Switching Frequency Loss Consideration in Surface Mounted Permanent Magnets

The paper proposes a particular modeling procedure for efficient switching frequency loss consideration in surface mounted permanent magnet rotors in cases of PWM supply. The model is based on 2D finite element analysis combined with circuit equations in the permanent magnet regions enabling end effects consideration associated with the switching frequency, which is responsible for the major part of eddy current losses in the magnets. The model’s accuracy is validated through measurements in a magnetic circuit. Comparison between measured and simulation losses by implementing a traditional loss separation analysis has illustrated the relative dominance of switching frequency eddy current losses in permanent magnets and the feasibility of the proposed methodology.

Lightweight cementite/Fe anchored in nitrogen-doped carbon with tunable dielectric/magnetic loss and low filler loading achieving high-efficiency microwave absorption

Magnetoelectric composites have promising application in electromagnetic wave absorption for their regulatory structures and interfacial interactions. In this research, a facile one-step pyrolyzing procedure was applied to achieve cementite/Fe nanoparticles anchored on nitrogen-doped carbon nanotubes (Fe3C/Fe/N-CNTs) composites. Fe3C/Fe encapsulated in nitrogen-doped carbon was generated through in-situ Fe-catalyzed carbothermal reactions.The obtained magnetoelectric composites displayed excellent microwave absorption properties with a minimum reflection loss of −54.4 dB at 10.4 GHz, a matching thickness of 2.3 mm, and low filler loading (15%). Moreover, even at a low matching thickness of 1.55 mm, the reflection loss was less than −10 dB in the range of 13.7–18.0 GHz, and an effective absorption bandwidth of 4.3 GHz was achieved. The outstanding microwave absorption performance can be summarized as follows. 1) The CNT network enriches the transmission path, enhancing the dielectric loss capability. 2) The hollow one-diameter CNT structure helps strengthen interfacial polarization, optimizing the impedance matching while promoting multiple reflections and scattering. 3) Magnetic Fe3C/Fe provides a strong magnetic dissipation ability and eddy current losses. 4) The heterogeneous magnetoelectric Fe3C/Fe/N-CNTs possess multiple interfaces, increasing the interfacial polarization and electromagnetic synergistic losses. This study provides a potential strategy for the large-scale synthesis of low filler loading magnetic–dielectric microwave absorbers.

Study on leakage magnetic field and magnetic field shielding for transformers

This paper deals with the leakage magnetic field calculation and magnetic field shielding design of transformers. A large-capacity traction transformer is firstly established, and its magnetic flux density and eddy current loss of the transformer tank are calculated by the layered subdivision method and the surface impedance method. To reduce the eddy current loss of the tank, plate-shaped magnetic shielding and electromagnetic shielding are installed on the surface of the tank. And the simulation results show that plate-shaped magnetic shielding has better shielding effectiveness compared with electromagnetic shielding. Then based on the plate-shaped magnetic shielding, the tile-shaped magnetic shielding is proposed to further reduce the magnetic flux density and loss of the tank. By analyzing the shielding effect of tile-shaped shielding at different heights and widths, the tile-shaped shielding structure with the best shielding effect is obtained. Finally, the advantages of tile-shaped shielding are verified by magnetic-thermal coupling analysis.

Torque analysis and stator windings influence research on negative-salient permanent magnet synchronous motor

Compared with the traditional motor, the negative-salient permanent magnet synchronous motor (NSPMSM) has the characteristics of wide-speed range, strong overload capacity and uneasily demagnetized permanent magnet. In this paper, a new rotor structure of NSPMSM is proposed by using magnetic bridge to increase the d-axis inductance (Ld) and W-type permanent magnet to decrease the q-axis inductance (Lq). Firstly, the electromagnetic torque performance of NSPMSM was analyzed from the parameters of permanent magnet (PM) thickness, magnetic bridge length, eccentricity distance and air-gap length using finite element method. At the same time, the electromagnetic torque ripple and cogging torque of the NSPMSM are further analyzed, which provides an effective basis for evaluating the optimal performance of the NSPMSM. Secondly, the effects of different stator slots and different winding layers on the air-gap magnetic flux density, electromagnetic torque, power and eddy current loss of PM of the NSPMSM were analyzed by finite element method under the condition of same rotor. The advantages and disadvantages of different windings are summarized, and the constant-power speed range of the NSPMSM is calculated, which provides the basis for the study of the flux weakening properties of the new motor. The results of theoretical analysis agree with those of simulation analysis, which verifies the effectiveness and feasibility of the new motor.

Simultaneous enhancement of coercivity and electric resistivity of Nd-Fe-B magnets by Pr-Tb-Al-Cu synergistic grain boundary diffusion toward high-temperature motor rotors

To high-power permanent magnetic motors, it is critical for Nd-Fe-B magnets to maintain the desirable coercivity at high-temperature operating conditions. To address this, two approaches have been proven effective: (1) enhancing the room temperature coercivity; (2) reducing the eddy current loss. However, these two items are difficult to be simultaneously achieved. Here, the grain boundary diffusion (GBD) of the Pr-Tb-Al-Cu-based source is applied to enhance the coercivity and electric resistivity at room temperature from 1101 kA m-1 and 2.13 × 10–6 Ω m to 1917 kA m-1 and 2.60 × 10–6 Ω m, and those at 120 °C from 384 kA m-1 and 4.31 × 10–6 Ω m to 783 kA m-1 and 4.86 × 10–6 Ω m, respectively. Such optimization is ascribed to the improved formation depth of Tb-rich 2:14:1 shells with large magnetocrystalline anisotropy and the increased intergranular Pr-based oxides with high electric resistivity, induced by the coordination effects of Tb and Pr, as proven by the atomic-scale observations and the first principles calculations. It thus results in the simultaneously improved output power and energy efficiency of the motor because of the combination of magnetic thermal stability enhancement and eddy current loss reduction, as theoretically confirmed by electromagnetic simulation.

Research on Motor Rotor Loss of High-Speed Air Compressor in the Application of Hydrogen Fuel Cell Vehicle

As an important component of hydrogen fuel cell vehicles, the air compressor with an air foil bearing rotates at tens of thousands of revolutions per minute. The heat generation concentration problem caused by the high-speed motor loss seriously affects the safe and normal operation of the motor, so it is very important to clarify the loss distribution of the high-speed motor and adopt a targeted loss reduction design for air compressor heat dissipation. In this paper, for an air compressor with a foil bearing with a rated speed of 80,000 rpm, an empirical formula and a three-dimensional transient magnetic field finite element model are used to model and calculate the air friction loss, stator core loss, winding loss and permanent magnet eddy current loss. The accuracy of the analytical calculation method is verified by torque test experiments under different revolutions, and the average simulation accuracy can reach 91.1%. Then, the distribution of the air friction loss, stator core loss, winding loss and eddy current loss of the air compressor motor at different revolutions is obtained by using this method. The results show that the proposed method can effectively calculate the motor rotor loss of a high-speed air compressor with air foil bearing. Although the motor efficiency increases with the increase in motor speed, the absolute value of loss also increases with the increase in motor speed. Stator core loss and air friction loss are the main sources of loss, accounting for 55.64% and 29% of the total motor loss, respectively. The electromagnetic loss of winding, the eddy current and other alloys account for a relatively small proportion, which is 15% in total. The conclusions obtained in this paper can effectively guide calculations of motor loss the motor heat dissipation design of a high-speed air compressor with an air foil bearing.

A New Optimized IPMSM for EVs With Reduced Magnet Loss for Over-Modulation Operation

In the traction motor drives of electric vehicle applications, the over-modulation strategy is usually implemented to enhance the output torque capability of the interior permanent magnet synchronous motor (IPMSM), so that the dc input voltage of the inverters can be fully utilized by operating the inverter up to the six-step mode. However, it will inevitably introduce rich harmonic components into phase current, leading to the worsening issue of magnet eddy-current loss (MECL). Therefore, a new hybrid magnet rotor structure for fractional-slot concentrated-winding IPMSM with optimum design for magnet loss reduction is employed with the vital improvement measures concluded as follows: first, high-resistivity ferrite magnets are introduced in the rotor flux paths of the <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 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis, respectively, to form a hybrid magnets rotor structure together with Nd–Fe–B magnets; second, a rotor structure is proposed by employing a V-type placement of Nd–Fe–B magnets in the <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 path with the angle of V-type as one of the critical optimization parameters. An optimized design is finally obtained by employing the multi-objective genetic algorithm optimizer in JMAG finite element analysis tools, which is tested to show that the MECL produced in the over-modulation operation can be significantly suppressed by the optimized design.

Rotor Loss Analysis of an External Rotor High‐Speed Permanent Magnet Motor Considering Current Harmonics and Thermal Analysis under High‐Temperature Gas

AbstractThis paper presents a strategy for direct‐driving a turbine with an external rotor high‐speed permanent magnet motor. It is used to improve the large footprint, low efficiency, high maintenance costs, and high vibration risk of turbines. Combining the characteristics of the working conditions of pipeline gas transmission, this paper takes a 200 kW, 10 000 rpm external rotor high‐speed permanent magnet motor as an example. This paper analyzes the eddy current losses in the rotor due to the armature magnetomotive force generated by the stator fundamental and harmonic currents. To reduce eddy current losses in permanent magnets, a circumferentially segmented pole structure is proposed for theoretical comparison and FEA with common surface‐mounted pole structures under different loads and work angles. The results confirm that the circumferentially segmented pole can effectively reduce the eddy current loss of the permanent magnet rotor. The effect of variations in the pole arc coefficient on eddy current losses in permanent magnets is also analyzed. Finally, the temperature field simulation of the motor is carried out under consideration of wind mill losses. By setting up three comparison groups with different conditions, this paper analyses the influence of the temperature and flow rate of the gas on the temperature rise and heat dissipation of the motor in a high‐temperature gas environment. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Optimization of Disk Magnetic Coupler Based on Orthogonal Test and Multiobjective Genetic Algorithm

In order to solve the optimization problem of the disk magnetic coupler, the two optimization schemes, the orthogonal test and multiobjective genetic algorithm, were used to optimize the disk magnetic coupler to maximize the magnetic torque while reducing the eddy current loss, and then the correctness of the optimization results was verified by electromagnetic simulation experiments. The eddy current loss and magnetic torque of the optimized disk magnetic coupler were normalized by using the comprehensive evaluation function. After orthogonal test and multiobjective genetic algorithm optimization, the comprehensive evaluation value of the disk magnetic coupler increased by 2.43 times and 3.30 times, respectively, and the optimization effect of multiobjective genetic algorithm is more significant. The relative errors between theoretical and simulated values of the maximum magnetic torque and eddy current loss by multiobjective genetic algorithm are 2.22%–4.72% and 1.13%–6.41%, respectively, suggesting that the optimization method is feasible. The research results show that the multiobjective genetic algorithm optimization can significantly improve the performance of magnetic disk coupler, which can provide theoretical and technical basis for the design of disk magnetic coupler.