Current Losses In Permanent Magnets Research Articles

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.

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.

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.

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.

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.

권선법에 따른 매입형 영구자석 전동기의 운전특성 분석 및 와전류 손실 저감에 관한 연구

Concentrated IPMSM has advantages in various aspects, such as space ratio, mass productivity, and copper loss, but concentrated winding has a limitation that the eddy current loss of permanent magnets is quite large compared to distributed winding. Eddy current loss means the heat of the rotor and becomes larger during high-speed operation. Therefore, in the concentrated IPMSM that requires high-speed operation, it is essential to design to reduce eddy current loss. In this paper, in order to reduce the eddy current loss of the IPMSM, a shape that increases the reluctance of the q-axis was applied to the rotor, and each was designed by dividing into concentrated winding and distributed winding. The number of pole slots of concentrated winding was selected as 6 poles and 9 slots, and the number of pole slots of distributed winding was selected as 6 poles and 27 slots. Through FEA, the voltammetry limit circle and T-N curve were compared according to each winding method. By comparing the d-axis inductance and q-axis inductance, a model that is advantageous at high speed was confirmed, and the no-load and load characteristics according to the operating speed were compared in detail.

Five-Phase Hybrid Single-/Double-Layer Fractional Slot-Winding PMSM for Torque Improvement Under Third Harmonic Current Injection Condition

A 60-slot/22-pole five-phase machine with hybrid single-/double-layer fractional slot winding is proposed to improve torque under third harmonic current injection condition. Design process of the proposed machine includes two steps of first combining two sets of 20-slot/22-pole machine windings and then shortening coil-pitch. Due to the special structure of the proposed machine, torque-contributing space harmonics in magnetomotive force (MMF) are improved, and redundant space harmonic in MMF which causes high eddy current loss in permanent magnets is suppressed. The proposed machine is evaluated under two modes of third harmonic current injection, namely constant rms and peak harmonic injection. Compared with 20-slot/22-pole machine, the proposed machine achieves higher torque and lower losses under both third harmonic current injection conditions. Besides, the performance of the proposed machine when injecting only the first or third harmonic current is also analyzed.

Analytical prediction of the flux reversal permanent magnet machine with Halbach array magnets in rotor slot considering saturation

This study presents an improved sub-domain analytical model for the characteristic evaluation of the flux reversal permanent magnet machine with Halbach array magnets (FRPMM-HAM) in rotor slot. The influence of iron saturation is considered by equating iron reluctances into airgap. Based on the different material magnetic permeabilities, the FRPMM-HAM is divided into several regions, including slots, permanent magnets (PMs), airgap and so on. By solving the Maxwell equations in polar coordinate for each region according to the boundary conditions, the vector magnetic potential can be derived. According to the vector magnetic potential, the airgap flux density distributions are predicted and the electromagnetic characteristics are calculated. The average magnetic density of the tooth and yoke is combined with the Bertotti model to calculate the iron loss. Besides, the eddy current loss of PMs is also calculated. The accuracy of analytical results is validated via the finite element method (FEM).

A New IPMSM With Hybrid Rotor Structure for Electrical Vehicle With Reduced Magnet Loss

Aiming at the problem of excessive eddy current loss of permanent magnets in fractional slot concentrated winding permanent magnet synchronous motors (FSCW-PMSM) at high speed, a new PMSM with hybrid rotor structure for electric vehicles (EV) is proposed in the article, the key is to introduce additional ferrite magnets in <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> - 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 magnetic flux paths, respectively. Furthermore, slotting on the rotor surface and genetic algorithm (GA) optimization are adopted to compensate for the side effects caused by the introduction of ferrite magnets and to obtain optimal parameters of the new motor. Compared with the traditional all-Nd-Fe-B structure, the proposed hybrid rotor structure can not only curb the magnet loss at high speed, but also present a cost-effective design approach for interior pemanent magnet synchronous motor (IPMSM) for EV applications with less usage of expensive Nd-Fe-B magnets as well as enhanced reluctance torque capability.

Analysis on reducing eddy current loss of axial motor by permanent magnet segmentation

This paper gives the causes of eddy current loss of permanent magnet in axial permanent magnet motor, and puts forward the method of reducing eddy current loss by circumferential and radial combined sectional insulation of permanent magnet. The principle analysis and analytical formula derivation of permanent magnet sectional insulation to reduce eddy current loss are carried out. Finally, Maxwell three-dimensional finite element simulation is used to verify that the circumferential and radial combined sectional insulation of permanent magnet can greatly and quickly reduce the eddy current loss of permanent magnet of axial motor.

Modeling and analysis of a mesh-based equivalent magnetic circuit for a flux switching PM machine

<p indent=0mm>To precisely and efficiently predict the performance of a flux-switching PM machine, this study proposes a novel equivalent magnetic circuit model based on a meshing approach. This method includes developing the cross-shape magnetic meshes and combining the magnetic circuit model with mesh branches. The cross-shape meshes are generated in disordered magnetic fields to self-adaptively represent the flux distributions without magnetic field predelineation. The flux leakage and local saturation can be simultaneously considered. Furthermore, the lumped parameter magnetic circuit model is utilized in the uniform magnetic path region to shorten the computing consumption. The modeling accuracy and efficiency are both guaranteed. Moreover, the original rotor and the rotor with a magnetic barrier are modeled based on the advantage of fixed meshes, which avoids the rearrangement of the structure and efficiently analyzes the electromagnetic performance. The effect of rotor magnetic barrier structure on reducing the eddy current loss of permanent magnet is evaluated quickly and accurately. Finally, the effectiveness of the proposed EMN model is verified via comparison with finite element analysis and experimental tests.

Interior Permanent Magnet Synchronous Motor Design for Eddy Current Loss Reduction in Permanent Magnets to Prevent Irreversible Demagnetization

We designed and analyzed an interior permanent magnet synchronous motor (IPMSM) to prevent irreversible demagnetization of the permanent magnets (PMs). Irreversible demagnetization of NdFeB PMs mainly occurs due to high temperature, which should thus be minimized. Therefore, it is necessary to reduce the eddy current loss in the PM through optimal design. The shape of the rotor core was optimized using finite element analysis (FEA) and response surface methodology. Three-dimensional (3-D) FEA is required for accurate computation of the eddy current loss, but there is huge time, effort, and cost consumption. Therefore, a method is proposed for indirectly calculating the eddy current loss of PMs using 2-D FEA. A thermal equivalent circuit analysis was used to calculate the PM temperature of the optimized model. For the thermal analysis, the copper loss, core loss, and eddy current loss in PMs were estimated and applied as a heat source. Based on the results, we confirmed the stability of the optimum model in terms of the PM demagnetization.

Prediction of Mechanical Loss for High-Power-Density PMSM Considering Eddy Current Loss of PMs and Conductors

This article proposes an indirect method for predicting mechanical loss by considering the eddy current loss of permanent magnets (PMs) and conductors under the no-load condition. The mechanical loss has been conventionally predicted indirectly through experiments and numerical methods. The conventional method uses the no-load loss measured through experiments and the no-load iron loss calculated through a numerical method. With the increase in the demand for high-power-density motors, the PMs with high energy density and winding technology with high fill factor are required. Thus, the proportion of eddy current losses of PMs and conductors is increasing among the electromagnetic losses. Therefore, we propose an indirect method for predicting the mechanical loss considering the eddy current losses. The accuracy of the proposed method is higher than that of the conventional method. Moreover, the proposed method is verified by comparing the estimated efficiency of the specimen obtained by using this method with the measured efficiency.

Analysis of the Eddy Current Losses of Permanent Magnets in Permanent Magnet Synchronous Motors for Electric Vehicles Under Weak Magnetic Conditions

Analysis of the Eddy Current Losses of Permanent Magnets in Permanent Magnet Synchronous Motors for Electric Vehicles Under Weak Magnetic Conditions

Development of spoke-type IPM magnetic gear

Magnetic gears can change output-torque and -speed without any mechanical contacts. Therefore, they have a low acoustic noise and vibration, and their maintainability and reliability are high. Especially, a flux-modulated type magnetic gear is expected to be put into practical use because its torque density is higher than that of other magnetic gears. For the practical use, further improvement of torque and losses is important, especially, reduction of eddy current loss in permanent magnets (PMs) due to asynchronous harmonic magnetic fluxes is necessary. This paper investigates an interior permanent magnet (IPM) structure to improve the efficiency by reducing the eddy current loss in PMs. In addition, this paper presents a method for increasing torque of the IPM magnetic gear by changing a position of magnetic-bridge.

Multiphysics modelling of a hybrid magnetic bearing (HMB) for calculating power loss and temperature with different loss minimization strategies

This paper represents a multiphysics modelling for calculating loss and temperature of a hybrid magnetic bearing (HMB) using finite element method (FEM). It also addresses the different loss minimization strategies for the HMB. The main sources of losses are identified as eddy current loss in permanent magnets, flywheel and copper loss in electromagnet. Due to these losses, the temperature distribution in different portions of HMB is computed using coupled field analysis. To minimize the eddy current loss, slits are fabricated in flywheel plate instead of a solid flywheel. The improvement of the control current is investigated by providing a coating of different metal, like copper, brass and stainless steel on the flywheel. A zero bias current (ZBC) scheme has been introduced where no bias current is required to levitate the rotor or to avoid singularity due to external disturbances, thus reducing the copper loss.

Loss estimation of magnetic gears

Reduction in losses is essential for the efficiency enhancement of magnetic gears. In this paper, the power losses of a coaxial magnetic gear are estimated, based on a developed convenient approach for loss analysis using a time-dependent finite element model. The results are confirmed by a sophisticated measurement system for magnetic gear testing. Eddy current losses in permanent magnets and magnetic cores, magnetic flux reluctance and harmonic distortion in magnetic materials during magnetic gear operation are determined. The output torque reduction, especially at high rotational speeds and high gear ratios caused by losses, is analyzed. Different permanent magnet material grades are utilized in order to evaluate the eddy currents and the torque transmission losses during the magnetic gear performance.

Eddy Current Calculation of a High-Speed Slotted Machine With Halbach Magnetization at No-Load Condition

The eddy current and the eddy current loss in permanent magnets (PMs) are important factors in high-speed machine design and performance prediction. The eddy current loss is related to the magnetic field, the shape of magnets, and rotating speed. In this article, the eddy current is analytically calculated with a 2-D method in a high-speed machine with the Halbach magnetization. This analytical method calculates the eddy current with two parts: one part is induced by the instantaneous radial flux density and the other part is induced by instantaneous tangential flux density. The instantaneous radial and tangential flux densities are varying in the PM when the rotor rotates. The flux density in the PM is calculated by the 2-D complex relative permeance method with the SC-Toolbox aid. When the slotted machine operated at no-load condition, the eddy current is analytically calculated in this article based on the instantaneous flux density, and the eddy current distribution in the magnet is compared with the finite-element method (FEM) solutions, the comparison shows that the 2-D analytical method is an effective method for the eddy current and eddy current loss calculation. In the slotted machine with the Halbach magnetization, the eddy current loss increases with the arc angle of the main segment magnet increases, the eddy current loss increases fast at high speeds and cannot be ignored, but Halbach magnetization can reduce it in the high-speed machine as long as the magnetization parameters are chosen properly.

Research on the Influences of Time Harmonics on Permanent Magnet Synchronous Motors with Hybrid Magnet Poles

With the development of electric electron technology and controlling technology, controller for driving permanent magnet synchronous motors is used widely. The using of a controller can expand the motor speed range and improve motor runtime performances. However, the output current of a controller contains lots of time harmonics that will have bad influences on motor torque and losses. In order to analyze the influences of the time harmonics on the motor performances, different time harmonic currents were injected into the motor armature. Taking a 750 W, 250 r/min permanent magnet synchronous motor with hybrid magnet poles (HPPMSM) as an example, the 2-D finite model was established. On this basis, the torque ripple and eddy current losses of permanent magnets with different time harmonics were obtained. The influences of time harmonics on motor torque ripple and eddy current losses were determined, and the impacting mechanism was revealed. The analyses may be helpful for the optimal design of HPPMSM.