Losses In Permanent Magnets Research Articles

Improved Analytical Determination of Eddy Current Losses in Surface Mounted Permanent Magnets of Synchronous Machine

In this paper, we investigate the eddy current losses in permanent magnets of surface mounted magnet synchronous machines. An original analytical method based on the magnetodynamic problem of a conductive ring is introduced and the obtained results are compared with the ones given by 3-D FEM analysis. The analytical model considers the effect of the width on the magnet loss. The axial effect is considered through a correction coefficient. The comparison includes the induced current density, the instantaneous losses, the impact of the circumferential segmentation, and the effect of the frequency on the magnet losses. By focusing on the importance of the skin effect and the magnetic reaction due to the magnet currents, the analytical model provides an accurate determination of the magnet eddy current losses.

A Combined Experimental and Finite Element Analysis Method for the Estimation of Eddy-Current Loss in NdFeB Magnets

NdFeB permanent magnets (PMs) are widely used in high performance electrical machines, but their relatively high conductivity subjects them to eddy current losses that can lead to magnetization loss. The Finite Element (FE) method is generally used to quantify the eddy current loss of PMs, but it remains quite difficult to validate the accuracy of the results with complex devices. In this paper, an experimental test device is used in order to extract the eddy current losses that are then compared with those of a 3D FE model.

Characteristic Analysis for Concentrated Multiple-Layer Winding Machine With Optimum Turn Ratio

Three-phase fractional slot concentrated winding synchronous machines (FCSM) has excellent electrical properties of high torque density, low cogging torque, and torque ripple, yet in armature, as vibration/noise characteristics are not good due to asymmetric MMF, and due to the presence of subspace harmonics in MMF, eddy-current loss of permanent magnet is increased. If multiple-layer winding with optimum turn ratio is applied to three-phase FCSM, this can improve these problems. In this paper, the turn ratio in concentrated multiple-layer winding machine is proposed to be applied. Considering the turn ratio, a general formula is derived to calculate the winding factor. Using the induced formula, the winding factor changes according to the changes in the turn ratio are calculated, and the turn ratio to remove the harmonic components that the MMF has is determined. To verify improvement in the motor characteristics for the proposed method, turn ratio is applied to motors of 16 pole 18 slot and 10 pole 12 slot. For the two models, MMF distribution in the air gap using FEM is calculated, and through harmonic analysis, reduction or removal of a particular harmonic is verified. In addition, through FEM transient analysis, reduced eddy-current loss in permanent magnet is to be identified, and improvements in vibration/noise are to be verified by deformation/acoustic noise analysis of stator.

Investigation of eddy current losses reduction in permanent magnets machines with slots skew optimization and demagnetization effect analysis

The aim of this study is to analyze and investigate some techniques to reduce eddy current losses in permanent magnets. First, a model using Maxwell's equations to analyze eddy current in permanent magnets is presented. Second, the effect of magnet circumferential segmentation on the eddy current losses in case of a surface mounted permanent magnets synchronous machine is investigated. A simple analysis of magnet demagnetization due to its eddy current losses is also studied. In a third step, second technique for reducing eddy current losses is presented. It relates to the stator slots skew, where the best skewing angle is obtained by means of an optimization process using genetic algorithm. A 2D nonlinear finite elements code is developed to achieve the purposes of the presented work.

Secondary Resistive Losses With High-Frequency Injection-Based Self-Sensing in IPM Machines

This paper investigates the impact of high-frequency-injection-based self-sensing on secondary resistive losses associated with the high-frequency carrier component in interior permanent magnet (IPM) machines. Two types of salient machines, a flux-weakening IPM (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</sub> > L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) and a flux-intensifying IPM (FI-IPM, L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</sub> <; L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) are investigated. Simulation with 3-D finite-element analysis is used to analyze the loss characteristics of the machines. Iron loss and eddy-current loss in permanent magnets dominate during high-frequency carrier-signal injection. The magnet eddy-current loss is found to be dependent on the magnet location and to be sensitive to loading, while the iron loss is dependent on stator and rotor structural designs and is less sensitive to loading. The understanding of this characteristic is useful for position and magnet temperature sensing. Experimental evaluation of losses on a built FI-IPM machine is used to evaluate the simulation results.

Influence of slot wedge material on permanent magnet losses in a traction motor with tooth coil windings

Permanent magnet (PM) machines with tooth coil windings are designed and analyzed. We study how the slot wedge material affects the behavior of PM losses when using tooth coil windings, which generate a significant air gap flux density harmonic content. The losses and cogging torques of a surface permanent magnet rotor and an interior permanent magnet rotor are compared in no-load and load situations. A finite element analysis applying Cedrat's Flux2D is made. Motors of this size can have high permanent magnet eddy current losses, and therefore, segmented magnets are often preferred even though interior magnets and semi-magnetic wedge material are used. The study shows that tooth coil windings may benefit from using semi magnetic material as a wedge material as it decreases the stator iron losses and, especially, losses in the permanent magnets.

Effect of DC Supply Voltage on Eddy Current Loss in Permanent Magnet of Permanent Magnetic Synchronous Motor for Electric Vehicle Application

The 2-D time-stepping finite element method is adopted to systematically analyze the effect of DC supply voltage of inverter on eddy current loss in permanent magnet of PMSM for EV application. The finite element model and inverter model are built to calculate the winding currents, eddy current losses in permanent magnet and air-gap flux densities with different DC supply voltages when the motor runs in flux-weakening area. Analysis shows that, the eddy current increases significantly with the increase of DC supply voltage, although the fundamental winding current decreases. The temperature-rise experiment of permanent magnet is carried out, proving the validity of analysis.

Consideration of Eddy Current Loss Estimation in SPM Motor Based on Electric and Magnetic Networks

This paper presents a method for calculating eddy current loss in permanent magnets of a surface permanent magnet (SPM) motor based on electric and magnetic networks. First, an electric network model to calculate the eddy current loss is indicated. Then, to find the resistivity of a Nd-Fe-B magnet, eddy current loss in the magnet is measured by using a test core. Next, a reluctance network analysis (RNA) model of the SPM motor considering the rotor rotation is presented. The eddy current losses in the magnet of the SPM motor from no load to full load conditions are calculated by the RNA model and electric network model. The eddy current losses calculated by the proposed model agree well with the ones obtained from three-dimensional finite-element analysis.

Nonlinear Modeling of Magnetization Loss in Permanent Magnets

Permanent magnets are commonly used in electromechanical energy conversion devices, especially in permanent magnet synchronous machines (PMSM). When designing such devices, it is necessary to take account for the operating conditions of the permanent magnets. Ideally, the operating point of the magnet lies on a linear reversible demagnetization characteristic. Nevertheless, the operating conditions (temperature, demagnetization field, etc.) may have great influence on the magnetic characteristic that becomes strongly nonlinear and may lead to magnetization loss in the magnet. Consequently, the impact is also observed on the electrical machine performances. This paper presents a nonlinear model accounting for magnetization loss of permanent magnets which magnetic characteristic presents knee points in the demagnetization curve. The presented model is applied to analyze the local magnetization loss in magnets of a PMSM.

Coupled 2-D and 3-D Eddy Current Analyses for Evaluating Eddy Current Loss of a Permanent Magnet in Surface PM Motors

To evaluate the eddy current losses of permanent magnets (PMs) in interior PM (IPM) motors accurately within the practical CPU time, we have already proposed a scheme to carry out the 3-D eddy current analysis of only the PM using the temporally varying flux distribution obtained from the 2-D magnetostatic analysis of the motor. In the 3-D eddy current analysis, the compensation field <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> generated by the eddy currents in PM itself only is taken account of. Moreover, the reluctance of the motor except the PM obtained from the 2-D magnetostatic analysis is also taken into account by adding a uniform equivalent gap on the PM. The effectiveness of the coupled 2-D and 3-D analyses was shown using an actual IPM motor. In this paper, the coupled analyses are improved to apply to a surface PM (SPM) motor. Namely, the uniform equivalent gap is improved to a variable equivalent gap in space to take account of the space variation of the gap width between the PM and the stator core. Moreover, the 2-D magnetostatic analysis of the motor is replaced to the 2-D eddy current analysis to take account of not only the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> by PM itself but also that by the neighboring PM. It is shown that the proposed coupled 2-D and 3-D eddy current analyses can improve the accuracies of the eddy current loss distribution in PMs of a SPM motor without increasing the CPU time.

철도차량용 매입형 영구자석 동기전동기의 영구자석 와전류 손실 분석 연구

본 연구에서는 철도차량용 추진시스템에 매입형 영구자석 동기전동기(IPMSM)를 적용하기 위하여 110kW급 고출력밀도 IPMSM을 집중권/분포권 모델로 각각 설계하였다. 집중권 모델은 6극 9슬롯 구조이고, 분포권 모델은 6극 36슬롯 구조이다. 일반적으로 IPMSM의 영구자석에서의 와전류 손실은 슬롯 고조파에 의해 발생된다. IPMSM의 고속 회전 시 와전류 손실에 의한 영구자석의 열적 감자현상은 특히 집중권 IPMSM에서 주요 문제가 된다. 영구자석에서의 와전류 손실을 줄이는 설계는 고속 운전을 필요로 하는 철도차량 추진시스템용 IPMSM 설계에 있어서 중요하다. 그러므로 본 논문에서는 영구자석에서의 와전류 손실을 줄이기 위하여 영구자석을 분할하는 방법을 제안한다. 저자는 영구자석의 분할 개수를 변화시면서 IPMSM 집중권 모델의 영구자석에서 발생되는 와전류 손실의 변화 특성을 분석한다. In order to apply Interior Permanet Magnet Synchronous Motor(IPMSM) to the propulsion system of the railway transit, 110kW class IPMSMs with high-power density are designed as a concentrated winding model and a distributed winding model in this study. The concentrated winding model designed in this study is 6 poles/9 slots and the distributed winding model is 6 poles/36 slots. In general, the eddy current losses in the permanent magnets of IPMSM are caused by the slot harmonics. The thermal demagnetization of the magnet by the eddy current losses at high rotational speed often becomes one of the major problems in the IPMSM with a concentrated windings especially. A design to reduce eddy current losses in permanent magnet design is important in IPMSM for the railway vehicle propulsion system which requires high-speed operation. Therefore, a method to devide the permanent magnet is proposed to reduce the eddy current losses in permanent magnet in this study. Authors analyze the variation characteristics of the eddy current losses generated in permanent magnet of the concentrated winding model by changing the number of the division of the permanent magnets.

Loss Study of a Dual-Air-Gap Axial Flux Permanent Magnet Machine

This paper presents the loss analysis of a dual-air-gap axial flux permanent magnet machine for a flywheel energy storage system. Losses in iron-core and permanent magnets caused by both space harmonics and time harmonics are respectively analysed using a three-dimensional finite element method. The effect of skew of magnets on machine losses is also taken into account. The analysis is validated by comparisons of calculated losses and measured values on a prototype. A solution to reduce eddy-current losses in the magnets for this machine is also presented. The eddy-current losses in the permanent magnets can be significantly lessened by both circumferential and radial segmentations.

Iron loss and eddy-current loss analysis in a low-power BLDC motor with magnet segmentation

Iron loss and eddy-current loss analysis in a low-power BLDC motor with magnet segmentation This paper considers a Brushless Direct Current (BLDC) machine prototype with six poles and 36 stator slots including a three phase double-layered distributed winding. Presented modifications of rotor construction are identified in order to achieve the best possible compromise of eddy-current losses and cogging torque characteristics. The permanent magnet (PM) eddy-current loss is relatively low compared with the iron loss; it may cause significant heating of the PMs due to the relatively poor heat dissipation from the rotor and it results in partial irreversible demagnetization. A reduction in both losses is achieved by magnet segmentation mounted on the rotor. Various numbers of magnet segmentation is analysed. The presented work concerns the computation of the no-load iron loss in the stator, rotor yoke and eddy-current loss in the magnets. It is shown that the construction of the rotor with segmented magnets can significantly reduce the PM loss (eddy-current loss). The eddy-current loss in PMs is caused by several machine features; the winding structure and large stator slot openings cause flux density variations that induce eddy-currents in the PMs. The effect of these changes on the BLDC motor design is examined in order to improve the machine performance. 3-D finite-element analysis (FEA) is used to investigate the electromagnetic behaviour of the BLDC motor.

Analytical Prediction of Open-Circuit Eddy-Current Loss in Series Double Excitation Synchronous Machines

This paper describes an analytical technique for prediction of open circuit eddy-current loss in armature windings and permanent magnets (PM) of series double excitation synchronous machines. First, a 2-D exact analytical solution of open circuit magnetic field distribution in idealized geometry of series double excitation synchronous machine is established. It involves solving Maxwell's equations in stator slots, air gap, PM region, and rotor slots. Then, magnetic vector potential solutions in the stator slots and PM regions are respectively used for prediction of resistance limited eddy currents in armature windings and permanent magnets. This analytical model is then used to estimate eddy-current loss in armature windings and permanent magnets. The validity of the developed model, which is also applicable to conventional designs of permanent-magnet machine, is verified by time-stepped transient finite-element analysis (FEA). The developed model is then used to quantify the effectiveness of segmenting the magnets and armature windings in reducing the eddy-current loss.

Rotor Losses Measurements in an Axial Flux Permanent Magnet Machine

MMF space harmonics and slot openings produce considerable rotor losses in permanent magnet (PM) machines, especially if fractional-slot windings are adopted. This paper aims to measure the rotor losses of a 12-slot 10-pole axial flux phase modulation machine. Both MMF space harmonics and slot openings are considered. The prototype is an axial flux machine with open slots, equipped with three different rotor disks: a disk without PMs, a disk with energized PMs, and a disk with de-energized PMs. A three-layer analytical model is used to interpret the experimental results, e.g., to split the losses in the different parts of the rotor.

Armature Reaction Magnetic Field of Tubular Linear Surface-Inset Permanent-Magnet Machines

This paper presents an exact 2-D analytical model for predicting the armature reaction magnetic field in idealized structures of permanent-magnet tubular linear machines with surface-inset mounted magnets. The armature reaction magnetic field distributions is analytically derived and compared to finite-element analyses. The analytical solution allows the prediction of the machine inductance and reluctance force in closed forms, and facilitates the evaluation of any possible partial irreversible demagnetization of the magnets. It can also be used to estimate resistance limited eddy-current losses in armature windings and permanent magnets. The developed analytical model can be advantageously used for the analysis and design of a class of linear tubular machines.

A study on characteristics of rotor losses for IPMSM considering slot-pole combination

In this paper, we investigated the effect of slot-pole combi nation on rotor loss in interior permanent magnet synchronous machine (IPMSM) with distributed armature windings. In order to study the characteristics of the rotor los ses, two machines for high-speed operation such as electric vehicle were designed. One is fractional slot winding and the other is conventional one. Based on 2-D time-stepped finite element m ethod (FEM) we analyzed both iron loss and eddy-current loss in the permanent magnet of the machines according to their driving conditions. From the analysis results, it was shown that rotor iron loss and eddy-current loss of PM of machine employing fractional slot-winding is definitely large at load condition .

Comparison of Axial Flux PM Synchronous Machines With Different Rotor Back Cores

Rotor losses of axial flux permanent magnet (PM) synchronous machines with fractional windings depend on stator magneto-motive force (MMF) harmonics. To reduce rotor losses, a soft magnetic composite rotor can be used. This paper focuses on the comparison between two machines with the same soft magnetic composite stator and different rotor cores: one of solid steel and another of soft magnetic composite. The study evidenced the composite rotor improved the power density and the efficiency. Moreover, it highlighted a nonlinear salient-pole operation of the composite rotor machine, mainly connected to spatial harmonics.

Further Study on Analytical Model for Iron Losses of Permanent Magnet Machine with Bevelling Magnet

This paper proposes bevelling magnet edges that can reduce iron losses in permanent magnet (PM) machines. The maximum flux density and time rate change of flux density in teeth and yoke are deduced, respectively, considering a random angle of bevelling magnet edges. The analytic models of the average eddy current and hysteresis loss in teeth and yoke are presented respectively. The torque ratio of bevelling 75° and right-angle magnet is 0.983, whereas the ratio of PM material required between two cases is 0.971. Experimental results were proposed to verify the analytic model of total iron losses.

Method for Evaluating the Eddy Current Loss of a Permanent Magnet in a PM Motor Driven by an Inverter Power Supply Using Coupled 2-D and 3-D Finite Element Analyses

To evaluate eddy current losses of permanent magnets (PMs) in motors driven by inverter power supplies in less computation time, we propose the coupled 2-D analysis of the motor and 3-D eddy current analysis of only the PM. In the proposed method, we carry out 2-D nonlinear magnetostatic analysis of the PM motor by rotating the rotor. We then perform 3-D eddy current analysis of only the PM using the temporally varying flux distributions in the PM obtained from the 2-D analysis. For 3-D eddy current analysis, we investigate methods that do and do not consider the compensation field generated by eddy currents. Moreover, for the case in which the compensation field is considered, we demonstrate the method of considering the reluctance of the motor core by the equivalent gap. Finally, we verify the proposed method by comparing results obtained using the proposed method and results obtained by full 3-D analysis for an interior PM motor. We show that the eddy current loss can be estimated in 1/15 of the computation time required for full 3-D analysis when the proposed method takes both the compensation field and the reluctance of motor core into account.