Current Losses In Permanent Magnets Research Articles

Analysis of Multi-Phase and Multi-Layer Factional-Slot Concentrated-Winding on PM Eddy Current Loss Considering Axial Segmentation and Load Operation

The effects of multi-phase and multi-layer windings of the 12-slots 10-poles surface-mounted permanent magnet synchronous machines (SPMSMs) on eddy current losses in permanent magnets (PMs) are mainly investigated using the 3-D finite element analysis in this paper. Eddy current losses in PMs considering its axial segmentation are also analyzed. It is demonstrated that dual three-phase four-layer (DTP-FL) winding layout has the minimum value of eddy current losses in PMs, when segmentation number $N = 4$ . It is because DTP-FL winding has smaller magnitude of high-order magnetomotive force harmonics relative to other four winding layouts. The average torque and torque ripple changing with multi-phase, multi-layer, and axial segmentation are also studied. Finally, the no-load and load experiment platform for an axial flux integrated-starter generator with DTP-FL winding and radial segmented PM are established in order to validate the proposed method under power generation mode.

Electromagnetic Performance Analysis of Hybrid Excited Segmental Rotor Flux Switching Machine

Due to the special rotor configuration, the coil flux linkage of permanent magnet (PM) excited segmental rotor flux switching machine (SRFSM) can be considered as the sum of the flux linkages produced by each of the adjacent PMs. Then, the hybrid excited SRFSM is obtained by replacing one PM in every pole pair by field winding to obtain high magnetic field regulation capacity. The configuration and operational principles are first discussed. To reduce the computation time, the analytical model of hybrid excited SRFSM with the subdomain method is developed. The electromagnetic performances such as the flux linkage, back electromotive force, electromagnetic torque, and eddy current loss in PM and rotor support are investigated using the analytical model. Furthermore, the effect of machine parameters on the torque ripple and average torque, and the effect of field current density on the flux weakening capability are also analyzed. The analytical results are verified by the finite-element method and prototype machine experiments.

Design and Analysis of Halbach Ironless Flywheel BLDC Motor/Generators

Halbach array-based permanent magnet (PM) brushless machines exhibit attractive features when compared with conventional PM brushless machines with normal segmented magnets, including the flux-concentration effect, essentially sinusoidal air-gap flux density due to PMs, and negligible cogging torque. However, as for a motor/generator used in flywheel, an external rotor composed of Halbach array and rotor back-iron is necessary to increase the inertia of flywheel system, which is different from the conventional external-rotor machines. In this paper, a Halbach array PM motor is studied compared with the radial magnet array. The relationship between the air-gap field distribution and the magnet array is discussed. Finally, the eddy current loss in PMs of the external-rotor ironless brushless dc motor is analyzed between the Halbach PM motor and the conventional PM motor.

A Coupled Method for Evaluating Eddy Current Loss of NdFeB Permanent Magnets in a Saturated Core Fault Current Limiter

Eddy-current loss of NdFeB permanent magnets (PMs) is widely analyzed in PM motors. This paper proposes a coupled 2-D transient finite-element analysis (FEA) of the saturated core fault current limiter (SCFCL) and 3-D analytical model of PMs to evaluate eddy-current loss in SCFCL. The comparison between the result from coupled method and that from 3-D FEA verifies the applicability of the coupled method in analyzing eddy current loss of PMs in SCFCL. The 3-D analytical model of PM is applied to analyze the effect of segmentation on the reduction of PM's eddy-current loss. And the results show that segmentation along width has a better performance, which is also verified by 3-D FEA.

Eddy current losses in permanent magnets of surface mounted permanent magnet synchronous machines\u2014Analytical calculation and high order finite element analyses

Permanent magnet exited synchronous machines always show three significant portions of their losses: Iron losses within the magnetic circuit, power losses within the stator winding and finally eddy current losses within the permanent magnets. In particular, surface mounted magnets are directly exposed to asynchronous components of the air-gap field caused by either higher harmonic waves or higher time harmonics. Analytical calculation of the eddy current losses within the permanent magnets for both linear as well as cylindrical arrangements describe fundamental characteristics in dependence on only few significant parameters. These results serve as reference results for detailed numerical calculations using the finite element method, too. The finite element analyses with various formulations of the shape functions show the significant influence of the higher order elements on the accuracy of the eddy current losses. Additionally, the effects of a various pole coverage can be obtained from the results of the numerical calculations. Therefore, a clear summary of the significant parameters influencing the eddy current losses within the permanent magnets for both linear as well as cylindrical arrangements will be established.

Analysis on Harmonic Loss of IPMSM for the Variable DC-link Voltage through the FEM-Control Coupled Analysis

This paper describes the loss analysis based on load conditions of the air conditioning compressor motors using variable dc-link voltage. The losses of PMSM (Permanent Magnet Synchronous Motor) should be analyzed by the PWM (Pulse Width Modulation) output of inverter. The harmonic loss by the PWM cannot consider that using the current source analysis of the inverter. In addition, when the voltage of dc-link is variable with the condition of variable speed and load conditions in motor, the losses of motor are also changeable, however it is hard to analyze those losses by only electromagnetic finite element method (FEM). Therefore, this paper proposes the analysis method considering the carrier frequency of the inverter and the varying state of the dc-link voltage through the FEM-control coupled analysis. Using proposed analysis method, additional core loss and eddy current loss of permanent magnet caused by PWM could be analyzed. Finally, the validity of the proposed analysis method is verified through the comparison the result of coupled analysis with experiment.

A five-phase 20-slot/18-pole PMSM for electric vehicles

Purpose – The purpose of this paper is to investigate a five-phase permanent-magnet synchronous machine (PMSM) that features high-power density and high-fault-tolerant capability for electric vehicles (EVs). Design/methodology/approach – The five-phase 20-slot/18-pole PMSM is designed by finite-element method. Two typical rotor structures which include Halbach array and rotor eccentricity are compared to achieve sinusoidal back electromotive force (EMF). The influence of slot dimensions on leakage inductance and short-circuit current is analyzed. The method to reduce eddy current loss of permanent magnets (PMs) is investigated. The machine performances under both healthy and fault conditions are evaluated. Finally, thermal behavior of the machine is studied by Ansys. Findings – With both no-load and load performances considered, rotor eccentricity is proposed to reduce the harmonic contents of EMF. Increasing slot leakage inductance is an effective way to limit the short-circuit current. By segmenting PMs in circumferential direction, the PM eddy current loss is reduced and the machine efficiency is improved. With proper fault-tolerant control strategy, acceptable torque performance can be achieved under fault conditions. The proposed machine can safely operate under Class F insulation. Originality/value – So far, many researches focus on multiphase PMSMs used in aviation fields, such as fuel pump and electric actuator. Differing from PMSMs used in aviation applications, machines for EVs require characteristics like wide speed ranges and variable operating conditions. Hence, this paper proposes a five-phase 20-slot/18-pole PMSM for EVs. The proposed design methodology is applicable to multiphase PMSMs with different slot/pole combinations.

A new analytical approach to determine slotting based eddy current losses in permanent magnets of PMSM taking into account axial and circumferential segmentation

Purpose – The purpose of this paper is to calculate slotting-based eddy currents in permanent magnet excited synchronous machine (PMSM) taking into account axial and circumferential segmentation of magnets. Design/methodology/approach – An analytical approach to calculate eddy current losses in PM caused by slotting harmonics of PMSM is presented. The eddy current reaction field is taken into account as well as axial and circumferential segmentation of the magnets. Findings – The analytical model provides results comparable to 3D-FEM calculations even at high frequencies at reduced computation costs. To generalize the results the magnetic Reynold’s number is introduced. Originality/value – Taking into account the axial and circumferential segmentation in the PDE; the approach is much more accurate compared to known approaches; accuracy is comparable to 3D-FEA.

REDUCTION OF EDDY CURRENT LOSS OF PERMANENT-MAGNET MACHINES WITH FRACTIONAL SLOT CONCENTRATED WINDINGS

Fractional slots concentrated windings (FSCWs) are characterized with high magnetic motive force (MMF) harmonics which results in undesirable effects on permanent-magnet (PM) machines. A new design technique is reported in this paper in order to simultaneously reduce the sub- and high MMF harmonics. By using multiple layer windings and different turns per coil, a new 18-teeth/10-poles FSCWs PM machine is designed. Then, this machine is evaluated as compared with a conventional 12-teeth/10-poles FSCWs PM machine. Both machines are designed under the same electrical and geometrical constrains. The obtained results verify the high performances of the newly designed machine. Due to the adopted new winding type, the proposed design can effectively reduce eddy current loss in PMs as compared with the conventional design.

Calculation analysis of thermal loss and temperature field of in-wheel motor in micro-electric vehicle

To improve the efficiency and life of in-wheel motor in micro-electric vehicle, thermal loss and temperature field are calculated and analyzed. The mathematical model of thermal loss and temperature field was established, the equivalent model of stator winding was adequately handled, convection heat transfer coefficients was calculated, and the heat distribution of in-wheel motor was analyzed. Winding copper loss, stator and rotor core loss and eddy current loss of permanent magnet were calculated, which were coupled to the temperature field as the heat sources. This paper effectively simplified and dealt with the inner complex radiating coefficient. Three-dimensional finite element model of temperature field was established, and static and transient state temperatures were simulated and analyzed. Overall temperature of the stator region is higher than that of the rotor region. Temperature of stator iron core is basically accord with the temperature of equivalent insulating film, but both are less than the temperature of equivalent winding. The conformity of the measurement results with the final simulation results shows that three-dimensional finite element method is accurate and feasible to analyze thermal loss and temperature distribution of in-wheel motor, which can afford a theoretical basis to optimize the in-wheel motor.

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.

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.

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.

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.

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.

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.

Eddy current losses in permanent magnets of the BLDC machine

PurposeThis study aims to calculate eddy current losses in permanent magnets of BLDC machine in the generator mode of operation with no‐load.Design/methodology/approachStator slot openings and special design of the stator poles cause changes in the magnetic flux density changes in permanent magnets. The stator windings are not connected to an outer source and no currents flow in them. The induced eddy currents in permanent magnets are dependent solely on the stator geometry. Analytical approach to calculate the eddy current density distribution in permanent magnets is based on known distribution of magnetic flux density in the air‐gap of BLDC. The magnetic flux density distribution is obtained from magneto‐static finite element model of BLDC. For verification of analytical approach the eddy current density distribution in permanent magnets is also calculated by magneto‐transient finite element model of BLDC.FindingsThe eddy current losses in PM obtained with the FEM indicate additional heating of the BLDC machine at high rotational speeds even when it operates at no load. When some special stator designs (the side of the air gap) are needed, the losses in PMs and their heating increase.Research limitations/implicationsTo get more precise results, the proposed analytical method for eddy current losses calculation in PM should be further analyzed. More geometric parameters of the BLDC design should be introduced to analytical formulations, especially those which affect variations in reluctance.Practical implicationsWhen some special stator designs (the side of the air gap) are needed, the losses in PMs should be observed. This is particularly recommended at higher rotation velocities. Any kind of magnetic flux density change induces eddy currents and together with them also power losses. These losses give rise to additional heating of PM. With this, the temperature‐dependent working characteristic of PM (second quadrant of the B‐H curve) moves toward the coordinate origin point. The overall machine performance is reduced. The presented work gives the view about happenings in permanent magnets regarding induced eddy current losses. It is a useful tool for fast estimation and reduction of eddy current losses in PM due to stator geometry.Originality/valueThe value of the paper is the closed view about happenings in permanent magnets regarding induced eddy currents and the calculation of eddy current losses in rotor permanent magnets of BLDC due to stator design. The originality is in the analytical approach to calculate the eddy current losses based only on known magneto‐static flux density distribution in air‐gap of BLDC.

Effects of coil current phase on eddy current loss of permanent magnets in IPM motors

PurposeAims to investigate the eddy current loss in permanent magnets of IPM motors.Design/methodology/approachUses the 3D finite element method (3D FEM).FindingsFinds that the effect of the current phase on the eddy current loss is very different according to the number of slots.Originality/valueInvestigates the eddy current loss in a permanent magnet of an IPM motor.

Measurement and analysis of AC loss of NdFeB sintered magnet

AbstractNdFeB sintered magnets are widely used in rotating machines. As the conductivity of NdFeB sintered magnets is fairly high compared with that of ferrite magnets, the eddy current loss due to slot ripple, etc., cannot be neglected. If the eddy current loss of permanent magnets becomes large, the temperature of the permanent magnet becomes high and the thermal demagnetization becomes serious. Therefore, it is required to evaluate AC loss of the permanent magnet. But the measurement of AC loss of the permanent magnet under serious operating conditions has not yet been reported. In this paper, the AC loss of NdFeB sintered magnet was measured using a newly developed closed‐type measuring equipment. It is shown that the coaxial double coil is useful for accurate measurement of the magnetic field. The eddy current loss and hysteresis loss of the permanent magnet are obtained by the loss separation. It is illustrated that the hysteresis loss is larger than the eddy current loss in the range of less than several hundred hertz. The appropriateness of measurement is verified by the numerical analysis. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 154(4): 8–15, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20213