Permanent Magnet Eddy Current Loss 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.

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.

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.

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.

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.

Temperature Field Analysis and Cooling Structure Optimization for Integrated Permanent Magnet In-Wheel Motor Based on Electromagnetic-Thermal Coupling

Aiming at the impact of heat generation and temperature rise on the driving performance of a permanent magnet (PM) motor, taking the PM in-wheel motor (IWM) for electric vehicles as an object, research is conducted into the temperature distribution of the electromagnetic–thermal effect and cooling structure optimization. Firstly, the electromagnetic–thermal coupling model considering electromagnetic harmonics is established using the subdomain model and Bertotti’s iron loss separation theory. Combined with the finite element (FE) simulation model established by Ansoft Maxwell software platform, the winding copper loss, stator core loss and PM eddy current loss under the action of complex magnetic flux are analyzed, and the transient temperature distribution of each component is obtained through coupling. Secondarily, the influence of the waterway structure parameters on the heat dissipation effect of the PM-IWM is analyzed by the thermal-fluid coupled relationship. On the basis, the optimization design of waterway structure parameters is carried out to improve the heat dissipation effect of the cooling system based on the proposed chaotic mapping ant colony algorithm with metropolis criterion. The comparison before and after optimization shows that the temperature of key components is significantly improved, the average convection heat transfer coefficient (CHTC) is increased by 23.57%, the peak temperature of stator is reduced from 95.47 °C to 82.73 °C, and the peak temperature of PM is decreased by 14.26%, thus the demagnetization risk in the PM is improved comprehensively. The research results can provide some theoretical and technical support for the structural optimization of water-cooled dissipation in the PM motor.

Analytical Model and Experimental Verification of Permanent Magnet Eddy Current Loss in Permanent Magnet Machines With Nonconcentric Magnetic Poles

Permanent magnet synchronous motors (PMSMs) with nonconcentric magnetic poles (NCMP) structure are widely used as high-precision servo motors. The current subdomain method mainly equates the NCMP to a rectangular magnet to make each subdomain boundaries of magnet parallel when calculating the magnet eddy current loss (ECL), which results in a lower accuracy of the calculation. This article divides the NCMP into nonconcentric region and concentric region along the radial direction. The nonconcentric region is further divided along the circumferential direction, and each divided region has a single thickness. Based on the subdomain method, a novel analytical method of magnet ECL in PMSMs with NCMPs is proposed. Moreover, the three-dimensional distribution coefficient of ECL in the NCMP is derived by the equivalent impedance method. The effects of eddy current reaction and stator slotting are taken into account to improve the calculation accuracy. Then, through theoretical derivation, the relationship between the minimum magnet loss and the pole parameters is obtained, which provides a reference for the design of NCMPs. Finally, the loss separation experiment is performed on four prototypes with NCMPs. The experimental results, finite element method results and analytical results are compared to verify the correctness of the model.

Design and analysis of a novel hybrid cooling method of high-speed high-power permanent magnet assisted synchronous reluctance starter/generator in aviation applications

To improve the heat dissipation performance, this paper proposes a novel hybrid cooling method for high-speed high-power Permanent Magnet assisted Synchronous Reluctance Starter/Generator (PMaSynR S/G) in aerospace applications. The hybrid cooling structure with oil circulation in the housing, oil spray at winding ends and rotor end surface is firstly proposed for the PMaSynR S/G. Then the accurate loss calculation of the PMaSynR S/G is proposed, which includes air gap friction loss under oil spray cooling, copper loss, stator and rotor core loss, permanent magnet eddy current loss and bearing loss. The parameter sensitivity analysis of the hybrid cooling structure is proposed, while the equivalent thermal network model of the PMaSynR S/G is established considering the uneven spraying at the winding ends. Finally, the effectiveness of the proposed hybrid cooling method is demonstrated on a 40 kW/24000 r/min PMaSynR S/G experimental platform.

Analysis of unidirectional and bidirectional magnetic-thermal coupling of permanent magnet synchronous motor

To analyze accurately the temperature variation of permanent magnet synchronous motor, a bidirectional magnetic-thermal coupling method is proposed. Firstly, a two-dimensional magnetic field model of permanent magnet synchronous motor was built in Ansoft Maxwell, and the magnetic flux density, magnetic line distribution and radial air gap magnetic flux of the motor have been simulated. Secondly, the calculated winding copper loss, core loss and permanent magnet eddy current loss were coupled into the temperature field of ANSYS Workbench as heat source, and the transient temperature field of each part of the motor was studied. Finally, the electromagnetic and temperature fields of the motor were analyzed and calculated at the same time, and were mutually updated based on their iterations. The process was repeated until stable magnetic and temperature fields were generated. The results showed that the bidirectional coupling method took into account the influence of motor temperature rise on electromagnetic field, and the temperature rise prediction was more accurate than the unidirectional coupling method.

Simplified 3-D Hybrid Analytical Modelling of Magnet Temperature Distribution for Surface-mounted PMSM With Segmented Magnets

In this article, a simplified three-dimensional (3-D) hybrid analytical thermal model for surface-mounted permanent magnet (PM) synchronous machines is proposed and applied to investigate the influence of PM segmenting strategies on the spatial PM temperature distributions and hotspots. The developed 3-D hybrid thermal model synergies the lumped-parameter thermal model and analytical method and is able to estimate 3-D spatial temperature distributions and hotspots for both unsegmented and segmented surface-mounted PMs accounting for the uneven PM eddy current loss distributions. Meanwhile, by utilizing the proposed matrix-based post-processing methods, the developed hybrid analytical thermal model has a simple mathematical expression but persists in high estimation accuracy. Finally, the proposed hybrid analytical modelling method is validated by 3-D electromagnetic-thermal coupled FEA and experiments.

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).

Estimation of 3-D Magnet Temperature Distribution Based on Lumped-Parameter and Analytical Hybrid Thermal Model for SPMSM

This paper presents a hybrid analytical thermal model by utilizing the synergies of the lumped-parameter thermal model (LPTM) and the analytical thermal model to estimate the 3-dimensional (3-D) permanent magnet (PM) temperature distribution as well as the hotspot for surface-mounted PM synchronous machines (SPMSMs). The hybrid analytical thermal model is firstly developed based on 2-dimensional analytical models in radial-circumferential and radial-axial planes, and then extended to three dimensions, in which the uneven distributions of PM eddy current loss are taken into account. The analytical solutions are obtained by solving the Poisson's equations under the Dirichlet and the convection boundary conditions, which are extracted from the synergized LPTM. The proposed hybrid thermal model is applied to a totally enclosed SPMSM and validated by the 3-D electromagnetic-thermal coupled finite element method and experiments.

Design and Analysis of a Novel Frequency Modulation Secondary for High-Speed Permanent Magnet Linear Synchronous Motor

High-speed permanent magnet linear synchronous motor (PMLSM) is desired by high-performance electromagnetic propulsion system. A novel frequency modulation (FM) secondary proposed here to overcome the issues resulting from a big pole pitch of high-speed PMLSM, as well as avoid a damage to the thrust characteristics. First, the topology structure of FM secondary is designed, modeling of the main magnetic field excited by permanent magnets (PMs) is accomplished. And the impacts of FM secondary on the main magnetic field and PM eddy-current loss are presented based on the analytical method and finite-element method (FEM). The electromagnetic thrust of PMLSM with FM secondary is calculated, and the influences of FM secondary on thrust characteristics are studied by FEM simulations. Finally, a prototype of PMLSM with FM secondary is manufactured, the experiments are provided to validate the analytical results and simulation results of FM secondary.

Torque and Loss Characteristics of Magnetic Gear by Bonded PM Magnetization Direction

As coaxial magnetic gears use NdFeB permanent magnets with high-energy density, they have a torque density comparable to that of mechanical gears, and active research activities have been conducted since. However, NdFeB permanent magnets have conductivity and cause high permanent magnet eddy current losses due to the driving characteristics of coaxial magnetic gears. Ferrite has no conductivity, but because of its weak magnetic force, its competitiveness is poor. In this article, Nd-bonded permanent magnet which has high magnetic force and no conductivity is used. Finite element analysis (FEA) calculations and experimental results of coaxial magnetic gears using Nd-bonded permanent magnets were compared, and the direction of applying Nd-bonded to coaxial magnetic gears was presented by comparing the magnetization method of Nd-bonded.

Magneto-Electric Coupling Network Model for Reduction of PM Eddy Current Loss in Flux-Switching Permanent Magnet Machine

This article proposes a mesh-based magneto-electric coupling network model for prediction and reduction of permanent magnet (PM) eddy current loss in a flux-switching permanent magnet machine. The key is to couple the electromagnetic inductions between the eddy current network and the equivalent magnetic network (EMN) in stator PMs dynamically. First, the eddy current networks of PMs are established with electric meshes. The electromotive forces of electric mesh are induced by considering double-side effects based on Maxwell's equations. Second, the stator meshing method is propose with PM segments, and combined in the EMN matching to the eddy current mesh. High efficiency and accuracy with detailed magnetic field distributions can be obtained. Then, the magnetic fields generated from EMN PM nodes are coupled in eddy current network to accurately predict the flow directions and density distributions. Finally, the original design and two other structures with rotor magnetic barriers are analyzed for reduction of eddy current losses. The effectiveness of the proposed model is verified by finite-element analyses and experimental results.

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.

Microstructure Role in Permanent Magnet Eddy Current Losses

The impact of granular microstructure on permanent magnets on eddy current losses is investigated. A numerical homogenization procedure for electrical conductivity is defined. Then, an approximated simple analytical model for the homogenized conductivity able to capture the main features of the geometrical and material dependences is derived. Finally, analytic calculations of eddy current losses are given, and the two asymptotic expressions for losses in the stationary conduction limit and advanced skin effect limit are derived and discussed.

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 Winding MMF and Loss for Axial Flux PMSM With FSCW Layout and YASA Topology

This article takes 12-slot/10-pole axial flux permanent magnet (PM) synchronous machine (AFPMSM) with fractional-slot concentrated windings and yokeless and armature (YASA) topology as the research object. Winding magnetomotive force (MMF) of three-phase double-layer layout is analyzed by three kinds of methods, which are star diagram method, winding function method, and holographic spectrum method. The analysis results of finite-element method (FEM) show that the three methods are effective and consistent in analyzing winding MMF. Comparative analysis of iron loss density and B–H magnetizing curves of four typical iron materials are studied. B–H hysteresis loops of silicon steel sheet and soft magnetic composite are measured by magnetizing and measuring equipment to validate iron core per unit mass. The three-dimensional FEM is used for analyzing eddy-current loss in PMs considering radial segmentation. Finally, an AFPMSM prototype is manufactured adopting YASA topology and segmented PM. Load experiments show that solid–liquid coupling computational fluid dynamics model can precisely predict temperature distribution of AFPMSM. Improved cooling jacket is beneficial to afford large current load.