Permanent Magnet Eddy Research Articles

A novel method for modeling the air gap flux density of the axial-flux permanent magnet eddy current coupler considering the end-effect

The virtual equivalent line method for the axial-flux permanent magnet eddy current coupler is proposed in this paper to solve the problem of the difference in the length of the magnetic flux path between the inner radius and outer radius of the axial section of the radial centerline of the magnetic pole. Different from the average radius equivalent method, the virtual equivalent line method adopts the function of variable pole radius instead of the fixed average radius, which establishes a uniform analytical expression of the air gap flux density and can accurately calculate the magnetic flux density at any magnetic pole radius. Furthermore, the end-effect compensation function is obtained. In order to investigate the effectiveness of the proposed method, the results calculated by the analytical method are compared with the finite element method. It is shown that the novel method proposed in this paper is highly consistent with the air gap flux density calculated by the finite element method.

Equivalent subdomain method for performance prediction of permanent magnet eddy current brakes

Equivalent subdomain method for performance prediction of permanent magnet eddy current brakes

Evaluation and analysis of novel flux‐adjustable permanent magnet eddy current couplings with multiple rotors

This article proposes a novel flux-adjustable permanent magnet eddy current coupling with multiple rotors. According to the different functions, the permanent magnet rotors are divided into fixed-flux and flux-adjustable rotors. By adjusting the relative position between two types of permanent magnet rotors, the magnetic field, torque, and output speed are controlled without changing the air-gap length. To quickly and easily analyse the torque performance, an analytical model for the torque of such devices is developed based on the non-linear magnetic equivalent circuit approach. In the modelling phase, a number of factors are considered, such as the skin effect, the inductance of eddy current field, the temperature effect, and so on. A three-dimensional finite element method is employed to validate the model results, and the comparative analysis shows the advantages and potential of the proposed topology. The further sensitivity analysis of the key parameters is also made, which offers helpful information for the preliminary design of such devices.

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.

Cost Minimization of a Permanent Magnet Eddy Current Brake by Multiobjective Particle Swarm Optimization Based on Nonlinear Reluctance Network Modeling

Design optimization of a permanent magnet eddy current brake (PM-ECB) is performed by applying multiobjective particle swarm optimization (MO-PSO) for cost minimization. A previously designed and patented PM-ECB is used as a reference model in the study. A quasi-3-dimensional (3D) analytical modeling approach based on a reluctance network considering the actual structure of the reference PM-ECB is proposed and verified. The Gauss–Seidel method is used as a nonlinear solver for the reluctance network modeling, and the braking torque is calculated considering both the skin effect and the armature reaction. Multiobjective optimization is developed by applying a particle swarm algorithm, and a 3D Pareto front is provided to demonstrate all non-dominating design points. Three cost functions, viz. rated braking torque, magnet mass, and magnetic flux density of the yoke, are selected as the objectives for the optimization problem, and the optimum design point is addressed in detail. The optimized design is validated by 3D-FEA and experiments. The results indicate that a 40% reduction in the magnet volume could be brought about by the optimized PM-ECB design with practically the same braking torque. Further, a 40% cost reduction in the optimized brake could be achieved compared with the reference one.

Characteristic and Thermal Analysis of Permanent Magnet Eddy Current Brake

In this paper, the subdomain analysis model of the eddy current brake (ECB) is established. By comparing with the finite element method, the accuracies of the subdomain model and the finite element model are verified. Furthermore, the resistance characteristics of radial, axial, and Halbach arrays under impact load are calculated and compared. The axial array has a large braking force coefficient but low critical velocity. The radial array has a low braking force coefficient but high critical velocity. The Halbach array has the advantages of the first two arrays. Not only the braking force coefficient is large, but also the critical speed is high. The parameter analysis of the Halbach array is further carried out. The inner tube thickness and air gap length are the sensitive factors of resistance characteristics. The demagnetization effect is significantly enhanced by the increase of the inner tube thickness. In order to ensure that the ECB does not overheat, the electromagnetic-thermal coupling model is established based on the heat transfer theory. The temperature rise of the inner tube is obvious while that of the permanent magnet is small. The temperature rise of the inner tube is more than 20 K each time, and that of the permanent magnet is less than 1 K each time.

Braking force characteristics of permanent magnet eddy current brake with high acceleration

Braking force characteristics of permanent magnet eddy current brake with high acceleration

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.

Analytical Prediction and Analysis of Electromagnetic-Thermal Fields in PM Eddy Current Couplings With Injected Harmonics Into Magnet Shape for Torque Improvement

To improve the output torque in permanent magnet (PM) eddy current couplings, a new structure based on harmonics injection into the magnet optimization theory is proposed. Then, a novel analytical electromagnetic-thermal model is established that can accurately reflect the 3-D distributions of the magnetic field and the eddy current. With the proposed analytical model, the eddy current loss, temperature distribution, torque characteristics and influence of the temperature rise caused by load increases on the torque are predicted and analyzed precisely. The maximum output torque can be improved by 11.22% with injected harmonics into the magnet shape. On this basis, an optimal design of the conductor plate structure is presented, based on the electromagnetic-thermal analytical model. An additional 13.05% torque improvement can be obtained, which leads to better torque characteristics and overload capability. Verification is conducted by a 3-D finite element analysis and measurements. The analytical model solves the multiphysics coupling analysis problem of PM eddy current couplings, and provides a fast and accurate calculation method to perform electromagnetic-thermal coupling analysis.

Electromagnetic Performance of the Novel Hybrid-Pole Permanent Magnet Machines for High Peak Torque Density

This paper proposes two novel hybrid rotors permanent magnet (PM) machines for the high torque density in short duration condition operation. In order to enhance the torque performance, the flux concentrated structure of spoke-type PM is employed to increase the air-gap flux density. Meanwhile, the non-magnetic connector of the rotor is employed to eliminate the magnetic flux leakage. The rotors of the conventional machines and the proposed machines are optimized by the finite element analysis (FEA). Furthermore, based on the comparisons of electromagnetic performances for the optimized machines, including the open-circuit flux density, torque, PM eddy current loss, overload capability, the characteristics of the proposed machines are analyzed. The results indicate that the proposed machine can improve the torque at rated and overload operation with growth rate 14.3% and 13.1%, respectively. Finally, a 12-slots/10-pole PM machine is prototyped and FEA is to be validated.

An Improved Analytical Model of Permanent Magnet Eddy Current Magnetic Coupler Based on Electromagnetic-Thermal Coupling

There is a serious nonlinear between the sensitive parameters and the transmission capacity of the permanent magnet eddy current magnetic coupler (PMEC), and how to establish the accurate analytical model is very important to study its characteristics, optimize design and improve control accuracy. In order to solve the problem that the accuracy of analytical model deteriorates under the variable parameters of the PMEC, based on the electromagnetic-thermal theory, the electromagnetic-thermal nonlinearity of materials, such as the thermal effect of magnetic properties, the thermal effect of permeability, the thermal effect of conductivity, the magnetic saturation effect, the skin effect, the eddy current inductive reactance, have been deeply studied in this paper. On this basis, the multi-field coupling analytical model of the PMEC sensitive parameters and material electromagnetic thermal nonlinearity is established by using the magnetic equivalent circuit theory and lumped parameter thermal network method. Combined with numerical simulation and experiment, the research on electromagnetic characteristics, temperature characteristics and transmission characteristics of the PMEC are carried out. The comparative study shows that the proposed analytical model can accurately analyze the electromagnetic characteristics, temperature characteristics and transmission characteristics of the PMEC without any correction coefficient under different parameters. The accuracy of the analytical model with variable parameters is effectively solved, and the model theory of the PMEC is improved. The accurate analytical modeling method has laid theoretical foundation for the rapid optimization design and wide application of the PMEC.

Modeling and optimization of tubular linear permanent magnet eddy current brake with Halbach array

This paper provides an analytical method for calculating the electromagnetic field of the tubular linear permanent magnet eddy current brake. The method of separating variables based on Fourier series is used to solve the boundary value problem, and the analytical solution of electromagnetic field is obtained. The braking force is obtained by calculating the Lorentz force. Then the accuracy of the analytical method is verified by comparing the analytical solutions with the solutions obtained by finite element method (FEM). In order to improve braking performance in a limited space, the parameter analysis is carried out to investigate the influence of various structural parameters on the braking characteristics. According to the results of parameter analysis, the range of design parameters is determined. Finally, a multi-objective optimization is applied to find the optimal design parameters of the eddy current brake. The braking force increases by 27% and the volume of permanent magnet decreases by 7.7% after optimization.

Modeling and Performance Analysis of an Axial-Radial Combined Permanent Magnet Eddy Current Coupler

The structure and magnetic circuits of axial-radial combined permanent magnet eddy current couplers are more complicated than those of axial or radial permanent magnet eddy current couplers, the degree of coupling is deeper, which will affect the device performance. In this paper, a novel analytical model for an axial-radial combined permanent magnet eddy current coupler is proposed based on the equivalent magnetic circuit method. The distribution of the magnetic field, the relationship between the slip and torque, the influence of the structural parameters on the transmission performance, the 3-D correction and thermal compensation are studied. Combined with the concept of the micro-element method, the air gap magnetic density, eddy current density and torque are accurately calculated, which solves the problem that the existing model cannot analyse the axial-radial combined structure. To show the effectiveness of the proposed analytical model, the transmission performance of an axial-radial combined permanent magnet eddy current coupler prototype is investigated, and the analytical calculation results are compared with the results of the finite element method simulations and experimental tests.

Investigation of PM Eddy Current Losses in Surface-Mounted PM Motors Caused by PWM

It is well known that spatial field harmonics will cause high eddy current losses in surface-mounted permanent magnets (PMs) especially for the fractional-slot PM motors. However, the influence of temporal current harmonics, especially of the high-order temporal harmonics caused by pulsewidth modulation voltages from an inverter, lacks attentions. This paper studies the eddy current losses of the PMs caused by high-order current harmonics. In order to simplify the calculation and save computation time, analytical methods are used to predict the current harmonics caused by the PWM inverter, and the armature reaction field, the eddy current density, and losses in the PMs generated by the current harmonics. Finite element analysis, coupling simulation, and experimental studies are used to verify the analytical results. The study results show that the high-order current harmonics cause much higher eddy current losses than those caused by slotting and fundamental current even though the amplitudes of the high-order current harmonics are much lower.

Analysis and Design Optimization of a Permanent Magnet Synchronous Motor for a Campus Patrol Electric Vehicle

This work presents the analysis, design and optimization of a permanent magnet synchronous motor (PMSM) for an electric vehicle (EV) used for campus patrol with a specific drive cycle. Firstly, based on the collected data like the parameters and speed from a test EV on the campus road, the dynamic calculation of the EV is conducted to decide the rated power and speed range of the drive PMSM. Secondly, according to these requirements, an initial design and some basic design parameters are obtained. Thirdly, optimization process is implemented to improve the performance of the designed PMSM. The permanent magnet (PM) structure, airgap length and stator core geometry are optimized respectively in this step. Different optimization processes are proposed to meet multiple optimization objectives simultaneously. Based on the finite element analysis (FEA) method, it is found that the harmonic of the optimized PMSM is lower than that of the initial design, and the torque ripple is reduced by 24%. The effectiveness of optimization on the core loss and PM eddy loss is validated and the temperature rise is suppressed effectively. Finally, a prototype is fabricated for the optimized PMSM and an experimental platform is developed. The test results verify that the optimized PMSM meets the requirements of the specific campus patrol EV well.

Electromagnetic buffering considering PM eddy current loss under intensive impact load

The intensive impact load will generate a huge acceleration in the primary part of the Electromagnetic buffers (EMBs), resulting in an instantaneous increase in the eddy current loss of the permanent magnet (PM). In this paper, the PM eddy current loss is taken into account in the electromagnetic buffering under intensive impact load. The reason why the eddy current damping force differs between two different buffer stages is analyzed. The experimental results signify that the model considering the PM eddy current loss is more accurate.

Magneto-thermal coupling analysis of the permanent magnet eddy current brake under intensive impact load

To more realistically describe the operation of an eddy current brake under intensive impact load, a magnetic-thermal bidirectional coupling model of the eddy current brake is established considering the existence of temperature. The variation of material and convective heat transfer coefficient with temperature are considered in the model. The iterative method is used to decouple the model. Through the analysis of the numerical simulation results, the temperature distribution and transmission of the brake during operation are obtained. By comparison, it is found that the calculated braking force of the magneto-thermal coupling model is lower than the calculated value without considering the temperature field due to the influence of temperature. And the higher the temperature, the greater the decrease.

Design and analysis of magnetic circuit of permanent magnet eddy current brake

The eddy current brake has the advantages of no frictional contact or hydraulic fluid, high structural reliability, etc. The existing linear eddy current brakes are mostly flat type. A cylindrical permanent magnet eddy current brake is proposed in this paper, whose air gap magnetic field is generated by a series of ring-shaped permanent magnets and guided by iron pole to conductor layers, and can achieve higher air gap magnetic flux density. This paper introduces its basic structure and working principle. In order to obtain the analytical model of magnetic circuit design, the equivalent magnetic circuit method is used to analyze and derive the magnetic circuit, and it is verified by the axisymmetric finite element model. To derive the braking force generated by the eddy current brake, the layer theory approach is applied. The influence of electromagnetic parameters on the force characteristic is obtained by finite element numerical calculation, which provides a theoretical basis for the optimal design of the eddy current brake.

Analysis of PM Eddy Current Loss in Four-Phase Fault-Tolerant Flux-Switching Permanent-Magnet Machines by Air-Gap Magnetic Field Modulation Theory

In this article, the permanent-magnet (PM) eddy current loss in a four-phase fault-tolerant flux-switching PM (FT-FSPM) machine is investigated from the perspective of air-gap magnetic field modulation. It can be found that the PM eddy current loss in FT-FSPM machines results from the relative motion between air-gap field space harmonics and PMs. Some effective working harmonics produce the major PM eddy current loss. The proportion of PM eddy current loss generated by each working harmonic is studied in detail, revealing that the low-order (third) harmonic is the main factor. Then, two new structures are proposed to reduce PM eddy current loss, in which magnetic flux barriers are designed by reducing low-order harmonics from the aspect of magnetic field modulation theory. Electromagnetic performance is investigated by finite element analysis. The results show that the proposed structure is effective to suppress PM eddy current loss. Finally, an experimental test platform is established to verify the theoretical analysis results.