Investigation on mechanism of magnetization reversal for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element methods

Magnetization configurations were calculated under various magnetic fields for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element method.According to the configurations during demagnetization process, the mechanism of magnetization reversal was analyzed.For the Pr2Fe14B with 10 nm grains or its composite with 10vol.% α-Fe, the coercivity was determined by nucleation of reversed domain that took place at grain boundaries.However, for Pr2Fe14B with 30 nm grains, coercivity was controlled by pinning of the nucle-ated domain.For Pr2Fe14B/α-Fe with 30vol.% α-Fe, the demagnetization behavior was characterized by continuous reversal of α-Fe moment.

3D Finite Element Analysis of the Stray Loss in Power Transformer Structure Parts

In order to analyze the leakage magnetic field and stray loss in power transformer, leakage magnetic field and stray loss in structure parts of a power transformer are calculated by three-dimensional (3-D) non-linear time harmonic finite element method (FEM). The results show that stray loss and loss density in structure parts are large and which may lead to local overheating and affect performance of the transformer. The magnetic shields are used to reduce the stray loss and loss density of power transformer. Effects of these shields on stray loss and loss density of structure parts are discussed. The results show that stray loss and local overheating can be reduced and eliminated effectively by adding magnetic shields. It provides some references for the analysis of stray loss and optimization design in transformer.

Finite Element Based Analysis of Magnetic Forces between Planar Spiral Coils

This paper elaborates on the magnetic forces between current carrying planar spiral coils. Direct and concentric rings methods are employed in order to calculate the magnetic force between these coils. The results obtained by two calculation methods show the efficiency of the replaced rings method in both simplicity and calculation time. Simula-tions using the Finite Element Method (FEM) are carried out to analyze the distribution of the magnetic flux density around the coils. Also, coils with precise size have been constructed and tested. The experimental results as well as the results obtained by FEM are used to validate the accuracy of the calculations.

Finite Element Assisted Numerical Comparison of Single and Two Phase Inductively Coupled Power Transfer Systems

Inductively coupled power transfer systems (ICPT) are becoming ubiquitous in industry. Many such systems are excited with single or multi-phase input current. This leads to increased complexity in comparing such systems when solely using the magnetic frequency analysis. This paper utilizes modern finite element method analysis software to propose a novel software methodology for the numerical comparison of single and two phase ICPT systems as demonstrated on a three dimensional (3D) battery charging system. The sinusoidal magnetic frequency response of a single phase system is compared to the magnetic transient response of a multi-phase current system by use of a novel software methodology proposed in this paper. This consists of a transient response analysis to determine compute the resulting magnetic response over the duration of an input current period on the two phase system. The resulting non-sinusoidal response is then integrated over a whole period to extract the root-mean-square value for comparison with that of a single phase system across a 3D cubic power zone.

Simulated Experiments for Teaching Mutually-Coupled Circuits CAD Techniques Using Analytic and Finite Element Solutions

The paper describes an approach to teaching mutually-coupled circuits CAD techniques to undergraduate students pursuing a degree course in electrical engineering or physics, and explains how a series of simulated experiments may be incorporated into the existing subjects. The simulated experiments make use of a two-dimensional open-access software based on the finite-element method. At the laboratory meetings, the students learn how to set up field problems for solution, and how to examine the results. Simulation tasks based on three axisymmetric open-boundary problems are used to introduce different numeric techniques to compute inductance and magnetic forces. The paper takes the reader to a step-by-step simulation journey, and provides all the basic elements required for further exploration of axially-symmetric systems.

Simulated Experiments for Teaching CAD Techniques Using Analytic and Finite Element Solutions of Electromagnetic Two-Dimensional Problems with Longitudinal Symmetry

The paper describes an approach to teaching low-frequency electromagnetic CAD techniques to undergraduate students pursuing a degree course in electrical engineering. The simulated experiments make use of a two-dimensional open-access software based on the finite-element method. At the laboratory meetings, the problems are initially solved analytically. Upon this, students learn how to create the numeric model and how to define the sequence of field problems that lead to the required solution. Simulation tasks based on a force-producing electromagnet are used to introduce numeric techniques to determine magnetic field distribution, evaluation of energy storage and generation of magnetic forces. The nature of the magnetic force generated in the air gaps of the C-core electromagnet is explained in detail. Magnetic forces are calculated by the classical and weighted versions of the method of Maxwell stress tensor. The paper provides all the basic elements required for further exploration of devices with longitudinal symmetry.

Design of Rotor Magnetic Barrier Structure of Built-in Permanent Magnet Motor Based on Taguchi Method

In this paper,a 20kW vehicle built-in permanent magnet synchronous motor is taken as an example,and a magnetic barrier structure is added to the rotor of the motor to solve the uneven saturation problem of the rotor side magnetic bridge.This structure improves the air-gap flux density waveform of the motor by influencing the internal magnetic flux path of the motor rotor,thus improving the sine of the no-load back EMF waveform of the motor and reducing the torque ripple of the motor.At the same time,Taguchi method is used to optimize the structural parameters of the added magnetic barrier.In order to facilitate the analysis of its uneven saturation phenomenon and improve the optimization effect,a simple equivalent magnetic network(EMN)model considering the uneven saturation of rotor magnetic bridge is established in this paper,and the initial values of optimization factors are selected based on this model.Finally,the no-load back EMF waveform distortion rate,torque ripple and output torque of the optimized motor are compared and analyzed,and the influence of magnetic barrier structure parameters on the electromagnetic performance of the motor is also analyzed.The results show that the optimized motor can not change the output torque of the motor as much as possible on the basis of reducing the waveform distortion rate of no-load back EMF and torque ripple.

基于热源网络法的永磁式电磁制退机热特性研究

永磁式电磁制退机以磁场为能量传输介质,有望彻底解决传统液压式制退机液体泄漏、阻力规律稳定性差等问题。然而电磁制退机工作过程中的热特性变化规律尚未探明,限制了电磁制退机的进一步发展。依据电磁制退机的结构,建立了热源网络温度场分析模型,计算了电磁制退机各主要部件的热参数,结合热路传播路径编写了温度场计算程序,得到了火炮后坐过程中电磁制退机不同时刻的瞬态节点温度,探究了电磁制退机瞬态工作过程中的温度传播规律与分布特性。同时建立有限元模型,对热源网络分析模型进行了验证。最后充分利用热源网络模型计算效率高的优势,开展了连发射击工况下电磁制退机的热特性研究、失效预测和冷却措施探究,为电磁制退机的工程设计提供了参考。

电磁波传播测井地层介电常数测量应用分析

受地层水矿化度的影响,复杂油气储层电性特征复杂,采用电阻率测量方法难以对复杂储层流体进行准确评价与识别;但介电常数受地层水矿化度影响小,并且水的介电常数远大于油气介电常数,通过电磁波传播测井仪测量地层介电常数可有效准确区分油气储层与水层,且其地层响应转换图版的精准性对复杂储层流体的准确评价至关重要。本文基于等效磁偶极子模型推导了层状介质中1 GHz电磁波传播计算公式,提出了将测量探头几何工程参数融入有限元的精确仿真方法,采用COMSOL Multiphysics建立1∶1有限元仿真模型,分析了探头几何工程参数对地层转换图版的影响。搭建实验系统验证了理论仿真的准确性,测量结果显示基于精确仿真方法得到介电常数与真实值的相对误差约为1%。研制出电磁波传播测井仪,并在某油田开展了非常规页岩油气测井应用,为油田复杂油气储层的评价提供了一种有效的测量方法。

基于有限元法的水下航行器地磁异常模拟研究

为改进水下航行器磁异常探测技术中磁异常实测数据难获得、现有磁体模型计算精度不高等问题,基于有限元仿真探讨建立无需区分近、远场的高精度混合磁体模型方法。应用有限元数值方法仿真复杂结构水下航行器的空间磁异常分布,以磁场数值解为收敛目标,建立以偶极子阵元数目、位置及磁矩为参数的均匀磁化椭球体与偶极子阵列混合的航行器磁异常解析模型,采用非线性最小二乘算法求解模型系数。仿真结果表明,基于该模型得到磁异常计算值与全空间内数值解的拟合度较高,测试平面平均误差为3%。该模型在磁场延拓、高精度建模等方面可以进一步应用。

复杂地形瞬变电磁三维正演模拟与地形效应分析

目前,地面瞬变电磁法凭借其优势已被广泛用于煤矿水文地质勘查中,然而,在野外实际勘探中,复杂地形环境常导致发射源几何形状的改变与信号接收偏差,降低了勘探精度。为此,采用理论分析、数值模拟和实际地形数据分析相结合的方式,系统研究了复杂地形条件下电性源与磁性源瞬变电磁场的响应特征。首先,基于二阶后退欧拉离散的矢量有限元正演模拟技术,详细探讨了山峰和山谷地形位于接收点和发射源位置时,对两种源系统的影响规律。结果表明:电性源系统会出现响应变号现象,源导线位置高于周围地形时响应增强,反之则被削弱;而磁性源无变号现象,但响应变化规律与电性源类似。其次,利用实测地形数据,采用四面体网格建立与实际地形高度吻合的三维正演模型。模拟结果显示:早期响应曲线能够清晰反映地形细节,曲线形态与地形特征一致;而晚期响应则逐渐趋于平缓,体现了深部背景的影响。研究成果可为复杂地形条件下瞬变电磁法的勘探装置布设、数据采集、处理和解释提供理论指导,对提高煤矿水文地质勘探精度具有重要意义。

Impact of a Magnetic Dipole on Heat Transfer in Non-Conducting Magnetic Fluid Flow over a Stretching Cylinder

The thermal behavior of an electrically non-conducting magnetic liquid flowing over a stretching cylinder under the influence of a magnetic dipole is considered.The governing nonlinear differential equations are solved numerically using a finite element approach,which is properly validated through comparison with earlier results available in the literature.The results for the velocity and temperature fields are provided for different values of the Reynolds number,ferromagnetic response number,Prandtl number,and viscous dissipation parameter.The influence of some physical parameters on skin friction and heat transfer on the walls of the cylinder is also investigated.The applicability of this research to heat control in electronic devices is discussed to a certain extent.

基于有限元法的永磁同步电机性能校核

针对纯电动汽车电机磁漏、能量转换及过载保护等多样化需求,提出一种自主设计的永磁同步驱动电机,围绕电机的建模、网格分层、电磁场特性及不同工况下的有限元解析等多维度进行研究。通过仿真软件Maxwell 2D建立完整的永磁同步电机模型;并进一步分析电机在空载状态下定子齿部磁密、轭部磁密、转子隔磁桥磁密及磁场漏磁等电磁场特性,确保永磁同步电机有限元模型准确可靠;在此基础上,对驱动电机在额定负载和过载工况下的特性进行分析。结果表明:电机在额定负载时,定子齿部的磁感应强度约为1.85 T,轭部约为1.44 T,未达到饱和状态,平均输出转矩约为66.22 N·m,转矩峰值约为72.65 N·m,磁力线分布较为均匀;电机在过载时,定子齿部及轭部磁密均已饱和,过载电流远超额定电流的2.5倍以上,平均输出转矩约为178.25 N·m,说明该电机具备出色的过载能力。

基于有限元模型的永磁同步电机结构振动特性研究

对电机模态固有频率的精确计算及准确分析是电机低噪声驱动设计的一个重要环节。由于用于电动汽车的永磁同步电机(PMSM)属于小型电机,机壳和端盖等装置对振动噪声的影响不容忽略,因此对不同电机结构部件以及耦合系统固有频率进行计算分析具有重要意义。基于一台12槽8极PMSM,利用有限元软件,考虑了铁心材料的各向异性、弹性模量、浸漆、机壳和端盖连接方式等影响,精确建立了定子铁心结构的计算模型,并用锤击法模态实验验证了有限元仿真模型的精确性。

FEMM在扬声器磁路分析中的应用

本文介绍了适用于低音扬声器的几种不同充磁方向的应用磁路,并引入有限元法,利用磁场有限元分析软件FEMM对选择的磁路进行分析,得到了较好的效果,指出了一种新的磁路分析途径。

永磁同步电机电磁性能仿真及影响因素分析

为进一步探究永磁同步电机不同结构参数对电磁性能的影响,通过使用Maxwell软件设计永磁同步电机,深入分析了电机槽口宽度、气隙长度以及永磁体宽度等结构参数对永磁同步电机电磁性能的影响。仿真结果表明:增加槽口宽度,电机空载气隙磁通密度基波幅值呈增加的态势,空载反电动势基波幅值呈减小趋势,齿槽转矩增加较为明显;增加气隙长度,电机气隙磁通密度基波幅值呈逐步减小趋势,空载反电动势呈减小态势,但减小幅值不大,气隙长度在一定范围内使得齿槽转矩先增加后减小;永磁体宽度的增加使得气隙磁通密度幅值、电机空载反电动势基波幅值以及齿槽转矩均呈增大态势。通过对不同电机结构参数对电磁性能的影响分析,可为设计优化永磁同步电机提供指导意义。

Permanent Magnet Shape Optimization Method for PMSM Air Gap Flux Density Harmonics Reduction

This paper proposed a permanent magnet optimization method to suppress the air gap flux density harmonic of permanent magnet synchronous motor(PMSM).The method corrected the effective air gap length of the motor,calculated the magnetization length of the permanent in the case of parallel magnetization,and took the influence of the permanent magnet relative permeability into consideration.Based on these works,for a given sinusoidal air gap flux density waveform,the corresponding structural parameters can be calculated,so as to achieve the optimization of the permanent magnet.By using this method to optimize the shape of the magnet,the fundamental wave of the air gap flux density can be retained to the greatest extent,so as to eliminate harmonics and maintain the output capacity at the same time.The feasibility and accuracy of the method have been verified by finite element analysis(FEA)and prototype machine experiment.This method is simple and time-saving,and has a satisfactory accuracy,which provides a reference method for permanent magnet optimization of PMSM.

Numerical-Analytical Method for Magnetic Field Computation in Rotational Electric Machines

A numerical-analytical method is applied for the two-dimensional magnetic field computation in rotational electric machines in this paper. The analytical expressions for air gap magnetic field are derived. The pole pairs in the expressions are taken into account so that the solution region can be reduced within one periodic range. The numerical and analytical magnetic field equations are linked with equal vector magnetic potential boundary conditions. The magnetic field of a brushless permanent magnet machine is computed by the proposed method. The result is compared to that obtained by finite element method so as to validate the correction of the method.

Characteristics of permanent magnet linear synchronous motor fed by spwm inverter based on field-circuit coupled method

Presented field-circuit coupled adaptive time-stepping finite element method to study on permanent magnet linear synchronous motor (PMLSM) characteristics fed by SPWM voltage source inverter.In air-gap field where the direction or magnitude of the field is changing rapidly,the smallest elements are demanded due to high accuracy to use adaptive meshing technique.The co-simulation was used with the status space functions and time-step finite element functions,in which time-step of the status space functions was the smallest than finite element functions'.The magnitude relation of the normal elec- tromagnetic force and tangential electromagnetic force and the period were attained,and current curve was very abrupt at current zero area due to the bigger resistance and leak- age reactance,including main characteristics of motor voltage and velocity.The simulation results compare triumphantly with the experiments results.