Irreversible demagnetization mechanism of permanent magnets during electromagnetic buffering

The permanent magnets will be irreversibly demagnetized under high temperature and high velocity during the electromagnetic buffering.In this study,the magnetic field induced by eddy currents and the self-demagnetizing field of permanent magnet are taken into consideration together for demagnetization analyse.The magnetic Reynolds number is used to express the eddy currents demagnetization.The correction coefficient being expressed as the index of the air-gap width,the inner cylinder thickness,iron pole axial length and the permanent magnet demagnetization coefficient is introduced by magnetic path analysis to represent the self-demagnetization effect and the demagnetization extent.The electromagnetic buffer(EMB)prototype is tested under intensive impact loads of different strengths at room temperature.The accuracy of the nonlinear irreversible demagnetization finite element model is verified by demagnetization on damping force,velocity and displacement.Finally,high-velocity demagnetization and high-temperature demagnetization are analysed in order to obtain the distribution law of irreversible demagnetization.

Numerical Simulation of the Demagnetization of a Permanent Magnet Retarder in High Temperature

As a auxiliary brake, Permanent Magnet Retarder （PMR） generates lots of energy and has greater temperature-rise when PMR works, so that it has a direct impact on PMR work performance and even causes demagnetization seriously. In order to analyze permanent magnet （PM） demagnetization in high-temperature in PMR, PMR mathematical model is established firstly, and the boundary conditions of finite element analysis are determined. Then the eddy current field distribution in the rotor is determined by solving eddy current demagnetization field, and PM dynamic permeance coefficient is obtained. Combined with PM demagnetization curve analysis, PMR permanent magnet demagnetization properties are analyzed. The analysis result is validated by the bench test. It shows that part of PM is demagnetized when PRM continues working for about 15 minutes, and the braking performance is declined. Finally, three PMR optimization design methods are proposed.

Micromagnetic Analysis on Demagnetization Process of Single-Phase Nanocrystalline Permanent Magnets with Different Degrees of Orientation

A three-dimentional finite element micromagnetic algorithm was developed to study the magnetization reversal of Pr2Fe14B single-phase nanocrystalline permanent magnets. A single-phase nanocrystalline Pr2Fe14B magnets composed of 216 irregular shaped grains was built. The magnetic hysteresis loops were simulated by micromagnetic finite element method. The contribution of intergrain exchange coupling ment degree （IGEC） to remanence enhancement is considered related to the alignin oriented magnets, and decreased with improved grain alignment. For the magnets with perfectly crystallo- graphic alignment of grains, the contribution of IGEC to remanence enhancement is nearly zero. The shape of demagnetization curve is not only dependent on grain alignment degree but also on the strength of IGEC in magnets.

Design and Parameter Analysis for Explosive-Driven Demagnetization Pulsed Power Source

We design a pulsed power source based on the technique for explosive-driven demagnetization. The physical process and geometry structure of this power source are described in detail and several formulae are deduced to predict some important properties of the power source. With a φ 40 mm × 20 mm× 10 mm cylindrical magnet, the maximum output voltage and current reaches 125.5 V and 862.9A, respectively. The rise time of the front edge of the output voltage is about 264ns. On the 0.05 Ω simulative load, the net power is 37kW.

THERMAL DEMAGNETIZATION AND RANDOMNESS OF DOMAIN NUCLEATION OF SINGLE PHASE Nd_2 Fe_(14) B

Based on the observation of temperature variation of both domain structure and magnetic con- trast.the thermal demagnetization and randomness of domain nucleation was discussed.

Interfacial effect on the reverse of magnetization and ultrafast demagnetization in Co/Ni bilayers with perpendicular magnetic anisotropy

For static magnetic properties of the Co/Ni bilayers,macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by the object oriented micromagnetic framework(OOMMF).It is found that when the bilayer systems are fully decoupled,the magnetizations of the two phases reverse separately.The coercivity of the bilayers decreases to a valley value sharply with increasing interfacial exchange coupling and then rises slowly to a platform.On the other hand,we have carried out an atomistic simulation for the laser-induced ultrafast demagnetization of the Co/Ni bilayer.A larger damping constant leads to a faster demagnetization as well as a larger degree of demagnetization,which is consistent with the first-principle theoretical results.For the magnetization recovery process,the damping constant has different influences on the recovery time with various peak electron temperatures,which is ignored in previous atomistic simulations as well as the Landau–Liftshit–Bloch(LLB)micromagnetic calculations.Furthermore,as the interfacial exchange coupling increases,the ultrafast demagnetization curves for Co and Ni become coincident,which is a demonstration for the transition from two-phase phenomenon to single-phase phenomenon.

Demagnetization Process and Coercivity for Anisotropic HDDR NdFeB Bonded Magnets

The demagnetization process and the coercivity mechanism for amsotropic HDDR Nd(Fe,Co)B bonded magnets were studied by comparing the dependence of coercivity on the alignment field applied while the powders were pressed. The results showed that both the remanence and the coercivity of magnet increased with increasing alignment field. The demagnetization process of the magnet can be classified as the nucleation process inside the grains and the domain-wall motion between the grains. The combined effect of two processes determines the coercivity of HDDR NdFeB bonded magnets.

Demagnetization Research on PMs in the Halbach Magnetized Pulsed Alternator

Demagnetization behavior of Halbach magnetized compensated pulsed alternator(CPA)is studied by using finite element method(FEM)under the different demagnetization factors in this paper.The effect of armature reaction magnetic field and thermal rise on demagnetization of PMs is analyzed.This paper investigates the effect of different demagnetization factors on magnetic field distribution,load current,and no-load phase voltage.A series of dynamic demagnetization points in Halbach array permanent magnet(PM)are evaluated to search the worst working point.Partial demagnetization risk can be represented by the worst working point,and the global demagnetization of the PM is represented by the no-load phase voltage characteristics after discharge.The research results demonstrated that the compensation shield with a certain thickness can increase the discharge current and weaken the demagnetization influence of armature reaction.The demagnetization effect of armature reaction on PMs at high temperatures will be strengthened.

The Study of Demagnetization of the Magnetic Orientation of Permanent Magnets for IPMSM with Field-Weakening Control under Hot Temperature

In this study, we investigate the demagnetization resistance of a concentrated winding IPMSM （interior permanent magnet synchronous motor） accounting for field weakening control by changing the magnetization direction of the permanent magnet under a high-temperature environment. IPMSMs are investigated by FEA （finite element analysis） using the same volume of the permanent magnet while changing the magnet’s width, thickness and magnetic field orientation angle. FEA found that a V-shaped angle Va = 100° and a changed magnet length of 97% using an oblique magnetic-field-oriented magnet strike a good balance between demagnetization resistance and torque at 180 ℃. Comparison between demagnetization of negative d-axis current （current phase β = 90°） and demagnetization of field weakening control （β = 80°） using concentrated winding IPMSM with V-shaped angle Va = 100° is conducted. With the demagnetization factor at β = 80° for β = 90°, the demagnetization factor 0.39 （2.6 times） at α = 0° decreases to 0.23 （4.3 times） at α = 20°. The demagnetization resistance in the field weakening control is further improved.

On the use of cross polarization in solid-state NMR:1 H spinlock versus adiabatic demagnetization in the rotating frame

Cross polarization(CP)is a widely used solid-state nuclear magnetic resonance(NMR)technique for enhancing the polarization of dilute S spins from much larger polarization of abundant I spins such as 1 H.To achieve such a polarization transfer,the I spin should either be spin-locked or be converted to the dipolar ordered state through adiabatic demagnetization in the rotating frame.In this work,we analyze the spin dynamics of the Hartmann-Hahn CP(HHCP)utilizing the 1 H spin-locking,and the dipolar-order CP(DOCP)having the 1 H adiabatic demagnetization.We further propose an adiabatic demagnetization CP(ADCP)where a constant radio-frequency pulse is applied on the S spin while 1 H is adiabatically demagnetized.Our analyses indicate that ADCP utilizes the adiabatic passage to effectively achieve the polarization transfer from the 1 H to S spins.In addition,the dipolar ordered state generated during the 1 H demagnetization process could also be converted into the observable S polarization through DOCP,further enhancing the polarized signals.It is shown by both static and magic-angle-spinning(MAS)NMR experiments that ADCP has dramatically broadened the CP matching condition over the other CP schemes.Various samples have been used to demonstrate the polarization transfer efficiency of this newly proposed ADCP scheme.

基于径向气隙磁密和定子电流的永磁同步电机均匀退磁故障诊断研究

该文提出一种基于径向气隙磁密和定子电流的永磁同步电机均匀退磁故障诊断方法。首先,建立电机的d轴等效磁路模型,分析均匀退磁故障后径向气隙磁密的变化规律;然后,获取电机的径向气隙磁密和定子电流信号,对各极下径向气隙磁密幅值进行归一化处理,并绘制雷达图,根据雷达图和比较相同定子电流幅值下健康电机和故障电机的各极下径向气隙磁密幅值的平均值,来诊断均匀退磁故障;利用空载各极下径向气隙磁密幅值的平均值计算故障程度。最后,仿真和实验结果均验证所提均匀退磁故障诊断方法的有效性。

反向消磁条件下磁流变脂隔震模拟试验研究

采用电磁线圈及永磁体共同控制磁场,自主设计一种可反向消磁的磁流变脂(MRG)剪切试验装置。利用ANSYS Electronics软件对该试验装置磁场分布进行仿真分析,并制备不同羰基铁粉质量分数的MRG,采用振动台对反向消磁条件下MRG的动态剪切性能开展试验测试,分别研究励磁电流、激振幅值和激励频率对MRG动态性能的影响。结果表明:羰基铁粉质量分数对MRG的动态性能影响显著;MRG的剪切应力随励磁电流的增大先快速增大后趋于平缓,阻尼力则逐渐减小;MRG的耗能能力随位移幅值的增加而增强;随着加载频率的增大,其阻尼力略有增加。

基于气隙磁密差信号峭度因子的永磁同步电机局部退磁故障诊断

该文提出一种新型基于气隙磁密信号差峭度因子的永磁同步电机局部退磁故障诊断方法。首先,建立永磁同步电机等效磁路模型,根据简化模型分析局部退磁故障后各极主磁路下径向气隙磁密的变化规律。然后,将预存健康电机空载状态下气隙磁密信号与测量的在线状态下气隙磁密信号作差并计算其峭度值,作为故障特征值。取健康电机空载状态下气隙磁密信号与不同工况下气隙磁密信号差峭度值的最大值作为参考值,根据故障特征值与参考值的大小诊断出局部退磁。最后,仿真和实验结果均验证提出的局部退磁故障诊断方法的有效性。

永磁同步电机故障诊断方法研究综述

永磁同步电机(permanent magnet synchronous motor,PMSM)具有结构简单、运行稳定、效率高和外形多样等显著优点,在生产制造领域得到广泛应用。PMSM在工作中不断受到速度变化和负载波动等复杂工况的影响,不可避免地会出现各种故障,如轴承故障、偏心故障、退磁故障和匝间短路故障等。文中综述了PMSM常见故障类型,并总结了自动化领域中基于信号的状态监测方法的现有研究,以用于各类电气和机械故障的检测和诊断。随后,对诊断方法进行了总结,并分析了其优势与限制,探讨了不同信号处理方法在应用中的利弊。最后,根据当前研究现状,讨论了PMSM故障监测与诊断存在的问题和未来发展方向。

电动汽车用永磁同步电机失磁机理与选区渗重稀土研究

由于电动汽车用永磁同步电机(PMSM)具有高功率密度的设计要求,使得磁钢更易受到电磁以及高温影响致使出现不可逆失磁,为此常在磁钢制备时加入大量镝、铽等贵重稀土元素,但该方法使得磁钢材料价格激增。本文以一台“三角”型内置式永磁同步电机为研究对象,分别研究了温度、电枢电流大小以及弱磁角这三个因素对电机磁钢的失磁特性影响,进而确定磁钢的易失磁位置及失磁扩散规律。在此基础上,通过将电机磁钢材料的牌号更改为较低的牌号,并提出合理的选区渗重稀土设计方案,实现了在不损失电机性能的情况下,减少重稀土元素用量的目的。最后,提出一种适用于计算选区渗重稀土设计方案中最大内禀矫顽力提升倍数的方法,可为电动汽车用永磁同步电机磁钢减重稀土研发设计提供参考。

火炮电涡流制退机用钕铁硼的热退磁特性

永磁式电涡流制退机是火炮后坐阻力高效控制领域中一种具有创新性的设计,在耗能密度大、工作环境相对密闭的火炮应用场景下电涡流制退机会出现严重的温升现象,高温会导致钕铁硼材料磁性能的下降继而影响制退特性,现阶段钕铁硼的热退磁过程尚不明晰且缺乏理论表达。为掌握钕铁硼热退磁特性,基于微磁模拟方法,从微观磁矩受热运动的角度定量分析不同温度下钕铁硼的退磁过程,得到宏观钕铁硼的退磁曲线。为使退磁曲线更好地指导工程设计,使用J-A模型对钕铁硼退磁行为进行理论描述,并进行实验验证。分别基于传统的剩余磁通密度模型和J-A模型开展钕铁硼退磁与阻力退化的磁热耦合数值计算,通过与原理样机试验结果进行对比发现,J-A模型对钕铁硼磁性能的描述更为准确。计算不同工作温度及膛压下制退机工作性能,分析温度场下钕铁硼退磁特性及制退机阻尼特性。研究结果表明,最恶劣工况下钕铁硼最大退磁量为0.351 T,制退机最大后坐位移为1108 mm,这为电涡流制退机的设计提供了理论参考。

基于遗传算法的绝热去磁制冷机中PID参数整定

在绝热去磁制冷系统中,PID控制器常用来控制等温磁化或等温去磁过程中磁热模块的温度稳定。由于ADR系统的非线性较强,传统的PID参数整定方法往往效果较差,实际ADR系统中PID的参数整定往往十分依赖于人工试错,耗费大量时间精力。而遗传算法在PID参数调试时对系统的依赖性小,非常适合复杂非线性系统的参数寻优。基于MATLAB语言和集总参数方法,实现了基于遗传算法的绝热去磁制冷机中GGG磁热模块的PID参数整定,为实际工程中的PID参数调节提供参考。

轴向磁场永磁同步电机耦合故障特征分析

轴向磁场永磁同步电机在潮湿、高温和振动的环境长时间运转,容易出现匝间短路和永磁体退磁耦合故障。为了实现对耦合故障产生的信号进行特征分析。首先从电机工作原理入手,建立了电机三维有限元模型,并通过对比实验数据和仿真结果,确定了所建电机模型和实际电机相符合。然后结合simplorer实现了有限元模型对匝间短路故障、永磁体退磁故障和耦合故障的模拟。最后,对比了不同故障状态下电机模型的电磁转矩、感应电势和故障相电流等特征量,并分析了特征量各阶次谐波含量的变化。研究结果确定了有效区分单一匝间短路故障、单一永磁体退磁故障和耦合故障的特征量分别为感应电势分数次谐波含量和故障相电流出现的周期为极对数的电流脉动,为该类电机故障特征分析提供一定的参考依据。

转子温度空间分布差异诱发永磁电机局部失磁特性研究

永磁材料磁特性受工作温度影响较大,高工作温度下存在的不可逆失磁现象是永磁电机高可靠性设计的主要瓶颈。针对内置式磁路结构的高功率密度永磁电机用钕铁硼永磁材料的不可逆失磁问题,基于电机全域空间损耗、温度分布的差异,该文提出一种永磁体局部失磁分析模型与特性计算方法。通过磁体虚拟分块法建立基于温度、退磁率等变量的永磁材料磁特性分析模型,利用电磁场和温度场双向耦合的三维多物理场计算方法,得到电机转子永磁体损耗、温度和局部失磁的空间分布特性。最后,通过对一台115 kW、8极永磁电机样机转子永磁体温度和转子表面磁场的实验测试,验证了分析模型与计算方法的准确性,为永磁电机局部失磁问题研究及精细化防失磁设计提供依据。

永磁同步电机耦合故障特征提取方法仿真

由于永磁同步电机故障的并发性,且耦合故障信号具有较强的关联性,导致永磁同步电机耦合故障特征提取较为困难。为此提出了采用负序电流法和磁链观测法对匝间短路-不均匀退磁耦合故障特征的提取方法。首先推导了正常电机的数学模型,在此基础上搭建仿真模型并验证了其可靠性;其次搭建了匝间短路和不均匀退磁单一故障的仿真模型,验证了负序电流法和磁链观测法在单一故障特征提取时的有效性;最后并对耦合故障的特征进行了对应的提取。结果表明,单一故障特征在耦合故障提取时也有较高的准确性。