Simultaneous resonance of an axially moving ferromagnetic thin plate under a line load in a time-varying magnetic field

In this paper,the simultaneous resonance of a ferromagnetic thin plate in a time-varying magnetic field,having axial speed and being subjected to a periodic line load,is studied.Based on the large deflection theory of thin plates and electromagnetic field theory,the nonlinear vibration differential equation of the plate is obtained by using the Hamilton′s principle and the Galerkin method.Then the boundary condition in which the longer opposite sides are clamped and hinged is considered.The dimensionless nonlinear differential equations are solved by using the method of multiple scales,and the analytical solution is given.In addition,the stability analysis is also carried out by using Lyapunov stability theory.Through numerical analysis,the variation curves of system resonance amplitude with frequency tuning parameter,magnetic field strength and external excitation amplitude are obtained.Different parameters that have significant effects on the response of the system,such as the thickness,the axial velocity,the magnetic field intensity,the position,and the frequency of external excitation,are considered and analyzed.The results show that the system has multiple solution regions and obvious nonlinear coupled characteristics.

External Magnetic Field Effect on Bifacial Silicon Solar Cell’s Electrical Parameters

The aim of this work is to present a theoretical study of external magnetic field effect on a bifacial silicon solar cell’s electrical parameters (peak power, fill factor and load resistance) using the J-V and P-V characteristics. After the resolution of the magneto transport equation and continuity equation of excess minority carriers in the base of the bifacial silicon solar cell under multispectral illumination, the photo-current density and the photovoltage are determined and the J-V and P-V curves are plotted. Using simultaneously the J-V and P-V curves, we determine, according to magnetic field intensity, the peak photocurrent density, the peak photovoltage, the peak electric power, the fill factor and the load resistance at the peak power point. The numerical data show that the solar cell’s peak power decreases with magnetic field intensity while the fill factor and the load resistance increase.

Influence of a Static Magnetic Field on Beam Emittance in Laser Wakefield Acceleration

The enhancement of trapping and the optimization of beam quality are two key issues of Laser Wakefield Acceleration (LWFA). The effect of a homogenous constant magnetic field B0, parallel to the direction of propagation of the pump pulse, is studied in the blowout regime via 2Dx3Dv Particle-In-Cell simulations. Electrons are injected into the wake using a counter-propagating low amplitude laser. Transverse currents are generated at the rim of the bubble, which results in the amplification of the B0 field at the rear of the bubble. Therefore the dynamics of the beam is modified, the main effect is the reduction of the transverse emittance when B0 is raised. Depending on beam loading effects the low energy tail, observed in the non-magnetized case, can be suppressed when B0 is applied, which provides a mono-energetic beam.

Thermo-magnetic analysis of thick-walled spherical pressure vessels made of functionally graded materials

This study presents an analytical solution of thermal and mechanical displacements, strains, and stresses for a thick-walled rotating spherical pressure vessel made of functionally graded materials (FGMs). The pressure vessel is subject to axisymmetric mechanical and thermal loadings within a uniform magnetic field. The material properties of the FGM are considered as the power-law distribution along the thickness. Navier’s equation, which is a second-order ordinary differential equation, is derived from the mechanical equilibrium equation with the consideration of the thermal stresses and the Lorentz force resulting from the magnetic field. The distributions of the displacement, strains, and stresses are determined by the exact solution to Navier’s equation. Numerical results clarify the influence of the thermal loading, magnetic field, non-homogeneity constant, internal pressure, and angular velocity on the magneto-thermo-elastic response of the functionally graded spherical vessel. It is observed that these parameters have remarkable effects on the distributions of radial displacement, radial and circumferential strains, and radial and circumferential stresses.

脉冲负载直流传输方案研究及验证

针对脉冲负载的直流供电线缆周围电磁场、谐振和谐波干扰、电力系统层面稳定性等问题,分别对电缆的不同排布方式,聚焦电磁场、磁力场、电热耦合分析,进行了一系列研究并提出了解决方案,降低了脉冲负载对电缆自身和周围环境的影响,确保了舰船电力系统的稳定可靠运行。

电机学中的一些“反常”现象及其成因分析

描述了电机学中的一些“反常”现象,分析了这些现象的成因,并用简明的语言进行归纳,为相关领域的研究人员提供一定参考。

受载砂岩变形破坏过程磁场响应规律研究

探寻岩石破坏过程新的物理响应规律,将会推动岩体监测预警技术的发展。利用磁通门弱磁检测技术,开展了单轴加载和循环加卸载砂岩受载破坏磁场监测试验,测试了砂岩在变形破坏过程中的磁场信号,分析了磁场与载荷、声发射之间的关系。结果表明:砂岩在变形破坏过程中能够产生磁场信号,在单轴加载过程中,随着载荷增加,压密阶段磁场信号波动上升,波动系数较大;弹性阶段磁场信号稳定增大,波动系数变小;塑性阶段磁场信号显著增加,塑性阶段后期波动系数开始增大;破坏阶段磁场信号快速增加,波动系数变化较大,与试样载荷降和主破坏对应。相对于波动系数,磁场信号方差在前3个受载阶段较为稳定,破坏阶段的方差逐渐增大,并出现显著突变。在循环加卸载过程中,当载荷增加时磁场信号逐渐增大,载荷减小时磁场信号逐渐减小,试样临近失稳破坏时,磁场信号快速增加,显著高于前期循环加卸载过程。磁场信号与声发射计数具有较好的对应关系,表明磁场的产生与试样变形破坏密切相关。在岩体变形破坏过程中,矿物颗粒发生非均匀变形,界面处的电平衡被打破,自由电荷产生、迁移,引起电流变化,运动电荷或电流变化产生了磁场信号。利用磁场信号评估岩体的稳定性,有望成为一种无损、非接触、可连续监测的新方法。

Magnet在无刷交流同步发电机空载瞬态电磁场计算中的应用

解析法在遇到电动机电磁场瞬态问题时凸显其弊端,有限元法是目前广泛引用的电磁数值计算方法。而针对航空交流电源中无刷同步发电机的有限元电磁分析的研究较少,因此以某型航空交流电源主发电机为研究对象,阐述了应用Magnet软件做电磁瞬态仿真的原理与建模步骤,并仿真了同步发电机在空载工况下的电磁场分布。通过实测对比,证明了模型的实用性。该模型也可以作为元件级封装在Simulink中做进一步的航空电源系统仿真研究,并对其它类型航空电源的计算机辅助设计提供了实际参考价值。

基于漏磁负载归一化Lissajous图形分析的变压器绕组故障诊断

漏磁检测作为变压器故障诊断最具潜力的在线方法之一,由于其漏磁信号受到外部环境和运行条件的影响,实用性还需进一步提升。为了解决这些问题,本文提出了一种基于Lissajous图形与卷积神经网络(CNN)相结合的变压器绕组故障诊断方法。首先,对变压器绕组进行仿真建模,并通过与实验平台测试数据进行一致性验证。然后,设置不同程度和位置的匝间短路故障,收集绕组外部不同位置的漏磁信号。最后,使用本文所提出的LG–CNN方法对绕组故障进行诊断。该方法包括以下3个关键步骤:1)对多工况变压器漏磁信号进行负载归一化;2)将负载归一化后的漏磁信号转换为2维Lissajous漏磁图像;3)使用卷积神经网络对2维漏磁图像进行特征提取并对绕组故障进行诊断。基于漏磁信号的Lissajous图像可以很好地整合各测点漏磁信息之间的关系,针对Lissajous图形随负载变化而变化的问题,本文提出了一种漏磁负载归一化方法,通过实体变压器和高仿真模型实验,验证了所提漏磁负载归一化方法的有效性以及所提检测方法在区分不同程度和位置绕组短路方面的可行性。

谐波下干式变压器铁心磁场-温度场仿真分析

为了更加准确地研究干式变压器铁心磁场和温度场分布,分析不同激励对干式变压器铁心磁场损耗和热点温升的影响,首先使用Maxwell计算了干式变压器瞬态磁场分布,得到空载条件下铁心磁场损耗。在此基础上提出了一种三维干式变压器磁场-温度场耦合计算方法,将磁场损耗耦合至Fluent作为温度场计算的热源,采用流固耦合的方法计算干式变压器温度场分布,获得铁心热点温度和位置。最后,基于上述方法对谐波下变压器铁心的磁场和温度场进行计算,分析了谐波次数和谐波含有率对干式变压器铁心损耗和温升的影响。所研究内容为谐波下变压器铁心温升监测提供了参考。

中频变压器铁心的磁-热耦合计算与实验

基于中频变压器磁耦合的电力电子变压器是新型电力系统中的关键装置。考虑频率对超薄硅钢磁化及损耗特性的影响,基于电磁场与温度场间接耦合的计算方法,对一台40 kV·A/400 Hz超薄硅钢中频变压器不同频率条件下铁心的电磁场与温度场分布进行求解,并开展变压器模型的空载实验,得到不同频率下的空载损耗和温升分布。通过仿真与实验数据的比较,误差均在允许范围内,验证了磁-热耦合分析的准确性,为中频变压器铁心散热和材料选择提供参考依据。

基于WELDINST的变压器抗短路能力校核计算方法

随着电力系统中非线性负荷的增加,电力变压器在工作过程中承受的漏磁场显著增强,这严重影响了变压器的抗短路能力。近年来,抗短路能力不足导致的变压器损坏事件频发,凸显了准确预测变压器抗短路能力的重要性。该文深入分析了变压器在不同短路工况下的短路电流和电磁力的计算原理,并介绍了一种基于WELDINST软件的变压器抗短路能力校核系统。该系统能够根据110 kV和220 kV电力变压器的原始设计参数以及返厂检修后的设计参数,对变压器的抗短路能力进行精确校核。通过该系统的应用,不仅可以提前识别变压器抗短路能力的潜在风险,还能有效管控新入网主变压器的质量。本文的分析结果显示,运用WELDINST技术对变压器的抗短路能力进行校核,为电网企业提供了一种有效的手段来实现新入网变压器的品控。

冲击载荷下电涡流阻尼器磁场研究

为研究冲击载荷下电涡流阻尼器的磁场特性,建立了永磁式电涡流阻尼器模型和等效磁路模型,分析了空气间隙处磁场强度与结构参数之间关系;利用有限元法对冲击载荷下电涡流阻尼器的静、动态磁场以及涡流场特性展开研究。研究发现:电涡流阻尼器静态磁场呈“几”字形,阵列式分布,冲击载荷下次级筒产生的电涡流将会与静态磁场相互作用形成一个时刻变化的“几”字形动态工作磁场,且变化情况与阻尼器受到的冲击载荷有一定关系,本文研究结果对提高冲击载荷下电涡流阻尼力控制具有一定的参考价值。

Magnetic-structure coupling dynamic model of a ferromagnetic plate parallel moving in air-gap magnetic field

Aiming at the air-gap magnetic field excited by wall armatures,Laplace’s partial differential equation of air-gap magnetic potential is achieved by means of the electromagnetic field theory.According to the magnetic boundary conditions and the method of separation of variables,the magnetic potential of the air-gap magnetic field is obtained.Based on the magnetization force model and Lorentz force of ferromagnetic thin-walled structures,and introducing the electromagnetic constitutive relations and boundary conditions,the calculation model of electromagnetic force of the soft ferromagnetic thin plate moving in air-gap magnetic field is established.Considering geometric nonlinearity,expressions of strain energy and kinetic energy of the elastic thin plate and the work of forces are given,respectively.The magnetic-structure coupling nonlinear vibration equations of ferromagnetic thin plate parallel moving in the air-gap magnetic field excited by armatures are obtained by using the Hamilton principle,which can be of the characterization of the system dynamics model with electro-magneto-velocity-mechanical interaction.Through numerical examples,primary resonance characteristics of the strip thin plate under the action of air-gap magnetic force are obtained.The results show that the two stable amplitude values will increase as amplitude of magnetic potential increases and thickness of air-gap decreases,and the amplitude’s multi-valued region will change due to the varieties of magnetic potential,air-gap and velocity.The model established in this paper is a theoretical reference for investigation on the multi-field coupling dynamic behaviors of structures moving in complex electromagnetic fields.

Performance investigation of plasma magnetohydrodynamic power generator

A magnetohydrodynamic （MHD） power generator system involves several subjects such as magnetohydrodynamics, plasma physics, material science, and structure mechanics. Therefore, the performance of the MHD power generator is affected by many factors, among which the load coefficient k is of great importance. This paper reveals the effect of some system parameters on the performance by three-dimensional （3D） numerical simulation for a Faraday type MHD power generator using He/Xe as working plasma. The results show that average electrical conductivity increases first and then decreases with the addition of magnetic field intensity. Electrical conductivity reaches the maximum value of 11.05 S/m, while the applied magnetic field strength is B = 1.75 T. When B 〉 3 T, the ionization rate along the midline well keeps stable, which indicates that the ionization rate and three-body recombination rate （three kinds of particles combining to two kinds of particles） are approximately equal, and the relatively stable plasma structure of the mainstream is preserved. Efficiency of power generation of the Faraday type channel increases with an increment of the load factor. However, enthalpy extraction first increases to a certain value, and then decreases with the load factor. The enthalpy extraction rate reaches the maximum when the load coefficient k equals 0.625, which is the best performance of the power generator channel with the maximum electricity production.

表贴式永磁游标电机电磁特性和实验验证

为验证表贴式永磁游标电机高转矩密度的基本原理,基于表贴式永磁游标电机基本方程的分析,研究了电机关键参数对转矩的影响。设计了电机参数,给出了结构示意图,根据定子槽数和极对数,分析了槽电动势星形图,并给出了绕组连接图。基于二维有限元模型深入分析了电机的电磁特性,包括空载磁链、空载电动势、两种励磁源单独作用时的气隙磁密、齿槽转矩和电磁转矩。制作了永磁游标电机实验样机,对其空载反电势进行了测试。仿真和实验结果验证了理论分析的正确性和二维有限元模型的准确性,为永磁游标电机的精确控制提供了有力支撑。

负载能力最大化的PMSM弱磁控制交轴电压给定策略

永磁同步电机通过弱磁控制可实现宽领域调速,其特有的交叉耦合现象使双电流调节器在进行弱磁控制时具有诸多限制。利用交叉耦合现象的单电流弱磁控制策略具有重要研究价值。定交轴单电流调节器弱磁策略存在电机带载能力未得到充分利用的不足。提出一种负载能力最大化的新单电流调节器弱磁控制策略。经仿真验证,该策略能够显著提高永磁同步电机在进行弱磁控制时的最大负载能力。

基于保角变换与等效磁路法的永磁直驱发电机气隙磁场计算

该文开展了负载工况下永磁直驱发电机气隙磁场研究。基于精确域求解和保角变换,计算考虑齿槽效应的气隙磁场标量磁势;采用离散线电流元,定量模拟发电机定转子局部出现的磁饱和现象;基于考虑几何尺寸的定转子非线性磁阻计算方法,建立包含发电机定转子结构以及气隙长度的等效磁路,给出相应的迭代求解流程。以实际在役兆瓦级永磁直驱风力发电机为对象,计算考虑齿槽效应的气隙磁场分布,分析了空载和负载工况下磁饱和效应对气隙磁场分布曲线波形和谐波成分的影响,并与有限元计算结果对比,验证了所提出的分析模型和求解方法的有效性。

V型内置式永磁同步电机空载气隙磁场解析计算

针对V型内置式永磁电机气隙磁场解析计算问题,提出一种新的V型内置式永磁同步电机空载气隙磁场的解析计算模型。在二维精确子域方法基础上,提出5条等效关键准则,用等效解析永磁体电机模型代替初始的V型永磁体电机模型。等效解析模型划分为定子槽、定子槽槽口、气隙、扇形和环形5个求解域。在定子槽、定子槽槽口和气隙区域建立拉普拉斯方程,在扇形和环形区域建立泊松方程。用分离变量法求解各区域的矢量磁位表达式,根据各个求解域的边界条件和交界条件求出矢量磁位表达式中的谐波系数。对等效解析模型计算结果与V型内置式永磁同步电机的有限元法仿真结果进行比较,误差仅为0.97%,验证了等效准则建立的解析计算模型计算V型内置式永磁同步电机空载气隙磁场的有效性。

基于双曲余切变换的Halbach阵列表贴式永磁电机转子偏心气隙磁场解析模型

精确计算气隙磁场是设计和分析永磁电机的关键。Halbach阵列永磁电机具有良好的转矩输出特性。转子偏心会对永磁电机产生不良影响,准确获得其偏心气隙磁场分布具有重要意义。采用双曲余切变换解析计算Halbach阵列表贴式永磁电机转子偏心气隙磁场。该文建立了Halbach阵列定子开槽、转子偏心永磁电机二维模型。将同心解析模型分为三类子区域,利用各区域边界条件求解拉普拉斯方程和泊松方程,通过矢量磁位求得同心气隙磁场,利用相对磁导函数对其进行修正,从而获得偏心空载气隙磁场,对其进行研究,并利用回归评价指标进行评估。不同偏心率下气隙磁通密度、不平衡磁拉力、齿槽转矩的解析结果同有限元结果吻合,验证了该文解析模型的有效性和正确性。