基于等效磁流法的平面近场测量技术研究

为了进一步论证等效磁流法的近场-远场变换算法在平面近场测量中的实用性与准确性,本文首先根据矩量法（MOM）建立了平面天线口径面上等效磁流的辐射电场方程,利用波导探头采集待测天线平面近场的电场分布,通过共轭梯度法求解矩阵方程,得到天线口径面上的等效磁流分布,之后由格林函数计算出天线远场方向图。最后,通过两种喇叭天线进行实验测试验证。同时将等效磁流法计算出的远场方向图以及由传统的平面波展开法计算出的远场方向图与紧缩场天线测试暗室的测量结果进行对比,结果发现本文算法反演出的远场方向图比平面波展开法在相同测试数据下反演出的远场方向图与紧缩场测量结果相比一致性更好,其中线性角锥喇叭天线的E面和H面方向图吻合度均达到,双脊喇叭天线的E面方向图吻合度达到,H面方向图吻合度达到,验证了等效磁流法算法在平面近场测量中的准确性。     

静电放电电磁脉冲辐射场数值建模与仿真

针对静电放电(ESD)电磁脉冲测试及其防护这一静电研究领域的难点问题,利用时域有限差分法并采用电偶极子辐射模式建立了ESD电磁脉冲辐射场的数值模型。在分析了拟合IEC 61000—4—2标准规定的ESD电流波形的5种数值模型后,根据t=0时刻电流值和电流导数为0的ESD电流要求,选择脉冲3项式作为ESD电流表达式进行仿真计算。采用4 kV放电电压作为脉冲源,通过仿真计算得出相对辐射源3个位置处的电磁场分量Ex和Hx。计算结果表明,ESD电磁脉冲辐射场在自由空间的时域特点是脉冲具有极快上升沿、幅度变化剧烈且衰减较快。仿真结果为ESD电磁脉冲测试及其防护提供理论支撑。     

风电机组内电子设备的雷电电磁干扰分析

为应对风电机组内电子设备所受雷电电磁干扰,提出了一种计算雷击情况下风力发电机组塔筒内电磁场分布的简化算法。该法将塔筒等效为一个耦合的电网络,雷电流视为注入此网络的电流源,通过求解电路方程得到塔筒上的暂态电流分布;在所计算的塔筒电流分布的基础上,根据麦克斯韦方程,先计算出塔内某一点处的矢量磁位,然后利用矢量磁位计算塔内空间的感应电场和磁场强度分布;将计算结果与文献中的近似有限差分法进行了比较,二者基本相符。不同因素对计算结果的影响,可为塔内电子系统的防雷设计提供依据。     

辐射取向永磁环的计算

本文藉助于两种永磁理论模型(标量磁位模型和向量磁位模型)以及两种计算磁场的算法(有限元素法和有限差分法,对辐射取向永磁环进行了多种方案的计算,简要介绍了各方案的具体计算公式,算法以及程序框图,并且列出它们的计算结果。     

高压开关设备特高频局部放电信号仿真特性研究

局部放电电磁波信号在通过开关柜缝隙处向外传播时受缝隙的影响而产生衰减变化。在开关柜缝隙处放置传感器是分析局部放电特性的一种方法,它可以接收开关柜中辐射出来的电磁波信号。为研究开关柜缝隙对UHF信号传播的影响,本文采用时域有限差分法对UHF信号的衰减特性进行了建模分析,研究了UHF信号在开关柜缝隙处的辐射场强时域参数变化特性;研究了UHF信号通过开关柜缝隙过程前后辐射场强时域参数变化特性。研究结果表明,电磁波通过开关柜缝隙时各个方向的场强分量是不同的;当电磁波通过开关柜缝隙向外传播时衰减幅度很大。     

线缆集总等效电磁干扰源测量模型研究

复杂电磁场激励下线缆终端的响应很难通过数值计算的方法准确获得。基于场线耦合理论,提出了线缆的集总等效电磁干扰源的测量模型。根据集总等效源与终端负载无关的性质,得到这一激励下的线缆终端的集总等效源,为分析和研究相同外场激励不同终端负载下的终端响应提供了条件。利用两线架空线模型,通过理论分析验证了该模型的有效性,并研究了终端含有动态元件网络的电磁干扰问题,该模型分析结果与时域有限差分法得到的瞬态时域结果波形和幅值均一致。应用该方法获得了两线串扰问题的集总等效源,并通过计算获得了不同端部负载下的电压响应,计算结果与实验结果误差≤8%。准确地获得电磁干扰等效源,通过建立抑制元件的宽频模型,可以系统地研究抑制措施的抑制效能。     

基于分布式串联电感雷电回击电磁模型的电流分布及辐射电磁场研究

雷电通道模型被广泛用于低电离层的瞬态光学发射、雷电高能辐射、地球电磁环境以及雷电与各种对象的相互作用的研究中,以确定电磁辐射源。雷电回击电磁模型采用麦克斯韦尔方程组进行全波求解,计算结果具有自洽性。本文对基于串联分布式电感雷电回击模型进行了研究,采用时域有限差分法(FDTD)获得通道中电流的时空分布,通过偶极子法计算相应的辐射电磁场。计算结果表明,分布电感值在2~10μH/m范围时,雷电流传播速度在c/3~2c/3范围之间;分布电感值越大,则雷电流传播速度越小,近区的辐射电场强度越高,同时其电场强度随距离的衰减也越剧烈;辐射磁场对分布电感值变化不敏感。     

用镜像法计算冲击脉冲辐射天线辐射电场

为方便地计算抛物面冲击脉冲辐射天线的辐射电场,根据由张量法得到的任意的线天线电场计算公式,利用镜像法推导得到了冲击脉冲辐射天线辐射电场的时域解析表达式;搭建了超宽带电磁脉冲实验系统,由横电磁波喇叭天线测试场设备测试抛物反射面超宽带辐射天线产生的辐射场;应用解析表达式计算了该实验系统的时域辐射场,并与实验测试结果进行了比较。结果表明解析计算得到的辐射场波形与测试结果能够较好地符合,峰峰值相差<1V,上升时间相差≤5ps,说明了解析计算的正确性。     

基于三维等效磁网络法计算混合励磁爪极发电机负载特性

用三维等效磁网络方法计算了一台新型混合励磁爪极发电机负载特性.传统的电路法和磁路法不适合求解此类发电机电磁场.等效磁网络方法计算时间短且计算精度较高,在给出新型结构发电机三维等效磁网络模型的基础上,进一步通过计算得到混合励磁爪极发电机负载特性,最后给出输出电流优化结果.与有限元计算结果的一致性验证了计算结果的有效性,对混合励磁发电机的优化设计具有一定的理论参考价值.     

基于有限差分和有限体积法相结合的油浸式变压器三维温度场计算

为准确计算油浸变压器的温度场,在对比有限体积法(FVM)和有限差分法(FDM)各自优点的基础上,提出了一种计算变压器温度场的混合计算方法。以驻马店金桥变电站的一台31.5 MVA主变为例,建立了3维模型,利用有限体积和有限差分混合计算方法,并在绕组和铁芯的热传导计算中采用了高精度的预条件共轭梯度解法(PCGM),计算了变压器的3维温度场。将利用混合方法的平均温度计算结果分别与实际监测数据、使用同样模型的FDM及FVM算法计算出的数据、以及使用IEEE导则模型计算出的数据进行了对比。对比结果表明:混合算法的计算精度明显高于利用IEEE导则模型、FDM算法和FVM算法的计算结果,证明了这种混合计算方法能更准确地计算油浸式变压器的内部温度场。     

Using WCS‐FDTD method to simulate various cylindrical metallic enclosures

The weakly conditionally stable (WCS) finite‐difference time‐domain (WCS‐FDTD) method in the cylindrical coordinate system is employed to compute the electromagnetic coupling and shielding of various cylindrical enclosures. In the WCS‐FDTD method, a larger time‐step size than that allowed by the Courant–Friedrich–Levy stability condition limitation can be set because the algorithm of this method is WCS. Consequently, an increase in computational efforts caused by fine cells due to thin sots can be prevented. The results from the WCS‐FDTD method agree well with the results from the conventional FDTD method, and the required CPU time for the WCS‐FDTD method is much shorter than that for the FDTD method. Careful investigation of different aspects of the shielding properties of the cylindrical enclosures is performed, and the shielding performance of the cylindrical enclosure and rectangular enclosure is compared. The result obtained in this paper can be used to design a practical cylindrical shielding enclosure. Copyright © 2010 John Wiley & Sons, Ltd.     

高次模传输线法分析有孔双层屏蔽腔体屏蔽效能

采用考虑了腔内高次模的传输线方法分析了有孔屏蔽腔体的屏蔽效能,与时域有限差分法(FDTD)结果的比较证明了它的有效性。把该方法扩展到双层屏蔽腔内电场的屏蔽系数的计算,它与单层屏蔽腔内屏蔽系数的比较表明:采用双层屏蔽使得腔体的屏蔽效能大为提高。进一步把单个孔缝推广为具有一定隔距、相同形状且轴对称分布的孔缝阵列,结果表明:在单层屏蔽腔体中,保持孔缝总面积不变时,随着孔阵中孔缝数量的递增,单层屏蔽腔体的屏蔽效能逐步的提高;把屏蔽腔体的单层孔阵改进为双层孔阵后,腔体的屏蔽效能随孔缝数量递增时的提高幅度,整体上比单层孔阵时的提高幅度要大。因此,把单层屏蔽改进为双层屏蔽,或者保持孔缝总面积不变时增加孔缝数量都可以有效地提高屏蔽效能。     

颅内压检测分析仪电磁屏蔽效能定量计算方法

提出一种定量计算无创颅内压检测分析仪电磁屏蔽效能的方法,使仪器电磁泄漏这一不可控因素变得可控。基于经典Schelkunoff原理及传输线理论推导出平面波屏蔽模型,并引入箱体孔隙修正系数对屏蔽模型进行修正;对修正前后的屏蔽模型进行仿真分析,获得箱体屏蔽效能计算模型;通过辐射发射试验对屏蔽前后仪器的辐射场强数据进行测试,对测试结果与模型计算结果进行比较。结果表明仪器的屏蔽效能计算值与试验值场强衰减一致,故将该计算模型作为颅内压检测分析仪电磁屏蔽效能定量计算的一种方法,同时为医用电气设备电磁兼容设计、测试及整改提供重要参考。     

金属屏蔽盒强瞬态电场屏蔽效能实验

基于实验室的强电磁脉冲(EMP)模拟器、强瞬态三维电场测量系统和弱瞬态电场测量系统,本文对带孔金属屏蔽盒强电磁脉冲屏蔽特性进行了系统的研究,提出应用时域电场强度最大值评估金属屏蔽盒的强瞬态电场屏蔽效能.基于快速傅里叶变换(FFT)本文还对带孔金属盒的强瞬态电场频域屏蔽效能进行了分析.     

基于FDTD法的连接器电磁屏蔽性的研究

基于FDTD法模拟研究了连接器的接线孔数目、大小对外壳屏蔽性的影响。结果显示,孔的总面积一定时,每侧采用双孔接线比通常单孔时的屏蔽性能更好。进入腔体内的电磁波发生谐振,谐振频率由腔体的内部结构决定,与表面上的孔无关。     

Three-dimensional magnetic field analysis of a system containing coil currents and iron elements using the virtual current method

This paper proposes a method of analyzing the three-dimensional magnetic field of a system containing coil currents and magnetic substances using virtual currents. Various methods have been presented for analysis of a three-dimensional static field in an open boundary space; however, in a large-scale problem, the computational size easily exceeds the acceptable limit of computing time and machine capacity. The basic idea of the proposed method is to divide the whole region into interior and exterior regions with an artificial boundary and to substitute virtual currents for source currents and magnetic substances within the boundary. The use of virtual currents reduces the number of elements to be analyzed and shortens computing time while maintaining accuracy of analysis. In this paper, a method of determining virtual current is proposed and principal parameters of virtual currents that affect accuracy of analysis are examined. The conditions under which the virtual current method can be applied are examined through analysis of errors introduced by the virtual current method. This method has been applied to analyze magnetic shielding of a magnet for magnetic resonance imaging. This example proves that the proposed method is effective in reducing the scale of analysis and computing time.     

Identification of Power Frequency Industrial Magnetic Field Sources for Shielding Purposes

In any industrial installation, power electric systems generate extremely low frequency magnetic fields. Field amplitude values must fulfill the limits related to health effects or to disturbances on electromagnetic devices, and a shielding system is sometimes necessary. The design of magnetic field shields requires the simulation of the sources and of the shields in order to evaluate the main parameters like geometry, material, and position with respect to sources. An alternative approach is proposed in this paper which requires one to measure a spatial distribution of the magnetic field amplitude. Actual field sources are simulated by means of suitable simplified sources handled by analytical relations. An identification process of measured magnetic fields is performed using a genetic algorithm applied to the simplified source system. The simplified system is a suitable combination of three-phase sources, and it seems able to create a realistic magnetic field distribution in both space and time. This paper presents the proposed method and its application to the design of a conductive shielding to reduce the leakage fluxes of a three-phase transformer without enclosure. The magnetic field to be shielded is evaluated with a simple 3-D model of a transformer constituted by three windings in air with current values deduced from the equivalent magnetomotive force which is considered the actual source. Unshielded fields on a plane region are used to identify the simplified source, and the effects of a conducting aluminum shielding are compared using actual and simplified sources. The influence of some parameters of the simplified sources on the results is discussed. Finally, the application for the design of a magnetic field shielding in real substation is presented.      

ESD辐射场与带孔缝金属腔体耦合的数值研究

采用FDTD法研究了ESD电流注入细导线所产生的辐射场在其近场区域与带孔缝金属腔体的耦合问题 ,建立了耦合数值模型。计算分析表明 ,在金属腔体内的孔缝周围区域存在较强的耦合场 ,腔体内被激励起以TE10 1模、TE2 0 1模和TE112 模为主的谐振场 ;对面积相等的方孔、矩形孔和孔阵 ,通过长边与导线垂直的矩形孔和方孔的耦合场比较强 ,而通过长边与导线平行的矩形孔和孔阵的耦合场比较弱     

Large‐scale magnetic field analysis by the hybrid finite element‐boundary element method combined with the fast multipole method

This paper describes a large‐scale magnetic field analysis by means of the hybrid finite element‐boundary element (FE‐BE) method. The hybrid FE‐BE method is well‐suited for solving open electromagnetic field problems that comprise movement, nonlinear media, and eddy current. In general, however, large memory and computational costs are required due to the dense blocks in the system matrix generated by the BE part of the hybrid formulation. In order to overcome the above difficulties, we introduce the fast multipole method (FMM) to the hybrid FE‐BE formulation developed by ourselves. Furthermore, we propose a novel preconditioning technique suitable for the hybrid FE‐BE method with the FMM. Some numerical results that demonstrate the effectiveness of the proposed approach are also presented. ©2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(1): 73–80, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20508