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《高电压技术》2015,(12)
柔性直流(VSC-HVDC)换流站的建立和输电电压等级的提高对换流系统的电磁兼容问题提出了很高的要求。为此,提出了柔性直流换流系统辐射电磁骚扰的计算方法,并基于华北电力大学新能源实验室的VSC-HVDC实验平台开展了测试实验:首先分析了换流系统运行状况并采用高分辨率探头和高性能示波器测量获得了辐射电磁骚扰源特性;然后,采用天线理论并结合矩量法,对换流系统的实际物理结构进行了建模;最后,在仿真软件FEKO中计算了换流系统产生的辐射电磁骚扰,并对换流系统各关键点的辐射电磁骚扰特性进行了分析。研究结果表明:换流阀、变压器、电抗器、交直流母线周边辐射电磁骚扰强度最大,二次设备处辐射电磁骚扰强度随频率上升而缓慢增大,在频率为20 MHz以后有下降的趋势;因为换流系统近场在频率为20 MHz时产生广义谐振,所以其辐射电磁骚扰强度最大。空间电磁场实际测量结果与计算结果的对比验证了该建模方法的有效性。 相似文献
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数字图像探测仪在电子测量领域中具有重要意义,它使电子测量由一维探测扩充为二维展示。本文具体介绍数字图像测控仪中的重要作用,电路结构,数字图像隔行扫描技术性,非CCIR601标准图像的技术处理、控制器工作原理等。 相似文献
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《智能电网》2016,(11)
取向硅钢因其具有优异的磁特性常应用于变压器铁心。在实际变压器运行工况下,铁心中的局部磁场同时包含交变磁场和旋转磁场,而传统的一维磁特性测量法只能测量电工钢片在交变磁场激励下的磁特性,不能体现旋转磁场下磁性材料的二维磁特性。忽略旋转磁场对硅钢片和铁心性能的影响,会给电气设备分析设计和能耗估算带来较大误差。本文简要阐述了电工钢片二维磁特性测量原理,详细介绍了包括转矩磁力计、十字叠片测量装置、Brix方形单片测量仪、六角旋转测量仪和垂直旋转单片测量仪等典型的二维磁特性测量平台及其优缺点,概述了二维磁特性测量系统主要构成要素及运行原理。在此基础上,提出了目前二维磁特性测量领域在测量平台设计和励磁波形反馈控制过程中存在的问题和改进的方向。 相似文献
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针对当前精密作动技术领域对精密定位系统提出越来越高的要求,设计了一种由蝶形直线超声电机驱动的二维精密定位平台系统。该定位平台系统行程为50 mm?50 mm,以直线型增量光栅编码器作为位置反馈元件,通过上位机编程实现运动控制卡对精密定位平台系统进行控制。为了实现直线超声电机的驱动,设计了一种新型直线超声电机驱动器,实现驱动电压和驱动频率的独立控制。在控制过程中,通过使用复合控制技术,同时结合直线超声电机具有高分辨率步进的控制特性,最终使系统达到高精度运动的控制效果。实验结果表明,在0~50 mm行程内,实现了小于0.28?m的定位精度。 相似文献
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Approximate image currents for the Sommerfeld half‐space problem with vertical electric and magnetic current sources above double negative half‐space is found using the discrete image theory and Laplace transform. This method would found its applications in investigation of dipole radiation above metamaterial half‐space and in describing the focusing mechanism of metamaterial lenses. In order to efficiently consider the effects of metamaterial half‐space, discrete image dipoles are defined by proposing an exponential series for reflection coefficient. Unknown constants (the loci of images) in the argument of the exponential function are determined by equating the coefficients of the Taylor series for exact reflection coefficient with those of the proposed approximate series. Thus, the calculation of integral with oscillating integrand reduces to the solution of polynomial equation for the zeros of polynomials. As an application for the proposed approach, the field focusing in double negative is investigated. Thanks to the fast and accurate methods for finding the zeros of polynomials, it is shown that in addition to its good accuracy, this method decreases the computational time for field calculations in comparison with the exact methods. It is seen that for the negative refractive index beside −1, the complex images approach to infinity and have negligible effect on the scattering field of dipole. For the other negative indexes the complex image blurs the real image. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Lightning Observation in 3D Using a Multiple LF Sensor Network and Comparison with Radar Reflectivity 下载免费PDF全文
SATORU YOSHIDA TING WU TOMOO USHIO YUJI TAKAYANAGI 《Electrical Engineering in Japan》2016,194(3):1-10
A three‐dimensional (3D) lightning mapper consisting of multiple low‐frequency (LF) sensors has been developed to monitor thunderstorms and to estimate their charge structure. We have been conducting an observation campaign using the 3D lightning mapper in Kansai, Japan, since October 2012. In this study, we determine 3D source locations of intracloud and cloud‐to‐ground flashes and compare them with the radar reflectivity estimated by phased‐array radar (PAR) with high temporal and spatial resolution. Most LF sources are located in high radar reflectivity regions, confirming that the 3D LF lightning mapper monitors thunderstorms. A lightning flash with heavy branches is clearly imaged. Based on the bidirectional leader theory that negative and positive ends of a lightning leader develop simultaneously, we estimate the positive and negative charge regions in a thundercloud from the LF source locations. The radar reflectivity estimated by PAR supports the charge structure estimated by LF source locations. 相似文献
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A modification of effective medium theory for two-component nonmagnetic metal–dielectric metamaterials is developed for use in the microwave frequency range. The metamaterial is represented as an unbounded isotropic dielectric host material with periodically embedded nonmagnetic metallic inclusions of cylindrical or spherical shape. The effective electromagnetic response of the metamaterial is represented by the tensor of the effective relative permittivity and tensor of the effective relative permeability. The losses of the metamaterial are also evaluated in this study. A physical interpretation for the nature of the effective properties of such metamaterials is given. Analytical models of the proposed effective medium theory are benchmarked against numerical simulations using commercial electromagnetic software. Two compact microwave rectangular dual-band patch antennas on such metamaterial substrates are designed in this study. 相似文献
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频率选择超材料是隐身雷达罩的理想罩体材料,内部存在大量周期性金属超结构单元,常规雷电屏蔽方法无法对其形成有效保护。该文利用环氧树脂基材制备一种频率选择超材料,研究雷电冲击电压下这种超材料表面的放电通道形貌特征,提出夹角因子参数并测量了50%沿面放电电压。在此基础上,利用夹角因子对超材料表面绝缘特性进行评估,得出沿面放电电压随偏离角变化的规律。结果表明,超材料表面放电通道呈折线型,由两类放电路径组成:第一类路径与超结构周期方向平行,第二类路径与超结构周期方向夹角45°。进一步分析发现,超材料沿面放电的主通道发生在沿绝缘间隙总长度最短的路径上。随着双电极连线偏离超结构周期方向角度的增大,沿面放电电压先增后减,当偏离角为0°或45°时,放电电压较低;当偏离角为22.5°时,放电电压较高。研究结果可为超材料隐身雷达罩的雷电防护提供参考。 相似文献
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为了高效收集空间存在的射频能量,提出了一种新型的射频能量收集系统:首先,设计了一种单极子微带天线,其性能稳定且易于加工;其次,结合超材料理论设计了一种基于开口环形谐振器的超材料单元,其内环采用曲流技术,从而使天线小型化;最后通过将超材料单元加载在微带天线上对其进行了改进,能够进一步减小天线尺寸,改善带宽、增益等性能。系统由小型化超材料天线、匹配电路、整流电路及负载组成,对天线及整流电路进行仿真优化。经过实际加工测试,系统在2.45 GHz时输出电压为318 mV,对应的最大整流效率为13.5%。 相似文献
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一种新型宽带单面异向介质结构的分析与设计 总被引:1,自引:0,他引:1
提出一种在4—7GHz频率范围内可实现双负特性的新型宽带单面异向介质结构,其有效相对带宽为54.5%,中心频率电尺寸为0.051。通过对比分析了粒子型异向介质与传输线型异向介质的优缺点,将两者结合起来,并基于电磁波入射到异向介质平板的传输和反射数据,根据NRW方法从中提取出该新型结构的有效介电常数和磁导率。结果表明:本文所提出的新型异向介质结构在特定频段范围内表现出双负特性;根据计算频率为5GHz时电磁波传播的相速,证明该新型宽带单面异向介质结构具有后向波特性。 相似文献
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Xunjun He Shuang Shi Xingyu Yang Shaopeng Li Fengmin Wu 《Integrated ferroelectrics》2017,178(1):131-137
ABSTRACTIn this paper, we proposed a voltage-tunable terahertz metamatrial, which is composed of the circular-ring deep-slot array fabricated by UV-LIGA process to form a controlled cavity embedded with the liquid crystal (LC). By changing the biased voltage, the transmission peak of the terahertz metamaterial can be continuously tuned within a frequency range of 38 GHz. Moreover, this metamaterial can work over a wide range of incident and polarization angle for both TE and TM waves due structure symmetry. In addition, a differential phase of 74° is obtained at 0.45 THz by tuning the biased voltage. Therefore, our results open new opportunities for the tunable THz bandpass filters and phase shifters. 相似文献
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土-结构动力相互作用(dynamic soil-structure interaction,DSSI)是结构动力分析中重要的研究分支。随着计算机技术和数值技术的发展,数值方法得到越来越广泛的应用。在采用数值方法解决土?结构动力相互作用问题时,常通过直接法或子结构法将开放的无限域体系转化成封闭的有限区域,并引入适当的人工边界来模拟无限土域对近场研究对象的影响。对近场的研究可涉及非线性问题,而远场问题的难点包括满足无穷远处的辐射条件和外源的动力输入。针对不同的问题,适用的数值方法不尽相同。本文就土?结构动力相互作用远场问题中作者认为常用的数值方法进行归纳总结。 相似文献
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We present the design, numerical simulations and characterization of a dynamically tunable dual band metamaterial absorber that shows two distinct absorption peaks in terahertz (THz) regime. The designed absorber consists of a metal ground plane fixed on substrate and a movable metamaterial suspended above the ground plane. Through applying a bias voltage to adjust the height between the suspended elements and metal ground plane, we can switch absorber's state between absorption and reflection. Moreover, the designed absorber is polarization-insensitive and can be operated over a wide range of incidence angles owing to the high degree symmetry of designed structure. 相似文献
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摘 要:研究污秽状态下支柱绝缘子的电场分布特性对于动车组的安全稳定运行具有重要的意义。本文以FQJG2-30-16-400-M型车顶复合支柱绝缘子为研究对象,进行如下研究:对绝缘子表面进行淋雨试验,同时施加40kV工频电压,靠近金具部分的伞裙首先发生闪络,且出现了干燥带,伞裙边缘形成大粒径的水珠时,容易引发局部放电。利用comsol有限元分析软件在绝缘子靠近金具的伞裙表面设置干燥带和水珠,护套表面存在干燥带时,电场畸变明显,杆径处的干燥带场强最大,上表面干燥带场强大于下表面干燥带场强,干燥带场强最大值随着干燥带数量增加反而减小。绝缘子表面出现水珠时,水珠附近的场强明显增大,越靠近中轴线水珠表面电场强度越大。靠近高压端的水珠的最大电场强度受半径的影响较大,低压端则不明显。 相似文献