一种基于模块化多电平换流器的三极直流输电系统

现有三极直流输电系统基于晶闸管换流器,存在一些与传统直流输电系统相似的固有缺陷。文中提出了一种改进系统:极3采用基于全桥子模块的模块化多电平换流器,极1和极2采用基于钳位双子模块的模块化多电平换流器。同时,提出了三极直流协调控制策略,并且为了抑制过渡阶段的暂态过电压,减小接地电流和功率波动,还提出了电压反向控制、电流维零控制和功率协调控制。采用PSCAD/EMTDC进行仿真验证,结果表明利用所提控制策略,三极直流输电系统能够获得较好的响应特性,在维持电容电压平衡的同时,能够抑制交直流间功率扰动和接地极电流波动。     

非中心化chi平方伽玛分布杂波模型

韦布尔和对数正态分布雷达杂波模型可描述海杂波的分布,但实现模型不同,且不能对杂波物理成因做出合理解释.这里提出一种非中心化chi平方伽玛分布模型,可精确地模拟海杂波,概率分布特性可与上述两者接近,并且能从物理含义说明杂波产生机理.模拟结果的概率密度分布和功率谱密度估计显示出这种模型具有很好的性能.     

Ultrathin wideband slot and patch FSS elements with sharp band edge characteristics

ABSTRACT

Two diverse applications of FSS as bandpass and bandstop filters with wideband and sharp band edge characteristics are investigated in this paper. The proposed design comprised of a tapered tripole element in aperture and patch type printed on either side of a dielectric material to act as bandpass and bandstop filters respectively. The structures are ultrathin in design; structures comprise two metallic layers, isolated by single thin substrates with a thickness of 0.027λ. In the case of bandpass, the structure shows a relative bandwidth (?1 dB) of 8.87% with insertion loss better than 0.2 dB at normal incidence. Whereas, in the case of bandstop, it shows 24.36% (?10 dB). Further, the parametric analysis is performed for obtaining optimal performance. Both structures in the proposed form have spectacular application in bandpass filtering (slot FSS) and electromagnetic shielding (patch FSS). Further, two design techniques are presented namely dielectric encapsulation and substrate integrated waveguide (SIW) based FSS structures to develop a periodic structure to cater the high power handling in microwave sources. Finally, a fabricated prototype along with experimental verification proves the validity of simulated results.     

高压直流三极输电技术

高压直流三极输电技术采用电流调制控制模式,同时利用三相导线,只需要对线路进行有限改造,就可有效提升原线路输送容量。因此高压直流三极输电技术是潜在的解决输电线路输送容量瓶颈效应的有效方案。为进一步推动高压直流三极输电技术的研究和应用,介绍了该技术的发展历程、系统结构、电流调制原理以及运行方式,详细分析了高压直流三极输电与常规高压直流输电相比的技术优势和经济特点,最后针对该技术的工程应用提出了需要重点研究的几个关键领域。     

基于架空线的城市电网紧凑化输电增容方案

城市用电负荷的快速增加使得提高现有城市电网的输送能力迫在眉睫。为了解决这一问题,文中提出了一种城市电网紧凑化输电增容方案,送端和受端通过半桥模块化多电平换流器和极间电流开关连接交流系统原有3条输电线,基于设计的电流调制策略,计算了该方案的增容效果;同时分析了系统的稳态运行机理和启动过程,并设计了启动策略;最后,采用PSCAD/EMTDC从启动和稳态运行2个方面对该方案进行了仿真验证。研究结果表明,提出的紧凑化输电增容方案有较好的增容效果,能够稳定运行。     

Design of a Multiband Frequency Selective Surface

A frequency selective surface (FSS), whose unit cell consists of a ternary tree loop loaded with a modified tripole, is proposed to block multiple frequency bands. Target frequency bands correspond to Korean personal communication services, cellular mobile communication, and 2.4 GHz industrial, scientific, and medical bands. Through the adjustment of inter‐element and inter‐unit cell gaps, and adjustment of the length of elements, we present an FSS design method that makes the precise tuning of multiple resonance frequencies possible. Additionally, to verify the validity of our approach, simulation results obtained from a commercial software tool and experimental data are also presented.     

月基甚低频射电干涉仪Tripole天线特性研究

对月基甚低频射电干涉仪所用Tripole矢量有源天线进行理论分析,计算了不同激励下的辐射方向图以及给定方向图时所需的激励。不同于传统的天线阵列方法,单一的Tri-pole(三阵子)天线即可实现对入射波达波方向(DOA)的估计。运用改进的基于单位矩阵束(UMP)和最小二乘法(LS)的算法实现了对Tripole天线达波方向的估计,该算法适用于对入射波不同频率分量的DOA估计,计算量小,且估计精度更高,仿真结果表明了算法的有效性。     

基于F-MMC和LCC的混合型三极直流系统及其控制策略

现有的三极直流输电系统因极3采用晶闸管换流器而存在交流电压易波动、过渡阶段易引发过电压和过电流等固有缺陷。为此提出了一种改进式的混合型系统,即极3换流站改用基于全桥子模块的模块化多电平换流器。为使系统获得较好的响应特性,提出了无功(电压)平衡、电流平衡和子模块电容电压平衡3个控制要求,并根据控制要求给出了模块化多电平换流器采用改进直流电流控制和交流电压控制、子模块采用电容电压平衡控制等控制措施。利用时域仿真软件PSCAD/EMTDC对所提出的系统进行了仿真研究,仿真结果验证了所提出的混合型三极直流系统及其控制策略能够很好地实现系统电压平衡、电流平衡和子模块电容电压平衡。