孤岛微电网逆变器电压不平衡控制策略

微电网孤岛运行时会因不平衡负载不断增加而产生负序电流和电压,传统的控制方法无法维持逆变器输出的电压始终平衡.为此本文提出了一种微电网逆变器输出电压的补偿方法,该方法建立在αβ静止坐标系下引入基于模糊PI控制算法的改进下垂控制,微源逆变器可以随着本地负载的变换再对功率分配进行改善;同时加入了采用负阻抗的虚拟阻抗环来更加灵敏地控制逆变器微电源的等效输出阻抗特性.通过采用PI调节器和PR调节器结合的电压电流环控制设计来实现电流、电压的无静差控制.仿真结果表明了该控制策略的有效性.     

轨道交通牵引电机轴承电压和轴承电流的综述（英文）

目的：脉冲宽度调制（PWM）变频驱动使轨道交通牵引电机获得了良好的运行性能,但由于输出电压存在共模分量,导致了轴承电压和轴承电流的产生,进而引起轴承早期失效。本文旨在回顾轴承电压根源、轴承电蚀失效模式、轴承电流形成机理、轴承电流共模等效电路、耦合回路阻抗提取和抑制对策等方面的研究现状,并重点围绕轨道交通牵引系统电机及负载接地状况对轴承电压的影响展开全面研究。创新点：1.总结PWM变频系统轴承电流分析与建模方法和抑制对策与效果;2.分析轨道交通牵引系统电机接地配置对轴承电压的影响,并通过共模等效电路模型成功模拟了不同转速下的轴承电压波形,验证了采用接地环和调整系统接地阻抗可以降低轴承电压。方法：1.通过文献搜索和调研,总结PWM变频系统轴承电流的研究方法和思路;2.结合实际轨道交通牵引电机系统接地状况,得到共模等效电路模型和提取回路阻抗参数,并通过仿真模拟与实际测量轴承电压波形,验证模型的正确性;3.通过实际测量,验证接地环和调整系统接地阻抗是否可以降低轴承电压。结论：1.轨道交通牵引系统电机轴承电压与定转子接地阻抗有关,可产生转轴接地型轴承电流;2.通过转轴侧接地共模等效电路,可以模拟...     

关于代维南定理的解析表达式

代维南定理指出:任何一个线性含源二端网络N,对其外电路(Z_L)来说,都可以用一条有源支路来等效。该有源支路的电动势E等于网络N的开路电压V_(oc),其阻抗等于网络N的除源网络N_o的等效阻抗Z_o(见图1)。 代维南定理(DeVnan)是电路理论中一个应用十分广泛的基本定理。常用教材中仅用迭加原理进行一般性证明,本文通过回路分析和节点分析,运用基尔霍夫电压定律(KVL)和电流电律(KCL)推异出线性含源二端网络的等效电压源和等效阻抗的解析表达式。 首先:设网络N具有L个基本回路,每个基本回路的电流分别为I_1,I_2,…,I_l其中流入外电路的电流为I_l(见图2)。     

电压异常对家用电器的危害与对策

我国居民用电电压是220 V,由于当电流通过线路时,线路的阻抗要产生压降,使用户端电压低于输送端电压.我国供电规则规定:低压照明用户电压变动幅度不应超过额定电压的-10%至 7%.近年我国家庭用电量急剧增加,而供电设施相对滞后,这一情况在农村和城市老居民区更加严重.在电力供应紧张的情况下,造成居民家中的电压异常(主要是偏低),     

用于电解盐水消毒的稳流电源设计

设计一种适用于电解设备的稳流电源,利用可控硅对变压器前级输入平均电压的调整,控制后级输出电压,根据阻抗变化调整电压以调节输出电流,并根据设定电流大小和实时采集的电流、电压数据保证输出电流稳定、输出电压在控制范围以内.     

Zynq-7000嵌入式多功能阻抗测试仪的设计与校准

介绍一种基于Zynq-7000FPGA和运算放大器相结合的阻抗测试仪。它利用XC7Z020系统板上的D/AC7621产生激励信号,通过内部的A/DC来采集被测阻抗的响应,并使用外部模拟电路来获取待测电压和电流,使用3参数正弦拟合算法来评估电压、电流的幅度和相位。提出了完整的校准和精度测试方法,在可用频率0. 1 Hz～100 kHz范围内对组抗范围10Ω～100 kΩ的测试精度不低于2%。     

基于MATLAB的电力系统稳态仿真分析

通过对输电线路的分布参数电路、π型等值电路、串联的集中参数阻抗电路等不同线路的模型分析,建立以Matlab/Simulink动态系统建模软件为基础的面向对象的电力系统稳态仿真电路,用Powergui模块的稳态电压电流进行分析,对比不同模型下稳态仿真结果,可获得对输电线路的等值电路模型的直观感受和深刻理解,有利于电力系统理论知识的学习。     

太赫兹温控电磁诱导透明人工电磁媒质的研究

利用新型人工电磁媒质来模拟电磁诱导透明(Electromagnetically Induced Transparency,EIT)现象是新兴的电磁学研究方向,有望让本属于量子光学领域的EIT现象的高Q值、低损耗和大群折射率等优势得到更广泛的应用。文章在传统太赫兹EIT人工电磁媒质的设计中引入了高温超导材料钇钡铜氧(YBCO),通过温控的方式改变YBCO的电导率进而影响YBCO薄膜的介电性质,实现了主动式的类EIT现象并对EIT人工电磁媒质的调谐特性进行了动态的分析,为开发利用类EIT效应的新型太赫兹调制器件和可调谐的慢光、延时器件提供了新思路。     

基于芯片尺寸封装功率器件的集成电力电子模块

采用三维封装结构取代传统的平面封装结构可获得高性能集成电力电子模块.在实验室完成由2只芯片尺寸封装MOSFET和驱动、保护等电路构成的三维封装半桥IPEM.从互连焊点形状的优化和封装工艺过程参数的控制出发,进行IPEM的可靠性控制.采用阻抗分析仪Agilent 4395A测量IPEM的寄生参数,建立了半桥IPEM的寄生参数模型;采用半桥IPEM构成12V/3A输出的同步整流Buck变换器,2只MOSFET的漏源极尖峰电压小,说明HB-IPEM的三维封装结构有效减小了寄生电感.运用Flotherm软件对半桥IPEM进行了热分析,给出了温度分布仿真结果.焊料凸点传热使芯片的最高结温明显降低,三维封装结构实现了良好的热设计.     

欧姆定律复习指南

27 欧姆定律 [知识要点] 一、电流跟电压、电阻的关系 1.研究电流跟电压的关系时,应控制__不变,调节___,获得三组对应的电流、电压值.最后得出结论:在__一定的情况下,导体中的电流跟导体两端的电压成___.     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help?     

只要努力,不要后悔

There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love.     

浅谈移民问题

Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject.     

Sister Carrie, an Adherent of Desires

Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities.     

Improvement of one-cycle controller by use of proportional integral differential controller

1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec…     

库克斯顿城堡

城堡, 是欧洲典型的建筑之一, 每个城堡都有一个美丽的传说或是一段历史。从本期开始, 我们将推出“城堡之旅”, 带各位读者去浏览、观赏欧洲各地的城堡, 开始一段文化与历史的旅途!     

胡主席在印度,我却在中国

Today, Sunday morning, I sit thinking and typing at my computer. My thoughts are in my homeland, India and my body is in China. The body is here and mind there for a good reason. Mr. Hu is president and I am resident and both are in each other's countries (what a difference the absence of one small letter makes!). Mr. Hu will return in a few days and I will stay on longer.