双馈风力发电系统低电压穿越的建模与控制

为提高双馈感应风力发电机组并网的运行稳定性,研究电网故障下双馈风电机组的运行特性,使发电机在电网故障时仍能保持不间断的运行。本文主要研究了基于Orowbar保护控制的低电压穿越运行的控制策略,通过Orowbar保护电路来限制电压跌落时转子回路的最大电流,并通过仿真分析了电压跌落的程度和旁路电阻的取值对控制的影响。仿真结果验证了在电网电压骤降下Crowbar保护电路的有效性,可实现双馈风力发电机不间断的运行。     

DSP在风力发电空载并网技术上的应用

针对风力发电机组直接并网和降压并网都会在并网瞬间产生很大的冲击电流。根据变速恒频双馈发电机组的运行特点,通过对其数学模型分析,建立了双馈异步发电机的空载数学模型,研究了基于电网电压定向的空载并网控制的策略,避免了由于定子磁链检测不准确造成的电网冲击。采用TMS320F2812实现了变速恒频双馈风力发电机组空载并网控制系统,给出了硬件和软件设计方案。实验表明系统动态性能强,稳定性好。该控制策略可以实现大容量风电机组的无冲击软并网,是一种理想的风电机组并网方式。     

几种双馈式变速恒频风电机组低电压穿越技术对比分析

新电网运行规则要求风力发电机组在电网故障出现电压跌落的情况下不脱网运行,并在故障切除后能尽·陕帮助电力系统恢复稳定运行,要求风电机组具有一定低电压穿越能力。由于双馈感应发电机（DFIG）励磁变换器容量有限,电网故障时会产生转子过电流和变换器直流环节过电压,须实行保护和控制。本文对国内外学术界和工程界对电网故障时双馈感应发电机的保护原理与控制策略进行了大量研究。以便具体设计时根据要求合理选择。     

电网不平衡条件下PWM整流控制策略的研究

通常情况下由于各种原因三相电网电压是不完全平衡的.这就使得常规的PWM整流器整流效率较低,为了提高电网不平衡条件下PWM整流器的整流效率,本文讨论了一种在电网不平衡条件下PWM整流的控制方法,在分析不平衡电网数学模型的基础上,建立了正、负序双电流控制策略的数学模型,利用Simplorer7.0对系统进行了仿真,通过对不平衡条件下常规的PWM整流器和不平衡条件下正、负序双电流控制的仿真结果进行对比,表明正、负序双电流控制可以提高网侧功率因数,改善系统的动态性能,同时得到较平稳的整流输出电压,有利于提高系统整体的运行效率。     

基于PSCAD的双馈风力发电机组低电压穿越的研究

针对双馈风力发电机组低电压穿越问题,研究了电网电压严重跌落情况下转子Crowbar电路、转子Crowbar和直流侧卸荷电路组成的组合保护电路的控制策略。基于PSCAD建立了双馈风力发电机组低电压穿越的仿真模型,验证了组合保护电路控制策略能够很好地抑制转子侧电流和直流侧电压的上升,实现低电压穿越。     

电网电压跌落时双馈感应风力发电系统无功功率控制策略

为提高双馈风力发电机在电网电压跌落时的不间断运行能力,提出了双馈风力发电机(DIFG)转子侧变流器无功支持控制策略,并进行了仿真研究。仿真结果表明,该控制方案在不增加硬件成本的基础上提供无功支持,降低了电网压降,减少了直流母线电压波动,提高了双馈风力发电系统的低压穿越能力。     

双馈风力发电机组自动化并网运行的分析

随着风电机组装机容量在电网中所占比例越来越大,其对电网的影响将不容忽视,所以研究风电机组的并网运行具有非常重要的意义。本文以目前最具发展潜力的双馈风力发电机组为研究对象,在对其结构和工作原理进行分析的基础上,对其并网运行做了详细的分析,提出了双馈风力发电机组与电网并联运行的电压和频率控制策略。     

风电接入对继电保护的影响——风电分散式接入配电网对电流保护影响探究

不同类型风力发电机组,其特征也会有很大的区别。双馈式及感应式风力发电机组均属于变速恒频发电系统,有可能会使风电接入点在上游的时候缩短了过流保护范围,接入点下游的过流保护误动;永磁直驱式风力发电机则属于变速恒频发电系统,受控制器限流作用的影响,故障时风机提供的短路电流比较小,对过流保护影响很小,几乎可以忽略不计。通过改变故障点位置、风电接入位置、风电接入容量及线路长度,可看出风电分流或助增电流作用对短路电流保护的影响。     

浅谈直接转矩控制在风力发电系统中的应用

变速恒频双馈风力发电机组以其独特的技术优势已逐步成为并网型风力发电机的主力机型,而直接转矩控制技术在双馈电机中的应用是一个研究热点.文章对变速恒频双馈风力发电机的直接转矩控制技术进行了理论分析,阐述了它的工作原理和系统结构,并对目前主流控制方案如积分变结构、模糊DTC、遗传优化模糊等给予分析、说明,并论述了此类型控制的研究方向.     

电网故障时双馈风力发电机励磁改进控制策略

双馈风力发电机（DFIG）在风能捕获过程中,传统的定子磁链定向控制都假定电网上的电压恒定不变,定子磁链也恒定不变,没有考虑定子励磁电流的动态响应过程,这个误差在电网故障时会对系统产生极不稳定的作用。为此应考虑该响应过程,对控制檳型进行修正,提出一种应对电网电压跌落时的励磁改迸策略,即在建立转子侧变换器控制模型时,把反映励磁电流过渡过程的定子电压变化量考虑进来。通过推导定子磁场定向下的转子电压方程,搭建定子磁链定向矢量控制模型,经过仿真结果比较,说明在加入励磁补偿电压项后,风电系统在应对电网电压故障时的电流控制性能得到明显改善,有效提升了系统的低电压穿越能力。     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

Teleportation of an arbitrary unknown N-qubit entangled state under the controlling of M controllers

A new quantum protocol to teleport an arbitrary unknown N-qubit entangled state from a sender to a fixed receiver under M controllers(M < N) is proposed. The quantum resources required are M non-maximally entangled Greenberger-Home-Zeilinger (GHZ) state and N-M non-maximally entangled Einstein-Podolsky-Rosen (EPR) pairs. The sender performs N generalized Bell-state measurements on the 2N particles. Controllers take M single-particle measurement along x-axis, and the receiver needs to introduce one auxiliary two-level particle to extract quantum information probabilistically with the fidelity unit if controllers cooperate with it.     

Diode-end-pumped Nd:YVO4/LBO lasers with 4.2W continuous-wave output at 457 nm

A continuous-wave (CW) 457 nm blue laser operating at the power of 4.2 W is demonstrated by using a fiber coupled laser diode module pumped Nd: YVO4 and using LBO as the intra-cavity SHG crystal With the optimization of laser cavity and crystal parameters, the laser operates at a very high efficiency. When the pumping power is about 31 W, the output at 457nm reaches 4.2 W, and the optical to optical conversion efficiency is about 13.5% accordingly. The stability of the out putpower is better than 1.2% for 8 h continuously working.     

A rigorous proof of MIMO channel capacity’s increase with antenna number

It is well known that adding more antennas at the transmitter or at the receiver may offer larger channel capacity in the multiple-input multiple-output（MIMO） communication systems. In this letter, a simple proof is presented for the fact that the channel capacity increases with an increase in the number of receiving antennas. The proof is based on the famous capacity formula of Foschini and Gans with matrix theory.     

Call for Papers

正Wireless Body-area Networks The last decade has witnessed the convergence of three giant worlds:electronics,computer science and telecommunications.The next decade should follow this convergence in most of our activities with the generalization of sensor networks.In particular with the progress in medicine,people live longer and the aging of population will push the development of wireless personal networks