考虑机组运行状态的海上风电场无功协调控制

针对由具有无功调节能力的双馈风机DFIG(doubly-fed induction generator)组成的海上风电场,结合海上风电场特点和无功补偿配置情况,在考虑风电场内机组crowbar动作情况、机端电压和因尾流效应导致的风速差异对双馈风机动态无功极限影响的基础上,提出在电网电压跌落期间通过调节转子电流,充分利用场内双馈风机的无功协调控制能力进行最大无功支撑实现低电压穿越;在电网电压恢复阶段,控制场内双馈风机快速输出感性无功抑制电网电压骤升,提高了低穿恢复阶段的过电压抑制能力。基于DIgSILENT/PowerFactory仿真平台,搭建风电场协调控制模型验证所提控制策略的效果。仿真结果表明,所提控制策略在电压低跌落状态下可以充分发挥风电机组的无功出力能力,协助电网电压快速恢复,有效提高故障电网的暂态电压水平。     

含STATCOM的双馈电机风电场无功电压协调控制策略

为增强风电场并网点电压稳定性,提出了变速恒频双馈风电场与动态无功补偿装置STATCOM间的无功电压协调控制策略。电网故障导致风电并网点不同深度的电压跌落时,根据双馈风机Crowbar保护投切状态,对DFIG风电机组转子侧及网侧变流器与STATCOM进行无功功率分配,协调控制促进风电场LVRT期间风电并网点电压的快速恢复。最后,在DIg SILENT/Power Factory仿真软件中建立了风电场和STATCOM控制模型,通过仿真验证该控制策略的有效性。     

提高双馈风电机组动态无功协调控制能力的实验研究

随着风电场规模不断增加,风电机组并网对电网的影响逐渐增大,故充分挖掘风电机组的无功电压调节能力和提高机组的无功响应速度对增强电力系统的电压稳定性具有重要作用。定量分析了蒙西电网某风电场单台双馈感应风力发电机(Doubly Fed Induction Generator, DFIG)的无功电压调节能力及限制因素,根据其单台机组的无功调节机理制定动态无功补偿协调控制策略。若系统无功需求超过DFIG无功出力极限时,在保证机组最大发电效益的基础上,提出基于无功差值的双馈感应风力发电机组有功附加控制。并且通过改进的遗传控制算法辨识得到附加控制器参数,该控制在降低机组最小出力的同时确保提高机组无功出力极限,进而满足系统无功需求。最后通过实验验证了所提出的双馈风电机组动态无功协调控制的可行性和准确性,增强了机组的电压稳定能力。     

考虑海缆充电功率的海上风电场无功补偿协调控制策略研究

针对海上风电场的特点,研究其有效利用风电机组无功调节能力的无功补偿协调控制策略。海上风电场并网的电压稳定性分析主要分为两个方面:海缆充电功率对并网系统电压稳定性的影响;如何有效地利用风机无功调节能力来改善系统的电压稳定性。针对上述问题,首先利用灵敏度分析法及Q-V曲线法分析了海缆充电功率对海上风电场并网系统电压薄弱点的影响,并分析出最薄弱点为海缆末端母线;其次,选择STATCOM作为海上风电场无功补偿设备,并对双馈风机两侧变流器及STATCOM的无功控制环节进行研究;最后,提出以海缆末端母线电压为控制目标的三者无功协调控制策略,从而更为有效地利用风机自身的无功能力,显著减小STATCOM的安装容量。通过软件DIg SILENT建立CIGRE B4-39标准风电场并网系统,利用此系统进行暂态故障仿真分析,验证该无功协调控制策略的有效性。     

静止同步补偿器与双馈风电场的无功电压协调控制

基于变速恒频双馈电机的风电场通常按单位功率因数方式运行,而引入无功补偿单元补偿风电场无功需求,这将限制电网波动及故障期间双馈风电场的无功调节能力.针对该问题,提出一种双馈风电场与静止同步补偿器(STATCOM)间的无功电压协调控制器.依据执行依赖启发式动态规划(ADHDP)原理,设计包含执行网络和评价网络的ADHDP控制器.该控制器能够充分发挥STATCOM的无功发生能力,并在故障期间协调双馈风电场产生无功参与并网点电压调节,而在无故障期间保证风电场的单位功率因数运行;而且ADHDP控制器起到附加阻尼作用,有效抑制了故障恢复过程中的电压振荡.算例仿真结果验证了所提控制器的有效性.     

基于STATCOM的双馈风电场无功电压控制的研究

基于STATCOM和DFIG的数学模型研究与控制器建模,提出一种由两者共同参与的风电场无功电压控制方案.该方案利用STATCOM的电压控制模式,并充分考虑到双馈风机的无功调控能力,将双馈风机集群电压控制分为无功需求决策层和无功协调优化分配层.此外,针对风电场出口发生三相短路的紧急状况,提出一种故障时双馈风力发电机组的改进控制策略,该策略通过故障时将转子侧变流器由功率控制模式切换为电压控制模式,有功电流优先切换为无功电流优先,网侧变流器由单位功率因数运行切换为极限无功功率运行的方式提高风电场的低电压穿越能力.仿真表明,该方案不仅能实现正常运行时对风电场并网点电压指令的快速跟踪,风速、系统负荷和系统电压波动时快速稳定风电场并网点电压,而且当风电场出口发生短路故障时,能显著减小故障对双馈风机的不利影响,加速故障后电压恢复.     

电网电压跌落时双馈风电系统无功支持策略

电网要求风电场/风电机组具有低电压穿越能力,其中包括风电场在电网故障期间应该提供无功支持,但是双馈风机转子侧变流器(RSC)为了实现自我保护会触发Crowbar而被旁路,失去对风机的功率控制。针对这个问题,建立了风机网侧变流器(GSC)的数学模型,分析了STATCOM的基本原理;提出一种无功支持策略,即电网电压跌落期间STATCOM与风机网侧变流器共同向电网提供无功功率,支持电网电压恢复。基于Matlab/Simulink平台进行仿真验证,结果表明,该无功支持策略能有效支持电网电压恢复,提高双馈风电系统的低电压穿越能力。     

双馈式风电场多阶段无功电压控制策略

为了应对大规模风电接入电网引起的电压稳定问题,提出了一种新型的多阶段无功电压协调控制策略。该策略首先基于风功率预测数据对电容器组的投切进行提前优化;稳态运行时,通过分析双馈风力机的PQ关系曲线,优先调整风电机组无功出力以实现对风电场的无功调控;电网故障时充分发挥静止无功补偿器的调节能力,并在故障切除后限制其出力以避免电压过冲,从而整体上实现无功电压的协调控制。最后以某一风电场系统的仿真结果验证了上述策略的有效性和可行性。     

双馈风电场新型无功补偿与电压控制方案

为均衡双馈感应发电机感性和容性无功调节能力,改善电压稳定性,提出双馈风电场并联无功补偿方案:在各机组机端装设电容器,其电容值为双馈感应发电机定子电感的倒数;同时在主变的低压侧装设静止无功补偿器(static varcompensator,SVC)进行集中补偿。在此基础上,设计电压协调控制方案:稳态时通过三层无功分配策略充分发挥双馈风电机组无功调节能力,减小风电场内有功损耗;电网故障时则结合送出线路纵联差动保护控制SVC的等效电纳,避免保护动作时发生电压过冲的现象,同时改变机组内部无功分配以提高双馈风电机组故障穿越能力。最后以实际算例仿真表明上述无功补偿与电压控制方案的可行性和有效性。     

储能型双馈风电场联合STATCOM的无功协调控制

针对传统双馈风电机组(DFIG)低电压穿越(LVRT)能力不足问题,提出了储能型双馈风电场联合STATCOM的无功协调控制。该控制是在网侧变流器（GSC）原有的模型上将超级电容经隔离型DC/DC变换器并联到风机直流侧,以此吸收故障期间直流侧产生的不平衡功率;在发生低电压故障时,根据超级电容投入情况,对两侧变流器和并联在风机出口母线上的STATCOM进行无功协调控制来支撑电网电压;同时超级电容储能装置采用电压电流双闭环控制,满足了系统稳定性和经济性的要求。仿真结果表明：该方法应用在风电并网系统中可以使DFIG的LVRT能力得到极大的提升。     

On a wing and a prayer

The article talks about recent Defense Research Projects Agency (DARPA) presolicitation notice in the area of hybrid insect micro-electromechanical systems (MEMs). DARPA's goal is to fund promising interdisciplinary research that will permit the creation of "insect-cyborgs"     

利用光伏电池给蓄电池充电

磷酸锂铁（LiFePO4）电池对比钻基德Li离子/聚合物电池,具有安全性性高、浮充电压小、自放电率低、使用寿命长等一系列优点。本文所述LT36521C为可实现太阳能跟踪、单块式补偿蓄电池充电的集成电路。当LT3652由单块太阳能电池板供电时,其输入调节回路能确保在最大输出功率下工作,充分体现出这一新型太阳能充电器的优越特性。     

Chaos in a series circuit with a nonlinear capacitor and a nonlinear inductor

This paper proposes a nonlinear circuit that generates chaotic oscillations. The proposed nonlinear circuit includes a nonlinear capacitor and a nonlinear inductor by using Generalized Impedance Converters. Both computational experiments and experiments on real circuits show that the region for chaotic oscillation is very wide, demonstrating that the proposed circuit is effective as a chaos generator. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 35–42, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10361     

Making a Case for a New Connector

The emergence of quick lock connectors, particularly quick lock versions of the SMA and N connectors (QMA and QN, respectively), was an inevitable development in the RF connector industry and is of significant importance in that nearly 50% of all practical applications for RF connectors are currently supported by either SMA or N. Once QMA and QN can achieve similarity in cost and performance to the present SMA and N connectors, they will take the place of their predecessors in most applications, creating a huge new market. Our RF team has long been dedicated to research and development of these two connector types in the hopes of creating an optimal design. In this article, we will show some of the results of our research.     

Optimization of a door seal structure of a microwave oven using a FDTD method

The optimum door seal configuration to prevent radiation leakage from a microwave oven is still a manufacturing concern. Here, we propose a numerical algorithm to simulate the radiation propagation along a door seal structure using the finite‐difference time domain method, which is used for a priori shielding efficiency tests. The results agree with experimental data. The critical dimensions of the choke structure were found and high shielding is anticipated for a simpler choke structure. Copyright © 2008 John Wiley & Sons, Ltd.     

Electric potential near a tip of a local discharge on a conductive film

To develop a propagation model of a local discharge on a wet polluted insulator, the authors have examined characteristics of the local discharge on an electrolytic solution simulating the wet polluted insulator surface. The local discharge was propagated on the solution under the impulse voltage. A shape of a contacting surface between the local discharge and the solution has been already obtained by the authors. By using the contacting surface, an electric potential near a tip of the local discharge on a conductive film of 1 mm in thickness was calculated. Furthermore, the potential was measured with a probe. The calculated values and the measured values of the electric potential agreed well regardless of the propagation length of the local discharge, the width of the conductive film, the resistivity of the conductive film, the peak value of the applied voltage and the applied voltage waveform.     

Power losses in a conducting ring enclosing a conductor with a transient current

Contents In the paper Joule power losses are calculated in a conducting ring enclosing a conductor with a transient current having an alternating component.—Theoretical calculation and numerical computation are worked out basing on a link Bubnov-Galerkin method in its numerical version using the finite elements for the conductor with the Time-Stepping algorithm for the time discretization.—On the basis of numerical computation, graphs of the relative power losses are plotted as a time function.

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Leistungsverluste in einem leitenden Ring, der einen Leiter mit einem instationären Strom umschließt

Übersicht In diesem Beitrag werden die Joulschen Leistungsverluste in einem leitenden Ring berechnet, der einen Leiter umschließt, in dem ein instationärer Strom mit Wechselanteil fließt. Die theoretischen Betrachtungen und numerischen Berechnungen hat man in Anlehnung an die Bubnov-Galerkin-Methode (in ihrer numerischen Variante, die von einen Leiter unter Verwendung der Methode der finiten Elemente realisiert wird) in Verbindung mit einem Schritt-Algorithmus mit der diskretisierten Zeit ausgeführt. Auf der Grundlage numerischer Berechnungen sind Diagramme für die relative Leistung in Abhängigkeit von der Zeit dargestellt.

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List of symbols Symbol Unit Physical parameter - B Wb/m² magnetic induction vector - H A/m magnetic field intensity vector - H, H A/m -component of the magnetic field vector - E V/m electrical field vector - E _r ,E _z V/m components of the electric field - f s^–1 frequency - I A current intensity (r.m.s. value) - L H inductance - P W power losses - P ₀ W power losses for d.c. - R resistance - t sec time - ^–1 m_–1 electric conductivity of the conductor - Hm^–1 magnetic permeability - _ijk m² finite element area - basis function - rad s^–1 pulsation - N _i ,N _j ,N _k function of finite element shape - 3.141593... - region - ² Laplace's operator - r, ,z cylindrical coordinates - ^h region approximating the region - ^e finite element region - M number of discretization points of the region - V number of finite elements - (N–1) number of steps - i, j, k indices of vertices of triangular finite element     

燃料电池-燃气轮机混合发电系统性能研究

文章对由燃料电池和燃气轮机组成的混合发电系统的性能进行了分析。该混合系统采用的是底层循环方式,并于常压下工作。分析表明,在设计点工况,混合系统的发电效率为58.7％;在非设计点工况,其发电效率也能达到56%以上。在设计点工况下,混合系统的功率约有80％来自燃料电池电堆,20%由燃气轮机提供。在非设计点工况时,燃料电池发电功率占混合系统总输出功率的比例随着混合系统输出功率的减少而增大;混合系统可以在其输出功率不低于设计点功率80%的工况下运行。     

Development of a deceleration control system for a winding machine based on a microcontroller

The development of an automatic deceleration system for a winding machine in a siderurgy factory is presented in this paper. The proposed system controls the speed of a winding machine in order to obtain the optimum stop point in terms of security and fast production. The system is based on a microcontroller and an extremely simple hardware. The system has been tested for two years and results evince a very good mean time between failures.