基于空间矢量的三相并网光伏逆变器控制系统设计

针对三相电压型并网光伏系统,阐述基于空间电压矢量的控制策略、变步长扰动观测法实现最大功率跟踪、有功无功独立控制算法。以上有机结合的综合控制策略,使得光伏并网系统既能实现最大功率跟踪,又能实现任意功率因数调节,有功无功独立控制。并利用Matlab/Simulink软件进行仿真,验证了该控制策略的正确性和优异特性。     

非并网风力发电系统的电压协调控制

在非并网风力发电系统中，当风能突然增加或负载突然减少时，系统的功率平衡将被打破，从而造成直流电网中出现电压尖峰和电压升高，可能造成系统中功率器件的损坏。文中通过改变负载电流、输电线电压或注入电网电流等参考值，从而改变从直流电网吸收或向直流电网注入的电流值，抑制了电压尖峰和电压升高。仿真分析结果表明该控制方法能够起到很好的抑制作用。     

两级式三相光伏并网系统无功补偿控制

光伏并网逆变器为最大限度利用太阳能,大部分情况下以接近单位功率因数运行,逆变器控制功能单一。为提高光伏发电系统的并网能力,同时对本地负载进行无功补偿,节约无功补偿设备的投资,改进了三相瞬时无功电流检测方法,使光伏并网逆变器能够在光伏发电的同时进行无功补偿。并网逆变器模型为电压型电流源方式并网,逆变器控制方法采用双闭环瞬时矢量控制技术。仿真结果表明了该方法可提高光伏发电系统接入电网的能力。     

逆变型分布式电源控制系统的设计

分布式发电系统并网运行时外特性控制是关系到其应用的关键问题之一。根据并网分布式电源的可控拟负荷外特性，设计了采用电流正弦脉宽调制（PWM）调节方法的电压型逆变控制器，整个体系充分考虑提高电能质量水平。该控制器的核心采用含有直流电压波动前馈补偿的双环串级PI结构。第1级为功率调节器，选择公共连接点（PCC）电压、电流作为反馈量，有功、无功可以分开独立调节；第2级为电流调节器，选择逆变器输出电流作为反馈量，考虑电流反馈解耦补偿，响应速度快。直流电压前馈补偿则可以降低直流侧缺少储能引发输入电压波动对控制效果的影响。输出滤波器的考虑则可进一步提高电能质量水平。仿真结果表明电流正弦PWM的双环串级PI控制系统能够较好地维持逆变型分布式电源恒功率电压源的拟负荷外特性，简单实用、设计灵活，可以得到较好的谐波注入。     

并网光伏电站动态建模及仿真分析

在假设并网光伏电站各交流器件的输出和输入变量只含有基波分量的前提下，提出了一种利用相量法和受控源法模拟并网光伏电站电能转换及传输系统特性的方法，并建立了包含光伏阵列，具有最大功率跟踪功能的逆变器、变压器及控制系统的并网光伏电站整体仿真模型。通过采用国内某地并网光伏电站的实测数据进行的仿真验证及误差分析可知，所提出的光伏电站模拟方法和数学模型是有效的。     

基于S-函数改进电导法的光伏阵列最大功率点的跟踪

光伏阵列最大功率点的控制策略是光伏递变器研究的重点之一,文章在深入研究传统电导增量法工作原理的基础上,提出一种基于S-函数的恒电压启动的变步长电导增量法来实现最大功率点跟踪,并在MATLAB/Simulink环境下搭建了光伏阵列的仿真模型,通过对比仿真结果可以证明,改进的电导增量法能够准确地反映出光伏阵列输出电压和电流的非线性特性,并且能快速高效地跟踪最大功率点。     

基于互补策略的新型单周控制有源滤波器

介绍了单周控制有源滤波器的原理，针对经典单周控制有源滤波器存在的诸如电流直流分量问题、局部稳定问题等，提出了单周控制有源滤波器的互补控制策略、电流直流分量负反馈策略和两路信号差值积分负反馈策略。新控制策略的采用彻底克服了经典单周控制有源滤波器的电流直流分量问题，实现了单周控制有源滤波器的全局稳定，并消除了电流交越失真，使得具有诸如无须参考信号、检测量少、控制简便、波形质量高、动态跟踪性能好、抗干扰能力强等显著优点的单周控制有源滤波技术达到实用化程度。实验结果证实了所述控制策略的有效性。     

可实现运行模式灵活切换的小型微网实验系统

为了能够对微网的运行特性进行深入的理论和实验研究,建立了一个小型实验室微网系统。该系统中的分布式电源采用光伏模拟单元和风机模拟单元,通过电力电子变换装置并入微网;系统以蓄电池为储能装置,并通过双向逆变器并入微网,用以维持微网的暂态功率平衡。当微网联网运行时,以外电网电压和频率为参考,蓄电池双向逆变器、光伏并网逆变器和风机并网逆变器采用恒功率控制;孤岛运行时,双向逆变器的控制策略切换为恒电压、恒频率控制,用以提供微网电压和频率参考。实验结果表明,该系统可以稳定地工作在联网模式和孤岛模式,并可实现二者之间的平滑切换,提高了能量供给的可靠性。     

直流母线电压控制实现并网与最大风能跟踪

针对永磁同步风力发电机加不控AC/DC和可控DC/AC结构，提出采用直流母线电压控制同时实现并网与最大风能跟踪。分析了可控DC/AC通过功率解耦控制直流母线电压的原理。提出采用可控DC/AC对直流电容充电的直接并网方法，并详细讨论了充电电流和限流电阻的取值范围。分析了直流母线电压与发电机转速之间的关系，提出采用直流电压变步长扰动代替转速定步长扰动实现最大风能跟踪，进一步提出采用功率变化量平方的比例值作为扰动值。详细的仿真验证了文中提出的控制策略简单、可行，适用于并网型永磁同步风力发电机。     

理想电网条件下可再生能源发电三电平并网逆变器

在可再生能源发电系统中,并网逆变器是实现电能馈送电网的重要环节。文中研究了二极管钳位型三电平逆变器及其并网运行控制策略。建立了并网逆变器在两相同步旋转坐标系下的数学模型;分析了并网模式下电压、电流的矢量关系;采用基于d-q坐标系的矢量控制策略及并网电流跟踪控制,实现了以单位功率因数馈送电能;分析了逆变器直流侧电容不均压的原因,提出了一种基于模糊控制的中点均压策略。仿真和实验结果验证了其有效性。     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.     

浙江省水域调查录入系统的设计和应用

浙江省水域调查录入系统将调查数据与电子地图相整合,对分类水域数据进行统计计算,并对输入数据进行合理性和完整性检查,得到调查范围内现有水域的详细数据,实现了水域调查数据输入、计算、统计和查询的数字化管理,提高了工作效率和工作质量,为各地下阶段水域保护规划编制和水域管理工作提供了数据支持。对该系统的设计原则、功能和技术设计等作了介绍。     

基于CT-连续加荷水泥乳化沥青混凝土细观损伤规律研究

利用CT技术对水泥乳化沥青混凝土的细观损伤过程进行实时扫描观测,获得了混凝土试件在连续加荷下的CT图像。通过采用直观分析法、CT数分析法、CT数与损伤变量关系3种方法分析表明,水泥乳化沥青混凝土的破坏过程可分为压密、扩容、裂纹扩展、破坏4个阶段,同时混凝土在受压过程中具有韧性,在极限荷载之前各断面处于压密和微扩容的强化阶段,极限荷载之后混凝土从损伤到破坏发展比较平稳。     

Automated system for removal and pneumatic transport of fly ash from electric precipitator hoppers

A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system, configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants of dry ash utilization and the advantages of producing of size-separated particles are considered. __________ Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008).     

The flood pulse advantage and the restoration of river-floodplain systems

The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed.     

浅谈天湖水电站水轮机运行故障及处理措施

简述天湖水电站投运以来各种故障的表现形式，分析其原因，提出了相应的处理方法及措施，并对合理利用国内外设备提出建议。