基于聚类的多运行方式下电力系统稳定器设计

将模式识别中的聚类算法用于电力系统多运行方式的分类,提出了一种多运行方式下电力系统稳定器的设计方法.选择所有节点注入功率或所有机电振荡阻尼比为表征系统运行方式的特征向量,基于基本顺序聚类算法确定类的数目,用层次聚类和 C 均值聚类算法得到每类的中心运行方式.电力系统稳定器的参数设计仅针对各类的中心运行方式进行,将此问题转化为一个非光滑优化问题,用信赖域法加以求解,求得的参数可用于该类别其余运行方式.示例系统的仿真结果表明,提出的方法可以显著降低多运行方式下控制器参数设计问题的规模,从而大大减小计算量.     

飞轮储能系统在抑制电力系统多模式振荡中的应用

推导了含有飞轮储能系统(FESS)的多机系统线性化模型,应用阻尼转矩分析法论证了单个FESS抑制复杂电力系统多模式振荡的可行性.在FESS独立的有功控制回路和电压控制回路上分别附加一个稳定器,以抑制系统的多模式振荡.基于现代控制理论的可观性和可控性准则,为各振荡模式选择控制回路和反馈信号,并采用改进的粒子群优化算法协调整定FESS中各附加稳定器的参数.以四机系统为例,FESS上附加的2个稳定器可将2个振荡模式的阻尼比分别从-0.013和0.052变化到0.106和0.102,说明单个FESS具有抑制复杂电力系统多模式振荡的能力.     

多机系统中电力系统稳定器与可控串联补偿器阻尼控制器的协调设计

针对电力系统稳定器（power system stabilizer，PSS）和可控串联补偿器（thyristor controlled series compensators，TCSC）的附加阻尼控制器能分别有效阻尼机间振荡和区域振荡的特点，提出一种采用单纯形-模拟退火法对PSS和TCSC阻尼控制器进行协调优化的设计方法．该方法结合单纯形算法局部搜索速度快和模拟退火算法全局搜索能力强的优点，将单纯形算法作为模拟退火算法的局部寻优算子，以增强算法的搜索能力和效率．同时，优化中使用的目标函数考虑了系统多种典型运行方式下的机电振荡模态性能，因而设计出的阻尼控制器具有较强的鲁棒性．在4机11节点电力系统上运用该优化方法完成了阻尼控制器的协调设计．特征值分析和非线性时域仿真结果显示，使用该方法设计的PSS和TCSC阻尼控制器对不同的运行方式都能有效抑制系统低频振荡．此外，算例分析结果证实了单纯形-模拟退火算法搜寻能力高、不强烈依赖初始值选择的优点。     

基于扫频法的直流附加控制器设计

将复转矩系数法的概念进行了推广,并应用到直流附加阻尼控制器的设计中.通过对交直流系统进行低频范围内的频率扫描,可以得到满足系统稳定性要求的控制器频域特性,并以此为约束条件确定控制器的结构和参数.采用该方法获得的各系数曲线结果直观,特别适合分析系统运行参数的变化对控制器效果的影响,有利于设计出能同时满足多种运行方式的鲁棒控制器.算例分析结果表明,当系统运行点发生较大范围变化时,所设计的附加控制器仍能有效阻尼两区域四机系统中的低频振荡.     

UPFC附加阻尼和PSS控制器参数协调优化方法研究

电力系统稳定器(PSS)与统一潮流控制器(UPFC)附加阻尼控制(POD),在抑制系统低频振荡方面得到了广泛的关注,PSS与POD控制器参数对其抑制能力具有决定作用.建立了UPFC及POD和PSS的数学模型,在PowerFactory平台搭建了UPFC并网并含有POD和PSS的四机两区系统仿真模型;根据模态分析理论,建立了量化控制器参数对系统阻尼和阻尼比影响的目标函数,通过改进惯性权重粒子群(PSO)算法寻找满足目标函数最小值的最优控制器参数组合,并通过特征值分析和时域仿真验证了参数优化方法可以有效地提高系统抑制振荡、保持稳定运行的能力.     

提高电力系统小干扰稳定性的全状态H_∞控制器

为了研究电力系统小干扰稳定分析和控制的有效方法,建立了多机系统小干扰稳定的鲁棒分析和控制模型,应用H∞理论分析多机系统小干扰稳定问题,提出用系统的H∞范数作为系统小干扰稳定裕度的指标,并提出了多机系统全状态H∞控制器的设计方法。对一个4机2区域测试系统进行了仿真,设计了该系统的全状态H∞控制器,并从系统的特征值和振荡模式的阻尼比、系统广义阻尼和系统H∞范数等方面评估和比较手动励磁控制、线性最优控制和H∞控制的综合性能。结果表明,系统H∞范数能够准确衡量系统小干扰稳定裕度,而全状态H∞控制器比现有的控制技术能够为系统提供更强的阻尼,提高系统的小干扰稳定性。     

提高电力系统小干扰稳定性的全状态H_∞控制器

为了研究电力系统小干扰稳定分析和控制的有效方法,建立了多机系统小干扰稳定的鲁棒分析和控制模型,应用H∞理论分析多机系统小干扰稳定问题,提出用系统的H∞范数作为系统小干扰稳定裕度的指标,并提出了多机系统全状态H∞控制器的设计方法。对一个4机2区域测试系统进行了仿真,设计了该系统的全状态H∞控制器,并从系统的特征值和振荡模式的阻尼比、系统广义阻尼和系统H∞范数等方面评估和比较手动励磁控制、线性最优控制和H∞控制的综合性能。结果表明,系统H∞范数能够准确衡量系统小干扰稳定裕度,而全状态H∞控制器比现有的控制技术能够为系统提供更强的阻尼,提高系统的小干扰稳定性。     

基于免疫网络理论的TCSC与PSS协调控制

电力系统稳定器(PSS)和可控串联补偿器(TCSC)被广泛用于电力系统的稳定控制,多个控制器之间的交互作用会影响彼此的控制效果.本文介绍了生物免疫系统中不同类型的抗体协调合作,共同清除抗原的协调机理.提出了基于免疫网络理论的协调控制方法,用于在线协调控制多个阻尼控制器,抑制电力系统的功率振荡.以装有多个PSS和TCSC的系统为例,对多个控制器进行在线协调阻尼控制.仿真结果表明该方法能够缩短抑制振荡所需的时间,具有有效性和鲁棒性.     

分散H∞低阶控制器在不确定电力系统中的应用

提出了一种新的方法为具有不确定性的实际电力系统设计分散鲁棒H∞阻尼控制器。采用多胞型模型将系统运行状态的各种变化描述为以若干个典型运行参数为顶点的凸集。分散H∞控制器的设计可以归结为基于同伦参数法的两个线性矩阵不等式的求解问题。所提的方法可以得出较低阶的鲁棒控制器，具有工程实用性。将其与系统模型降阶法相结合，可进一步减轻计算负担，进而适用于实际电力系统的控制器求解。算法分别用于SVC的分散附加阻尼控制器和19机IEEE标准测试系统的PSS设计。算例结果表明，分散控制器相互协调，不但显著地提升系统的阻尼比，使其具有良好的抗干扰能力，且对于严重故障后产生的持续振荡具有很好的抑制作用。     

交直流电力系统中附加控制器与稳定器的协调设计

交直流电力系统低频振荡是运行中的一个严重问题.在交流系统中装设电力系统稳定器PSS,在直流系统中配置附加的控制器DCM可以有效地抑制低频振荡.本文应用分散控制器的参数设计思想,提出一种适用于交直流电力系统中装设DCM与PSS及其参数协调的设计方法,对抑制低频振荡可以达到预期的效果.     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Jane Eyre——A Feminist In The 19th Century

In the 19th century the society was controlled by men, and women were just appendants of them, they had not any rights and freedom. But Jane was an exception, she showed some characteristics of early feminist. Jane showed her characteristics of feminism in three aspects: rebellion, equality, and independence. These characteristics were helpful to her success, and feminism is the only way out for women of that time.     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

Editorial note for the special topic on ＂Nanopore Analysis＂

The concept of nanopore analysis, using the pore-forming protein a-hemolysin to detect individual nucleic acids at a single-molecule level, was first proposed in 1996. Over the past two decades, tremendous progress has been made in the nanopore field, and nanopore analysis has become a label-free and high-throughput method for probing bio- molecules and other analytes with single-molecule sensi- tivity, especially holds the promising for ＂third generation＂ DNA sequencing. However, challenges still remain in the experimental strategies and the design of whole nanopore-based instruments. Here, we proudly present a special topic dedicated to the topic of ＂Nanopore Analysis＂, with 8 reviews/articles providing up to date coverage of the experimental strategies, theoretical calcu- lations and simulations, and instrument design. Reviews and articles on the experimental strategies cover control of DNA partitioning into a nanopore, detection of target DNA, and the advantages of nanopore-based DNA sequencing. The theoretical calculations and simulations discuss the translocation behavior of DNA, and an inte- grated measurement system and data analysis software are presented for instrument design.     

Effects of climate change on biodiversity

1 Rise of studies on climate change＇s effects on biodiversity
Until the 1980s, climate change and biodiversity were studied as two independent disciplines for more than a century. In 1992, the Ecological Society of America＇s annual report named climate change, biodiversity, and the sustainable ecological system as the three major global environmental issues of the twenty-first century [1].     

Discussing the Expansive Learning in Modern Organizations

<正>1 Introduction Endeavours on learning methods have long occupied the mind spaces of scholars and there have been theories abound on how people learn and in what way organisations can use some of the knowledge gained in the art of learning to maximise human productivity.While the theories by themselves are not solutions to problems,they are steps of inquiry that provide us with interesting perspectives that we can use to extend our knowledge of the dimensions of learning.This paper is an exploratory work on the theories postulated by three notable scholars including Zimmerman