多机电力系统中STATCOM与发电机励磁的协调控制

针对一个典型的两区域且区间联络线中间带STATCOM的4机电力系统，应用信息结构约束下的最优协调控制理论与算法，设计了输出反馈的线性二次型（LQ）分散控制规律，得到的励磁控制器考虑了机组原有PID自动电压调节器（AVR）的结构约束，并通过在STATCOM安装处构造一个能反映区间振荡模式的就地观测量，以抑制区间低频振荡。应用数字仿真研究了所得控制规律的性能，结果表明，协调控制器大大地提高了系统暂态稳定水平和区间传输容量，而且，由于采用了完全分散的信息模式和输出反馈方式，控制器实现代价低、可靠性高，易于实际应用。     

单元机组协调控制系统发展和现状

总结协调控制系统的研究成果，包括模型的建立及各种控制手段如PID、自整定、模糊、神经网络、最优、预见、鲁棒、容错、反馈线性及多变量频域控制、工程中常用的直接能量平衡方法及与协调控制系统密切相关的均衡燃烧控制、采用辐射能信号的串级控制等，为协调控制系统的继续深入研究提供一些有益参考。并指出协调控制系统存在问题及一些解题思路和方法。     

可编程控制器在协调磷酸盐处理控制系统中的应用

可编程控制器在电站锅水协调磷酸盐处理控制系统中的应用取得了良好的效果。为此，以OMRON公司生产的C200Hα系列可编程控制器为例，介绍了系统的组成和控制器的结构。考虑到协调磷酸盐控制系统为两输入、两输出系统，为了简化系统的硬件组成和控制算法，采用了专家系统的方法对被控对象实施控制，并给出了加药品种选择算法和加药泵转速控制算法的语言模型。     

最优控制策略搜索工具(OCDT)

电力系统最优控制策略搜索工具能够在给定的电力系统典型方式下，根据事先设定的电网关键线路潮流、预想故障集、候选控制措施代价，全面、快速、自动计算出每一个预想故障的暂稳控制量和热稳控制量及其稳定裕度，搜索出最佳控制策略，形成全网的控制策略表供电力系统技术人员分析、决策。文中介绍了该工具的基本原理以及软件功能，并结合山东区域稳定控制系统给出了应用实例。     

Spatial indexing of high-dimensional data based on relative approximation

We propose a novel index structure, the A-tree (approximation tree), for similarity searches in high-dimensional data. The basic idea of the A-tree is the introduction of virtual bounding rectangles (VBRs) which contain and approximate MBRs or data objects. VBRs can be represented quite compactly and thus affect the tree configuration both quantitatively and qualitatively. First, since tree nodes can contain a large number of VBR entries, fanout becomes large, which increases search speed. More importantly, we have a free hand in arranging MBRs and VBRs in the tree nodes. Each A-tree node contains an MBR and its children VBRs. Therefore, by fetching an A-tree node, we can obtain information on the exact position of a parent MBR and the approximate position of its children. We have performed experiments using both synthetic and real data sets. For the real data sets, the A-tree outperforms the SR-tree and the VA-file in all dimensionalities up to 64 dimensions, which is the highest dimension in our experiments. Additionally, we propose a cost model for the A-tree. We verify the validity of the cost model for synthetic and real data sets. Edited by T. Sellis. Received: December 8, 2000 / Accepted: March 20, 2002 Published online: September 25, 2002     

Acquiring Customers' Requirementsin Electronic Commerce

A key role for Artificial Intelligencetechnology in electronic commerce is in findingproducts and services that meet a user'srequirements. This may be implemented as athree-stage process of requirementselicitation, product search, and finallyproduct presentation. Alternatively the searchof the product space may happen in tandem withthe requirements elicitation process. It isalso possible to use product presentation as amechanism to focus and give context torequirements elicitation. A variety ofdifferent approaches to this issue of matchingproducts to requirements have been explored inAI research. Thus, while the focus in thispaper is on different approaches torequirements elicitation, these related issuesof product search and product presentation arealso discussed in detail. The paper concludesby placing the other papers in this specialissue in the context of this structuredoverview.     

SAT Local Search Algorithms: Worst-Case Study

Recent experiments demonstrated that local search algorithms (e.g. GSAT) are able to find satisfying assignments for many hard Boolean formulas. A wide experimental study of these algorithms demonstrated their good performance on some inportant classes of formulas as well as poor performance on some other ones. In contrast, theoretical knowledge of their worst-case behavior is very limited. However, many worst-case upper and lower bounds of the form 2 ⁿ (<1 is a constant) are known for other SAT algorithms, for example, resolution-like algorithms. In the present paper we prove both upper and lower bounds of this form for local search algorithms. The class of linear-size formulas we consider for the upper bound covers most of the DIMACS benchmarks; the satisfiability problem for this class of formulas is NP-complete.     

Modular visions: Referents, context and strategies for database open media works

The processes of constructing meaning in digital database environments entail a paradigm shift from previous models of audio-visual communication. Media emerging from the Electro-mechanical era (film/TV/video) present fixed spatio-temporal linearity and material conditions which objectify and render passive viewer and process. The problematic aspects of cinematic communication were addressed by Latin American filmmakers of the Third Cinema movement. Their concerns and approach presaged and assisted an understanding of the radical redefinition of audio-visual communication possible with digital databases. The conceptual and aesthetic aspirations of Third Cinema artists such as Julio Garcia Espinosa and Fernando Solanas were ultimately contradictory to linear media and find their fitting medium in digital modular construction. The materiality of database expression lacks an intrinsic temporal or spatial state and permits a more dynamic and multidirectional set of power relationships between author/s, piece, viewer/s. Other important referents for contextualising database art are modern art practitioners that rejected linear representational space and fractured the centrality of authorship. The author's own work, ...two, three, many Guevaras, an exploratory database environment, embraces the redefinition of process as artistic expression, the empowerment of interacting generative forces, and serves to illustrate the revolutionary potential of the new media.     

Asymmetric Rendezvous Search on the Circle

The rendezvous search problem asks how two blind searchers in a known search region, having maximum speed one, can minimize the expected time needed to meet. Suppose that two players are placed an arc-distance x [ 0,1/2] apart on a circle of circumference 1, and faced in random directions. If x has a continuous density function h which is either decreasing and satisfies ht( 1/2) h(0)/2,or increasing, we determine an optimal rendezvous strategy. Furthermore if h is strictly monotone, this strategy (which depends in a simple manner on h) is uniquely optimal. This work extends that of J. V. Howard, who showed for the uniform density h(x) = 2 that search and wait is optimal , with expected search time 1/2. We also show that the uniform density is the only counterexample on the circle to S. Gal's conjecture (which he proved for the line) on the nonoptimality of search and wait.     

An effective fuzzy-nets training scheme for monitoring tool breakage

Recent research results show that fuzzy logic and the neural networks systems are very effective in detecting the breakage of cutting tools during machining processes. In the present study, a fuzzy-nets training procedure was developed to build the rule banks to meet the dynamic requirements of machining processes. The system is capable of responding and adapting in real-time to either shut down the machine when a tool fracture occurs or tune the process parameters on-line. The training procedure was validated in a back-up truck problem. Furthermore, two fuzzy-nets systems were combined to serve as a tool breakage detection system for an end milling operation. When the system was evaluated for end milling, the adaptive capability (of the fuzzy-nets system) was shown to enable detection of tool breakage to occur on-line, approaching a real-time base.