A new hybrid control technique for operation of DC microgrid under islanded operating mode

This study proposes a novel combined primary and secondary control approach for direct current microgrids, specifically in islanded mode. In primary control, this approach establishes an appropriate load power sharing between the distributed energy resources based on their rated power. Simultaneously, it considers the load voltage deviation and provides satisfactory voltage regulation in the secondary control loop. The proposed primary control is based on an efficient droop mechanism that only deploys the local variable measurements, so as to overcome the side effects caused by communication delays. In the case of secondary control, two different methods are devised. In the first, low bandwidth communication links are used to establish the minimum required data transfer between the converters. The effect of communication delay is further explored. The second method excludes any communication link and only uses local variables. Accordingly, a self-sufficient control loop is devised without any communication requirement. The proposed control notions are investigated in MATLAB/Simulink platform to highlight system performance. The results demonstrate that both proposed approaches can effectively compensate for the voltage deviation due to the primary control task. Detailed comparisons of the two methods are also provided.     

瞬间永恒——天津国庆彩车展演服装设计中的思考

人物展演服装设计,是天津国庆彩车整体设计系统中的重要组成部分。文章从主题设计、意象表现与造型特点等角度分析了天津国庆彩车中展演服装设计的特质与创意点,指出展演服装设计的关键在于准确定位,并以服装设计独特的艺术语言表述其它设计元素所不能表达的语意内涵。     

浅谈现代教育技术在《高等数学》教学中的应用

介绍现代教育技术在《高等数学》教学中的重要性,现代教育技术被越来越多的学校所利用,也给《高等数学》的教学带来巨大的生机,成为高等数学教师必不可少的工具。分析现代教育技术应用在高等数学教学中存在的一些问题,针对这些问题,结合笔者的教学经验,提出一些改进的方法。     

现代远程教育之网络技术研究与探讨

现代远程教育是近年来国际教育发展的重要趋势。介绍了我国现代远程教育状况,就现代远程教育的解决方案中的网络技术进行了深入地研究和讨论。     

Potential of Modern Data Types for Future Water Resources Management

Abstract

Presently a change of paradigm in the field of planning and operation of water management schemes can be observed. The introduction of the principle of sustainable development by the United Nations and the principle of integrated river basin management postulated by the European Union play a major role in this context. Introduction of these new principles requires development of new planning tools, which in turn require a much better data basis than available hitherto. This paper deals with new data types already partly available now, partly to be expected to be developed in the medium-range future. The present data situation is discussed, along with the obvious deficits of conventional data. New data types will not be limited to point measurements, but rather must comprise information covering large areas with a higher resolution in time and space than presently available. Remote sensing data will play a more important role in the future. Furthermore, digital maps, digital elevation models, etc. are also of growing importance and will be processed, together with remote sensing and other data, within Geographical Information Systems of future generations also exposing the potential for working with multi-temporal imagery. In the paper it is shown that in the future more accurate data will be available, not only in terms of data quality, but also resolution in time and space. It is shown how the new types of hydrometeorological data postulate new types of hydrological models. Here, distributed system models are of growing importance. Furthermore, it is shown how the combination of remote sensing with other information leads to new data types that allow integrated planning of water resources systems. The potential of real time data is highlighted, particularly in the context of real time operation of water resources systems, especially for flood control. The potential of large-scale data schemes in the context of regional and continental water management schemes is discussed. Global atmospheric models coupled to hydrological models are discussed, and their potential to consider long-distance effects of certain phenomena (e.g., El Niño) are mentioned. For sustainable development of water resources, the potential of long-term data prediction scenarios is evaluated, and an example of this principle for planning future water supply systems is presented. The paper ends with a vision of future developments in planning water management schemes on the basis of new data types     

南水北调天津干线水土流失治理对策

天津干线分流井至西河泵站输水工程是南水北调工程天津市内配套工程的一部分。依据该工程的水文、气象、地质等条件,主要对其水土流失量进行预测,并针对性地提出了防治对策,以期对相关工作人员有所参考。     

天津西站配套市政公用工程中道桥项目后评价指标研究

天津西站交通枢纽配套市政公用工程项目作为一项重大工程,意义重大.道桥工程作为重要的子项目之一,根据相关要求,必须进行项目后评价.科学设置相应的评价指标,对提升后评价的科学性具有重要作用.本文基于道桥工程的特点,从系统的角度出发,在投资决策过程、项目实施过程、项目效果和经济效益、项目环境和社会效益、项目目标和可持续发展几方面开展研究,以期为道桥项目的后评价提供依据.     

天津滨海新区湿地生态恢复需水量评估

生态需水量的核算是湿地水文生态恢复的关键步骤。通过分析计算,评估天津滨海新区湿地生态系统各类生态需水的3个特征值:最低生态需水量(即湿地生态系统丧失生态功能的临界需水量)、最适生态需水量(即维持湿地生态功能最佳状态的需水量)、最高生态需水量(即湿地生态系统所能承受的最大水量),得出如下结论:天津滨海地区湿地的生态需水主要包括蒸发蒸散需水量、湿地土壤需水量、补给地下水、湿地生物栖息地需水量4个部分;湿地的最低生态需水量为177.68×106～276.85×106 m3,最适生态需水量539.23×106～807.81×106 m3,最高生态需水量1 206.55×106～1 409.02×106 m3。     

加快江西现代物流业发展的对策建议

现代物流业作为促进经济增长的”加速器”和”第三利润源泉”,在改善区域投资环境,培育经济新的增长点方面发挥着重要作用。江西现代物流业在规模总量和发展质量取得长足发展的同时,也存在诸如综合管理部门缺位、物流园区布局不合理、物流骨干企业不多、第三方物流发展缓慢、物流运作平台建设滞后等问题,应通过理顺物流业管理体制,优化物流业布局,壮大物流业企业,完善物流运行平台,培养物流人才等措施,促进江西物流业快速健康发展。     

基于网站用词调查的现代维吾尔语词干提取和应用研究

通过对维吾尔文网站的词干应用状况调查,进而对现代维吾尔文词干的提取和应用进行研究。陈述调查使用的语料媒体来源、应用领域、采集的语料时间跨度与统计方法;介绍词干概念;讨论现代维吾尔语词干提取系统;研究词干在网络媒体语料中应用形式;介绍和讨论词干分布结果,最后总结以上内容。