基于EMD的电能质量扰动检测与分类方法

针对电能质量扰动信号的检测和分类问题,提出了一种基于EMD的电能质量扰动检测与分类方法,并对常见的几种扰动信号进行仿真。应用该方法检测扰动发生时间、持续时间以及扰动的频率与幅值。仿真结果表明,所提算法简洁有效,能够准确分析电能质量扰动信号,可以估计电压凹陷、电压凸起以及电压中断等扰动信号的变化幅度和频率。     

Short-term changes in upper extremity dynamic mechanical response parameters following power hand tool use

Dynamic mechanical response parameters (stiffness, damping and effective mass), physiological properties (strength and swelling) and symptoms of the upper limb were measured before power tool operation, immediately following and 24?h after power tool operation. Tool factors, including peak torque (3 Nm and 9 Nm) and torque build-up time (50?ms and 250?ms), were controlled in a full factorial design. Twenty-nine inexperienced power hand tool users were randomly assigned to one of four conditions and operated a pistol grip nutrunner four times per min for 1?h in the laboratory. Isometric strength decreased immediately following tool use (15%) (p?<?0.01) and 24?h later (9%) (p?<?0.05). Mechanical parameters of stiffness (p?<?0.05) and effective mass (p?<?0.05) were affected by build-up time. An average decrease in stiffness (43%) and effective mass (57%) of the upper limb was observed immediately following pistol grip nutrunner operation for the long (250?ms) build-up time. A previously developed biomechanical model was used to estimate handle force and displacement associated with the tool factors in the experiment. The conditions associated with the greatest predicted handle force and displacement had the greatest decrease in mechanical stiffness and effective mass, and the greatest increase in localized discomfort.     

500kV变电仿真培训系统应用与研究

主要论述计算机仿真技术在500kV变电站的一个具体应用.大型变电站是一个设备庞大、系统复杂的系统,随着变电电压等级升高,大量新变电站和新设备投入运行,对变电设备和系统的研究、分析,尤其是对变电运行值班员的培训,在实际变电站上直接进行已不可能.变电仿真培训系统提供了一个连续的实时运行环境,它真实地模拟了整个变电站的运行系统,为培训运行人员和管理人员提供了平台.变电仿真的应用大大提高了变电站运行的安全性和经济性.     

坪北油田伴生气的回收利用

坪北油田开发初期,富余伴生气直接放空燃烧,既浪费能源,又污染环境。要解决这个问题可以三个方面入手:一是建设集气管网,增压回收套管气;二是完善配套工艺,回收更多伴生气;三是研发节能设备,减少伴气损耗。同时要应利用富余伴生气发电,提高能源利用率,降低电力成本。     

电厂热力系统在线性能计算软件变量二维顺序及索引模型研究

分析在线性能计算软件在我国电厂的应用情况,把在线性能计算软件分为两类:编程式软件和组态式软件。编程式软件里的计算模型和变量值是完全被封装的,软件基本不具备扩展性。现有的组态式软件虽然具备一定的扩展性和可分析性,但是功能仍不够完善。提出在线性能计算软件变量二维计算顺序及索引模型,该模型包括三方面内容:第一,定义及构造了与计算变量和计算顺序相关的一系列集合和有序序列;第二,提出了变量二维排序算法;第三,建立了变量之间的引用和被引用关系,建立了变量二维索引图表。基于变量二维索引图表,可以方便地逐级追踪计算模型和计算变量的值,有利于增强组态软件的可分析性、扩展性和组态功能。     

Combined quasi-static backward modeling and look-ahead fuzzy control of vehicles

Vehicle modeling can play an important role in vehicle power train design, control and energy management investigation. This paper presents a method for vehicle power train modeling. The key feature of the method is its presentation of the dynamic of vehicle based on the road information. This ability makes the method suitable for look-ahead energy management and fuel economy optimal control problems. With the aid of a road slope database, road geometry ahead of the vehicle is extracted. A fuzzy controller is developed that receives this information and controls the velocity of the vehicle with respect to its fuel consumption. In order to maintain the operation of the combustion engine near its efficient region, the fuzzy controller commands a continuously variable transmission. Simulations are carried out using real road data. The results are presented and discussed.     

以太网供电技术及受电端电路设计

为解决具有以太网接口的小型功率设备供电不便的问题,在分别分析IEEE 802.3af标准中的以太网供电系统构成、以太网供电传输方式、以太网供电过程及其他电气特性的基础上,提出了一种通过以太网获取电源的解决方案,并给出了详细的电路设计原理图。该方案可同时支持以太网供电输入和其他辅助电源输入,并可以同时输出3.3 V和5 V这2种电压供系统使用。测试结果表明,该设计方案具有较低的成本和较高的效率,能够很好地解决小型功率设备供电不便的问题。     

基于F410的分布式小电流接地系统故障选线装置

介绍了一种基于C8051F410单片机为核心构成的分布式小电流选线装置,并详细阐述了其硬件结构及选线原理。该装置硬件结构简单,安装方便,对提高城市配电网安全运行有很大的意义。     

嵌入式Power PC Linux环境下基于Net-SNMP的代理开发

在Linux for Power PC环境下，使用Net—SNMP软件开发工具开发了一个基于SNMP协议的代理，在该代理中将原有的标准MIB进行了私有MIB的扩展。详细给出了运用Net—SNMP开发工具在嵌入式Power PC平台上开发代理进行私有MIB扩展的实现方法。     

内蕴电压平衡控制的飞跨电容逆变器的PWM方法

采用多电平结构是逆变器实现高电压大容量化的有效途径。飞跨电容逆变器因为只需要一个独立直流供电电源、电平数易扩展、控制灵活等优点而备受青睐，但是电容电压的平衡问题却制约其推广应用。针对此问题，该文提出一种内蕴电压平衡控制的PWM方法，该方法由直接PWM算法和基于最大单元电压偏差抑制的开关状态选择法则组成，前者是由给定的ABC坐标系下的参考电压来确定逆变器所需输出的电平电压、相应的作用时间及作用顺序；后者是确定逆变器的开关状态以产生已确定的电平电压，同时控制电容电压的平衡。该PWM方法理论上适用于任意电平的飞跨电容逆变器，它不但能够有效控制电容电压的平衡，而且还能够保证功率开关频率的均衡、便于数字化实现。该文给出了该方法的数字化实现原理。最后，基于飞跨电容五电平变频器对所提出的PWM方法，做了详尽的仿真分析和大量的实验验证。