Implementation of a three-phase high-power-factor rectifier with NPC topology

A three-phase four-wire power factor corrector based on neutral-point-clamped (NPC) topology is adopted to reduce the current harmonics and increase the input power factor. Using the NPC topology, the voltage stress of power switches can be reduced to the half of the dc-link voltage. With the dc-link voltage controller and the phase locked loop circuit, the balanced and sinusoidal line currents can be drawn from the ac supply system under the balance and unbalance mains voltages. The hysteresis current comparators are adopted in the current control loop to track the line current commands. Three voltage levels are generated on the ac terminal to the neutral point. Simulations and experiments are provided to verify the validity and the effectiveness of the proposed control scheme.     

航天遥感仪器的反射镜轻量化的研究

反射镜轻量化是航天遥感仪器轻型化的重要技术途径之一。阐述了反射镜轻量化的意义,反射镜材料的选择,玻璃反射镜轻量化的结构型式和设计要求、设计方案和计算以及温度试验结果。     

波导分支线定向耦合器计算方法

利用模匹配方法和网络理论分析计算了一种卫星天线系统中常用的波导分支线定向耦合器,计算结果与实验结果非常吻合。该方法为波导分支线定向耦合器提供一种有力的设计手段。它可直接用于设计Ku 波段通信卫星天线的波束形成网络,也可以用来设计各种耦合度的波导分支线定向耦合器。     

纵向短周期模态试飞方法和选择

对几种纵向短周期模态试飞方法及其适用性进行了初步分析。结合实际飞行经验,提出了初步判断飞机短周期特性及选择试飞方法。     

炉渣滤床技术处理亚麻生产废水

为了确定处理包头亚麻厂亚麻生产废水的设计方案，设计之前在现场进行了生产试验。在包头亚麻厂污水处理站，模拟炉渣滤床制造了3米高的炉渣滤层，滤渣从工厂锅炉房取用，将实际排放的亚麻煮漂车间、细纱车间、粗纱车间的生产废水混合后，通过炉渣滤层过滤处理，处理后出水由厂化验室和包头环保局化验。试验结果表明，处理后的排水各项指标完全达到国家排放标准。该工艺处理费用低，运行效果稳定，管理简便，具有明显的经济效益、环境效益和社会效益。     

Earthshine and Asteroseismology Telescope (East) Network

Several automated optical telescopes have been setup at appropriate longitudes around the globe to study earthshine variations and asteroseismology. The first telescope has been setup at Teide Observatory, Tenerife, Spain in October 2004. The intensity of earthshine relates to the average of Earth’s albedo, and in turn relates to the global temperature of the Earth. A global network is necessary because each site can measure the earthshine reflected from only a part of the Earth. The network will also be used for asteroseismology study. It can measure photometric variations of pulsating stars. The long-term and continuous measurements allow the accurate determination of mode frequencies of stellar pulsations, which provides information on the properties of stellar interior.     

英语课堂教学中学生的厌烦心理及其分析

分析英语课堂教学中学生厌烦心理，转变教学观念，培养学生学习兴趣，真正发挥课堂教学的作用。     

谈"材料成型及控制工程专业"人才培养规格

材料成型及控制工程专业是机械热加工领域的新型专业,正确认识专业,确定人才培养规格是搞好专业建设的基础.     

基于PCI总线的石英晶体元件电参数测试仪

首先介绍PCI总线控制专用芯片S5920的组成,Mailboxs、FIFO、Pass-Thru的基本概念、性能和使用方法。其次介绍测量石英晶体元件参数的阻抗计法和π网络法。对基于PCI总线控制器S5920为核心的π网络法石英晶体元件电参数测试仪的设计和实现作了说明。该方法测量的频率可达2005MHz。利用GPs高精度的授时信号作为频率校准信号校准信号源的精度。