燕宾课堂——小孙学变频 第三章变频调速系统的加、减速及保护功能(五)

6变频器的保护功能过载和过电流的区别厂里使用的变频器多了,难免不出现各种各样的故障跳闸。怎样查找跳闸的原因,小孙感到有些困惑,就又来请教张老师。他提出的第一个问题是:"大多数电气设备里,过载和过电流是一回事,过载必过电流,过电流也一定过载。为什么变频器里把过载保护和过电流保护分开了呢?"     

有限流保护功能的霍尔电流传感器

简单介绍了闭环式霍尔电流传感器的工作原理,在其基础上提出了一种限流保护电路,使得霍尔电流传感器原边电流过载时输出电流钳位,保障其满足3倍甚至更高倍过载要求,并通过了试验验证。     

通用变频器的故障类型及案例分析（三） 第3讲 通用变频器的过载故障及排除

1引言电动机能够旋转,但运行电流超过了额定值,称为过载。过载的基本特征是:电流虽然超过了额定值,但超过的幅度不大,一般也不形成较大的中击电流(否则就变成过流故     

漏电防火报警系统中连续过载电流调度算法的实现

漏电防火报警系统又称剩余电流报警系统,通过探测线路中漏电流的大小来判断火灾的发生的可能性,从而能够提早预防火灾发生,起到与现有消防系统相互补充的重要作用。针对供电系统实际情况,提出基于比例因子的连续过载电流调度算法,考虑到过载长延时,过载短延时以及短路情况的不同,进一步改进控制算法,使得这种控制算法比较适合在该系统中推广。经过现场试验和时间验证,这种对多规格延时的过载电流的调度算法能够反映实际现场情况,较为满意地实现过载电流的控制。     

具有过载保护的交流固态继电器设计

针对现有的交流固态继电器对过载有较大的敏感性,必须用快速熔断器或RC阻尼电路对其进行过载保护的缺点,提出一种新型交流固态继电器的设计方法。在原有固态继电器电路中嵌入电流监控电路监控电流输出,可设定过载保护电流,在达到预设的电流值时自动关闭输出,并锁定。试验表明,该设计能在过载时有效保护固态继电器,减少元器件的损害,增加了系统的可靠性和可维护性。     

汽车BCM的故障诊断设计及实现

本文针对BCM的负载控制功能设计了一种电流反馈电路及过载、短路、开路故障诊断方法,能够实时监测负载的工作电流,根据负载电流的变化情况及驱动方案选型,准确判断出是否发生过载故障、短路故障及开路故障,以正常启动或关断负载,不仅能够实现既定的负载控制功能,还能够在发生过载、短路故障时及时关断保护.     

燕宾课堂一小孙学变频 第十二章变频器跳闸原因分析

第十二章变频器跳闸原因分析第二节过电流跳闸IOC）的原因分析过电流与过载的区别小孙问：“在许多情况下,过电流和过载常常是同一回事,在变频器里为什么把它们区别开呢？”1．过电流的保护对象张老师说：“因为设计人员在决定电动机容量时,根据的是发热原则。就是说,只要电动机的温升不超过允许值,短时间的过载是允许的,而变频器则不允许。     

反时限电子过流保护装置在电力设备中的应用

本文研究了庆过载情况下信号取样与变化,讨论了反时限电子过流保护装置的工作原理,并比较两种延时整定曲线,进一步探讨了如何限制过载电流。     

稳压电源中抑制冲击电流的方法

一般通用型的稳压电源都设有过载保护电路.这些过载保护电路对于冲击电流所造成的损害是无能为力的.这是因为开机瞬间的冲击电流使保护电路动作,而将调整管截止,切断了电流的输出.保护电路灵敏度愈高,速度愈快,也就愈无法开机工作.为了开机工作,有的设计了在开机瞬间,保护电路暂时被延迟到一定的时间,到负载元件中的电流达到正常的额定值     

开关电源的过载保护电路设计

基于UC3842的反激式开关电源,文中从原理和实验两方面分析了恒功率控制和恒电流控制的过载保护电路,阐述了各自的特点,并提出了一种适用于短暂过载场合的延时锁定关断过载保护电路,实验证明此电路工作于保护模式时开关元件无开关应力,为高峰值负载电源过载保护电路的设计提供了一种有效的方法。     

Alternative Schemes for Dynamic Secure VPN Deployment in UMTS

Three alternative schemes for secure Virtual Private Network (VPN) deployment over the Universal Mobile Telecommunication System (UMTS) are proposed and analyzed. The proposed schemes enable a mobile node to voluntarily establish an IPsec-based secure channel to a private network. The alternative schemes differ in the location where the IPsec functionality is placed within the UMTS network architecture (mobile node, access network, and UMTS network border), depending on the employed security model, and whether data in transit are ever in clear-text, or available to be tapped by outsiders. The provided levels of privacy in the deployed VPN schemes, as well as the employed authentication models are examined. An analysis in terms of cost, complexity, and performance overhead that each method imposes to the underlying network architecture, as well as to the mobile devices is presented. The level of system reliability and scalability in granting security services is presented. The VPN management, usability, and trusted relations, as well as their behavior when a mobile user moves are analyzed. The use of special applications that require access to encapsulated data traffic is explored. Finally, an overall comparison of the proposed schemes from the security and operation point of view summarizes their relative performance. Christos Xenakis received his B.Sc. degree in computer science in 1993 and his M.Sc. degree in telecommunication and computer networks in 1996, both from the Department of Informatics and Telecommunications, University of Athens, Greece. In 2004 he received his Ph.D. from the University of Athens (Department of Informatics and Telecommunications). From 1998–2000 was with the Greek telecoms system development firm Teletel S.A., where was involved in the design and development of advanced telecommunications subsystems for ISDN, ATM, GSM, and GPRS. Since 1996 he has been a member of the Communication Networks Laboratory of the University of Athens. He has participated in numerous projects realized in the context of EU Programs (ACTS, ESPRIT, IST). His research interests are in the field of mobile/wireless networks, security and distributed network management. He is the author of over 15 papers in the above areas. Lazaros Merakos received the Diploma in electrical and mechanical engineering from the National Technical University of Athens, Greece, in 1978, and the M.S. and Ph.D. degrees in electrical engineering from the State University of New York, Buffalo, in 1981 and 1984, respectively. From 1983 to 1986, he was on the faculty of Electrical Engineering and Computer Science at the University of Connecticut, Storrs. From 1986 to 1994 he was on the faculty of the Electrical and Computer Engineering Department at Northeastern University, Boston, MA. During the period 1993–1994 he served as Director of the Communications and Digital Processing Research Center at Northeastern University. During the summers of 1990 and 1991, he was a Visiting Scientist at the IBM T. J. Watson Research Center, Yorktown Heights, NY. In 1994, he joined the faculty of the University of Athens, Athens, Greece, where he is presently a Professor in the Department of Informatics and Telecommunications, and Director of the Communication Networks Laboratory (UoA-CNL) and the Networks Operations and Management Center. His research interests are in the design and performance analysis of broadband networks, and wireless/mobile communication systems and services. He has authored more than 150 papers in the above areas. Since 1995, he is leading the research activities of UoA-CNL in the area of mobile communications, in the framework of the Advanced Communication Technologies & Services (ACTS) and Information Society Technologies (IST) programmes funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS, ANWIRE). He is chairman of the board of the Greek Universities Network, the Greek Schools Network, and member of the board of the Greek Research Network. In 1994, he received the Guanella Award for the Best Paper presented at the International Zurich Seminar on Mobile Communications.     

企业VPN技术应用实施浅析

随着企业规模逐渐扩大,远程用户、分支机构、合作伙伴也在不断增多,关键业务的需求增加,出现了一种通过公共网络（如Internet）来建立自己的专用网络的技术,这种技术就是虚拟专用网（简称VPN）。本文首先介绍了VPN的概念,对VPN的实现技术进行了分类和适用性分析,然后分析了各种类型的企业在信息安全方面的需求和限制,根据不同企业的特点提出了不同的VPN解决方案,最后,对VPN在集成电路企业中的应用做了简单的拓朴展示。     

接入控制器安全网络管理系统的设计与实现

在讨论了接入控制器(AC)网络管理系统安全重要性的基础上,分析了SNMP协议的应用,包括对其3个版本SNMPv1、SNMPv2及SNMPv3的优缺点的对比,并解释了该设备网络管理系统采用SNMPv3版本的原因.详细介绍了AC所实现的管理信息库的内容,包括RFC1213协议、IEEE 802.1x协议、RMON协议、Web DHCP、EAP_OTP、EAP_MD5、EAP_TLS、EAP_SIM等多种认证协议以及网络管理系统的五大功能.最后阐述了AC安全网络管理系统结构的设计与实现.     

SOI Technologies Overview for Low-Power Low-Voltage Radio-Frequency Applications

Thanks to their structure, the SOI technologies present several intrinsic advantages for analog and RF applications. Indeed, as it is well established now, these technologies allow the reduction of the power consumption at a given operating frequency. Moreover, the high-insulating properties of SOI substrates, in particular when high resistivity substrate is used, make that these technologies are perfect candidates for mixed-signal applications. In the present paper, we will discuss the performances of the SOI technologies in radio-frequency range. First of all, the high-frequency behavior of SOI substrates, thanks to the characterization of transmission lines, will be shown. The impact of the SOI substrate resistivity on the performances of passive components will also be analyzed. Then, an overview of RF performances of SOI MOSFETs for two different architectures, fully- and partially-depleted, will be achieved and compared to the bulk ones. Finally, the influence of some specific parasitic effects, such as the kink effect, the self-heating effect and the kink-related excess noise, on the RF performances of SOI devices will be studied, thanks to a specific high-frequency characterization.     

自动测试系统中的总线技术

自动测试系统满足现代科研生产中对测试高速度和高精度的要求,其发展方向是标准化、模块化和系列化,而标准的总线技术是满足这三化的关键技术,总线技术作为自动测试系统的核心,其发展推动了自动测试系统的更新换代.按照自动测试系统中出现的总线技术的顺序,依次对GPIB,VXI,PXI,LXI的基本特性、优缺点及应用进行概括,重点是结合在实际中组建自动测试系统对总线的选型,从宏观上比较了选取传统的卡式仪器总线或基于以太网的新型总线的因素.从而使用户在选取总线时更有针对性和目的性.     

雷达探鸟技术发展与应用综述

探鸟雷达已成为机场鸟击防范、风力发电场鸟击风险评估、鸟类自然保护区鸟情观测与科学研究的重要工具。文中首先论述了探鸟雷达的主要组成部分。然后,分析了地面杂波、空域杂波和其他无关目标对探鸟雷达探测效果的影响,进而介绍了传统的杂波抑制方法和相参雷达杂波抑制技术,以及先进的探鸟雷达采用的目标检测、目标跟踪、目标显示、数据记录和雷达组网等数据处理技术。接着,给出了当前的探鸟雷达能够获取的目标轨迹、回波大小、回波强度、信号波动、飞行速度、飞行高度等反映飞鸟目标特性的主要指标。最后,描述了国内外四种典型雷达探鸟系统,并针对雷达探鸟技术的未来发展提出了一些思考及可行性建议。     

CPLD在雷达发射机控制检测单元中的应用

随着雷达发射机技术的不断发展,越来越多的新技术应用于发射机设计中。复杂可编程逻辑器件CPLD和现场可编程门阵列FPGA,同以往的PAL和GAL器件相比,这些器件含有数量众多的可编程逻辑宏单元或逻辑块,规模大,组合能力强,设计成功能各异的逻辑电路,适合于时序、组合等逻辑电路。本文用CPLD对发射机控制功能进行综合处理,控制命令产生部分根据信号处理机通过串行链发来的控制命令产生控制命令,然后对发射机进行相应的控制,并对相关命令根据时序和故障情况进行逻辑链锁,达到最终控制发射机的目的。     

事件科普营销模式探究

从事件的视角看科普,已形成了社会公共事件、社会热点事件、社会突发事件等社会事件中嵌入科普的应急科普模式。但从科普的视角看事件,应急科普模式只是依托事件展开科普的组成部分,结合事件营销和科普营销的已有研究基础,本文提出事件科普营销模式,界定其依借公益性、聚焦性和危机性事件的内涵和依附性、新闻性、策划性三个特征,并从科学技术渗透疆常生活、资源整合、投入产出效率等角度论述其兴起的内在依据,并提出借势方式和造势方式下的四种路径。     

基于高斯分布的基站天线最佳方向角定位算法

为提高天馈问题被发现的准确性和维护效率,提出了基于高斯分布的最佳方向角解决方案来诊断运营商天馈覆盖问题。首先计算 UE 上报的具有定位信息的每个 MR 采样点与基站之间的位置方向信息,然后按照位置方向的一定角度间隔逐个统计各区间的MR采样点占比,取MR采样点占比最大的角度区间为该扇区的、基于用户热点分布的最佳天线方向角,最后将该最佳方向角与后台天线基础数据库中基站方向角进行比对,发现天馈系统接反、天线覆盖方向不合理、后台天线数据库错误等一系列天馈相关问题。经验证,采用该算法发现天馈问题的成本、准确率和效率较现有方法有明显改善?。     

关于物流机器人配送在社区疫情隔离中的应用探讨

机器人系统通常用于人工介入成本过高、危险过大或者效率过低的任务。近年来,随着人工智能、自动驾驶、物联网等众多相关学科的全面发展,机器人在很多行业的应用也越来越广泛、成熟;与民众生活密切相关的物流机器人的配送应用也在逐步发展;互联网下,电商的充分发展为物流机器人的配送应用提供了明确的应用场景。而在抗击新型冠状病毒肺炎疫情时期,区域人群需要实行严格隔离,隔断病毒人传人的感染途径。针对这样的状况,物流机器人可发挥其巨大优势,为民众提供物资配送服务,可有效隔断病毒人际传播,避免人员配送过程中可能带来的病毒扩散风险,针对性地解决疫情隔离阶段物资供给最后一里的难题。