1906_阀门电动装置设计
1906_阀门电动装置设计,阀门,电动,装置,设计
黄河科技学院本 科 毕 业 设 计 (论文) 任 务 书工 学院 机械 系 机械设计制造及其自动化 专业 08 级 3 班 学号 080105651 学生 刘华鸽 指 导 教 师 李 长 诗 毕业设计(论文)题目 阀门电动装置设计 毕业设计(论文)工作内容与基本要求(目标、任务、途径、方法,应掌握的原始资料(数据) 、参考资料(文献)以及设计技术要求、注意事项等) (纸张不够可加页)一主要内容:1.分析课题条件要求,查阅文献,拟定总体设计方案;2.机构设计;3.编写设计说明书,翻译外文,编写文献综述。二要求:1. 机构设计;2. 设计说明书设计说明书不少于 6000 字;3. 查阅文献资料不少于 12 篇,其中外文资料不少于 2 篇;献综述不少于3000 字。 三主要参考资料:机械设计手册 化学工业出版社现代机床电器 机械工业出版社四、时间安排:1-4 周 完成开题报告、文献翻译、文献综述及总体方案设计5-10 周 完成总体设计、完成电路图及程序并撰写说明书10-12 周 修改论文、资格审查等13 周 毕业答辩毕业设计(论文)时间: 2012 年 2 月 13 日至 2012 年 5 月 15 日计 划 答 辩 时 间: 2012 年 5 月 19 日专业(教研室)审批意见:审批人(签字):黄河科技学院毕业设计(论文)开题报告表课题名称 阀门电动装置的设计课题来源 教师拟订 课题类型 AX 指导教师 李长诗学生姓名 刘华鸽 专 业 机械设计制造及其自动化 学 号 080105651一、调研资料的准备根据任务书的要求,在做本课题前,查阅了与课题相关的资料有:机械设计、现代机床电器、机械制图、机械设计手册、机械制造工艺学、减速器设计、毕业设计指导等以及与设计相关的手册。二、设计的目的与要求 毕业设计是大学教学中最后一个实践性教学环节,通过该设计过程,可以检验学生所学的知识,同时培养学生处理工程中实际问题的能力,因此意义特别重大。阀门电动装置是实现阀门程控、自控和遥控不可缺少的驱动设备,其运功过程可有行程、转矩或轴向推力的大小来控制。其工作特性和利用率取决于阀门的种类、装置工作规范及阀门在管线或设备上的位置。三、设计的思路与预期成果 1、设计思路电动装置主要有电动机与减速器组合而成,与阀门连接起来,经过安装调试后成为电动阀,它由 DCS 系统来控制,电动阀使用电能作为动力来接通电动执行机构驱动阀门,实现阀门的开关、调节动作。从而达到对管道介质的开关或是调节目的。2、预期的成果(1)完成文献综述一篇,不少与 3000 字,与专业相关的英文翻译一篇,不少于 3000 字(2)完成内容与字数都不少于规定量的毕业设计说明书一份(3)绘制装配图,部分零件图(4)刻录包含本次设计的所有内容的光盘一张四、任务完成的阶段内容及时间安排1 周2 周 收集设计资料并完成开题报告3 周4 周 完成英文资料翻译并写出文献综述5 周6 周 进行总体设计和部分零部件的选择与设计7 周10 周 绘制装配图和部分零件图、编写毕业设计说明书11 周 修改整理,准备答辩五、完成设计(论文)所具备的条件因素本人已修完机械设计、现代机床电器、机械制图、液压与气压传动、机电一体化技术、机械制造技术基础、减速器设计、数控原理与系统、PLC 与电气控制与毕业设计指导等课程,借助图书馆的相关文献资料,以及相关的网络等资源。指导教师签名: 日期: 课题来源:(1)教师拟订;(2)学生建议;(3)企业和社会征集;(4)科研单位提供课题类型:(1)A工程设计(艺术设计) ;B技术开发;C软件工程;D理论研究;E调研报告(2)X真实课题;Y模拟课题;Z虚拟课题要求(1) 、 (2)均要填,如 AY、BX 等。 毕业设计文献综述院 ( 系 ) 名 称 工 学 院 机 械 系专 业 名 称 机 械 设 计 制 造 及 其 自 动 化学 生 姓 名 刘 华 鸽指 导 教 师 李 长 诗2012 年 03 月 10 日黄 河 科 技 学 院 毕 业 设 计 (文 献 综 述 ) 第 1 页 阀门电动装置摘要:本文介绍了阀门电动装置的组成性能、选用要求、以及国内外阀门电动装置市场的发展趋势。通过这些对阀门电动装置有一个大致的了解,为设计做准备。关键词:阀门;电动装置 前言阀门是石油、化工、电站、长输管线、宇航以及海洋采油等国民经济各部门不可缺少的流体控制设备。上述工业的发展和需要,推动了阀门工业的发展。近年来,在满足各方面高参数新要求的同时,对阀门的结构、材料和生产工艺等方面,对如何做到更好地提高性能、可行性及降低成本等也予以密切关注 【1】 。因此,对阀门要求进一步严格控制内在质量阀门电动装置是实现阀门程控、自控和遥控不可缺少的驱动设备,其运动过程可由行程、转矩或轴向推力的大小来控制。由于阀门电动装置的工作特性和利用率取决于阀门的种类、装置工作规范及阀门在管线或设备上的位置 【2】1.阀门电动装置的发展自 80 年代我国改革开放至今,我国的化工行业得到了长足的发展,发生了翻天覆地的变化,化工设计行业也随之发生了很大的变化。由于国外先进技术的不断引进及国内化工技术开发力度的不断加大,化工产品种类不断增多,品种越来越齐全.随着国家经济水平的提高,化工设计行业对阀门制造业的要求也越来越高,尤其是对阀门的性能的可靠性、耐用性等要求越来越高。从整个阀门市场来看,主要有两个 【3】 :(1)国内市场国内市场又分新建、扩建程项目市场,老装置维修、改造项目市场。从这两块市场来看,普通阀门产品严重供大于求,其次,企业之间竟相压仰,无序竞争,假冒伪劣,市场很不规范,导致某些阀门生产企业在惨烈的竞争中,连年大幅度亏损。从这两块市场的需求来看,随着市场经济的发展和完善,特别是进步世界贸易组织(WTO),其市场变化越来越大,企业受市场的影响越来越深,用户对市场产品的需求黄 河 科 技 学 院 毕 业 设 计 (文 献 综 述 ) 第 2 页 越来越高,对产品开发、生产周期的需求越来越短。(2)国外市场国外市场近几年十分活跃,竞争相当激烈。东亚和东南亚的阀门进出口增长迅速,北美的欧共体等发达国家间的市场贸易持续发展,德国、意大利、日本、中国等国家和地区的出口扩大,美国、英国、法国等国家进口的高速增长,形成了国际阀门市场繁荣的支撑点,再者由于世界经济进一步国际化,跨国公司将不断推动国际阀门市场的发展国际贸易地区化是毕成为另一大特点。 2.阀门电动装置组成电动装置一般由下列部分组成 【4】 【5】 :专用电动机,特点是过载能力强起动转矩大转动惯量小,短时 断续工作。减速机构,用以减低电动机的输出转速。行程控制机构,用以调节和准确控制阀门的启闭位置。转矩限制机构,用以调节转矩(或推力)并使之不超过预定值。手动电动切换机构,进行手动或电动操作的联锁机构。开度指示器,用以显示阀门在启闭过程中所处的位置。3.国内阀门的种类(1)城市建筑用阀门:城建系统一般采用低压阀门,目前正向环保型和节能型方向发展。环保型的胶板阀、平衡阀及中线蝶阀、金属密封蝶阀正在逐渐取代低压铁制闸阀。国内城市建筑需用阀门多为平衡阀、软密封闸阀、蝶阀等 【6】 。(2)城市供热用阀门:城市代热系统中,需用大量的金属密封蝶阀、水平平衡阀及直埋式球阀、因这类阀解决管道纵向、横向水力失调问题,达到节能、代热平衡的目的。(3)环保用阀门:国内环保系统中,给水系统主要需用中线蝶阀、软密封闸阀、球阀、排气阀(用于排除管道中的空气) 。污水处理系统主要需用软密封闸阀、蝶阀。(4)城市燃气用阀门:城市燃气占整个天然全市场的 22%,阀门用量大其类型也多主要需要球阀、旋塞阀、减压阀、安全阀。(5)长输管线用阀门:长输管线主要为原油、成品没及天然管线。这类管线需用量居多的阀门是锻钢三体式全通径球阀、抗硫平板闸阀,安全阀,止回阀。黄 河 科 技 学 院 毕 业 设 计 (文 献 综 述 ) 第 3 页 (6)石化装置用阀门:a、炼油装置,炼油装置需用的阀门大多是管道阀门,主要为闸阀、截止阀、止回阀、安全阀、球阀、蝶阀、疏水阀、其中,闸阀需量占阀门总数的 80% 左右, (阀门占装置总投资的 3%5%) 。b、化纤装置,化纤产品主要有涤纶、晴纶、维纶三大类。其需用的阀门的球阀、夹套阀(夹套球阀、夹套闸阀、夹套截止阀) 。c、丙烯晴装置。该装置一般需用 API 标准生产的阀门,主要为闸阀、截止阀、止回阀、球阀、疏水阀、针型阀、旋塞阀、其中,闸阀占阀门总量的 75% 左右。d、合成氨装置。由于合成氨原和净化方法不同,其工艺流程不同,所需阀门的技术性能也不同。目前,国内合成氨装置主要需用闸阀、截止阀、止回阀、疏水阀、蝶阀、球阀、隔膜阀、调节阀、针型阀、安全阀、高温低温阀。其中,截止阀占装置用阀总数据的 53.4%,闸阀占 25.1%,疏水阀占 7.7%,安全阀占 2.4%,调节阀和离低温阀及其它占 11.4%。e、乙烯装置,乙烯装置是石油化工的龙头装置,其需用阀门种类繁多。闸阀、截止阀、止回阀、升降杆式球阀占大多数,其中闸阀需居首。 “十五”规划,全国还需建年产 66 万吨的乙烯装置 6 套,其阀门需求量可观。另外,大型乙烯和高压聚乙烯装置还需用超高温,越低温及超高压阀门系列产品。f、空分装置。 “空分”即空气分离,该装置主要需用截止阀、安全阀、止回阀、调节阀、球阀、蝶阀、低温阀。g、聚丙烯装置,聚丙烯易是以丙烯为原料,经聚合而成的高分子化合物,该装置主要需用闸阀、截止阀、止回阀、针型阀、球阀、疏水阀。(7)电站用阀门:我国电站的建设正向大型化方向发展,所以需用大口径及高压的安全阀、减压阀、截止阀、闸阀、蝶阀、紧急切断阀及流量控制阀、球面密封仪表截止阀, (根据国家“十五”规划,除内蒙、贵州两省还可建 20 万千瓦以上机组外,其它省市则只能建 30 万千瓦以上的机组) 【7】 。(8)冶金用阀门:冶金行业中氧化铝行为主要需用耐磨料浆阀(在流式截止阀) 、调节疏水阀。炼钢行业主要需用金属密封球阀、蝶阀及氧化球阀、截止阀和四通换向阀。(9)海洋平合用阀门:随着海上油田开采的发展,其海洋平发需用阀门的量也逐黄 河 科 技 学 院 毕 业 设 计 (文 献 综 述 ) 第 4 页 渐增多。海洋平台需用关断球阀、止回阀、多路阀。(10)食品医药用阀门:该行业主要需用不锈钢球阀、无毒全塑球阀及蝶阀。4. 根据阀门类型选择电动执行器(1) 角行程电动执行器(转角360 度) 适用于闸阀、截止阀等。电动执行器输出轴的转动大于一周,即大于 360 度,一般需多圈才能实现阀门的启闭过程控制。(3) 直行程(直线运动) 适用于单座调节阀、双座调节阀等。电动执行器输出轴的运动为直线运动式,不是转动形式。5 根据阀门所需的扭力确定电动执行器的输出扭力阀门启闭所需的扭力决定着电动执行器选择多大的输出扭力,一般由使用者提出或阀门厂家自行选配,做为执行器厂家只对执行器的输出扭力负责,阀门正常启闭所需的扭力由阀门口径大小、工作压力等因素决定,但因阀门厂家加工精度、装配工艺有所区别,所以不同厂家生产的同规格阀门所需扭力也有所区别,即使是同个阀门厂家生产的同规格阀门扭力也有所差别,当选型时执行器的扭力选择太小就会造成无法正常启闭阀门,因此电动执行器必需选择一个合理的扭力范围 【10】 【11】 。6 正确选择阀门电动装置的依据:操作力矩:操作力矩是选择阀门电动装置的最主要参数,电动装置输出力矩应为阀门操作最大力矩的1.21.5倍 【12】 【13】 【14】 。操作推力:阀门电动装置的主机结构有两种:一种是不配置推力盘,直接输出力矩;另一种是配置推力盘,输出力矩通过推力盘中的阀杆螺母转换为输出推力。输出轴转动圈数:阀门电动装置输出轴转动圈数的多少与阀门的公称通径、阀杆螺距、螺纹头数有关,要按MH/ZS计算(M为电动装置应满足的总转动圈数,H为阀门开启高度,S为阀杆传动螺纹螺距,Z为阀杆螺纹头数) 。黄 河 科 技 学 院 毕 业 设 计 (文 献 综 述 ) 第 5 页 阀杆直径:对多回转类明杆阀门,如果电动装置允许通过的最大阀杆直径不能通过所配阀门的阀杆,便不能组装成电动阀门。因此,电动装置空心输出轴的内径必须大于明杆阀门的阀杆外径。对部分回转阀门以及多回转阀门中的暗杆阀门,虽不用考虑阀杆直径的通过问题,但在选配时亦应充分考虑阀杆直径与键槽的尺寸,使组装后能正常工作。输出转速:阀门的启闭速度若过快,易产生水击现象。因此,应根据不同使用条件,选择恰当的启闭速度。黄 河 科 技 学 院 毕 业 设 计 (文 献 综 述 ) 第 6 页 参考文献1 洪勉成, 陆培文.阀门设计计算手册M.北京:中国标准化出版社,1994.2 杨源泉.阀门设计手册M.第一版.北京:机械工业出版社,1992.3 陆培文.阀门选用手册M.北京:机械工业出版社,20014 孙晓霞.实用阀门技术问答M.北京:中国标准出版社,2001,17:3-85 陆培文.国内外阀门新结构M.北京:中国标准出版社,1997.6 钢制压力容器 GB150-1998S7API Sepecification 6DS,Twenty-second Edition.American Petroleum Institute.January,20028 ASME BPV Code Section VIIIS,Division3,1986 Edition9 章华友,晏泽荣.阀门与选用M.北京:北京科学技术出版杜,199410 刘极峰.计算机辅助设计与制造M.北京:高等教育出版社,2004.11 张锁龙,庞明军,包健,陈蓉.大口径球阀阀体设计J.农业机械学报,2006, 37(2):154-15612 张锁龙,何云松,裴峻峰,殷舜时,邓学风,秦志坚.大口径球阀的结构设计和强度计算J.江苏工业学院学报,2004,16(4):36-3913 朱喜平.天然气管道球阀的维护及故障排除技术J.天然气工业,2005,7:102-10414 http:/mw.newmaker.com/art_21337.html. 毕业设计文献翻译院 ( 系 ) 名 称 工 学 院 机 械 系专 业 名 称 机 械 设 计 制 造 及 其 自 动 化学 生 姓 名 刘 华 鸽指 导 教 师 李 长 诗2012 年 03 月 10 日黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 1 页Belt Conveying Systems Development of driving systemNagwa Abd-elhalim, Nabil Hammed, Magdy Abdel-hady,Shawki Abouel-Seoud and Eid S. MohamedHelwan UniversityAbstract:Among the methods of material conveying employed,belt conveyors play a very important part in the reliable carrying of material over long distances at competitive costConveyor systems have become larger and more complex and drive systems have also been going through a process of evolution and will continue to do soNowadays,bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuang Mine)The ability to control drive acceleration torque is critical to belt conveyors performance An efficient drive system should be able to provide smooth,soft starts while maintaining belt tensions within the specified safe limitsFor load sharing on multiple drivestorque and speed control are also important considerations in the drive systems design. Due to the advances in conveyor drive control technology,at present many more reliable Cost-effective and performance-driven conveyor drive systems covering a wide range of power are available for customers choices1.Keywords :Conveyor systems;efficient;drive system1 Analysis on conveyor drive technologies11 Direct drivesFull-voltage startersWith a full-voltage starter design,the conveyor head shaft is direct-coupled to the motor through the gear driveDirect full-voltage starters are adequate for relatively low-power, simple-profile conveyorsWith direct fu11-voltage startersno control is provided for various conveyor loads anddepending on the ratio between fu11- and no-1oad power requirements,empty starting times can be three or four times faster than full loadThe maintenance-free starting system is simple,low-cost and very reliableHowever, they cannot control starting torque and maximum stall torque; thereforethey are limited to the low-power, simple-profile conveyor belt drivesReduced-voltage starters As conveyor power requirements increase,controlling the 黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 2 页applied motor torque during the acceleration period becomes increasingly importantBecause motor torque 1s a function of voltage,motor voltage must be controlledThis can be achieved through reduced-voltage starters by employing a silicon controlled rectifier(SCR)A common starting method with SCR reduced-voltage starters is to apply low voltage initially to take up conveyor belt slackand then to apply a timed linear ramp up to full voltage and belt speedHowever, this starting method will not produce constant conveyor belt accelerationWhen acceleration is completethe SCRs, which control the applied voltage to the electric motor are locked in full conduction, providing fu11-line voltage to the motorMotors with higher torque and pullup torque,can provide better starting torque when combined with the SCR starters, which are available in sizes up to 750 KWWound rotor induction motorsWound rotor induction motors are connected directly to the drive system reducer and are a modified configuration of a standard AC induction motor By inserting resistance in series with the motors rotor windingsthe modified motor control system controls motor torqueFor conveyor starting,resistance is placed in series with the rotor for low initial torqueAs the conveyor accelerates,the resistance is reduced slowly to maintain a constant acceleration torqueOn multiple-drive systemsan external slip resistor may be left in series with the rotor windings to aid in load sharingThe motor systems have a relatively simple designHowever, the control systems for these can be highly complex,because they are based on computer control of the resistance switchingToday,the majority of control systems are custom designed to meet a conveyor systems particular specificationsWound rotor motors are appropriate for systems requiring more than 400 kW DC motorDC motorsavailable from a fraction of thousands of kW ,are designed to deliver constant torque below base speed and constant kW above base speed to the maximum allowable revolutions per minute(r/min)with the majority of conveyor drives, a DC shunt wound motor is usedWherein the motors rotating armature is connected externallyThe most common technology for controlling DC drives is a SCR device which allows for continual variable-speed operation The DC drive system is mechanically 黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 3 页simple, but can include complex custom-designed electronics to monitor and control the complete systemThis system option is expensive in comparison to other soft-start systemsbut it is a reliable, cost-effective drive in applications in which torque,1oad sharing and variable speed are primary considerationsDC motors generally are used with higher-power conveyors,including complex profile conveyors with multiple-drive systems,booster tripper systems needing belt tension control and conveyors requiring a wide variable-speed range12 Hydrokinetic couplingHydrokinetic couplings,commonly referred to as fluid couplingsare composed of three basic elements; the driven impeller, which acts as a centrifugal pump;the driving hydraulic turbine known as the runner and a casing that encloses the two power components Hydraulic fluid is pumped from the driven impeller to the driving runner, producing torque at the driven shaftBecause circulating hydraulic fluid produces the torque and speed,no mechanical connection is required between the driving and driven shaftsThe power produced by this coupling is based on the circulated fluids amount and density and the torque in proportion to input speedBecause the pumping action within the fluid coupling depends on centrifugal forcesthe output speed is less than the input speedReferred to as slipthis normally is between l% and 3% Basic hydrokinetic couplings are available in configurations from fractional to several thousand kW Fixed-fill fluid couplingsFixed-fill fluid couplings are the most commonly used soft-start devices for conveyors with simpler belt profiles and limited convex/concave sectionsThey are relatively simple,1ow-cost,reliable,maintenance free devices that provide excellent soft starting results to the majority of belt conveyors in use todayVariable-fill drain couplingsDrainable-fluid couplings work on the same principle as fixed-fill couplingsThe couplings impellers are mounted on the AC motor and the runners on the driven reducer high-speed shaftHousing mounted to the drive base encloses the working circuitThe couplings rotating casing contains bleed-off orifices that continually allow fluid to exit the working circuit into a separate hydraulic reservoirOil from the reservoir is pumped through a heat exchanger to a solenoid-operated hydraulic valve that 黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 4 页controls the filling of the fluid couplingTo control the starting torque of a single-drive conveyor system,the AC motor current must be monitored to provide feedback to the solenoid control valveVariable fill drain couplings are used in medium to high-kW conveyor systems and are available in sizes up to thousands of kW The drives can be mechanically complex and depending on the control parametersthe system can be electronically intricateThe drive system cost is medium to high, depending upon size specifiedHydrokinetic scoop control driveThe scoop control fluid coupling consists of the three standard fluid coupling components:a driven impeller, a driving runner and a casing that encloses the working circuitThe casing is fitted with fixed orifices that bleed a predetermined amount of fluid into a reservoirWhen the scoop tube is fully extended into the reservoir, the coupling is l00 percent filledThe scoop tube, extending outside the fluid coupling,is positioned using an electric actuator to engage the tube from the fully retracted to the fully engaged positionThis control provides reasonably smooth acceleration ratesto but the computer-based control system is very complexScoop control couplings are applied on conveyors requiring single or multiple drives from l50 kW to 750 kW.13 Variable-frequency control(VFC)Variable frequency control is also one of the direct drive methodsThe emphasizing discussion about it here is because that it has so unique characteristic and so good performance compared with other driving methods for belt conveyor VFC devices Provide variable frequency and voltage to the induction motor, resulting in an excellent starting torque and acceleration rate for belt conveyor drivesVFC drivesavailable from fractional to several thousand(kW ), are electronic controllers that rectify AC line power to DC and,through an inverter, convert DC back to AC with frequency and voltage contro1VFC drives adopt vector control or direct torque control(DTC)technology,and can adopt different operating speeds according to different loadsVFC drives can make starting or stalling according to any given S-curvesrealizing the automatic track for starting or stalling curvesVFC drives provide excellent speed and torque control for starting conveyor belts and can also be designed to provide load sharing for multiple driveseasily VFC 黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 5 页controllers are frequently installed on lower-powered conveyor drives,but when used at the range of medium-high voltage in the pastthe structure of VFC controllers becomes very complicated due to the limitation of voltage rating of power semiconductor devices,the combination of medium-high voltage drives and variable speed is often solved with low-voltage inverters using step-up transformer at the output,or with multiple low-voltage inverters connected in seriesThree-level voltage-fed PWM converter systems are recently showing increasing popularity for multi-megawatt industrial drive applications because of easy voltage sharing between the series devices and improved harmonic quality at the output compared to two-level converter systems With simple series connection of devicesThis kind of VFC system with three 750 kW /23kV inverters has been successfully installed in ChengZhuang Mine for one 27-km long belt conveyor driving system in following the principle of three-level inverter will be discussed in detail2 Neutral point clamped(NPC)three-level inverter using IGBTsThree-level voltage-fed inverters have recently become more and more popular for higher power drive applications because of their easy voltage sharing features1ower dv/dt per switching for each of the devices,and superior harmonic quality at the outputThe availability of HV-IGBTs has led to the design of a new range of medium-high voltage inverter using three-level NPC topologyThis kind of inverter can realize a whole range with a voltage rating from 23 kV to 41 6 kV Series connection of HV-IGBT modules is used in the 33 kV and 41 6 kV devicesThe 23 kV inverters need only one HV-IGBT per switch2,3.21 Power sectionTo meet the demands for medium voltage applicationsa three-level neutral point clamped inverter realizes the power sectionIn comparison to a two-level inverterthe NPC inverter offers the benefit that three voltage levels can be supplied to the output terminals,so for the same output current quality,only 1/4 of the switching frequency is necessaryMoreover the voltage ratings of the switches in NPC inverter topology will be reduced to 1/2and the additional transient voltage stress on the motor can also be reduced to 1/2 compared to that of a two-level inverter黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 6 页The switching states of a three-level inverter are summarized in Table 1UV and W denote each of the three phases respectively;P N and O are the dc bus pointsThe phase U,for example,is in state P(positive bus voltage)when the switches S1u and S2u are closed,whereas it is in state N (negative bus voltage) when the switches S3u and S4u are closedAt neutral point clamping,the phase is in O state when either S2u or S3u conducts depending on positive or negative phase current polarity,respectivelyFor neutral point voltage balancing,the average current injected at O should be zero22 Line side converterFor standard applicationsa l2-pulse diode rectifier feeds the divided DC-link capacitorThis topology introduces low harmonics on the line side For even higher requirements a 24-pulse diode rectifier can be used as an input converterFor more advanced applications where regeneration capability is necessary, an active frontend converter can replace the diode rectifier, using the same structure as the inverter23 Inverter controlMotor Contro1Motor control of induction machines is realized by using a rotor fluxoriented vector controllerFig2 shows the block diagram of indirect vector controlled drive that incorporates both constant torque and high speed field-weakening regions where the PW M modulator was used In this figure,the command flux is generated as function of speedThe feedback speed is added with the feed forward slip command signal . the resulting frequency signal is integrated and then the unit vector signals(cos and sin )are generatedThe vector rotator generates the voltage and angle commands for the PW M as shownPWM ModulatorThe demanded voltage vector is generated using an elaborate PWM modulatorThe modulator extends the concepts of space-vector modulation to the three-level inverterThe operation can be explained by starting from a regularly sampled sine-triangle comparison from two-level inverterInstead of using one set of reference waveforms and one triangle defining the switching frequency, the three-level modulator uses two sets of reference waveforms Ur1 and Ur2 and just one triangleThus, each switching transition is used in an optimal way so that several objectives are reached at the same time黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 7 页Very low harmonics are generatedThe switching frequency is low and thus switching losses are minimizedAs in a two-level inverter, a zero-sequence component can be added to each set of reference waveform s in order to maximize the fundamental voltage componentAs an additional degree of freedom,the position of the reference waveform s within the triangle can be changedThis can be used for current balance in the two halves of the DC-1ink3 Testing resultsAfter Successful installation of three 750 kW /23 kV three-level inverters for one 27 km long belt conveyor driving system in Chengzhuang MineThe performance of the whole VFC system was testedFig3 is taken from the test,which shows the excellent characteristic of the belt conveyor driving system with VFC controllerFig3 includes four curvesThe curve 1 shows the belt tensionFrom the curve it can be find that the fluctuation range of the belt tension is very smal1Curve 2 and curve 3 indicate current and torque separatelyCurve 4 shows the velocity of the controlled beltThe belt velocity have the“s”shape characteristicA1l the results of the test show a very satisfied characteristic for belt driving system4 ConclusionsAdvances in conveyor drive control technology in recent years have resulted in many more reliable Cost-effective and performance-driven conveyor drive system choices for users Among these choices,the Variable frequency control (VFC) method shows promising use in the future for long distance belt conveyor drives due to its excellent performancesThe NPC three-level inverter using high voltage IGBTs make the Variable frequency control in medium voltage applications become much more simple because the inverter itself can provide the medium voltage needed at the motor terminals,thus eliminating the step-up transformer in most applications in the pastThe testing results taken from the VFC control system with NPC three1evel inverters used in a 27 km long belt conveyor drives in Chengzhuang Mine indicates that the performance of NPC three-level inverter using HV-IGBTs together with the control strategy of rotor field-oriented vector control for induction motor drive is excellent for belt conveyor driving 黄 河 科 技 学 院 毕 业 设 计 (文 献 翻 译 ) 第 8 页system
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