自动化相关专业英语翻译.docx

自动化相关专业英语翻译.docx

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自动化相关专业英语翻译

ACMachines

Introduction

Theelectricalmachinethatconvertselectricalenergyintomechanicalenergy,andviceversa,istheworkhorseinadrivesystem.Amachineisacomplexstructureelectrically,mechanically,andthermally.Althoughmachineswereintroducedmorethanonehundredyearsago,theresearchanddevelopmentinthisareaappearstobenever-ending.However,theevolutionofmachineshasbeenslowcomparedtothatofpowersemiconductordevicesandpowerelectronicconverters.Traditionally,ACmachineswithaconstantfrequencysinusoidalpowersupplyhavebeenusedinconstant-speedapplications,whereasDCmachineswerepreferredforvariable-speeddrives.Butinthelasttwoorthreedecades,wehaveseenextensiveresearchanddevelopmenteffortsforvariable-frequency,variable-speedACmachinedrivetechnology,andtheywillprogressivelyreplaceDCdrives.Inmostcases,newapplicationsuseACdrives.

ACmachinescangenerallybeclassifiedasfollows:

Inductionmachines:

Cageorwoundrotor（doubly-fed）,Rotatingorlinear;

Synchronousmachines:

Rotatingorlinear,Reluctance,Woundfieldorpermanentmagnet,Radialoraxialgap（disk）,Surfacemagnetorinterior（buried）magnet,Sinusoidalortrapezoidal;

Variablereluctancemachines:

Switchedreluctance,Stepper.

InductionMachines

AmongalltypesofACmachines,theinductionmachine,particularlythecagetype,ismostcommonlyusedinindustry.Thesemachinesareveryeconomical,rugged,andreliable,andareavailableintherangesoffractionalhorsepower（FHP）tomulti-megawattcapacity.Low-powerFHPmachinesareavailableinsingle-phase,butpoly-phase（three-phase）machinesareused,mostofteninvariable-speeddrives.Fig.1-6A-1showsanidealizedthree-phase,two-poleinductionmotorwhereeachphasewindinginthestatorandrotorisrepresentedbyaconcentratedcoil.Thethree-phasewindingsaredistributedsinusoidallyandembeddedinslots.Inawound-rotormachine,therotorwindingissimilartothatofthestator,butinacagemachine,therotorhasasquirrelcage-likestructurewithshortedendrings.Basically,themachinecanbelookeduponasathree-phasetransformerwitharotatingandshort-circuitedsecondary.Bothstatorandrotorcoresaremadewithlaminatedferromagneticsteelsheets.Theairgapinthemachineispracticallyuniform

（non-salientpole）.

Oneofthemostfundamentalprinciplesofinductionmachinesisthecreationofarotatingandsinusoidallydistributedmagneticfieldintheairgap.Neglectingtheeffectofslotsandspaceharmonicsduetonon-idealwindingdistribution,itcanbeshownthatasinusoidalthree-phasebalancedpowersupplyinthethree-phasestatorwindingcreatesasynchronouslyrotatingmagneticfield.Therotationalspeedcanbegivenasequation（1-6A-1）.Neiscalledsynchronousspeedinrpmand

isthestatorfrequencyinHz.Pisthepolenumbersofamachine.

Therotorwindingwillbesubjectedtoasweepingmagneticfield,andhaveinducingcurrentintheshort-circuitedrotor.Theinteractionofairgapfluxandrotormmfproducestorque,maketherotorrotate.Butthespeedoftherotorislessthansynchronousspeed.Soitcalledinductionmachineorasynchronousmachine.Tomeetthevariousstartingandrunningrequirementsofavarietyofindustrialapplications,severalstandarddesignsofsquirrel-cagemotorsareavailablefrommanufacturers’stock.Thetorque-speedcharacteristicsofthemostcommondesigns,readilyavailableandstandardizedinaccordancewiththecriteriaestablishedbytheNationalElectricalManufacturers’Association（NEMA）,areshowninFig.1-6A-2.Themostsignificantdesignvariableinthesemotorsistheeffectiveresistanceoftherotorcagecircuits.

ClassAMotorsThesemachinesaresuitableforapplicationswheretheloadtorqueislowatstart（suchasfanorpumploads）sothatfullspeedisachievedrapidly,therebyeliminatingtheproblemofoverheatingduringstarting.Inlargemachines,low-voltagestartingisrequiredtolimitthestartingcurrent.

ClassBMotorsMotorsofthisclassaregoodgeneral-purposemotorsandhaveawidevarietyofindustrialapplications.Theyareparticularlysuitableforconstant-speeddrives,wherethedemandforstartingtorqueisnotsevere.Examplesaredrivesforfans,pumps,blowers,andmotor-generatorsets.

ClassCMotorsClassCmotorsaresuitablefordrivingcompressors,conveyors,andsoforth.

ClassDMotorsThesemotorsaresuitablefordrivingintermittentloadsrequiringrapidaccelerationandhigh-impactloadssuchaspunchpressesorshears.Inthecaseofimpactloads,aflywheelisfittedtothesystem.Asthemotorspeedfallsappreciablywithloadimpact,theflywheeldeliverssomeofitskineticenergyduringtheimpact.

SynchronousMachines

Asynchronousmachine,asthenameindicates,mustrotateatsynchronousspeed,thatis,thespeedisuniquelyrelatedtothesupplyfrequency,asindicatedinEquation（1-6A-1）.Itisaseriouscompetitortotheinductionmachineinvariable-speeddriveapplications.

Fig.1-6A-3showsanidealizedthree-phase,two-polewoundfieldsynchronousmachine.Thestatorwindingofthemachineisidenticaltothatoftheinductionmachine,buttherotorhasawindingthatcarriesDCcurrentandproducesfluxintheairgapthathelpsthestator-inducedrotatingmagneticfieldtodragtherotoralongwithit.TheDCfieldcurrentissuppliedtotherotorfromastaticrectifierthroughslipringsandbrushes,orbybrushlessexcitation.Sincetherotoralwaysmovesatsynchronousspeed,thesynchronouslyrotatingde-qeaxesarefixedwiththerotor,wherethedeaxiscorrespondstothenorthpole,asshown.Thereisnostator-inducedinductionintherotor,andtherefore,therotormmfissuppliedexclusivelybythefieldwinding.Thispermitsthemachinetorunatanarbitrarypowerfactoratthestatorterminal,thatis,leading,lagging,orunity.Ontheotherhand,inaninductionmachine,thestatorsuppliestherotorexcitationthatmakesthemachinepowerfactoralwayslagging.

Themechanismoftorqueproductionissomewhatsimilartothatofaninductionmachine.Themachineshownischaracterizedasasalientpolebecauseofthenonuniformairgaparoundtherotor,whichcontributestoasymmetricalmagneticreluctanceinthedandqaxes.Thisisincontrasttoamachinewithacylindricalrotorstructurehavingauniformairgap（suchasaninductionmotor）,definedasanonsalientpolemachine.Forexample,low-speedsynchronousgeneratorsinhydro-electricpowerstationsusesalientpolemachines,whereashigh-speedgeneratorsinsteam-powerstationsusenonsalientpolemachines.Inadditiontofieldwinding,therotorusuallycontainsanamortisseur,ordamperwinding,whichislikeshort-circuitedsquirrelcagebarinaninductionmotor.Themachineismoreexpensivebutefficiencyissomewhathigher.Woundfieldmachinesarenormallyusedforhigh-power（multi-megawatt）drives.

VariableReluctanceMachine（VRM）

Avariableordoublereluctancemachine（VRM）,asthenameindicates,hasdoublesaliency,meaningithassaliencyinthestatoraswellasintherotor.Asmentionedbefore,theVRMhastwoclassifications:

switchedreluctancemachine（SRM）andsteppermotor.Thesteppermotorisbasicallyadigitalmotor,i.e.,itmovesbyafixedsteporanglewithadigitalpulse.Smallsteppermotorsarewidelyusedforcomputerperipheral-typeapplications.However,sincethemachineisnotsuitableforvariable-speedapplications,therewillnotbeanyfurtherdiscussionofit.

Therehasbeeninterestinswitchedreluctancemotordrivesintheliterature,andrecently,greatefforthasbeenmadetocommercializethemincompetitionwithinductionmotors.Fig.1-6A-4showsthecross-sectionofafour-phasemachinewithfourstator-polepairsandthreerotor-polepairs（8/6motor）.ThemachinerotordoesnothaveanywindingorPM.Thestatorpoleshaveconcentratedwinding（insteadofsinusoidalwinding）,andeachstator-polepairwinding,asshowninthefigure,isexcitedbyaconverterphase.Forexample,thestator-polepairA-A'isenergizedwhentherotorpole-paira-a'approachesittoproducethetorquebymagneticpull,butisde-energizedwhenpolealignmentoccurs.Allfourmachinephasesareexcitedsequentiallyandsynchronouslywiththehelpofarotorpositionencodertogetunidirectionaltorque.Themagnitudeoftorquecanbegivenas:

.Wherem=inductanceslopeandi=instantaneouscurrent.Thecurrenticanbemaintainedconstantlybyduringtheinductanceslope.Athighspeeds,therotor-inducedCEMFishigh.

Thefavorableattributesofthiselectronicmotoraresimplicityandrobustnessofconstruction;potentially,itissomewhatcheaperthanotherclassesofmachines.However,thetorquegenerationispulsatinginnatureandthereareseriousacousticnoiseproblems.

交流机

简介

将电能转换成机械能或将机械能转换成电能的电机是传动系统中的主要组成部分。

从电学、机械学和热学的角度看，电机具有复杂的结构。

虽然一百多年前就开始使用电机，关于电机的研究与开发工作一直在继续。

但是，与电力电子器件和电力电子变换器相比，电机的发展十分缓慢。

从传统观念上，由恒频正弦电源供电的交流机一直用于恒速场合，而直流机则用于变速场合。

但在最近二、三十年，我们已经看到在变频、变速交流机传动技术上取得的研究与开发成果，并且它们正逐渐取代直流传动。

在大多数情况下，新设备都使用交流传动。

一般可将交流机分类如下：

感应电机：

鼠笼或绕线式转子（双馈），旋转或直线运动；

同步电机：

旋转或直线运动，启动、绕线式激磁（转子）或永磁磁铁，径向或轴向气隙（圆盘状），凸磁极或内（隐）磁极，正弦波磁场或梯形波磁场；

变阻抗电机：

开关磁阻电机，步进电机。

在所有的交流电机中，感应电机，尤其是鼠笼型感应电机，在工业上得到了最广泛的应用。

这些电机价格便宜、结实、可靠，并且从不到一个马力到数兆瓦容量的电机都可买到。

感应电机

小容量电机一般是单相电机，但多相（三相）电机经常用于变速传动。

图1-6A-1给出了一台理想的三相、两极感应电机，图中定子和转子的每一个相绕组用一个集中线圈来表示。

三相绕组在空间上按正弦分布并嵌入在槽里。

对绕线式转子电机而言，转子绕组与定子绕组类似，但鼠笼式电机的转子具有鼠笼状结构，并且有两个短路环。

基本上，感应电机可以看作是一个具有旋转并且短路的二次绕组的一台三相变压器。

定子和转子的核用层压铁磁钢片制成，电机内的气隙实际上是均匀的（非凸极结构）。

感应电机的一个最基本的原理是在气隙中建立旋转和按正弦分布的磁场。

如果忽略槽和由于非理想分布的绕组产生的空间谐波的影响，可以证明，在三相定子绕组中能以三相对称电源建立一个同步旋转的旋转磁场。

旋转速度由公式（1-6A-1）给出。

Ne称作同步转速，单位是转/分，

是定子频率，单位是赫兹。

P是电机的极对数。