電氣專業(yè)英語課后練習(xí)翻譯教材

PART1U1T1、Inadditiontothevariouspowertransformers,twospecial-purposetransformersareusedwithelectricmachineryandpowersystems.Thefirstofthesespecialtransformersisadevicespeciallydesignedtosampleahighvoltageandproducealowsecondaryvoltagedirectlyproportionaltoit.Suchatransformerisapotentialtransformer.Apowertransformeralsoproducesasecondaryvoltagedirectlyproportionaltothatthepotentialtransformerisdesignedtohandleonlyaverysmallcurrent.Thesecondtypeofspecialtransformerisadevicedesignedtoprovideasecondarycurrentmuchsmallerthanbutdirectlyproportionaltoitsprimarycurrent.Thisdeviceiscalledacurrenttransformer.除了各種電源變壓器、兩個專用變壓器使用電動機械和電力系統(tǒng)。第一個特殊變壓器是一個高電壓設(shè)備專門設(shè)計的樣品和生產(chǎn)較低的二次電壓成正比。這樣一個變壓器電壓互感器。電力變壓器也產(chǎn)生二次電壓成正比的電壓互感器的設(shè)計目的是處理只有一個很小的電流。第二種類型的特殊變壓器是一個裝置,旨在提供一個次級電流小得多,但它的主要電流直接成比例。這種裝置稱為電流互感器。U1T2、Inelectronicpowersuppliesthereisoftenaneedtoisolatetheoutputfromtheinputandreducetheweightandcostoftheunit.Inotherapplications,suchasinaircraft,thereisastrongincentivetominimizeweight.Theseobjectivesarebestachievedbyusingarelativelyhighfrequencytransformer.Thus,inaircraftthefrequencyoftransformersistypically400Hz,whileinelectronicpowersuppliesthefrequencyoftransformersmayrangefrom5kHzto50kHz.在電子電源通常需要隔離的輸出輸入,減少單位的重量和成本。在其他應(yīng)用程序,如飛機,有強烈的動機來減少體重。這些目標(biāo)是最好通過使用一個相對高頻變壓器。因此,在飛機變壓器通常是400赫茲的頻率,而在電子電源變壓器可能范圍從5khz的頻率50千赫U2T1、Ingeneral,theoutstandingadvantageofDCmachinesliesintheirflexibilityandversatility.BeforethewidespreadedavailabilityofACmotordrives,DCmachineswereessentiallytheonlychoiceavailableformanyapplicationsrequiringahighdegreeofcontrol.TheirprincipaldisadvantagesstemfromthecomplexityassociatedcomplexityincreasethecostovercompetingACmachines,italsoincreasestheneedformaintenanceandreducesthepotentialreliabilityofthesemachines.一般來說,直流機的突出優(yōu)勢在于他們的靈活性和通用性。交流電動機驅(qū)動的廣泛可用性之前,直流機基本上是唯一可用的選擇對于許多應(yīng)用程序要求高度的控制。主要缺點源于復(fù)雜關(guān)聯(lián)的復(fù)雜性增加了成本在競爭交流的機器,它也增加了對維護的需要,減少了潛在的這些機器的可靠性。U2T2、Therearethreebasictypeofrotatingmachines:synchronous,induction,andDCmachines.Inallofthemthebasicprinciplesareessentiallythesame.Voltagesaregeneratedbytherelativemotionofamagneticfieldwithrespecttoawinding,andtorquesareproducedbytheinteractionofthemagneticfieldsofthestatorandrotorwindings.有三種基本類型的旋轉(zhuǎn)機器:同步,感應(yīng),直流機器。在所有這些基本原則基本上是相同的。電壓的相對運動產(chǎn)生的磁場對繞組,和扭矩的交互作用是由定子和轉(zhuǎn)子繞組的磁場。U3T1、Synchronousmachinescanbeclassifiedascylindrical-rotororsalient-polemachines.Thecylindrical-rotorconstructionisusedinhigh-speedsteam-turbine-drivengenerators.Thearmaturewindingsconsistoflaminatedconductorsplacedinthestatorslots.TherotorcarriestheDCfieldwinding.Mostofturbinegeneratorsbeingbuiltatpresentfor60Hzserviceare2-pole3600revolutionsperminutemachines.Becauseoftheeconomiesofhigh-speedhigh-temperaturehigh-pressuresteamturbines,muchstudyandsomerealpioneeringworkhavebeendevotedtoimprovementsinmaterialsanddesignofbothgeneratorsandturbines同步機可分為圓柱形轉(zhuǎn)子或凸極機。圓柱形轉(zhuǎn)子建設(shè)用于高速steam-turbine-driven發(fā)電機。電樞繞組由疊層導(dǎo)體放置在定子槽。轉(zhuǎn)子直流磁場繞組。目前大部分渦輪發(fā)電機建60赫茲服務(wù)2-pole每分鐘3600轉(zhuǎn)的機器。因為經(jīng)濟的高速高溫高壓蒸汽渦輪機,多學(xué)習(xí)和一些真正的開創(chuàng)性工作一直在致力于改進材料和設(shè)計的發(fā)電機和發(fā)電機U3T2、Rotatingelectricmachinestakemanyformsandareknownbymanynames:DC,synchronous,permanent-magnet,induction,etc.Althoughthesemachinesappeartobequitedissimilarandrequireavarietyofanalyticaltechniques,thephysicalprinciplesgoverningtheirbehaviorarequitesimilar,andinfactthesemachinescanoftenbeexplainedfromthesamephysicalpicture.Aninductionmachine,inspiteofmanyfundamentaldifferences,worksonexactlythesameprinciple;onecanidentifyfluxdistributionsassociatedwiththerotorandstator,whichrotateinsynchronismandwhichareseparatedbysometorque-producingangulardisplacement.旋轉(zhuǎn)電機采取多種形式和已知許多名字:直流、同步、永磁、感應(yīng),等等。雖然這些機器似乎是相當(dāng)不同的,需要各種分析技術(shù),管理他們的行為非常相似的物理原則,事實上這些機器通?？梢越忉審南嗤奈锢韴D像。感應(yīng)式電機,盡管許多根本性的差異,同樣的原理工作;一個可以識別通量分布與轉(zhuǎn)子和定子,在同步旋轉(zhuǎn),由一些torque-producing角位移U4T1、ThesignificanceofVRMsinengineeringapplicationsstemsfromtheirlowcost,reliability,adncontrollability.Becausetheirtorquedependsonlyonthesquareoffappliedstatorcurrentsandnotontheirdirection,thesemachinescanbeoperatedfromunidirectionaldrivesystems,reducingthecostofthepowerelectronics.However,itisonlyrecently,withtheadventoflow-cost,flexiblepowerelectroniccircuitryandmicroprocessor-basedcontrolsystems,VRMshavebeguntoseewidespreadapplicationinsystemsrangingfromtractiondrivestohigh-torque,precisioncontrolsystemsforroboticsapplications.VRMs在工程應(yīng)用的意義源于他們的低成本、可靠性、可控性。因為他們的轉(zhuǎn)矩只取決于廣場采用定子電流,而不是他們的方向,這些機器可以從單向操作驅(qū)動系統(tǒng),減少電力電子的成本。然而,直到最近,隨著低成本、靈活的電力電子電路和基于微處理器控制系統(tǒng),VRMs已經(jīng)開始看到廣泛應(yīng)用系統(tǒng)從牽引驅(qū)動高扭矩,為機器人精度控制系統(tǒng)應(yīng)用程序U4T2、Thehybridsteppingmotorcombinescharacteristicsofthevariable-reluctanceandpermanent-magnetsteppingmotors.Thehybridsteppingmotorcanachievesmallstepsizeseasilyandwithasimplemagnetstructurewhileapurelypermanent-magnetmotorwouldrequireamultipolepermanentmagnet.Inaddition,thehybridsteppingmotorwilltendtomaintainitspositionwhenthestatorexcitationisremoved,asdoesthepermanent-magnetdesign.混合式步進電機結(jié)合可變磁阻和永磁步進電動機的特性。混合式步進電機可以實現(xiàn)小步大小很容易和磁鐵結(jié)構(gòu)簡單而純粹的永磁電動機需要多極永磁。此外,混合步進電機將傾向于保持其位置移除定子勵磁時,永磁設(shè)計一樣。U5T1、Relayisakeycomponentinanypowersystemprotectionscheme.Itisadevicethat,basedoninformationreceivedfromthepowersystem,performsoneormoreswitchingactions.Theinformationreferredtoconsistsofsignalsandcurrents,typicallytheoutputofinstrumenttransformers.Therelaydecidestoclose(oropen)oneormoresetsofnormallyopen(orclose)contacts.Theswitchingactiontypicallyenergizesthetripcoilofacircuitbreaker,whichthenopensthepowercircuit.繼電器是一個關(guān)鍵的組件在任何電力系統(tǒng)保護方案。一個設(shè)備,從電力系統(tǒng)根據(jù)收到的信息,執(zhí)行一個或多個開關(guān)動作。指由信號和電流的信息,一般儀器的輸出變壓器。繼電器決定關(guān)閉(或打開)一個或多個組常開(或接近)接觸。開關(guān)行動通常激發(fā)斷路器的脫扣線圈,然后打開電源電路。U5T2、Acontactorisalargerelay,usuallyusedtoswitchcurrenttoanelectricmotororotherhigh-powerload.Largeelectricmotorscanbeprotectedfromovercurrentdamagethroughtheuseofoverloadheatersandoverloadcontacts.Iftheseries-connectedheatersgettoohotfromexcessivecurrent,thenormally-closedoverloadcontactwillopen,de-energizingthecontactorsendingpowertothemotor.接觸器是一種大型繼電器,通常用于切換當(dāng)前電動馬達或其他大功率負(fù)載。大型電動機可以免受過載損壞通過使用超載加熱器和過載聯(lián)系人。如果過度的串聯(lián)暖氣太熱電流,將打開閉合過載來接觸,接觸器斷開的發(fā)送功率電動機。U6T1、Circuit-interruptingdevicesinpowersystemsareofmanyforms,rangingfromthesmallkeyswitchestotheenormouscircuitbreakersthatflowofpowerinhigh-voltagenetworks.Circuitbreakerisadeviceforinterruptingacircuitbetweenseparablecontactsundernormalorabnormalconditions.Theabnormalconditionsduringwhichacircuitbreakermaybeaskedtooperateareprimarilythosewhichexistduringshortcircuits.Thecircuitbreakerisdesignedtowithstandtheseshort-duration,high-magnitudecurrentsandtointerruptthemifnecessary.斷路裝置在電力系統(tǒng)的多種形式,從巨大的小鑰匙開關(guān)在高壓斷路器,流動的權(quán)力網(wǎng)絡(luò)。斷路器是中斷的設(shè)備電路在正?；虍惓l件下分離之間的聯(lián)系。異常條件中斷路器操作可能會被要求主要是那些存在在短路。斷路器的設(shè)計能夠承受這些短期高震級水流和必要時打斷他們。U6T2、Themaincontactsofacircuitbreakerarecommonlymadeofcopper,silver,orsilveralloy,andaresubjecttodiversetemperaturelimitations.Coppercontactsarenotnormallyfitforcontinuousoperation;theirtemperaturetendstorisewithtime.Mostcircuitbreakercontactsarethereforemadeofsilveralloy,whichprovidesgoodconductivityandlowstabletemperaturerise.的主要聯(lián)系人斷路器通常由銅、銀或銀合金,受不同溫度的限制。銅接觸通常不適合連續(xù)操作;他們的溫度趨向于上升時間。大多數(shù)斷路器接觸因此銀合金做的,它提供了良好的導(dǎo)電性和較低的穩(wěn)定的溫度上升。U7T1、Aswitchcanbeconstructedwithanymechanismbringingtwoconductorsintocontactwitheachotherinacontrolledmanner.Thiscanbeassimpleasallowingtowcopperwirestotoucheachotherbythemotionofalever,orbydirectlypushingtwometalstripsintocontact.However,agoodswitchdesignmustberuggedandreliable,andavoidpresentingtheoperatorwiththepossibilityofelectricshock.Therefore,industrialswitchdesignsarerarelythiscrude.Theconductivepartsinaswitchusedtomakeandbreaktheelectricalconnectionarecalledcontacts.Contactsaretypicallymadeofsilverorsilver-cadmiumalloy,whoseconductivepropertiesarenotsignificantlycompromisedbysurfacecorrosionoroxidation.Goldcontactsexhibitthebestcorrosionresistance,butaresurfacecorrosionoroxidation.Goldcontactsexhibitthebestcorrosionresistance,butarelimitedincurrent-carryingcapacityandmay"coldweld"ifbroughttogetherwithhighmechanicalforce.Whateverthechoiceofmetal,theswitchcontactsareguidedbyamechanismensuringsquareandevencontact,formaximumreliabilityandminimumresistance.一個開關(guān)可以由任何機制帶來了兩個導(dǎo)體接觸彼此以一種受控制的方式。這可以簡單允許兩個銅導(dǎo)線相互接觸的運動桿,或通過直接將兩個金屬條接觸。然而,一個好的開關(guān)設(shè)計必須堅固,可靠,并避免呈現(xiàn)的操作符電擊的可能性。因此,工業(yè)開關(guān)設(shè)計很少這原油。開關(guān)的導(dǎo)電部分用于制造和打破的電氣連接被稱為聯(lián)系。聯(lián)系人通常由銀或銀鎘合金,其導(dǎo)電性能沒有顯著的表面被腐蝕或氧化。黃金接觸表現(xiàn)出最好的耐腐蝕性能,但表面腐蝕或氧化。黃金接觸表現(xiàn)出最好的耐蝕性,但在載流容量是有限的,可能“冷焊”如果與機械力高。任何金屬的選擇,開關(guān)接觸是由一種機制確保廣場甚至接觸,最大可靠性和最小阻力。U7T2、Ifthepartingcontactsaremadeoflow-melting-pointmaterialsuchasbrassofcopper,thearcwillgooutatthefirstcurrentzeroasthevoltageisinsufficienttoreestablishacathodespotaftercurrentreversal.Thenecessaryinsulationmustbesopositionedastoavoidcharringfromtheheatofthearc.Ifcharringoccursthecarbonproducedmayserveasanelectrodefromwhichthermionicelectronsmaybereleasedandsoreignitethearcfollowingcurrentzero.如果分開聯(lián)系是由低熔點材料如銅、黃銅弧將出去第一電流零的電壓不足以重建一個陰極電流換向后現(xiàn)貨。必要的絕緣必須定位,避免電弧的熱量燒焦。如果發(fā)生炭化生成的碳可以作為一個電極的熱離子電子可能被釋放,所以重燃弧后電流零。U8T1、INordertoconfirmandguaranteethereliabilityofelectricalcontacts,alotofexperienceisrequired,especiallyonhowtodevelopadditionaltestingmethodsontopoftherequirementsgiventhroughnationalandinternationalstandards.Itisveryimportantthatthemanufacturersofdeviceswithelectricalcontactsaredevelopingsuchmethods(temperaturerisetests,shortcircuittests,highvoltagetests,etc.)andcontinuouslyareusingthemasroutinetestsinordertoconfirmthereliabilityofelectricalcontacts.為了確認(rèn)和保證電接觸的可靠性,需要豐富的經(jīng)驗,特別是在如何開發(fā)額外的測試方法的要求通過國家和國際標(biāo)準(zhǔn)。是非常重要的,設(shè)備的制造商與電接觸正在開發(fā)這種方法(溫升測試、短路測試,高壓測試,等等),不斷使用它們作為常規(guī)檢測,以確認(rèn)電接觸的可靠性。U8T2、Thereliabilitymeanstheabilitythattheproductfulfillsthestipulatedconditions.Thereliabilityworkingscopeisquitelarge,forexample:thereliabilityorganizationmanagement,thereliabilitydate,thereliabilitycangiveareferencetoimprovethecircuit-breakerquality.可靠性意味著產(chǎn)品滿足規(guī)定條件的能力?？煽啃怨ぷ鞯姆秶窍喈?dāng)大的,例如:組織管理、可靠性可靠性日期,可以給一個參考改善斷路器可靠性質(zhì)量。PartIIu1TextAElectromechanicaldeviceswhichemploymagneticfieldsoftenuseferromagneticmaterialsforguidingandconcentratingthesefields.Becausethemagneticpermeabilityofferromagneticmaterialscanbelarge(uptotensofthousandstimesthatofthesurroundingspace),mostofthemagneticfluxisconfinedtofairlywell-definedpathsdeterminedbythegeometryofthemagneticmaterial.機電設(shè)備,采用磁場經(jīng)常使用鐵磁材料進行指導(dǎo)和集中這些字段。因為鐵磁材料的磁導(dǎo)率可以大(成千上萬倍,周圍的空間),大多數(shù)的磁通量局限于相當(dāng)明確的路徑由磁性材料的幾何形狀決定。TextBDuetothehystersiseffect,therelationshipbetweenBandHforaferromagneticmaterialisbothnonlinearandmultivalued.Ingeneral,thecharacteristicsofthematerialcannotbedescribedanalytically.Theyarecommonlypresentedingraphicalfromasasetofempiricallydeterminedcurvesbasedontestsamplesofthematerial.ThemostcommoncurveusedtodescribeamagneticmaterialisB-Hcurveorhystersisloop.由于磁滯效應(yīng),B和H之間的關(guān)系對鐵磁材料的非線性和多值。一般來說,材料的特性不能被描述分析。它們通常在圖形從一組經(jīng)驗確定曲線基于測試的樣品材料。最常見的曲線用于描述磁性材料磁化曲線和磁滯回路。Unit2TextATheMeshCurrentMethodisquitesimilartotheBranchCurrentMethodinthatitusessimultaneousequations,Kirchhoff`sVoltageLaw,andOhm`sLawtodeterminetheunknowncurrentsinanetwork.ItdiffersformtheBranchCurrentmethodinthatitdoesnotuseKirchhoff`sCurrentLaw,anditisusuallyabletosolveacircuitwithlessunknownvariablesandlesssimultaneousequations,whichisespeciallyniceifyou`reforcetosolvewithoutacalculator.當(dāng)前網(wǎng)格方法非常類似于分支電流方法,它使用聯(lián)立方程,基爾霍夫電壓定律和歐姆定律來確定網(wǎng)絡(luò)中未知的電流。形式分支電流方法不同,它不使用基爾霍夫電流定律,而且通常能解決電路更少的未知變量和更少的聯(lián)立方程,這是特別好的如果你力量來解決沒有計算器。TextBThestrategyusedintheSuperpositionTheoremistoeliminateallbutonesourceofpowerwithinanetworkatatime,usingseries/parallelanalysistodeterminevoltagedrops(and/orcurrent)withinthemodifiednetworkforeachpowersourceseparately.Then,oncevoltagedropsand/orcurrentshavebeendeterminedforeachpowersourceworkingseparately,thevaluesareall“superimposed”ontopofeachothertofindtheactualvoltagedrops/currentswithallsourceactive.疊加定理中使用的策略是消除網(wǎng)絡(luò)內(nèi)的所有只有一個電源,使用串聯(lián)/并聯(lián)分析來確定電壓下降(和/或電流)在修改網(wǎng)絡(luò)分別為每個電源。然后,一旦電壓下降和/或電流已經(jīng)被確定為每個單獨電源工作,的值都是“疊加”的發(fā)現(xiàn)實際的電壓/電流與所有源活性下降。Unit3TextAThefiniteelementprocedureconsistsofpartitioningordiscretizinginteriordomainΩintoanumberofsubdomainsorfiniteelements.Thefieldisapproximatedovereachelementbyaninterpolatingorshapefunctiondependingonvaluesatdiscretenodesonorintheelement.Toprovidesomedegreeoffieldcontinuityacrosselementboundaries,mostofthediscretenodesaredefinedontheelementsurfaceandsharedbyadjacentelement.Providedthattheycoverthedomain,theelementsandshapefunctionsmaybecompletelyarbitrary.有限元程序由分區(qū)或離散化內(nèi)部域Ω成子域或有限元素的數(shù)量。字段由插值近似在每個元素或形狀函數(shù)根據(jù)值在離散節(jié)點或元素。提供某種程度的領(lǐng)域跨元素邊界連續(xù)性,大多數(shù)離散節(jié)點上定義元素的表面和共享的相鄰元素。提供覆蓋域,馬英九的元素和形狀函數(shù)。TextBDiscretenumeralmethodslikefiniteelementsorfinitedifferencesarenecessarilyformulatedonfinitespatialgrids-whetheractualdomainbeingmodeledisfiniteorinfinite.Thisdomaintruncationintroducesartificialboundariesthatmustbetreatedwithspecialcareinordertominimizenonphysicalwavereflections.Thesetrapenergythatwouldotherwiseberadiatedandestablishundesirableresonanceswithinthegrid.Notethatthisistrueregardlessofthesolutionschemeapplied,ineitherthetime-domainorfrequency-domain.離散的數(shù)字方法如有限元素或有限的差異必然是制定有限空間grids-whether實際域建模是有限的還是無限的。這個領(lǐng)域截斷引入了人工邊界,必須特別小心處理,以減少非物質(zhì)波反射。這些陷阱能量,否則被輻射,建立不良網(wǎng)格內(nèi)的共振。注意,這是真正的不管應(yīng)用解決方案,無論是在時間Unit4TextACouplingcanalsooccurincircuitsthatsharecommonimpedances.Forinstance,twocircuitsthatsharetheconductorcarryingthesupplyvoltageandtheconductorcarryingthereturnpathtoground.Ifonecircuitcreatesasuddendemandincurrent,theothercircuit`svoltagesupplywilldropduetothecommonimpedancebothcircuitssharebetweenthesupplylinesandthesourceimpedance.Thiscouplingeffectcanbereducedbydecreasingthesupplylinesandthecommonimpedance.Couplingalsocanoccurwithradiatedelectricandmagneticfieldswhicharecommontoallelectricalcircuits.Whenevercurrentchanges,electronmagneticwaresaregenerated.Thesewavescancoupleovertonearbyconductorsandinterferewithothersignalswithinthecircuit.耦合也可以發(fā)生在共享公共阻抗的電路。例如,兩個電路共享導(dǎo)體攜帶電源電壓和導(dǎo)體攜帶的返回路徑。如果一個電路產(chǎn)生電流的突然需求,其他電路的電壓供應(yīng)將會下降,由于公共阻抗電路供給線之間的分享和源阻抗。這種耦合效應(yīng)可以減少減少供應(yīng)線和常見的阻抗。耦合也可能發(fā)生TextBThemajorityofmoderndigitalintegratedcircuits(IC)aremanufacturedusingcomplementarymetaloxidesemiconductor(CMOS)technology.ThestaticpowerconsumptionofCOMSdevicesmaybelower,butwithfastswitchingratestheCMOSdevicedemandstransientpowerfromthesupply.ThedynamicpowerdemandofahighspeedclockedCOMSdevicesmayexceedanequivalentbipolardevice.Therefore,decouplingcapacitorsmustbeusedonthesedevicestoreducethetransientpowerdemandfromthepowersupply.大多數(shù)的現(xiàn)代數(shù)字集成電路(IC)制造使用互補金屬氧化物半導(dǎo)體(CMOS)技術(shù)。設(shè)備的靜態(tài)功耗COMS可能較低,但快速交換率的互補金屬氧化物半導(dǎo)體元件要求瞬時功率供應(yīng)。的動態(tài)電力需求高速時鐘COMS設(shè)備可能超過一個等價的雙極型設(shè)備。因此,去耦電容器必須在這些設(shè)備上使用,以減少瞬態(tài)電源的電力需求。Unit5TextAGiantMagnetostrictiveMaterial(GMM)isnewfunctionalmaterialwhichhasbi-directionaltransductioneffects,itcanbemadeintoGiantMagnetostrictiveActuator(GMA)byusingthedirect,alsocanbemadeintosensorsbyusingtheconverseeffect.Comparedwithpiezoelectricactuator,GMAownstheadvantagesoflargerloadcapacity,rapiderresponse,higherreliabilityandlowervoltagedrive,etc.Ithasapromisingprospectinprecisionpositioning,activenoiseandvibrationcontrolandfluidcontrol(pump,value)fields.超磁致伸縮材料(GMM)是新型功能材料具有雙向傳導(dǎo)效果,它可以制成超磁致伸縮驅(qū)動器(GMA)通過使用直接,也可以制成傳感器利用相反的效果。與壓電致動器相比,該協(xié)會擁有的優(yōu)勢更大的負(fù)載能力,更快捷的反應(yīng),高可靠性和低電壓驅(qū)動等。它在精密定位,具有廣闊的發(fā)展前景,積極的噪聲和振動控制和流體控制(泵、瓦爾TextBMagnetostrictive(MS)linearpositionsensorsconstituteaninterestingpossibilityasgenericall-usesensorsbecausetheyarebyprinciplenon-contractandabsolute.Theseareverydesirablecharacteristicsformachinetooloperation,aswellastheirnon-opticalnaturewhichmakesthemresistanttotypicalcontaminantsofthemachinetoolenvironmentlikeshavingsandmetalworkingcoolantfluid.磁致伸縮(MS)線性位置傳感器構(gòu)成傳感器一般都使用一個有趣的可能性,因為他們是由原則non-contract和絕對的。機床操作,這些都是非常可取的特征以及他們?yōu)榱俗匀皇顾麄儗C床的典型污染物環(huán)境刨花和金屬加工冷卻液等。PartIIIUnit1ASofar,allthepowersemiconductordevicesdiscussedexclusivelyusesiliconasthebasicrawmaterial,andthiswillpossiblycontinue,atleastinthenearfuture.however,newtypesoflargeband-gapmaterials,suchassiliconcarbideandsemi-conductingdiamond,areshowinghighpromiseforthefuturegenerationofpowerdevices.siliconcarbideisparticularlymorepromisingbecauseitstechnologyismore“mature”thanfordiamond.Thematerialhashighcarriermobility,fasterminoritycarrierlifetime,andhighelectricalandthermalconductivities.Thesepropertiespermithigh-voltageandhigh-powercapabilities,fastswitching(i.e.,highswitchingfrequency),lowconductiondrop,goodradiationhardness,andhighjunctiontemperature.Allkeydevices,suchasdiodes,powerMOSFETS,thyristors,GTO,etc,arepossiblewithnewmaterial.到目前為止,專門討論的所有電力半導(dǎo)體器件用硅作為基本原料,而這可能會持續(xù)下去,至少在不久的將來。然而,新類型的大帶隙材料、碳化硅和半導(dǎo)體等鉆石,顯示高承諾未來一代的電力設(shè)備。碳化硅尤為更有前途,因為其技術(shù)比鉆石更“成熟”。該材料具有高載流子遷移率,更快的少數(shù)載流子壽命,高電氣和熱導(dǎo)率。這些屬性允許高壓和大功率功能,快速交換(即高開關(guān)頻率),低傳導(dǎo),輻射硬度好,和高結(jié)溫。所有關(guān)鍵設(shè)備,如二極管,功率mosfet,晶體閘流管,之所以與新材料等,是有可能的。BPowersemiconductordevicesconstitutetheheartofmodernpowerelectronicapparatus.Theyareusedinpowerelectronicconvertersintheformofamatrixofon-offswitches,andhelptoconvertpowerformAC-to-ACatthesame(ACcontroller)ordifferentfrequencies(cycloconverter).Theswitchingmodepowerconversiongiveshighefficiency,butthedisadvantageisthatduetothenonlinearityofswitches,harmonicsaregeneratedatboththesupplyandloadsides.Theswitchesarenotideal,andtheyhaveconductionandturn-onandturn-offswitchinglosses.Convertersarewidelyusedinapplicationssuchasheatingandlightingcontrols,ACandDCpowersupplies,electrochemicalprocesses,DCandACmotordrives,activeharmonicfiltering,etc.Althoughthecostofpowersemiconductordevicesinpowerelectronicequipmentmayhardlyexceed20~30percent,thetotalequipmentcostandperformancemaybehighlyinfluencedbythecharacteristicsofthedevices.Anengineerdesigningequipmentmustunderstandthedevicesandtheircharacteristicsthoroughlyinordertodesignefficient,reliable,andcost-effectivesystemswithoptimumperformance.Itisinterestingtonotethatthemoderntechnologyevolutioninpowerelectronicshasgenerallyfollowedtheevolutionofpowersemiconductordevices.Theadvancementofmicroelectronicshasgreatlycontributedtotheknowledgeofpowerdevicematerials,fabrication,packaging,modeling,andsimulation.功率半導(dǎo)體器件構(gòu)成現(xiàn)代電力電子設(shè)備的核心。它們用于電力電子轉(zhuǎn)換器的形式的一個矩陣開關(guān)開關(guān),同時幫助轉(zhuǎn)換能量形式AC-to-AC控制器(AC)或不同頻率(回旋轉(zhuǎn)換器)。開關(guān)模式電源轉(zhuǎn)換效率高,但缺點是由于非線性開關(guān)、諧波產(chǎn)生供應(yīng)和負(fù)載。開關(guān)并不理想,他們有傳導(dǎo)和接通和斷開開關(guān)損失。轉(zhuǎn)換器廣泛用于取暖和照明控制等應(yīng)用,交流和直流電源、電化學(xué)過程中,直流和交流電機驅(qū)動器、有源諧波濾波等。雖然電力半導(dǎo)體器件在電力電子設(shè)備的成本可能不超過20~30%,設(shè)備總成本和性能可能會受到設(shè)備的特點。一個工程師設(shè)計設(shè)備必須了解設(shè)備及其特點完全為了設(shè)計高效、可靠和具有成本效益的系統(tǒng)最優(yōu)性能。有趣的是注意到,現(xiàn)代電力電子技術(shù)發(fā)展已普遍遵循電力半導(dǎo)體器件的發(fā)展。微電子技術(shù)的進步極大地促進了知識的力量設(shè)備材料、制造、包裝、建模和仿真。UNIT2AThemodernpowerdevicesincludethediode,SCR,GTO,BJT,powerMOSFET,IGBT,MCTandIGCT.Powersemiconductordevicesconstituteavastandcomplexsubject,andthetechnologyisgoingthroughcontinuousevolution.Itisneedlesstosaythatapowerelectronicsengineerresponsiblefordesigninganapparatusshouldbethoroughlyfamiliarwiththedifferentdevicestoachieveoptimumcostandtheperformancegoalsofthesystem.Traditionally,SCR-typedeviceshavebeenverypopularinpowerelectronicsystemsandmanyapplicationscanbefoundonthisarea.MOS-gateddevices,particularlypowerMOS-FETsandIGBTs,havebeenappliedextensivelyinrecentyears.TheIGCTisarecentmemberinthedevicesfamilywithgoodpotential,andweareyettoseeitsgrowthofapplicationsincompetitionwithIGBTsandGTOs.Itisinterestingtoseethattheadventofnewpowersemiconductordevices,growthoftheirpowerratings,andimprovementoftheircharacteristicsarecontinuallydrivingthepowerelectronicsandmotordrivestechnologiesforward.SufficeittosaythatifthedevicesevolutionwouldhavestoppedattheSCRlevel,thepowerelectronicstechnologywouldhavestalledhopelesslyintheprimitivestage.現(xiàn)代電力設(shè)備包括二極管、可控硅,之所以是機器、電力MOSFET、IGBT,MCT和IGCT。功率半導(dǎo)體器件構(gòu)成一個龐大而復(fù)雜的話題,和技術(shù)正在經(jīng)歷不斷進化。不用說,電力電子工程師負(fù)責(zé)設(shè)計一個裝置應(yīng)該徹底熟悉不同的設(shè)備來實現(xiàn)最優(yōu)成本和系統(tǒng)的性能目標(biāo)。傳統(tǒng)上,SCR-type設(shè)備已經(jīng)非常流行在電力電子系統(tǒng)和許多應(yīng)用程序可以在這個地區(qū)找到。MOS-gated設(shè)備,特別是電力MOS-FETs和igbt,近年來已被廣泛應(yīng)用。IGCT是一個最近設(shè)備家族成員具有良好的潛力,我們尚未看到經(jīng)濟增長的應(yīng)用程序的競爭對手igbt和矩形脈沖斷開。有趣的是發(fā)現(xiàn)新型功率半導(dǎo)體器件的出現(xiàn),增長他們的力量評級,改善他們的特點是不斷推動電力電子和電機驅(qū)動技術(shù)。我只想說,如果設(shè)備進化會停止在可控硅層面,電力電子技術(shù)將會停滯在原始階段的不可救藥。BOnlyafewdefinestatementscanbamadeincomparingthesedevicessinceanumberofpropertiesmustbeconsideredsimultaneouslyandbecausethedevicesarestillevolvingatarapidpace.However,thequalitativeobservationsgiveninTable3-1canbemade.Itshouldbenotedthatinadditiontotheimprovementsinthesedevices,newdevicesarebeinginvestigated.Theprogressinsemiconductortechnologywillundoubtedlyleadtohigherpowerratings,fasterswitchingspeeds,andlowercosts.Ontheotherhand,theforced-commutatedthyristor,whichwasoncewidelyusedincircuitsforcontrollableswitchapplications,isnolongerbeingusedinnewconverterdesignswiththepossibleexceptionofpowerconvertersinmulti-MVAratings.Thisisapertinentexampleofhowtheadvancesinsemiconductorpowerdeviceshavemodifiedconverterdesign.只有幾個定義語句可以英航在比較這些設(shè)備,因為許多屬性必須同時考慮,因為設(shè)備仍在快速發(fā)展。然而,表3-1中給出的定性觀察。應(yīng)該指出的是,除了這些設(shè)備的改進,新設(shè)備正在接受調(diào)查。半導(dǎo)體技術(shù)的進步無疑將導(dǎo)致更高的評級,更快的開關(guān)速度,并降低成本。另一方面,forced-commutated晶閘管,曾廣泛應(yīng)用于電路可控開關(guān)應(yīng)用,不再是被用于新的轉(zhuǎn)換器設(shè)計可能除了multi-MVA電力轉(zhuǎn)換器的評級。這是一個相關(guān)的例子半導(dǎo)體電力設(shè)備的進步轉(zhuǎn)換器設(shè)計修改。UNIT3ADiodesandphaseconvertersconstitutethelargestsegmentofpowerelectronicsthatinterfacetotheelectricutilitytoday.Thehistoryoftheseconvertersextendsnearlyonehundredyears,andoftendefinedasclassicalpowerelectronics.Beforetheadventofsolid-statediodesandthyristors,whichareinvariablyusedpresently,gas-filledglass-bulbdevicessuchasmercury-arcrectifiers,phanotrons,andthyratrons,andignitronsweredominantintheearlypartofthiscentury.Then,duringWorldWar2,saturable-coremagneticamplifierswereintroduced.Thisclassofconvertersmainlyconversion50/60HzACtoDC(rectification),butaselectgroupcanalsofunctionforDCtoACconversion(inversion).Theefficiencyoftheconvertersishighbecauseofsoftswitching,accompaniedwithlowconductionloss.二極管和相位轉(zhuǎn)換器構(gòu)成最大的電力電子接口的部分電力。這些轉(zhuǎn)換器擴展了近一百年的歷史,而且經(jīng)常定義為古典電力電子。出現(xiàn)之前的固態(tài)二極管和晶體閘流管,總是使用目前,充氣玻璃燈泡設(shè)備如汞弧整流器、phanotrons,和閘流管,引燃管是在本世紀(jì)初占統(tǒng)治地位。然后,在二戰(zhàn)期間,飽和鐵芯磁放大器。這類轉(zhuǎn)換器主要轉(zhuǎn)換50/60Hz交流到直流(整流),但選擇組還可以為DCAC轉(zhuǎn)換函數(shù)(反演)。轉(zhuǎn)換器的效率很高,因為軟切換,伴隨著低傳導(dǎo)損耗。BThevoltageandcurrentsinapowercircuitarefrequentlynotpuresinewaves.Thelinevoltagesusuallyhaveasatisfactorywave-shapebutthecurrentsaresometimesbadlydistorted.Thedistortionmaybecausedbymagneticsaturationinthecoreofatransformer,bytheswitchingactionofthyristors.Harmonicvoltageandcurrentsareusuallyundesirable,butinsomeaccircuitstheyarealsounavoidable.Harmonicsarecreatedbynonlinearloads,suchaselectricarcsandsaturatedmagneticcircuits.Itisimportanttoknowhowacircuitrespondstoharmonics.Inlinearcircuitscomposedofresistors,inductors,capacitors,andtransformers,thevariousharmonicsactindependentlyofeachother.Thefundamentalandeachharmonicsbehaveasiftheotherswerenothere.Insolvingsuchacircuitsforaparticularharmonic,thevoltagessourcesoftheotherharmonics,includingthatofthefundamental,arereplacedbyashort-circuit,.Then,thetotalrmscurrentineachbranchisequaltothealgebraicsumoftheeffectivefundamentalcurrentandtheeffectivevaluesoftheindividualharmoniccurrents.InACcircuits,thefundamentalcurrentandfundamentalvoltagetogetherproducesafundamentalpower.Thisfundamentalpoweristheusefulpowerthatcausesamotortorotateandanarcfurnacetoheatup.Theproductofaharmonicvoltagetimesthecorrespondingharmoniccurrentalsoproducesaharmonicpower.ThelatterisusuallydissipatedasheatintheACcircuitand,consequently,doesnousefulwork.Harmoniccurrentandvoltagesshouldthereforebekeptassmallaspossible.電源電路中的電壓和電流常常不是純正弦波。線電壓通常有一個令人滿意的波形,但電流有時被嚴(yán)重扭曲。磁飽和引起的失真也許在變壓器的核心,通過晶體閘流管的開關(guān)動作。諧波電壓和電流通常是不受歡迎的,但在一些交流電路也是不可避免的。諧波是由非線性負(fù)載,如電弧和飽和磁回路。重要的是要知道電路諧波響應(yīng)。在線性電路由電阻、電感、電容和變壓器,各種諧波彼此獨立的行動。的根本,每個諧波表現(xiàn)得像其他人并不在這里。在解決這樣一個特定諧波電路,其他諧波的電壓源,包括基本的、被短路,取代。然后,totalrms在每個分支電流的代數(shù)和等于有效基本電流和單個諧波電流的有效值。在交流電路中,基本電流和基本電壓在一起產(chǎn)生一個基本力量。這個基本權(quán)力是有用的力量,使電動機的旋轉(zhuǎn)和電弧爐加熱。諧波電壓的產(chǎn)品時間也相應(yīng)的諧波電流產(chǎn)生諧波功率。后者通常以熱能的形式散失的交流電路,因此,沒有有用的工作。諧波電流和電壓應(yīng)保持盡可能小。Unit4 TextAInsomepowersystemsthereisaneedtotransformDCpowerfromoneDCvoltageleveltoeitherahigherorlowerDClevel.Forexample,inapublictransportationsystem,a4000VDCoverheadlinemanybethesourcetodrivea300VDCmotorinabus.Inothercases,a12Vbatterymanyhavetopoweradeviceratedas120VDC.Inalternatingcurrentsystemsthevoltagestep-uporstep-downcanbedonewithatransformer.ButinDCsystems,anentirelydifferentapproachisrequired.ItinvolvestheuseofaDC-to-DCswitchingconverter,sometimescalledachopper.IntheDC-DCconverterstheswitchisactuallyaGTO,MOSFET,orIGBTwhoseon/offstateiscontrolledbyasignalappliedtothegate.Thecombinationofelectronicswitch,inductor,anddiodeconstituteswhatisknownasastep-downDC-DCconverter,orbuckchopper.Inanyconvertercircuitoperatinginsteadystate,acapacitorcanberepresentedbyitsinstantaneousvoltageasanequivalentvoltagesource.Similarly,aninductorcanberepresentedbyitsinstantaneouscurrentasanequivalentcurrentsource.在一些電力系統(tǒng)需要直流電源轉(zhuǎn)換從一個直流電壓級別較高或較低的直流級別。例如,在公共交通系統(tǒng)中,4000v直流架空線路多源驅(qū)動一個300v直流電機在一輛公共汽車。在其他情況下,一個12v電池許多設(shè)備被評為120v直流。在交流系統(tǒng)的電壓升壓或降壓變壓器可以做。但在直流系統(tǒng)中,一個完全不同的方法是必需的。它涉及DC-to-DC開關(guān)轉(zhuǎn)換器的使用,有時也被稱為直升機。直流-直流轉(zhuǎn)換器的開關(guān)實際上是一個GTO、MOSFET、IGBT的開/關(guān)狀態(tài)由一個信號控制應(yīng)用于門。電子開關(guān)