comparison文章

导读：　comparison文章篇一：作文资料Comparison and Contrast 比较和对照的写作 ...

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comparison文章篇一：作文资料Comparison and Contrast 比较和对照的写作

Comparison and Contrast 比较和对照的写作

1. 目标：掌握英语作文中比较和对照的写作方法（比较相似点，对

照强调不同之处）

2. 使用比较和对照写作方法一般是说明文和议论文，常见的比较对

照有两种方式：

1. 块状比较方式：(block method )先A 后B,即A1，A2，A3----; B1,B2,

B3----。

2. 逐点比较方式：(point-by-point method ) AB交错，即A1，B1;A2，

B2;A3，B3----

范文一：(块状比较法)

Country life and City life

It is really hard to say which is better than the other,city life or rural life .Both have their merits and shortcomings .living in the city has a great many advantages .,First ，you can enjoy various kinds of foods， both foreign and domestic .Second, there are more cultural activities in the city —you can go to the concert ,the theatre ,the movies or the disco club after a day’s hard work .But city life has many problems too. The overcrowded population ,traffic jam , industrial pollution ,and the lack of understanding between people may result in disease and unhappiness .living in the country ,however ,you can watch the magnificent sunrise and sunset and listen to the bird singing in the tree. If you want ,you can certainly have a huge garden while a

small green space seems a luxury in the city .In the country ,you don’t have so much worries .You can enjoy the pleasure of work by planting seeds in the soil and watching them grow into flowers and finally into fruits or food .But rural life may not perfect .Things are going so slowly that sometimes you may feel that you are absolute left behind in some remote corners of the world .You may again miss the parties ,friends and movies in the city .

Like anything else ， country life and city life have their

Advantages and disadvantages .The best solution may be that you enjoy pleasure of both lives and get rid of their inconveniences.

范文二：（逐点比较法 ）

Middle School life and college Life

There are many differences between middle school and the college .First , in the middle school , we have to listen to what the teacher says in class to understand the content of the text .But in college ,we must study by ourselves before class. If not ,we couldn’t follow the teacher .Second ,there are lots of rules in the middle school .For example , we should wear the uniform ,the girls must have their hair cut short .and we are not allowed to make boy-girl friends . However ,in college ,we have more freedom .We can wear the clothes we like .And the girls could have long

beautiful hair . We are also free to make boy or girlfriends .The third ,in the middle school ,we must study first .That means we could do nothing but study .In contrast ,we have to do everything by ourselves in college .That means we must plan our time carefully .There are also other differences between our school life and our college life .We have to learn to adapt ourselves to college life .

comparison文章篇二：作文训练-comparison_and_contrast

comparison文章篇三：大学英语四级作文指导之Comparison and Contrast

comparison文章篇四：comparison and contrast写作教案

Instructional plan

New Century English S2B

Ways of organization---comparison and contrast

设计者 崇明县堡镇中学 陈洁 2015/5/6

【教材分析】

本课的任务是用比较与对比的手法写作。本单元恰好学习了两位科学家，爱因斯坦和袁隆平。两篇课文分别从人生经历、主要成就以及性格爱好等方面介绍了两位科学家，这两篇课文提供了很好的语言素材，学生们学完后可以对这两位科学家进行比较与对比的写作。

【学情分析】

学生学完两篇课文之后，对两位科学家已经比较熟悉，并且能够用所学短语句型对两位科学家做简单介绍。但是学生对比较和对比这一写作手法是完全陌生的，还不会用表示相似与不同的连接词来连句成文，对两位科学家作比较与对比的写作。

【教学目标】

By the end of the activities, the students are expected

 to tell whether a paragraph is comparison or contrast and find the connecting

words used in comparison and contrast

 to find some differences and similarities of Einstein and Yuan Longping by using

the connecting words such as while, however, in contrast, similarly, in the same way, etc.

 to write a paragraph about Einstein and Yuan Longping by comparison and

contrast

【活动设计】

Activity 1：

1. We have learned about two scientists. Can you tell me their names?

2. Can you find some similarities?

3. Can you find some differences?

设计意图：引入话题，让学生知道什么是比较，什么是对比。

Activity 2：

1. read two paragraphs and tell whether they are comparison or contrast

2. find the connecting words to show comparison and contrast

设计意图: 学生会辨别比较与对比的语段，并找出用来比较与对比的常用连接词。

Activity 3：

1. find related information about Einstein and Yuan Longping

2. make a contrast of the two scientists by using the connecting words

设计意图：用表示对比的连接词描述两位科学家的不同点。

Activity 4:

1. discuss the similarities between Einstein and Yuan Longping

2. speak out the similarities one by one

设计意图：从两位科学家的不同点中找出相同点，为写作做好内容上的铺垫。 Activity 5:

1. find the topic sentence, supporting sentence and details of the passage

2. tell which sentence is a better supporting sentence and know why

设计意图：从范文中找出主题句、支撑句和细节，为写作做出结构上的铺垫。并且知道如何写支撑句和细节。

Activity 6:

1. Write a supporting sentence and details

2. present their writing and make comments

设计意图：写作实践，并且进行同伴互评，为课后完成作文指明方向。

【作业布置】

• Finish your writing according to the outline.

• Use expressions showing comparison and contrast

comparison文章篇五：英语作文写法-Comparison and Contrast

comparison文章篇六：19-comparison of direct-drive and geared generator好文章

ComparisonofDirect-DriveandGearedGenerator

ConceptsforWindTurbines

HenkPolinder,Member,IEEE,FrankF.A.vanderPijl,Gert-JandeVilder,andPeterJ.Tavner

Abstract—Theobjectiveofthispaperistocomparefivediffer-entgeneratorsystemsforwindturbines,namelythedoubly-fedin-ductiongeneratorwiththree-stagegearbox(DFIG3G),thedirect-drivesynchronousgeneratorwithelectricalexcitation(DDSG),thedirect-drivepermanent-megnetgenerator(DDPMG),thepermanent-magnetgeneratorwithsinglestagegearbox(PMG1G),andthedoubly-fedinductiongeneratorwithsingle-stagegearbox(DFIG1G).Thecomparisonisbasedoncostandannualenergyyieldforagivenwindclimate.TheDFIG3Gisacheapsolutionusingstandardcomponents.TheDFIG1Gseemsthemostattrac-tiveintermsofenergyyielddividedbycost.TheDDPMGhasthehighestenergyyield,butalthoughitischeaperthantheDDSG,itismoreexpensivethanthegeneratorsystemswithgearbox.IndexTerms—Direct-drive,doublyfedinductiongenerator(DFIG),permanent-magnetgenerator,single-stagegearbox,syn-chronousgenerator,windturbine.

I.INTRODUCTION

T

HEobjectiveofthispaperistocomparefivedifferentgeneratorsystemsforwindturbines,namelythedoubly-fedinductiongeneratorwiththree-stagegearbox(DFIG3G),thedirect-drivesynchronousgeneratorwithelectricalexci-tation(DDSG),thedirect-drivepermanent-magnetgenerator(DDPMG),thepermanet-magnetgeneratorwithsinglestagegearbox(PMG1G)andthedoubly-fedinductiongeneratorwithsingle-stagegearbox(DFIG1G).

Thethreemostcommonlyusedgeneratorsystemsforwindturbinesareasfollows[1],[2].

1)Untilthelate1990s,mostwindturbinemanufacturersbuiltconstant-speedwindturbineswithpowerlevelsbe-low1.5MWusingamultistagegearboxandastandardsquirrel-cageinductiongenerator,directlyconnectedtothegrid.

2)Sincethelate1990s,mostwindturbinemanufacturershavechangedtovariablespeedwindturbinesforpowerlevelsfromroughly1.5MW,mainlytoenableamoreflex-iblematchwithrequirementsconsideringaudiblenoise,powerquality,andenergyyield.Theyhaveusedamulti-stagegearbox,arelativelylow-coststandardDFIGanda

Fig.1.Photoofa1.5-MWdirect-drivewindturbinewithpermanent-magnetgeneratorofZephyros.Source:ZephyrosBV.

ManuscriptreceivedMay25,2005;revisedJanuary30,2006.ThisworkwassupportedinpartbyZephyrosBV,Hilversum,TheNetherlandsandinpartbyATOMaritiemPlatform,DenHelder,TheNetherlands.Paperno.TEC-00176-2005.

H.PolinderandF.F.A.vanderPijlarewiththeElectricalPowerProcessingGroupofDelftUniversityofTechnology,2628CDDelft,TheNetherlands.TheyarealsowithDUWIND,theInterfacultyDelftUniversityWindEnergyResearchInstitute(e-mail:h.polinder@tudelft.nl;f.vanderpijl@tudelft.nl).G.-J.deVilderiswithHarakosanEuropeBV,1213NSHilversum,TheNetherlands(e-mail:g.de.vilder@harakosan.nl).

P.J.TavneriswiththeSchoolofEngineering,DurhamUniversity,DurhamDH13LE,U.K.(e-mail:peter.tavner@durham.ac.uk).DigitalObjectIdentifier

10.1109/TEC.2006.875476

powerelectronicconverterfeedingtherotorwindingwithapowerratingofapproximately30%oftheratedpoweroftheturbine.

3)Since1991,therehavealsobeenwindturbinemanufac-turersproposinggearlessgeneratorsystemswiththeso-calleddirect-drivegenerators,mainlytoreducefailuresingearboxesandtolowermaintenanceproblems.Apowerelectronicconverterforthefull-ratedpoweristhenneces-saryforthegridconnection.Thelow-speedhigh-torquegeneratorsandthefullyratedconvertersforthesewindturbinesareratherexpensive.

Mostdirect-driveturbinesbeingsoldatthemomenthavesyn-chronousgeneratorswithelectricalexcitation.However,[3]–[7]claimbenefitsforpermanentmagnetexcitation,whichelim-inatestheexcitationlosses.Inthispaper,thisdifferenceisquantified.Fig.1depictsanexampleofawindturbinewithapermanent-magnetdirect-drivegenerator[8].

Fortheincreasingpowerlevelsanddecreasingspeeds,thesedirect-drivegeneratorsarebecominglargerandevenmoreex-pensive.Therefore,ithasbeenproposedtouseasingle-stagegearbox(withagearratiointheorderof6orhigher)andapermanent-magnetgenerator[7].Thissystem,calledthemulti-bridsystem,isillustratedinFig.2.

Ontheonehand,theresultingsystemcombinessomeofthedisadvantagesofboththegearedanddirect-drivesystems:thesystemhasagearboxandithasaspecialandthereforeexpensivegeneratorandafullyratedconverter.Ontheotherhand,comparedtodirect-drivesystems,asignificantdecrease

0885-8969/$20.00©2006IEEE

Fig.2.Sketchofthesystemwithasingle-stagegearbox.Source:WinWinD.

inthegeneratorcostandanincreaseinthegeneratorefficiencycanbeobtained.

Further,thequestionariseswhetherthissystemwithasingle-stagegearboxcouldbeusedincombinationwithaDFIG.Be-causethegeneratortorqueisstillratherhighandthespeedratherlow,thegeneratorcanbeexpectedtohavealargediameterandairgap,andthereforeahighmagnetizingcurrentandhighlosses.However,theratingoftheconvertercouldbereducedtoroughly30%,givinganimportantbenefitincostandefficiency.Thisnewsystemisintroducedandfurtherinvestigatedinthispaper.

Forbothsystemswithasingle-stagegearbox,theuseofagearboxleadstoasignificantreductionoftheexternaldimen-sions,enablingtheinstallationofsucha3-MWwindturbineonlocationsthatarecurrentlylimitedfromalogisticpointofviewto1.5-MWturbines.

Theobjectiveofthispaper,therefore,istocomparefivewindturbinegeneratorsystems,namely:1)theDFIG3Gascurrentlyused;2)theDDSGascurrentlyused;3)theDDPMG;4)thePMG1G;5)theDFIG1G.

Tocomparethefivegeneratorsystems,a3-MW,15-r/minwindturbineisused.Forthisturbine,anapproximatedesignofthegeneratorsismadetogetindicationsofweightandcost.Thedifferencesinannualenergyyieldarecalculatedforagivenwindclimate.ThiscomparisonandtheproposaltouseaDFIGincombinationwithasingle-stagegearboxaretheoriginalcon-tributionsofthispaper.

Anearlycomparisonoftheefficiencyofthreewindturbinegeneratorsystemsisgiven

inIn[6]moregenera-torsystemswerecomparedandmorecriteriaweretakenintoaccount.Thecontributionofthispaperisthatitintroducesthe

TABLEI

MODELINGCHARACTERISTICS

DFIG1G,andcomparesitwithfourothergeneratorsystems.Italsoquantifiesthedifferencebetweentheelectrical-exciteddirect-drivegeneratorandthePMdirect-drivegenerator.

Thepaperstartswithasectionaboutmodelingofthewindturbine,thegearbox,theconverter,andthegenerator.Nextthefivegeneratordesignsarebrieflydescribedandtheresultingperformanceisgiven.Thepaperconcludeswithacomparisonofthefivegeneratorconcepts.

II.MODELINGTHEGENERATORCONCEPTS

A.WindTurbineModeling

TableIgivesthecharacteristicsofthewindturbinethatwasusedtocomparethedifferentgeneratorsystems.Usingthesecharacteristics,theavailableshaftpowerPcanbecalculatedasafunctionofthewindspeedas[2],[10]

P=

1ρairCp(λ,θ)πr232

vw(1)

whereρairisthemassdensityofair,risthewindturbinerotorradius,vwisthewindspeed,andCp(λ,θ)isthepowercoefficientortheaerodynamicefficiency,whichisafunctionofthetipspeedratioλ(tipspeeddividedbywindspeed)andthepitchangleθ.

Fig.3illustratestherotorspeed,whichisassumedtobepro-portionaltothewindspeedatmaximumaerodynamicefficiencyatlowwindspeedsandequaltotheratedrotorspeedathigherwindspeeds(above9m/s).Atwindspeedsabovetherated

POLINDERetal.:COMPARISONOFDIRECT-DRIVEANDGEAREDGENERATORCONCEPTSFORWINDTURBINES

727

Fig.3.RotorspeedandWeibulldistributionofthewindasafunctionofwind

speed.

windspeed,thebladesarepitchedtoreducetheaerodynamicefficiencyandsothepower.

Forenergyyieldcalculations,anaveragewindspeedof7m/swithaWeibulldistribution[10]isusedasillustratedinFig.3.Integratingtheareabelowthecurvegivesavalueof1.

TableIalsogivessomeapproximatenumbersforthecostoftherestofthewindturbine.Becausethepaperconcentratesonthegeneratorsystem,thesenumbersarenotextensivelyvali-datedandmustbeseenonlyasindicators.B.GearboxModeling

Thegearratioofthesingle-stagegearboxischosenas6.SomereferencessuggesthighergearHowever,atthemoment,thisisnotseenasprovenaguaranteedlifetime.Fromthecommerciallyavailablegearboxes,itappearstobecheapertousegearboxeswithmorestagesforhighergearratios.AcostestimateofthegearboxisgiveninTableI.

Accordingto[11],aviscouslossof1%oftheratedpowerpergearboxstageisareasonablemodel.Thismeansthatthelossesareproportionaltothespeed

P=Pn

geargearm

n(2)ratedwherePgearmisthelossinthegearboxatratedspeed(3%ofratedpowerforathree-stagegearbox[11]and1.5%forasingle-stagegearbox,seeTableI),nistherotorspeed(r/min),andnratedistheratedrotorspeed(r/min).C.ConverterModeling

Aback-to-backvoltagesourceinverterisusedtoensurethatthegeneratorcurrentsandthegridcurrentsaresinusoidal.AcostestimateisgiveninTableI.

Therearevariouswaysofmodelingconverterlosses[12].Themodelusedheredividesthemintothreeparts[13]:

1)asmallpartthatisconstantandconsistsofpowerdis-sipatedinpowersupplies,gatedrivers,control,coolingsystemsandsoon2)alargepartthatisproportionaltothecurrentandconsistsofswitchinglossesandconductionlosses;

3)apartthatisproportionaltothecurrentsquaredandcon-sistsofconductionlossesbecausetheon-statevoltageofasemiconductorincreaseswiththecurrent.

Therefore,thelossesintheconverterPconvarePP

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