太阳能毕业设计外文翻译Word文档下载推荐.doc
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MaximumPowerPointTracking,frequentlyreferredtoasMPPT,isanelectronicsystemthatoperatesthePhotovoltaic(PV)modulesinamannerthatallowsthemodulestoproduceallthepowertheyarecapableof.MPPTisnotamechanicaltrackingsystemthat“physicallymoves”themodulestomakethempointmoredirectlyatthesun.MPPTisafullyelectronicsystemthatvariestheelectricaloperatingpointofthemodulessothatthemodulesareabletodelivermaximumavailablepower.Additionalpowerharvestedfromthemodulesisthenmadeavailableasincreasedbatterychargecurrent.MPPTcanbeusedinconjunctionwithamechanicaltrackingsystem,butthetwosystemsarecompletelydifferent.
TounderstandhowMPPTworks,let’sfirstconsidertheoperationofaconventional(non-MPPT)chargecontroller.Whenaconventionalcontrollerischargingadischargedbattery,itsimplyconnectsthemodulesdirectlytothebattery.Thisforcesthemodulestooperateatbatteryvoltage,typicallynottheidealoperatingvoltageatwhichthemodulesareabletoproducetheirmaximumavailablepower.ThePVModulePower/Voltage/CurrentgraphshowsthetraditionalCurrent/Voltagecurveforatypical75Wmoduleatstandardtestconditionsof25°
Ccelltemperatureand1000W/m2ofisolation.ThisgraphalsoshowsPVmodulepowerdeliveredvsmodulevoltage.Fortheexampleshown,theconventionalcontrollersimplyconnectsthemoduletothebatteryandthereforeforcesthemoduletooperateat12V.Byforcingthe75Wmoduletooperateat12Vtheconventionalcontrollerartificiallylimitspowerproductionto≈53W.
Ratherthansimplyconnectingthemoduletothebattery,thepatentedMPPTsysteminaSolarBoostchargecontrollercalculatesthevoltageatwhichthemoduleisabletoproducemaximumpower.Inthisexamplethemaximumpowervoltageofthemodule(VMP)is17V.TheMPPTsystemthenoperatesthemodulesat17Vtoextractthefull75W,regardlessofpresentbatteryvoltage.AhighefficiencyDC-to-DCpowerconverterconvertsthe17Vmodulevoltageatthecontrollerinputtobatteryvoltageattheoutput.Ifthewholesystemwiringandallwas100%efficient,batterychargecurrentinthisexamplewouldbeVMODULE÷
VBATTERYxIMODULE,or17V÷
12Vx4.45A=6.30A.Achargecurrentincreaseof1.85Aor42%wouldbeachievedbyharvestingmodulepowerthatwouldhavebeenleftbehindbyaconventionalcontrollerandturningitintouseablechargecurrent.But,nothingis100%efficientandactualchargecurrentincreasewillbesomewhatlowerassomepowerislostinwiring,fuses,circuitbreakers,andintheSolarBoostchargecontroller.
Actualchargecurrentincreasevarieswithoperatingconditions.Asshownabove,thegreaterthedifferencebetweenPVmodulemaximumpowervoltageVMPandbatteryvoltage,thegreaterthechargecurrentincreasewillbe.CoolerPVmodulecelltemperaturestendtoproducehigherVMPandthereforegreaterchargecurrentincrease.ThisisbecauseVMPandavailablepowerincreaseasmodulecelltemperaturedecreasesasshowninthePVModuleTemperaturePerformancegraph.Moduleswitha25°
CVMPratinghigherthan17VwillalsotendtoproducemorechargecurrentincreasebecausethedifferencebetweenactualVMPandbatteryvoltagewillbegreater.Ahighlydischargedbatterywillalsoincreasechargecurrentsincebatteryvoltageislower,andoutputtothebatteryduringMPPTcouldbethoughtofasbeing“constantpower”.Whatmostpeopleseeincoolcomfortabletemperatureswithtypicalbatteryconditionsisachargecurrentincreaseofbetween10–25%.Coolertemperaturesandhighlydischargedbatteriescanproduceincreasesinexcessof30%.Customersincoldclimateshavereportedchargecurrentincreasesinexcessof40%.Whatthismeansisthatcurrentincreasetendstobegreatestwhenitisneededmost;
incoolerconditionswhendaysareshort,sunislowonthehorizon,andbatteriesmaybemorehighlydischarged.Inconditionswhereextrapowerisnotavailable(highlychargedbatteryandhotPVmodules)aSolarBoostchargecontrollerwillperformasaconventionalPWMtypecontroller.
WHYMPPT?
MPPTloadssolarpanelthatitoperatesatthemaximumpowerpoint.MPPTisaDC-DCconverterthatuseshighfrequencyswitchingandcontrolalgorithm.Itisdesiredtodesignthecircuitathighefficient,lightweight,smallsize,andreliablefortheevent.Solarcellsaredependentonenvironmentconditionsliketemperature,sunlight,andloadvoltage.Whilethisparametersalwayschangingdaytime,solarcellorsolarpaneloutputcharacteristicsvaryalso.Somehoursphotovoltaicsystemmaygivelowerpowerthanratedpowerofload.Ifsolarpanelisconnectedtobatterybydirectly,apowerlossoccursinthesystemsincesolarpaneloperatingcharacteristicwillchangeatsomeperiodoftimeuptoenvironmentconditions.Thisproblemcanbesolvedbyusinglargersolarpanels,butthesolutionisexpensive.Insteadofthis,maximumpowerpointtrackercircuitislocatedbetweensolarpanelandbattery.
INCREASESOLARCHARGINGWITHANMPPTPOWERTRACKINGCHARGECONTROLLER
Anewfeatureisshowingupinchargecontrollers.It'
scalledmaximumpowerpointtracking(MPPT).ItextractsadditionalpowerfromyourPVarray,undercertainconditions.Thisarticleexplainstheprocessbyamechanicalanalogy,forpeoplewhodonotunderstandbasicelectricity.ThefunctionofaMPPTisanalogoustothetransmissioninacar.Whenthetransmissionisinthewronggear,thewheelsdonotreceivemaximumpower.That'
sbecausetheengineisrunningeitherslowerorfasterthanitsidealspeedrange.Thepurposeofthetransmissionistocoupletheenginetothewheels,inawaythatletstheengineruninafavorablespeedrangeinspiteofvaryingacceerationandterrain.
Let'
scompareaPVmoduletoacarengine.Itsvoltageisanalogoustoenginespeed.Itsidealvoltageisthatatwhichitcanputoutmaximumpower.Thisiscalleditsmaximumpowerpoint.(It'
salsocalledpeakpowervoltage,abbreviatedVpp).Vppvarieswithsunlightintensityandwithsolarcelltemperature.Thevoltageofthebatteryisanalogoustothespeedofthecar'
swheels.Itvarieswithbatterystateofcharge,andwiththeloadsonthesystem(anyappliancesandlightsthatmaybeon).Fora12Vsystem,itvariesfromabout11to14.5V.Inordertochargeabattery(increaseitsvoltage),thePVmodulemustapplyavoltagethatishigherthanthatofthebattery.IfthePVmodule'
sVppisjustslightlybelowthebatteryvoltage,thenthecurrentdropsnearlytozero(likeanengineturningslowerthanthewheels).So,toplayitsafe,typicalPVmodulesaremadewithaVppofaround17Vwhenmeasuredatacelltemperatureof25°
C.Theydothatbecauseitwilldroptoaround15Vonaveryhotday.However,onaverycoldday,itcanriseto18V!
WhathappenswhentheVppismuchhigherthanthevoltageofthebattery?
Themodulevoltageisdraggeddowntoalower-than-idealvoltage.TraditionalchargecontrollerstransferthePVcurrentdirectlytothebattery,givingyouNObenefitfromthisaddedpotential.Now,let'
smakeonemoreanalogy.Thecar'
stransmissionvariestheratiobetweenspeedandtorque.Atlowgear,thespeedofthewheelsisreducedandthetorqueisincreased,right?
Likewise,theMPPTvariestheratiobetweenthevoltageandcurrentdeliveredtothebattery,inordertodelivermaximumpower.IfthereisexcessvoltageavailablefromthePV,thenitconvertsthattoadditionalcurrenttothebattery.Furthermore,itislikeanautomatictransmission.AstheVppofthePVarrayvarieswithtemperatureandotherconditions,it"
tracks"
thisvarianceandadjuststheratioaccordingly.ThusitiscalledaMaximumPowerPointTracker.
WhatadvantagedoesMPPTgiveintherealworld?
Thatdependsonyourarray,yourclimate,andyourseasonalloadpattern.ItgivesyouaneffectivecurrentboostonlywhentheVppismorethanabout1Vhigherthanthebatteryvoltage.Inhotweather,thismaynotbethecaseunlessthebatteriesarelowincharge.Incoldweatherhowever,theVppcanriseto18V.Ifyourenergyuseisgreatestinthewinter(typicalinmosthomes)andyouhavecoldwinterweather,thenyoucangainasubstantialboostinenergywhenyouneeditthemost!
中文翻译
什么是最大功率点跟踪(MPPT),它是又如何工作的?
光伏发电作为可再生能源变得日益重要,它有许多有点,如不需燃料、没有污染、需要很少的维护费用、没有噪声等等。
光电模块的转换效率依然很低,所以控制光伏阵列的最大功率点跟踪成为光伏系统的要点。
光伏系统产生的能量取决于阵列的开路电压。
PV的最大功率点(MPP)随光照强度和和温度变化。
它的V-I和V-P特性曲线表示了一个特定的工作点,在这个点上可以提供最大功率。
在最大功率点上,光伏系统工作具有最高效率。
所以许多方法被用来确定最大功率跟踪。
最大功率点跟踪,经常被称为MPPT,是一个使光电(PV)模块工作在一种特定运作模式的电子系统,这种运作模式能够让模块产生它们所能够产生的最大电力。
MPPT不是一种移动模组本身来使它们更直接面对太阳的机械跟踪系统。
MPPT是完全的电子系统,它通过改变模组的电特性工作点,让模块能够提供最大可用电力。
从模块得到的额外电力将以电池充电电流的形式得到利用。
MPPT可与机械跟踪系统配合使用,但这两个系统完全不同。
为了了解MPPT使如何工作的,我们先了解一下常规的(非MPPT)充电控制器是如何工作的。
当一个常规控制器在为用完的蓄电池充电的时候,它只是简单的将光伏模组与电池直接相连。
这
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