Základní koncept
Three-phasecircuitinstantaneousreactivepowertheoryisthemainbasictheoryforthedevelopmentofAPF;APFhastwotypes:paralleltypeandseriestype,theformerismostlyused;parallelactivefilterThemainpurposeofthefilteristocontrolcurrentharmonics,andtheseriesactivefilterismainlytocontroltheproblemscausedbyvoltageharmonics.Comparedwithpassivefilters,activefiltershaveabettergovernanceeffect.Theycanfilteroutmultipleandhigherharmonicsatthesametimewithoutcausingresonance,butthepriceisrelativelyhigh!
Základní principy
Activepowerfilterisanewtypeofpowerharmoniccontrolspecialequipmentmadebymodernpowerelectronictechnologyanddigitalsignalprocessingtechnologybasedonhigh-speedDSPdevices.Itiscomposedoftwomainparts,thecommandcurrentcalculationcircuitandthecompensationcurrentgenerationcircuit.Thecommandcurrentarithmeticcircuitmonitorsthecurrentinthelineinrealtime,convertstheanalogcurrentsignalintoadigitalsignal,andsendsittoahigh-speeddigitalsignalprocessor(DSP)toprocessthesignal,separatetheharmonicfromthefundamentalwave,andmodulateitwithpulsewidth(PWM)signalformsendsdrivingpulsestothecompensationcurrentgeneratingcircuit,drivesIGBTorIPMpowermodule,generatescompensationcurrentwiththesameamplitudeandoppositepolarityasthegridharmoniccurrent,andinjectsitintothegrid,compensatesorcancelstheharmoniccurrent,andactivelyeliminatesitPowerharmonics.
TechnicaladvantagesGreen
Účinnost je 97,2 %, což ušetří asi 6 500 kWh za rok ve srovnání s aktivním filtrem s účinností 95 %.
Řídicí algoritmus s vylepšenou topologií vyšší účinnosti
Thermaldesignandstructuraloptimizationbasedonaccuratemodels
Miniaturizace
ThevolumeisonlythemainstreamofthesameclassBrand1/6,occupieslessspace,
Itcanadapttodifferentworkingconditions.Installationinnovation,wall-mountedorrack-mountedinstallationuseslessrawmaterialsandprotectstheenvironment.
Inteligentní
Compensatethespecifiedorderofharmonics,adjustableinductiveandcapacitivereactivepowercompensationcompensationsystem,automaticdetectionofunbalancedload,suppressionofsystemresonance,full-functionmonitoringsystem
modularizace
N+1redundancy,significantlyimprovessystemreliability,assemblylineproduction,betterqualityassurance,reducessystemsinglepointsoffailure,flexibleparallelconnection,andadaptstodifferentworkingconditions
Funkční vlastnosti
SimultaneousfilteringInadditiontothe2~50thharmonic,orselectanynumberofharmonicswithinthe2~50thorderforcompensation,theresponsetimeislessthan300μs
Itadopts3DSP+CPLDall-digitalcontrolmethodandinternationallyrenownedbrandhigh-speedIGBT,closed-loopcontrol,Preciselyfilteroutharmonics
Usingfour-phaselinetechnologytoeliminateneutrallinecurrent
Automaticallyeliminateresonance,notaffectedbychangesingridimpedanceandsystemimpedance,withcompensationforharmonics;simultaneouscompensationHarmonicandreactivepower;threeworkingmodesofcompensatingharmonics,reactivepowerandloadthree-phasecurrentimbalanceatthesametime
Elektronická ochrana proti přetížení
InvertercontrolisequippedwithamachineFastFPGA,powerdigitalsignalprocessingfunction
Modulardesign,easytoexpandmulti-machineparallelcentralizedmonitoringfunction,remotenetworkmonitoringfunction
Easytomaintain,workinaworkingenvironmentthatmeetstherequirements,Non-machinefailurewithoutmaintenance
ProductDesignStandard
Mezinárodní standard
EN50091-3,EN61000-6-2,EN55011,EN50178:1997,IEC62040-3,IEC50178:1997,AS62040-3(VFISS111),CISPR11
Národní standard
GB/T14549-93"Kvalita napájení:PublicGridHarmonics"
GB/T15543-1995 "Kvalita napájení: Třífázové napětí Povoleno Nevyváženost"
GB/T15945-1995"Kvalita napájení:Elektrický systémFrequencyAllowable Deviation"
GB/T12326-2000 "Kvalita napájení: Kolísání napětí a blikání"
GB/T12325-2003"Kvalita napájení:SupplyVoltageAllowableDeviation"
p>GB/T18481-2001 "Kvalita napájení: dočasné přepětí a přechodné přepětí"
GB/T15576-2008"LowVoltageCompleteReactivePowerCompensationDevice"
GB7625.11998"LowVoltageElectricalLimitsofharmoniccurrentsemittedbyelectronicproducts"
GB4208-2008 "Úroveň ochrany krytu (IP kód)"
Vstupní rozsah napětí
Theratedworkingvoltageis380V,canwithstandvoltagefluctuationsof-40%～+20%,andthefrequencyis50/60Hz,canwithstand+/-5%frequencyfluctuations,adaptingtovariouspowerqualityenvironmentsunderdifferentworkingconditions.Atthesametime,ifthevoltagefluctuationexceedstheupperandlowerlimits,themachinewillautomaticallyblocktheoutputandissueanalarm.
Automatické omezení proudu
Theoutputisautomaticallylimitedto100%withintheratedcapacity.Iftheharmoniccurrentontheloadsideisgreaterthantheratedcapacityofthemachine,themachinewillContinuetooutputcurrentcompensationharmonicswithinthecapacity,andnooverloadwillcauseitsownoverloadorexitoperation.
Ochrana proti zkratu zátěže
Itcanwithstandtheimpactofamomentaryshort-circuitoftheload,andrestartaftertheshort-circuitiseliminated.
Paralelně nezávislé ovládání
Parallelconnectiontothegridwillnotcauseapowerfailureinthegridduetomachinefailure.FormultipleYW-APFactivepowerfiltersinparallelsystem,ifonequitsoperationduetoafailure,theremainingmachinescanstillworknormallytoachievethefilteringfunction.
Třífázové nezávislé ovládání
Eachphasecurrentisindependentlycontrolled,single-phaseinjectioncurrent,notaffectedbythesystemthree-phasecurrentimbalance,neutrallineThefilteringcapacityisthreetimesthatofthephaseline.
IPprotectionlevelandlightningprotection
TheIPprotectionlevelisIP20;thelightningprotectioncapacityis20kA.
Monitorovací systém
Thesystemhasafastandcompletefaultself-checkfunction,includingmainsundervoltageorovervoltage,busovervoltageorovercurrent,Variousfaultself-checkssuchasfanfailure,powerdeviceover-temperature,inputfuseblown,etc.AllfaultsarealarmedthroughtheLCDdisplayandLEDoperatingstatuslights,andthemachineautomaticallyadoptsthecorrespondingoperationprotectionsystem.Themonitoringsystemcansave500faultrecordsinthecaseofpowersupplyorpowerfailure,whichisconvenientforanalyzingthecauseandtroubleshooting.
Metoda návrhu
Thedesignmethodofactivefiltercanberoughlysummarizedintotwocategories:cascademethodandanalogmethod.
Kaskádová metoda
Accordingtotherequirementsoftechnicalindicators,findthetransferfunctionthatcanbephysicallyrealized(usuallycanbefoundintheoff-the-shelfactivefiltermaterialsandmanuals),andthenItisdecomposedintotheproductoflow-orderfunctions(mainlysecond-orderfunctions),andtheselow-orderfunctionsarerealizedbyactivecircuitsandthencascadedtorealizetheoriginaltransferfunction.Circuitsthatimplementlow-orderfunctionsaregenerallycalledbasicsections,andtherearemanytypicalsecond-orderbasicsectioncircuitsfordesignerstochoosefrom.Accordingtothenumberofamplifiersusedinthebasicsection,itcanbedividedintosingle-amplifiercircuit,double-amplifiercircuit,three-amplifiercircuit,andfour-amplifiercircuit.Figure1showsseveralbasicsectionexamples.Thecascademethoddesignprocessisrelativelysimple,thecircuitcharacteristicadjustmentiseasy,therealizedcircuitisrelativelyeconomical,itisacommonlyusedmethod.
Simulační metoda
FirstdesignanLCfilterthatcanmeetthetechnicalspecificationsasadesignprototype,andthenuseanactivecircuittosimulateit.Thismethodcanbedividedintocomponentsimulationmethodandfunctionalsimulationmethod,andtheprototypeismostlybasedontheLCladder-typefilterwithdouble-terminalterminationresistor.Generally,theanalogmethodrequiresmorecomponentsthanthecascademethod.
(1)Metoda simulace prvků
ReplacetheinductanceelementintheLCfilterwithananaloginductor(anactivecircuitwithoutinductanceelementsthatcanachieveinductancecharacteristics).Theperformanceoftheexistingfloatinganaloginductorcircuitisnotgoodenough,anditisusedless.WhentheLCfiltercontainsfloatinginductance,itisofteneliminatedbymeansoftransformation.RLC-CRDconversionisacommonlyusedone.ItusesthefactorK/s(sisthecomplexfrequencyandKistherealconstant)toincreasetheimpedanceofeachelementinthecircuitbyafactorofK/s.Thisconversionwillnotchangethetransmissioncharacteristicsoftheoriginalcircuit,butmakestheR,L,andCcomponentsintheoriginalcircuitbecomeC,R,andD(frequency-dependentnegativeresistance)components,respectively.Figure2isanexample.
(2)FunctionalsimulationmethodFirstmakethesignalflowdiagramofeachvoltageandcurrentintheLCprototypefiltercircuit,andthenusetheactivecircuitsuchasintegrator,adder,andmultipliertorealizeit.
Základní aplikace
Hlavní harmonické:
·Increasetheloadofpowerfacilities,reducethepowerfactorofthesystem,andreducetheeffectivecapacityofpowergeneration,transmissionandpowerequipmentAndefficiency,resultinginequipmentwaste,linewasteandpowerloss;
·Causesreactivepowercompensationcapacitorresonanceandharmoniccurrentamplification,resultingindamagetothecapacitorbankduetoovercurrentorovervoltageorunabletoputintooperation;
·Thegenerationofpulsatingtorquecausesthemotortovibrate,whichaffectsproductqualityandmotorlife;
·Duetoeddycurrentandskineffect,additionalpowerlossoccursinmotors,transformers,transmissionlines,etc.Overheating,wastingelectricalenergyandacceleratinginsulationaging;
·Theharmonicvoltageincreasestheelectricfieldstrengthoftheinsulatingmediuminproportiontoitspeakvoltageandreducestheservicelifeoftheequipment;
·ZeroSequence(multipletimesof3)harmoniccurrentswillcausetheneutrallineofthethree-phasefour-wiresystemtooverload,andgeneratecirculatingcurrentinthedelta-connectedtransformerwindings,causingthewindingcurrenttoexceedtheratedvalue,andevencauseaccidentsinseverecases.
·Harmonicswillchangetheactioncharacteristicsoftheprotectionrelay,causethemalfunctionoftherelayprotectionfacilities,andcausetheoperationofautomaticdevicessuchasrelayprotectiontobedisordered;
·TheharmonicchangeshavechangedThechangerateandpeakvalueofvoltageorcurrentdelaythearcextinguishmentandaffectthebreakingcapacityofthecircuitbreaker;
·Makethemeteringinstrument,especiallytheinductiontypeelectricenergymeterproducemeasurementerrors;
·InterferenceNeighboringpowerelectronicequipment,industrialcontrolequipmentandcommunicationequipmentaffectthenormaloperationoftheequipment.
Ekonomické výhody harmonického ovládání:
1. Úspora energie 5 % – 8 %
7setsof400KVAUPSuninterruptiblepowersuppliesinanIDCcomputerroom,theelectricityexpenditurein2008isabout15millionyuan,annualelectricitycostsavingsof1.1millionyuanafterharmoniccontrol,energy-savingeffectof7.3%.
2. Odlehčení pro snížení investic do transformátorů, jističů a kabelů
AfactoryinstalledGuodianZhongzi'sactivefilterandreturnedatransformertothepowersupplybureau,savingmorethan1millioninvestmentProtectequipmentandreduceequipmentinvestment;
TheharmonicsgeneratedbythefrequencyconverterofapapermillinHenanburneddowntwofanseverymonthandlost30,000yuaneverymonth.
3.Improveproductivityandmaintaincontinuouspowersupply
ThedailyoutputofDaqingAcrylicFiberPlantincreasedfrom197tonsto210tonsafterharmoniccontrol.
Výhody a nevýhody
Advantages:Itcandynamicallyfilteroutvariousharmonics,andcancompletelyabsorbtheharmonicsinthesystem;itwillnotproduceresonance.
Disadvantages:thecostistoohigh;duetohardwarelimitations,itcannotbeusedinlarge-capacityoccasions:thesinglesetofactivefiltercapacitydoesnotexceed100KVA,andthemaximumapplicablegridvoltagedoesnotexceed690V.
Aplikace
Activepowerfilterscanbewidelyusedinthedistributionnetworksofindustries,commerce,andorganizations,suchas:powersystems,electrolyticplatingcompanies,watertreatmentequipment,Petrochemicalcompanies,largeshoppingmallsandofficebuildings,precisionelectronicscompanies,airport/portpowersupplysystems,medicalinstitutions,etc.Accordingtodifferentapplicationobjects,theapplicationofactivepowerfilterwillplayaroleinensuringthereliabilityofpowersupply,reducinginterference,improvingproductquality,extendingequipmentlifeandreducingequipmentdamage.
■Communicationsindustry
Inordertomeettheoperationalneedsoflarge-scaledatacentercomputerrooms,theuseofUPScapacityinthecommunicationpowerdistributionsystemisincreasingsignificantly.Accordingtothesurvey,themainharmonicsourceequipmentofthecommunicationlow-voltagepowerdistributionsystemisUPS,switchingpowersupply,inverterairconditioner,etc.Theharmoniccontentproducedbythemisrelativelyhigh,andthedisplacementpowerfactoroftheseharmonicsourcedevicesisextremelyhigh.Theuseofactivefilterscanimprovethestabilityofthecommunicationsystemandthepowerdistributionsystem,extendtheservicelifeofthecommunicationequipmentandpowerequipment,andmakethepowerdistributionsystemmoreinlinewiththedesignspecificationsoftheharmonicenvironment.
■Semiconductorindustry
Thethirdharmonicinmostsemiconductorindustriesisveryserious,mainlyduetothelargenumberofsingle-phaserectifierequipmentusedinenterprises.Thethirdharmonicisazero-sequenceharmonic,whichhasthecharacteristicofconvergingontheneutralline,whichleadstoexcessivepressureontheneutrallineandevensparking,whichposesagreatproductionsafetyhazard.Harmonicscanalsocausecircuitbreakerstotripanddelayproductiontime.Thethirdharmonicformsacirculatingcurrentinthetransformer,whichacceleratestheagingofthetransformer.Severeharmonicpollutionwillinevitablyaffecttheefficiencyandlifeoftheequipmentinthepowerdistributionsystem.
■Petrochemicalindustry
Duetoproductionneeds,therearealargenumberofpumploadsinthepetrochemicalindustry,andmanypumploadsareequippedwithinverters.Thelargenumberofapplicationsoffrequencyconvertersgreatlyincreasetheharmoniccontentinthepowerdistributionsystemofthepetrochemicalindustry.Mostoftheinverterrectificationlinksuse6pulsestoconvertACtoDC,sotheharmonicsgeneratedaremainlythe5th,7th,and11th.Themainhazardsarethehazardstopowerequipmentanddeviationsinmeasurement.Theuseofactivefilterscansolvethisproblemwell.
■Chemicalfiberindustry
Inordertogreatlyincreasethemeltingrate,improvethemeltingqualityofglass,andextendthefurnacelifeandsaveenergy,electricityiscommonlyusedinthechemicalfiberindustryFluxheatingequipment,withthehelpofelectrodes,sendselectricitydirectlyintothefuel-heatedglasskiln.Thesedeviceswillgeneratealotofharmonics,andthespectrumandamplitudeofthethree-phaseharmonicsarequitedifferent.
■Steel/IntermediateFrequencyHeatingIndustry
Theintermediatefrequencyfurnaces,rollingmills,electricarcfurnacesandotherequipmentcommonlyusedintheironandsteelindustrywillhaveasignificantimpactonthepowerqualityofthepowergrid.Asaresult,thecapacitorcompensationcabinethasfrequentoverloadprotectionactions,thetransformerandthepowersupplylinegenerateseriousheat,andthefuseisfrequentlyblown,whichmayevencausevoltagedropsandflicker.
■Automobilemanufacturing
Weldingmachineisanindispensableequipmentintheautomobilemanufacturingindustry.Duetoitsrandomness,rapidityandimpactThecharacteristicmakesthelarge-scaleuseofweldingmachinescauseseriouspowerqualityproblems,resultinginunstableweldingqualityandhighdegreeofautomationrobotscannotworkduetounstablevoltage,andthereactivepowercompensationsystemcannotbeusednormally.
■DCmotorharmoniccontrol
Thelarge-scaleDCmotorsiteneedstoconvertACpowertoDCpowerthroughrectifierequipment.BecauseoftheloadofsuchprojectsThecapacityislarge,sothereisseriousharmonicpollutionontheACside,causingvoltagedistortion,andaccidentsinseverecases.
■Useofautomatedproductionlinesandprecisionequipment
Inautomatedproductionlinesandprecisionequipment,harmonicswillaffecttheirnormaluse,makingintelligentcontrolsystems,PLCsystem,etc.malfunction.
■Hospitalsystem
Hospitalshaveverystrictrequirementsonthecontinuityandreliabilityofpowersupply.Thetimeforautomaticrestorationofpowersupplyincategory0placesisT≤15S,Automaticpowerrecoverytime0.5S≤T≤15Sforcategory1places,T≤0.5Sautomaticpowerrecoverytimeforcategory2places,THDu≤3%ofvoltagetotalharmonicdistortion,X-raymachines,CTmachines,andnuclearmagneticresonanceareallharmonicsVeryhighload.
■Theater/Gymnasium
Thyristordimmingsystems,large-scaleLEDequipment,etc.areallharmonicsources,whichwillgeneratealotofThethirdharmonicnotonlycausesthelowefficiencyofthepowerequipmentofthepowerdistributionsystem,butalsocausesthelightstoflicker,noiseandevenmalfunctionstoweakelectricalcircuitssuchascommunicationsandcabletelevision.
Stav vývoje
Withtheadvancementofpowerelectronictechnologyandcontroltechnology,domesticactivefiltershavereplacedimportedproductsinvariousmajorprojects.Onlyin2012,domesticallyproducedThesalesofactivefilterproductshavesurpassedthatofimportedbrandsby5times.ActivepowerfilterAPFwilleventuallyreplacetraditionalpassivefilterPFwithitshugetechnicaladvantages,powerfulfunctions,anddecliningprice.
DuringthedevelopmentofAPF,modularactivefilterequipmenthasgraduallyreplacedthetraditionalcabinet-typeAPFwithitsadvantagessuchassmallsize,easyinstallation,highdegreeofintegration,stablework,andconvenientexpansion.Inthenext5years,thecombinationofmodularactivefilterAPFandstaticvargeneratorSVGwillsurelybecomethemostpowerfulsolutioninthepowerqualityindustryandwillbewidelyrecognizedbythemarket.
Pracovní princip
TheactivefilterusesacurrenttransformertocollectthecurrentontheDCline.Aftersampling,thecurrentsignalisprocessedbytheharmonicseparationalgorithmtoobtainaharmonicThewavereferencesignal,asthemodulationsignal,iscomparedwiththetrianglewavetoobtaintheswitchingsignal.Thisswitchingsignalisusedtocontrolthesingle-phasebridge.Accordingtotheprincipleoftechnology,theswitchingsignalsoftheupperandlowerbridgearmsarereversedtoobtaintheTheharmoniccurrentswiththesamemagnitudeandoppositedirectionsoftheharmonicsignalscancelouttheharmoniccurrentsontheline.Thisisthefeedforwardcontrolpart.Thentheharmoniccomponentsofthelinecurrentaftertheactivefilteraccesspointarefedback,astheinputoftheregulator,toadjusttheerrorofthefeedforwardcontrol
Vlastnosti produktu
1.Highfilteringaccuracy,harmoniccurrentfilteringratecanreachmorethan97%;
2. Široký rozsah filtrování, frekvence filtrování: 2--50 harmonických a meziharmonických;
3. Rychlejší odezva na výkyvy zatížení, doba odezvy je1us;
4.Dynamicinjectionofcurrenttosuppressharmonicsandcompensatepowerfactor;
5.Nebude interagovat se systémem Dochází k rezonanci;
6.Pro rozšíření kapacity lze kombinovat více jednotek;
7.Suppresssystemovervoltageandimprovesystemvoltagestability
8.Systém tlumící sílyPoweroscilace;
9.Může potlačit blikání napětí, kompenzovat třífázovou nerovnováhu a zlepšit účiník;
10.Systém má silnou sebeochranu a stabilitu.
Technické parametry
1.Jmenovité pracovní napětí:380V/220V,50Hz
2. Jmenovitá harmonická kompenzační kapacita: 50A/100A/150A/200A
3. Spotřeba energie celého stroje: méně než 3 % kapacity
4.Harmonicsuppressioneffect:meettherequirementsofthenationalstandard,andthesteady-stateTHDcanbereducedtolessthan5%
5. Jmenovité izolační napětí: 3000VAC, 2500VDC
Popis výkonu
1.Dynamické aktivní filtrování, celkové zlepšení kvality výkonu;
2.DSPfulldigitalcontrol,20KHzswitchingfrequency,rapidresponsetodynamicchangesoftheload;
3.Thenumberofharmoniccompensationcanbeselected,andthe50thharmoniccanbefilteredoutatmost;
4.Suttonsactivepowerfiltercanchoosetocompensatereactivepoweratthesametime;
5.S možností kompenzace třífázové nerovnováhy;
6. S funkcí automatického omezení proudu nedochází k přetížení;
7.Vysoká účinnost,ztráta při plném zatížení je menší než 2,57;
8. Paralelní instalace, jednoduchá instalace a malé rozměry;
9.ReducecircuitLoss,eliminatetheheatoftransformerandmotorcausedbyharmonics,realizesystemenergysavinggreatly;
10.Thefilteringeffectofactivepowerfilterisnotaffectedbysystemimpedancechanges,andcanautomaticallysuppresssystemresonance;
11.Accordingtothepowerdistributionstructure,partialcompensation,partialcompensationortotalcompensationcanbeselected.CTcanbelocatedonthepowersideortheloadside;
12.Easytoexpandandredundantdesign,canbeUpto10unitscanbeoperatedinparallel.
Vyhlídky
Theimprovementofactivefiltersdependsontheprogressofcomponentsandintegrationtechnologyontheonehand,andontheinnovationofcircuitstructureanddesignontheotherhand.AlthoughRCactivefilterscanbemixedandintegrated,thecompleteintegrationofhigh-qualityRCactivefiltershasnotyetbeenresolved.Themaindifficultyisthathigh-precisionresistorsandcapacitorscannotbedirectlyintegratedonthechip,andthechipareaoccupiedbylargeresistorsandlargecapacitorsistoolarge.Switchedcapacitorfilterhasopenedupthewaytosolvethisproblemandrealizedfullintegration;butitisadiscrete-timeanalogfilter,andthereareproblemssuchaslowworkingfrequencybandthatneedtobeimproved.Asolutiontoachieveaccurateresistanceinanintegratedfilteristousethelinear(ie,non-saturated)regioncharacteristicsoftheMOStubeasananalogresistance.Thisisavoltage-controlledresistancecontrolledbythegatevoltage,soitcanbeusedoff-chip(ie,non-saturated).Outsidethechip)referencevalues,suchascrystalclocksorexternalRCcomponents,cooperatewiththeon-chipcontrolcircuittopreciselyadjustthetimeconstantofthecircuit.Thisisaverypromisingprogram.Thereisalsoanactivefiltercomposedofatransconductanceoperationalamplifier(OTA)andacapacitorC,whichisalsoaverypromisingfullyintegratedsolution.
>Asearlyasthe1880s,resistorandcapacitorfiltercircuitshaveappeared.Theinductanceandcapacitanceresonantcircuitwithfrequencyselectionfunctioncanbeusedasthesimplestfilter.
In1915,K.W.WagnerofGermanyandG.A.CampbellofBellLabsoftheUnitedStatesrespectivelypublishedpapersonfilters,andtheyhavebeenrecognizedastheindependentinventorsoffiltersintheworld.
After1923,O.J.ChabellofBellLaboratoriesproposedadesignmethodoffixedK-typeandm-inducedvideoparameterfilters.
In1939,W.KaurofGermanyandS.DarlingtonoftheUnitedStatesrespectivelyproposedworkingparameterfilterdesigntheories.Becausemanycircuitsandsystemshavetodistinguishsignalsofdifferentfrequencies,filtersarewidelyusedincommunications,broadcasting,radar,andmanyinstrumentsandequipment.
Manycomplexmulti-poleLCfiltershaveexistedformanyyears,andtherearemanybooksinthisareathatdescribetheworkofsuchfilters.
Theoldestformsofelectronicfiltersarepassiveanaloglinearfiltersconstructedusingresistorsandcapacitorsorresistorsandinductors.TheyarecalledRCandRLsingle-polefilters,respectively.
Peoplehavealsodevelopedsomehybridfilters.Typicalexamplesincludecombininganalogamplifierswithmechanicalresonatorsordelaylines.DevicessuchasCCDdelaylinesarealsousedasdiscretetimefilters.Duetothewidespreadapplicationofdigitalsignalprocessing,activedigitalfiltershavebecomecommon.