Основна концепция
Three-phasecircuitinstantaneousreactivepowertheoryisthemainbasictheoryforthedevelopmentofAPF;APFhastwotypes:paralleltypeandseriestype,theformerismostlyused;parallelactivefilterThemainpurposeofthefilteristocontrolcurrentharmonics,andtheseriesactivefilterismainlytocontroltheproblemscausedbyvoltageharmonics.Comparedwithpassivefilters,activefiltershaveabettergovernanceeffect.Theycanfilteroutmultipleandhigherharmonicsatthesametimewithoutcausingresonance,butthepriceisrelativelyhigh!
Основни принципи
Activepowerfilterisanewtypeofpowerharmoniccontrolspecialequipmentmadebymodernpowerelectronictechnologyanddigitalsignalprocessingtechnologybasedonhigh-speedDSPdevices.Itiscomposedoftwomainparts,thecommandcurrentcalculationcircuitandthecompensationcurrentgenerationcircuit.Thecommandcurrentarithmeticcircuitmonitorsthecurrentinthelineinrealtime,convertstheanalogcurrentsignalintoadigitalsignal,andsendsittoahigh-speeddigitalsignalprocessor(DSP)toprocessthesignal,separatetheharmonicfromthefundamentalwave,andmodulateitwithpulsewidth(PWM)signalformsendsdrivingpulsestothecompensationcurrentgeneratingcircuit,drivesIGBTorIPMpowermodule,generatescompensationcurrentwiththesameamplitudeandoppositepolarityasthegridharmoniccurrent,andinjectsitintothegrid,compensatesorcancelstheharmoniccurrent,andactivelyeliminatesitPowerharmonics.
TechnicaladvantagesGreen
Ефективността е 97,2%, което спестява около 6500 kWh годишно в сравнение с неактивен филтър с ефективност от 95%.
Алгоритъм за управление с подобрена топология с висока ефективност
Thermaldesignandstructuraloptimizationbasedonaccuratemodels
Миниатюризация
ThevolumeisonlythemainstreamofthesameclassBrand1/6,occupieslessspace,
Itcanadapttodifferentworkingconditions.Installationinnovation,wall-mountedorrack-mountedinstallationuseslessrawmaterialsandprotectstheenvironment.
Интелигентен
Compensatethespecifiedorderofharmonics,adjustableinductiveandcapacitivereactivepowercompensationcompensationsystem,automaticdetectionofunbalancedload,suppressionofsystemresonance,full-functionmonitoringsystem
модулиране
N+1redundancy,significantlyimprovessystemreliability,assemblylineproduction,betterqualityassurance,reducessystemsinglepointsoffailure,flexibleparallelconnection,andadaptstodifferentworkingconditions
Функционални характеристики
SimultaneousfilteringInadditiontothe2~50thharmonic,orselectanynumberofharmonicswithinthe2~50thorderforcompensation,theresponsetimeislessthan300μs
Itadopts3DSP+CPLDall-digitalcontrolmethodandinternationallyrenownedbrandhigh-speedIGBT,closed-loopcontrol,Preciselyfilteroutharmonics
Usingfour-phaselinetechnologytoeliminateneutrallinecurrent
Automaticallyeliminateresonance,notaffectedbychangesingridimpedanceandsystemimpedance,withcompensationforharmonics;simultaneouscompensationHarmonicandreactivepower;threeworkingmodesofcompensatingharmonics,reactivepowerandloadthree-phasecurrentimbalanceatthesametime
Електронна защита от претоварване
InvertercontrolisequippedwithamachineFastFPGA,powerdigitalsignalprocessingfunction
Modulardesign,easytoexpandmulti-machineparallelcentralizedmonitoringfunction,remotenetworkmonitoringfunction
Easytomaintain,workinaworkingenvironmentthatmeetstherequirements,Non-machinefailurewithoutmaintenance
Продуктов дизайнСтандартен
Международен стандарт
EN50091-3,EN61000-6-2,EN55011,EN50178:1997,IEC62040-3,IEC50178:1997,AS62040-3(VFISS111),CISPR11
Национален стандарт
GB/T14549-93"PowerQuality:PublicGridHarmonics"
GB/T15543-1995 "Качество на захранването: Трифазно напрежение, разрешено небалансиране"
GB/T15945-1995 "Качество на мощността: Допустимо отклонение на честотата на системата за електричество"
GB/T12326-2000 "Качество на захранването: Флуктуация на напрежението и трептене"
GB/T12325-2003 "Качество на захранването: допустимо отклонение на захранващото напрежение"
p>GB/T18481-2001 "Качество на захранването: Временно пренапрежение и преходно пренапрежение"
GB/T15576-2008 "Устройство за компенсиране на реактивна мощност при ниско напрежение"
GB7625.11998"LowVoltageElectricalLimitsofharmoniccurrentsemittedbyelectronicproducts"
GB4208-2008 "Ниво на защита на корпуса (IPкод)"
Диапазон на входно напрежение
Theratedworkingvoltageis380V,canwithstandvoltagefluctuationsof-40%～+20%,andthefrequencyis50/60Hz,canwithstand+/-5%frequencyfluctuations,adaptingtovariouspowerqualityenvironmentsunderdifferentworkingconditions.Atthesametime,ifthevoltagefluctuationexceedstheupperandlowerlimits,themachinewillautomaticallyblocktheoutputandissueanalarm.
Автоматично ограничаване на тока
Theoutputisautomaticallylimitedto100%withintheratedcapacity.Iftheharmoniccurrentontheloadsideisgreaterthantheratedcapacityofthemachine,themachinewillContinuetooutputcurrentcompensationharmonicswithinthecapacity,andnooverloadwillcauseitsownoverloadorexitoperation.
Защита от късо съединение на товара
Itcanwithstandtheimpactofamomentaryshort-circuitoftheload,andrestartaftertheshort-circuitiseliminated.
Паралелно независимо управление
Parallelconnectiontothegridwillnotcauseapowerfailureinthegridduetomachinefailure.FormultipleYW-APFactivepowerfiltersinparallelsystem,ifonequitsoperationduetoafailure,theremainingmachinescanstillworknormallytoachievethefilteringfunction.
Трифазен токонезависим контрол
Eachphasecurrentisindependentlycontrolled,single-phaseinjectioncurrent,notaffectedbythesystemthree-phasecurrentimbalance,neutrallineThefilteringcapacityisthreetimesthatofthephaseline.
IPprotectionlevelandlightningprotection
TheIPprotectionlevelisIP20;thelightningprotectioncapacityis20kA.
Система за наблюдение
Thesystemhasafastandcompletefaultself-checkfunction,includingmainsundervoltageorovervoltage,busovervoltageorovercurrent,Variousfaultself-checkssuchasfanfailure,powerdeviceover-temperature,inputfuseblown,etc.AllfaultsarealarmedthroughtheLCDdisplayandLEDoperatingstatuslights,andthemachineautomaticallyadoptsthecorrespondingoperationprotectionsystem.Themonitoringsystemcansave500faultrecordsinthecaseofpowersupplyorpowerfailure,whichisconvenientforanalyzingthecauseandtroubleshooting.
Метод на проектиране
Thedesignmethodofactivefiltercanberoughlysummarizedintotwocategories:cascademethodandanalogmethod.
Каскаден метод
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.
Симулационен метод
FirstdesignanLCfilterthatcanmeetthetechnicalspecificationsasadesignprototype,andthenuseanactivecircuittosimulateit.Thismethodcanbedividedintocomponentsimulationmethodandfunctionalsimulationmethod,andtheprototypeismostlybasedontheLCladder-typefilterwithdouble-terminalterminationresistor.Generally,theanalogmethodrequiresmorecomponentsthanthecascademethod.
(1) Метод на симулация на елементи
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.
Основно приложение
Основни хармоници:
·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.
Икономически ползи от хармоничния контрол:
1. Икономия на енергия5% ~ 8%
7setsof400KVAUPSuninterruptiblepowersuppliesinanIDCcomputerroom,theelectricityexpenditurein2008isabout15millionyuan,annualelectricitycostsavingsof1.1millionyuanafterharmoniccontrol,energy-savingeffectof7.3%.
2. Намаляване на стойността за намаляване на инвестициите в трансформатори, прекъсвачи и кабели
AfactoryinstalledGuodianZhongzi'sactivefilterandreturnedatransformertothepowersupplybureau,savingmorethan1millioninvestmentProtectequipmentandreduceequipmentinvestment;
TheharmonicsgeneratedbythefrequencyconverterofapapermillinHenanburneddowntwofanseverymonthandlost30,000yuaneverymonth.
3.Improveproductivityandmaintaincontinuouspowersupply
ThedailyoutputofDaqingAcrylicFiberPlantincreasedfrom197tonsto210tonsafterharmoniccontrol.
Предимства и недостатъци
Advantages:Itcandynamicallyfilteroutvariousharmonics,andcancompletelyabsorbtheharmonicsinthesystem;itwillnotproduceresonance.
Disadvantages:thecostistoohigh;duetohardwarelimitations,itcannotbeusedinlarge-capacityoccasions:thesinglesetofactivefiltercapacitydoesnotexceed100KVA,andthemaximumapplicablegridvoltagedoesnotexceed690V.
Приложения
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.
Състояние на развитие
Withtheadvancementofpowerelectronictechnologyandcontroltechnology,domesticactivefiltershavereplacedimportedproductsinvariousmajorprojects.Onlyin2012,domesticallyproducedThesalesofactivefilterproductshavesurpassedthatofimportedbrandsby5times.ActivepowerfilterAPFwilleventuallyreplacetraditionalpassivefilterPFwithitshugetechnicaladvantages,powerfulfunctions,anddecliningprice.
DuringthedevelopmentofAPF,modularactivefilterequipmenthasgraduallyreplacedthetraditionalcabinet-typeAPFwithitsadvantagessuchassmallsize,easyinstallation,highdegreeofintegration,stablework,andconvenientexpansion.Inthenext5years,thecombinationofmodularactivefilterAPFandstaticvargeneratorSVGwillsurelybecomethemostpowerfulsolutioninthepowerqualityindustryandwillbewidelyrecognizedbythemarket.
Принцип на работа
TheactivefilterusesacurrenttransformertocollectthecurrentontheDCline.Aftersampling,thecurrentsignalisprocessedbytheharmonicseparationalgorithmtoobtainaharmonicThewavereferencesignal,asthemodulationsignal,iscomparedwiththetrianglewavetoobtaintheswitchingsignal.Thisswitchingsignalisusedtocontrolthesingle-phasebridge.Accordingtotheprincipleoftechnology,theswitchingsignalsoftheupperandlowerbridgearmsarereversedtoobtaintheTheharmoniccurrentswiththesamemagnitudeandoppositedirectionsoftheharmonicsignalscancelouttheharmoniccurrentsontheline.Thisisthefeedforwardcontrolpart.Thentheharmoniccomponentsofthelinecurrentaftertheactivefilteraccesspointarefedback,astheinputoftheregulator,toadjusttheerrorofthefeedforwardcontrol
Характеристики на продукта
1.Highfilteringaccuracy,harmoniccurrentfilteringratecanreachmorethan97%;
2. Широк обхват на филтриране, честота на филтриране: 2--50 хармоници и интерхармоници;
3.Бърза реакция при колебания на натоварването, времето за реакция е 1 us;
4.Dynamicinjectionofcurrenttosuppressharmonicsandcompensatepowerfactor;
5.Няма да взаимодейства съссистемата Възниква резонанс;
6. Множество единици могат да се комбинират за разширяване на капацитета;
7.Suppresssystemovervoltageandimprovesystemvoltagestability
8. Затихваща система за мощност Мощност на колебание;
9. Може да потисне трептенето на напрежението, да компенсира трифазния дисбаланс и да подобри фактора на мощността;
10. Системата има силна самозащита и стабилност.
Технически параметри
1. Номинално работно напрежение: 380V/220V, 50Hz
2. Номинален капацитет на хармонична компенсация: 50A/100A/150A/200A
3. Консумирана мощност на цялата машина: по-малко от 3% от капацитета
4.Harmonicsuppressioneffect:meettherequirementsofthenationalstandard,andthesteady-stateTHDcanbereducedtolessthan5%
5. Номинално изолационно напрежение: 3000 VAC, 2500 VDC
Описание на изпълнението
1.Динамично активно филтриране, цялостно подобряване на качеството на мощността;
2.DSPfulldigitalcontrol,20KHzswitchingfrequency,rapidresponsetodynamicchangesoftheload;
3.Thenumberofharmoniccompensationcanbeselected,andthe50thharmoniccanbefilteredoutatmost;
4.Suttonsactivepowerfiltercanchoosetocompensatereactivepoweratthesametime;
5. С възможност за компенсиране на трифазен дисбаланс;
6. С функция за автоматично ограничаване на тока не възниква претоварване;
7.Висока ефективност, загуба на пълно натоварване по-малка от 2,57;
8. Паралелна инсталация, проста инсталация и малък размер;
9.ReducecircuitLoss,eliminatetheheatoftransformerandmotorcausedbyharmonics,realizesystemenergysavinggreatly;
10.Thefilteringeffectofactivepowerfilterisnotaffectedbysystemimpedancechanges,andcanautomaticallysuppresssystemresonance;
11.Accordingtothepowerdistributionstructure,partialcompensation,partialcompensationortotalcompensationcanbeselected.CTcanbelocatedonthepowersideortheloadside;
12.Easytoexpandandredundantdesign,canbeUpto10unitscanbeoperatedinparallel.
Перспективи
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.