Basicconcept
Three-phasecircuitinstantaneousreactivepowertheoryisthemainbasictheoryforthedevelopmentofAPF;APFhastwotypes:paralleltypeandseriestype,theformerismostlyused;parallelactivefilterThemainpurposeofthefilteristocontrolcurrentharmonics,andtheseriesactivefilterismainlytocontroltheproblemscausedbyvoltageharmonics.Comparedwithpassivefilters,activefiltershaveabettergovernanceeffect.Theycanfilteroutmultipleandhigherharmonicsatthesametimewithoutcausingresonance,butthepriceisrelativelyhigh!
Basicprinciples
Activepowerfilterisanewtypeofpowerharmoniccontrolspecialequipmentmadebymodernpowerelectronictechnologyanddigitalsignalprocessingtechnologybasedonhigh-speedDSPdevices.Itiscomposedoftwomainparts,thecommandcurrentcalculationcircuitandthecompensationcurrentgenerationcircuit.Thecommandcurrentarithmeticcircuitmonitorsthecurrentinthelineinrealtime,convertstheanalogcurrentsignalintoadigitalsignal,andsendsittoahigh-speeddigitalsignalprocessor(DSP)toprocessthesignal,separatetheharmonicfromthefundamentalwave,andmodulateitwithpulsewidth(PWM)signalformsendsdrivingpulsestothecompensationcurrentgeneratingcircuit,drivesIGBTorIPMpowermodule,generatescompensationcurrentwiththesameamplitudeandoppositepolarityasthegridharmoniccurrent,andinjectsitintothegrid,compensatesorcancelstheharmoniccurrent,andactivelyeliminatesitPowerharmonics.
TechnicaladvantagesGreen
Theefficiencyis97.2%,whichsavesabout6,500kwhperyearcomparedtoanactivefilterwithanefficiencyof95%.
Higherefficiencytopology-enhancedcontrolalgorithm
Thermaldesignandstructuraloptimizationbasedonaccuratemodels
Miniaturization
ThevolumeisonlythemainstreamofthesameclassBrand1/6,occupieslessspace,
Itcanadapttodifferentworkingconditions.Installationinnovation,wall-mountedorrack-mountedinstallationuseslessrawmaterialsandprotectstheenvironment.
Intelligent
Compensatethespecifiedorderofharmonics,adjustableinductiveandcapacitivereactivepowercompensationcompensationsystem,automaticdetectionofunbalancedload,suppressionofsystemresonance,full-functionmonitoringsystem
modularization
N+1redundancy,significantlyimprovessystemreliability,assemblylineproduction,betterqualityassurance,reducessystemsinglepointsoffailure,flexibleparallelconnection,andadaptstodifferentworkingconditions
Functionalfeatures
SimultaneousfilteringInadditiontothe2~50thharmonic,orselectanynumberofharmonicswithinthe2~50thorderforcompensation,theresponsetimeislessthan300μs
Itadopts3DSP+CPLDall-digitalcontrolmethodandinternationallyrenownedbrandhigh-speedIGBT,closed-loopcontrol,Preciselyfilteroutharmonics
Usingfour-phaselinetechnologytoeliminateneutrallinecurrent
Automaticallyeliminateresonance,notaffectedbychangesingridimpedanceandsystemimpedance,withcompensationforharmonics;simultaneouscompensationHarmonicandreactivepower;threeworkingmodesofcompensatingharmonics,reactivepowerandloadthree-phasecurrentimbalanceatthesametime
Electronicoverloadprotection
InvertercontrolisequippedwithamachineFastFPGA,powerdigitalsignalprocessingfunction
Modulardesign,easytoexpandmulti-machineparallelcentralizedmonitoringfunction,remotenetworkmonitoringfunction
Easytomaintain,workinaworkingenvironmentthatmeetstherequirements,Non-machinefailurewithoutmaintenance
ProductDesignStandard
InternationalStandard
EN50091-3,EN61000-6-2,EN55011,EN50178:1997,IEC62040-3,IEC50178:1997,AS62040-3(VFISS111),CISPR11
NationalStandard
GB/T14549-93"PowerQuality:PublicGridHarmonics"
GB/T15543-1995"PowerQuality:Three-phaseVoltageAllowableUnbalance"
GB/T15945-1995"PowerQuality:ElectricitySystemFrequencyAllowableDeviation"
GB/T12326-2000"PowerQuality:VoltageFluctuationandFlicker"
GB/T12325-2003"PowerQuality:SupplyVoltageAllowableDeviation"
p>GB/T18481-2001"PowerQuality:TemporaryOvervoltageandTransientOvervoltage"
GB/T15576-2008"LowVoltageCompleteReactivePowerCompensationDevice"
GB7625.11998"LowVoltageElectricalLimitsofharmoniccurrentsemittedbyelectronicproducts"
GB4208-2008"Enclosureprotectionlevel(IPcode)"
Voltageinputrange
Theratedworkingvoltageis380V,canwithstandvoltagefluctuationsof-40%～+20%,andthefrequencyis50/60Hz,canwithstand+/-5%frequencyfluctuations,adaptingtovariouspowerqualityenvironmentsunderdifferentworkingconditions.Atthesametime,ifthevoltagefluctuationexceedstheupperandlowerlimits,themachinewillautomaticallyblocktheoutputandissueanalarm.
Automaticcurrentlimiting
Theoutputisautomaticallylimitedto100%withintheratedcapacity.Iftheharmoniccurrentontheloadsideisgreaterthantheratedcapacityofthemachine,themachinewillContinuetooutputcurrentcompensationharmonicswithinthecapacity,andnooverloadwillcauseitsownoverloadorexitoperation.
Loadshort-circuitprotection
Itcanwithstandtheimpactofamomentaryshort-circuitoftheload,andrestartaftertheshort-circuitiseliminated.
Parallelindependentcontrol
Parallelconnectiontothegridwillnotcauseapowerfailureinthegridduetomachinefailure.FormultipleYW-APFactivepowerfiltersinparallelsystem,ifonequitsoperationduetoafailure,theremainingmachinescanstillworknormallytoachievethefilteringfunction.
Three-phasecurrentindependentcontrol
Eachphasecurrentisindependentlycontrolled,single-phaseinjectioncurrent,notaffectedbythesystemthree-phasecurrentimbalance,neutrallineThefilteringcapacityisthreetimesthatofthephaseline.
IPprotectionlevelandlightningprotection
TheIPprotectionlevelisIP20;thelightningprotectioncapacityis20kA.
Monitoringsystem
Thesystemhasafastandcompletefaultself-checkfunction,includingmainsundervoltageorovervoltage,busovervoltageorovercurrent,Variousfaultself-checkssuchasfanfailure,powerdeviceover-temperature,inputfuseblown,etc.AllfaultsarealarmedthroughtheLCDdisplayandLEDoperatingstatuslights,andthemachineautomaticallyadoptsthecorrespondingoperationprotectionsystem.Themonitoringsystemcansave500faultrecordsinthecaseofpowersupplyorpowerfailure,whichisconvenientforanalyzingthecauseandtroubleshooting.
Designmethod
Thedesignmethodofactivefiltercanberoughlysummarizedintotwocategories:cascademethodandanalogmethod.
Cascademethod
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.
Simulationmethod
FirstdesignanLCfilterthatcanmeetthetechnicalspecificationsasadesignprototype,andthenuseanactivecircuittosimulateit.Thismethodcanbedividedintocomponentsimulationmethodandfunctionalsimulationmethod,andtheprototypeismostlybasedontheLCladder-typefilterwithdouble-terminalterminationresistor.Generally,theanalogmethodrequiresmorecomponentsthanthecascademethod.
(1)Elementsimulationmethod
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.
Basicapplication
Mainharmofharmonics:
·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.
Economicbenefitsofharmoniccontrol:
1.Energysaving5%～8%
7setsof400KVAUPSuninterruptiblepowersuppliesinanIDCcomputerroom,theelectricityexpenditurein2008isabout15millionyuan,annualelectricitycostsavingsof1.1millionyuanafterharmoniccontrol,energy-savingeffectof7.3%.
2.Deratingtoreduceinvestmentintransformers,circuitbreakers,andcables
AfactoryinstalledGuodianZhongzi'sactivefilterandreturnedatransformertothepowersupplybureau,savingmorethan1millioninvestmentProtectequipmentandreduceequipmentinvestment;
TheharmonicsgeneratedbythefrequencyconverterofapapermillinHenanburneddowntwofanseverymonthandlost30,000yuaneverymonth.
3.Improveproductivityandmaintaincontinuouspowersupply
ThedailyoutputofDaqingAcrylicFiberPlantincreasedfrom197tonsto210tonsafterharmoniccontrol.
AdvantagesandDisadvantages
Advantages:Itcandynamicallyfilteroutvariousharmonics,andcancompletelyabsorbtheharmonicsinthesystem;itwillnotproduceresonance.
Disadvantages:thecostistoohigh;duetohardwarelimitations,itcannotbeusedinlarge-capacityoccasions:thesinglesetofactivefiltercapacitydoesnotexceed100KVA,andthemaximumapplicablegridvoltagedoesnotexceed690V.
Applications
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.
Developmentstatus
Withtheadvancementofpowerelectronictechnologyandcontroltechnology,domesticactivefiltershavereplacedimportedproductsinvariousmajorprojects.Onlyin2012,domesticallyproducedThesalesofactivefilterproductshavesurpassedthatofimportedbrandsby5times.ActivepowerfilterAPFwilleventuallyreplacetraditionalpassivefilterPFwithitshugetechnicaladvantages,powerfulfunctions,anddecliningprice.
DuringthedevelopmentofAPF,modularactivefilterequipmenthasgraduallyreplacedthetraditionalcabinet-typeAPFwithitsadvantagessuchassmallsize,easyinstallation,highdegreeofintegration,stablework,andconvenientexpansion.Inthenext5years,thecombinationofmodularactivefilterAPFandstaticvargeneratorSVGwillsurelybecomethemostpowerfulsolutioninthepowerqualityindustryandwillbewidelyrecognizedbythemarket.
Workingprinciple
TheactivefilterusesacurrenttransformertocollectthecurrentontheDCline.Aftersampling,thecurrentsignalisprocessedbytheharmonicseparationalgorithmtoobtainaharmonicThewavereferencesignal,asthemodulationsignal,iscomparedwiththetrianglewavetoobtaintheswitchingsignal.Thisswitchingsignalisusedtocontrolthesingle-phasebridge.Accordingtotheprincipleoftechnology,theswitchingsignalsoftheupperandlowerbridgearmsarereversedtoobtaintheTheharmoniccurrentswiththesamemagnitudeandoppositedirectionsoftheharmonicsignalscancelouttheharmoniccurrentsontheline.Thisisthefeedforwardcontrolpart.Thentheharmoniccomponentsofthelinecurrentaftertheactivefilteraccesspointarefedback,astheinputoftheregulator,toadjusttheerrorofthefeedforwardcontrol
Productfeatures
1.Highfilteringaccuracy,harmoniccurrentfilteringratecanreachmorethan97%;
2.Widefilteringrange,filteringfrequency:2--50harmonicsandinter-harmonics;
3.Fastresponsetoloadfluctuations,theresponsetimeis1us;
4.Dynamicinjectionofcurrenttosuppressharmonicsandcompensatepowerfactor;
5.WillnotinteractwiththesystemResonanceoccurs;
6.Multipleunitscanbecombinedtoexpandcapacity;
7.Suppresssystemovervoltageandimprovesystemvoltagestability
8.DampingpowersystemPoweroscillation;
9.Itcansuppressvoltageflicker,compensatethree-phaseunbalance,andimprovepowerfactor;
10.Thesystemhasstrongself-protectionandstability.
Technicalparameters
1.Ratedworkingvoltage:380V/220V,50Hz
2.Ratedharmoniccompensationcapacity:50A/100A/150A/200A
3.Powerconsumptionofthewholemachine:lessthan3%ofcapacity
4.Harmonicsuppressioneffect:meettherequirementsofthenationalstandard,andthesteady-stateTHDcanbereducedtolessthan5%
5.Ratedinsulationvoltage:3000VAC,2500VDC
Performancedescription
1.Dynamicactivefiltering,overallimprovementofpowerquality;
2.DSPfulldigitalcontrol,20KHzswitchingfrequency,rapidresponsetodynamicchangesoftheload;
3.Thenumberofharmoniccompensationcanbeselected,andthe50thharmoniccanbefilteredoutatmost;
4.Suttonsactivepowerfiltercanchoosetocompensatereactivepoweratthesametime;
5.Withthree-phaseunbalancecompensationcapability;
6.Withautomaticcurrentlimitingfunction,noOverloadoccurs;
7.Highefficiency,fullloadlossislessthan2.57;
8.Parallelinstallation,simpleinstallationandsmallsize;
9.ReducecircuitLoss,eliminatetheheatoftransformerandmotorcausedbyharmonics,realizesystemenergysavinggreatly;
10.Thefilteringeffectofactivepowerfilterisnotaffectedbysystemimpedancechanges,andcanautomaticallysuppresssystemresonance;
11.Accordingtothepowerdistributionstructure,partialcompensation,partialcompensationortotalcompensationcanbeselected.CTcanbelocatedonthepowersideortheloadside;
12.Easytoexpandandredundantdesign,canbeUpto10unitscanbeoperatedinparallel.
Prospects
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.