Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 122 PI, FUZZY LOGIC CONTROLLED SHUNT ACTIVE POWER FILTER FOR THREE-PHASE FOUR-WIRE SYSTEMS WITH BALANCED, UNBALANCED AND VARIABLE LOADS B.SURESH KUMAR1, K.RAMESH REDDY2, V.LALITHA3 B.Suresh Kumar and V.Lalitha are with EEE Department, CBIT, Hyderabad. () Dr.K.RameshReddy is with EEE Department, GNITS, Hyderabad, Mail

ABSTRACT This paper presents a fuzzy logic, PI controlled shunt active power filter used to compensate for harmonic distortioninthree-phasefour-wiresystems.Theshuntactivefilteremploysasimplemethodforthe calculationofthereferencecompensationcurrentbasedonFastFourierTransform.ThepresentedShunt ActivePowerfilteris able to operate in balanced, unbalanced and Variable load conditions. Classic filters maynothavesatisfactoryperformanceinfastvaryingconditions.Butautotunedactivepowerfiltergives better results for harmonic minimization, reactive power compensation and power factor improvement. The proposedautotunedshuntactivefiltermaintainstheTHDwellwithinIEEE-519standards.Theproposed methodologyisextensivelytestedforwiderangeofdifferentLoadswithImproveddynamicbehaviorof shuntactivepowerfilterusingfuzzylogic,PIcontrollers.Theresultsarefoundtobequitesatisfactoryto mitigate harmonic Distortions, reactive power compensation and power factor improvement. Keywords Active power filter, Power quality improvement, Fuzzy logic controller, PI controller, Power factor correction 1. INTRODUCTION n recent years, power quality distortion has become seriousprobleminelectricalpowersystemsdueto theIncreaseofnonlinearloadsdrawingnon-sinusoidalcurrentsActivefiltershavebeenwidely usedforharmonicmitigationswellasreactive powercompensation,loadbalancing,voltage regulation,andvoltageflickercompensationIn three-phasefour-wiresystemswithnonlinearloads ahighlevelofharmoniccurrentsinboththethree line conductors and more significantly in the neutral wirehasbeenenrolled.Unbalancedloadsalso resultsinfurtherdeclinationoftheSupplyquality [1].Variousharmonicmitigationtechniqueshave beenproposedtoreducetheeffectofharmonics. Thesetechniquesincludephasemultiplication, passivefilters,activepowerfilters(APFs),and harmonicinjection.OneofthemostpopularAPFs is the shunt active power filter. It is mainly a current source,Connectedinparallelwiththenon-linear loads.Conventionally,ashuntAPFiscontrolledin suchawayastoinjectharmonicandreactive compensationcurrentsbasedoncalculated referencecurrents.Theinjectedcurrentsaremeant tocanceltheharmonicandreactivecurrentsdrawn bythenonlinearloads[2].Recently,fuzzylogic controllerhasgeneratedagreatdealofInterestin variousapplicationsandhasbeen introduced in the power electronics field [3]-[4]. Theadvantagesoffuzzylogiccontrollersoverthe conventional PI controller are that they do not need anaccuratemathematicalmodel;theycanwork withimpreciseinputs,canhandlenonlinearity,and maybemorerobustthantheconventionalPI controller.Useoffuzzylogicforminimizationof harmonics and improvement of power quality is not anewissuerathervariousauthorshaveintroduced someinnovativemethodologiesusingthese tools[5].Themostimportantobservationfromthe workreportedbyvariousresearchersforpower qualityimprovementistheDesignofactivepower filter under fixed load conditions or for loads with slowandsmallvariation[6].Asloadsinpractical lifearemostlyvariable,thereistheneedtodesign anactivepowerfilter,whichiscapableof maintainingtheTHDwellwithintheIEEEnorms [7],undervariableloadconditions.Thispaper, Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 123 therefore, presents an auto tuned active power filter usingMamdanifuzzy-controllertocontrolthe harmonicsundervariableloadconditionsapart from balanced and unbalanced load conditions.

2. SHUNT ACTIVE POWER FILTER In a modern electrical distribution system, there has beenasuddenincreaseofnonlinearloads,suchas powersupplies,rectifierequipment,domestic appliances,and adjustable speed drives (ASD), etc. Asthenumberoftheseloadsincreased,harmonics currents generated by these loads may become very significant. These harmonics can lead to a variety of differentpowersystemproblemsincludingthe distortedvoltagewaveforms,equipment overheating,malfunctioninsystemprotection, excessiveneutralcurrents,lightflicker,inaccurate powerflowmetering,etc.Theyalsoreduce efficiencybydrawingreactivecurrentcomponent fromthedistributionnetwork[8].Inorderto overcometheseproblems,activepowerfilters (APFs)havebeendeveloped.Thevoltage-source-inverter(VSI)-basedshuntactivepowerfilterhas been used in recent years and recognized as a viable solutionthecontrolscheme,inwhichtherequired compensatingcurrentsaredeterminedbysensing linecurrentsonly,whichissimpleandeasyto implement.Theschemeusesaconventional proportionalplusintegral(PI)controllerforthe generation of a reference current A. Basic compensation principal APF.Acurrentcontrolledvoltagesourceinverter withnecessarypassivecomponentsisusedasan APFasshowninfig1.Itiscontrolledto draw/supplyacompensatedcurrentfrom/tothe utility, such that it eliminates reactive and harmonic currentsofthenon-linearload.Thus,theresulting total current drawn from the ac mains is sinusoidal. Ideally,theAPFneedstogeneratejustenough reactiveandharmoniccurrenttocompensatethe non-linear loads in the line. . Fig.1Connectionofshuntactivefilterwithnon-linear load 3. REFERENCE COMPENSATION CURRENT CALCULATION Thefollowingequationsdescribetheprocedure usedforreferencecompensationcurrent calculations ( ) 1 + =i i i harmonics loadfund load ( ) 2 sin = ti i loadfund loadfundThe load current is a periodic function and according to Fourier series ( ) ( ) [ ]=+ + =10sin cos2nn n loadt n t nb aai Where ( ) 3 + =i i i dc loadfund s The reference compensating current is ( ) ( ) 4 sin + =ti i i dc loadfund s ( ) 5 = i i i load s f ( ) ( )i i i i i harmonics loadfund dc loadfund ft + + = sin( ) 6 sin =i i i harmonics dc ft ( )dt ti a load =10( ) ( )dt nt ti a load ncos1=( ) ( )dt nt ti b load nsin1=( )b a i n n loadfund2 2+ =Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 124 B. Fuzzy Logic Current Controller Thedesiredswitchingsignalsforthefilterinverter circuitaredeterminedaccordingtotheerrorinthe filtercurrentusingFuzzylogiccontroller[8]-[9]. Theparametersforthefuzzylogiccurrent controllerusedinthispaperareasfollows.The designusescentrifugaldefuzzificationmethod. Therearetwoinputs;erroranditsderivativeand oneoutput,whichisthecommandsignaltothe PWMofthefilerinverter.Thetwoinputuses Gaussianmembershipfunctionswhiletheoutput usetrianglemembershipfunction.TheFig.2,Fig.3 andFig.4representthetestsystemsimulationwith balanced, unbalanced and variable loads Fig.2 The test system simulation with unbalanced nonlinear load safpulsespowerguiDiscrete,Ts = 5e-005v+-gABC+-Unit Delayz1TrigonometricFunctionsinVabcIabcABCabcNABCSubsystemABCSine Wave 2Sine Wave 1Sine WaveScope 8Scope 7Scope 6Scope 4Scope 3Scope 2Scope 11Scope 10Scope 1ProductMean Value(linear )In MeanIabcVabcVdcGoto3ILGoto 2IFundGoto1IFGain-K-IabcVabcVabcVdcILIFundIFFromsafpulsesFcnf(u)Display 1DisplayDiscrete 3-phasePWM GeneratorUrefwtP1P2InMagPhaseInMagPhaseInMagPhaseDiscretePI Controller 1PIDiscretePI ControllerPIDiscrete3-phase PLLVabc (pu)FreqwtSin_Cosi+ -i+ -i+ -i+ -i+ -i+ -Constant200Active & ReactivePowerVIpowerfactor3-phase Instantaneous Active& Reactive PowerVabcIabcPQ Fig.3 The test system simulation with Variable or dynamic nonlinear load Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 125 Fig.4 The test system simulation with balanced nonlinear load Fig.5.Control strategy for shunt APF with Fuzzy. Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 126 Fig.6. Control strategy for shunt APF with PI-Controller C. Proposed PI control scheme Theactivepowerfiltercompensationsystemand theschematicdiagramofthePIcontrolscheme, respectively[8]-[9].Inordertoimplementthe controlalgorithmofa shunt active power filter, the DC capacitor voltage (Vdc) is sensed and compared withthereferencevalue(Vdcref).TheInputofPI controlleris the value of Error, e Vdcref Vdc, anditsoutput,afteralimit,isconsideredasthe magnitudeofpeakreferencecurrentmaxI.The switchingsignalforthePWMconverterare obtained from comparing the actual source currents ( isa , isb ,isc ) with the reference current templates (Isa*,Isb*,Isc*)inahysteresiscurrent controller.Theoutputpulsesareappliedtothe switchingdevicesofthePWMconverter[14]. SincecoefficientsofPI controller, K p and Ki , are fixedinthismodel,theperformanceofactive power filter under random load variation conditions isnotaswellasfixedloadcondition.To overcomethisproblemandmakearobust controller,afuzzylogiccontroller(FLC)is designedtotuneKpandKionthebaseofload current value. The following Fig.7 fig. 8 shows FIS editor and FIS fileviewerFuzzydegreeofmembershipforthe erroranditsderivativeandthecommandsignal respectively.

Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 127 FIG.7. FIS EDITOR Fig.8 FIS File Viewer Fig.8(a) Fig.8(b)Fig.8(c) Fig.8 The degree of membership for (a) the error, (b) derivative, and (c) the command signal Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 128 Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 129 4. .COMPARISONOF%THD,POWERFACTORANDREACTIVECOMPENSATION TABLE FOR PI, FUZZY 5. CONCLUSION TheproposedShuntActiveFilter(SAF)can compensateforbalanced,unbalancedandVariable nonlinearloadcurrents.ProposedSAFadaptitself tocompensateforvariationinnonlinearcurrents. SimulationresultsshownthatsystemlimitsTHD percentageofsourcecurrentunderlimitsofIEEE-519standard(5%).andalsoobservedthatPower factorandReactivepowercompensationis improved. REFERENCES [1]A.Elmitwally,S.Abdelkader,M.Elkateb Performanceevaluationoffuzzycontrolled threeandfourwireshuntactivepower conditionersIEEEPowerEngineering SocietyWinterMeeting,2000.Volume3, Issue,23-27Jan2000Page(s):1650-1655 vol.3. [2]G.K.Singh,Powersystemharmonics research:asurveyEuropeanTransactions onElectricalPower,2009Page(s):151 172.[3]B.K.Bose,ExpertSystems,FuzzyLogic andNeuralNetworkApplicationinPower Electronics and Motion Control. Piscataway, NJ: IEEE Press, 1999, ch. 11. [4]DellAquila,A.Lecci,andV.G.Monopoli, Fuzzycontrolledactivefilterdrivenbyan innovativecurrentreferenceforcost reduction,inproc.IEEEInt.symp.Ind. Electron., vol. 3, May 26-29, 2002, pp. 948-952. [5]B.Singh,A.Chandra,andK.Al-Haddad, Computer-aidedmodelingandsimulation ofactivepowerfilters,Elect.Mach.Power Syst., vol. 27, pp. 1227-1241, 1999. [6]G.K. Singh, A.K. Singh, R. Mitra., a simple fuzzylogicbasedrobustactivepowerfilter forharmonicsminimizationunderrandom loadvariationElectr.PowerSyst.Res. (2006). [7]RecommendedPracticesandRequirements forHarmonicControlinElectronicPower Systems,IEEEStandard519-1992,New York, 1993 [8]S.S.Mortazavi,R.Kianinezhad,A. GhasemiAutoTunedRobustActivePower FilterforPowerQualityImprovementunder Fast Load Variation [9]AhmedA.Helal,NahlaE.Zakzouk,and Yasser G. Desouky Fuzzy Logic Controlled ShuntActivePowerFilterforThree-phase Four-wireSystemswithBalancedand Unbalanced Loads

Journal of Theoretical and Applied Information Technology 2005 - 2011 JATIT & LLS. All rights reserved. www.jatit.org 130 AUTHOR PROFILES: B.Suresh Kumar Asst.Professor, EEE Dept, CBIT,Hyderabad Mail:bskbus@gmail.com Dr.K.Ramesh Reddy Professor HOD & Dean EEE dept G.Narayanamma Institute of technology Hyderabad-27 Mail:kollirameshreddy@yahoo.com