PSO Fractional-Order PID Controller Design for DC Component Suppression of Grid-Connected Converters

Key Words: DC current suppression, Grid connected converters, particle swarm optimization, Fractional order controller,PIDcontroller.

3Graduated, School of Information and Communication Engineering, UESTC, Chengdu, China ***

Hassen Ahmed Y.1 , Kedir Abdurezak N.2 , Ali Ebrahim A.3 Kassie Samrawit D.2

Abstract Recently, due to widelydistributedandabundant natural resources, solar and wind energy has been paid more attention for renewable energy. However,DCcurrentinjection into the grid remains a significant issue for a transformerless grid connected converter. Injection of DC componentsinto the grid, if excessive, can lead to problems suchasacceleratingthe corrosion of underground network cables and pipelines, and etc. In order to overcome the above issues, in this paper, a new control strategy is proposed to suppress DC current injection for three phasetransformerlessgrid connectedPVinverters.It is based on accurately extracting the DC component fromgrid current output combined with a swarm particle optimization algorithm to adjust parameters of the DC suppression loop fractional Order PID controller. The performance of the proposed method is evaluated and compared with the pre existing methods. The simulation and experimental results clearly show the proposed method can suppress dc components within 0.1% of rated current.

1.INTRODUCTION

Due to widely distributed, non polluting and abundant naturalresources,solarandwindenergyhasbeenpaidmore andmoreattentioninrecentyears.Inordertoutilizethis renewable energy resource, Grid Connected Inverters are thekeyfacilitiesofthesystem.Eventhoughtheapplications ofelectronicpowerinvertersingrid connectedsystemsare obvious,thereareseveralissuesthatstillexisttoenhance theefficiencyandreliabilityofsuchsystems.Inparticular, DC current injection into the grid remains a significant concern for a grid connected inverter. Ideally, the output current of the inverter will be purely alternating current (AC). However, in practice, due to various reasons, unless specialmeasuresaretaken,itwillcontainasmallamountof DCcomponents. Thereareseveralreasonstogeneratedc currentcomponentssuchaszero driftandscalingerrorsof currentandvoltagesensors,asymmetriesintheturn onand turn offcharacteristicsof semiconductorswitches,turn on/ offdelaysonthedevice,gatedrivecircuitsdelay,smallDC offsets errors in PWM signals, and digital controller quantizationerrors,etc.InjectionofDCcomponentintothe grid, if excessive, can lead to problems such as 1) acceleratingcorrosionofundergroundnetworkcablesand pipelines,andetc.Moreover,itcausesextralossontheloads connected to the grid. As a result, strict national and internationalguidelinesandstandardsarenormallyinplace tolimitthedccurrentinjectionintothegrid.Forexample, according to the IEEE 929 2000 standard in the USA, the maximumdccurrentpermittedfortransformerlessinverter shouldnotexceed0.5%oftheratedcurrent[4].

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2Undergraduate Student, School of Mechanical and Electrical Engineering, UESTC, Chengdu, China

Certified Journal | Page974

1Graduate Student, School of Astronautics, Beihang University, Beijing, China

OneofthesimplestmethodstosuppressDCinjectionisto includealinetransformerbetweenthepowerconverterand the grid [1 4] recently, a transformer less grid connected converterdrawsgreatinterest,whichhasmeritsofhigher efficiency,lowercost,smallersize,andoverallreducedmass [2].However,asstatedearlier,DirectCurrent(DC)injection is still a serious issue in Transformer less grid connected inverters,whichdegradepowerquality.Inordertominimize DCcurrentinjectionintothegridfortransformer lessgrid connectedinverters,severalcontroltechniqueshavebeen proposed in the literature [5 19]. One type of methods is blockingdccurrentwithaphysicalcapacitor[5 7]. Thesecondtypeofmethodsisusingthedcoffsetvoltage detection and feedback control to prevent the dc current injectiontothegrid[8 9].Thismethoddetectsthedcoffset voltageattheinverteroutput,andthedccomponentinthe grid current is eliminated by feeding back the dc offset voltage to the inner loop current controller. A detecting methodofdcoffsetvoltageintroducedbySharma[8] Thethirdtypeofmethodsisusingthedccurrentdetection andfeedbackcontroltopreventthedccurrentinjectionto thegrid[12 20].Havetheadvantageofdirectcontrollingdc current.However,itseffectivenessislimitedbytheaccuracy ofthesensortodetectDCcurrent. In[19],aneuralnetwork basedadaptiveBP PIDcompensationtechniqueisproposed. However, due to the complexityoftheBP neural network algorithm,itrequiresextensivecomputationtimeandlarge datastorage.Asmainstreamliteraturecontinuestoshow,dc component suppression is a challenging problem in grid connectedinverterapplicationsonlybyusingaconventional controller.Forthisreason,thisresearchcombinesfractional calculus with conventional PID controller to overcome shortcomingsoftraditionalPIDcontroller.Comparedwith the classical PID controller, the Fractional order PID controllerhastwoadditionalparameters:integralorderand differential order, which makes the setting range of the controlparameterslarger.Asaresult,abetterrobustcontrol effectcanbeobtained.First,thedccurrentisextractedfrom the grid current waveform utilizing a Second Order Generalized Integrator (SOGI), and a FOPID controller is

4 and 5, respectively. The simulation and experimental resultsarepresentedinsection6 2.

A three phase transformerless grid connected inverter is studiedinthispaper,whichisshowninFig.1.Asdepictedin the figure, an LCL filter is used to interface between the inverter and the grid. Where, vga, vgb and vgc are the three phasegridvoltages, L1 istheinvertersideinductor, L2 isthe gridsideinductor, i1a,i1b,i1c arethree phaseinvertercurrent, iga,igb,igc are respective three phase grid current C is filter capacitor, vca,vcb,vcc are respective three phase capacitor voltageandVd,representsthevoltageofthedcsource. Fig 1: Originalschemediagramofthree phasePVgrid connectedinverterwithouttheproposedmethod

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3. THE PROPOSED PSO FPID CONTROL STRATEGY

International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 09 Issue: 02 | Feb 2022 www.irjet.net p ISSN: 2395 0072 © 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page975 ��g �� = �� +�� = ��0 +��1��(ω�� +��) ��1 ��1 �� =u�� 1R1 �� 2 ��g �� =�� gR2 ��g �� =��1 ��g designedtomitigatedccurrentinjection. PSOalgorithmis utilized for adjusting the five parameters of FOPID controllers. The main contributions of this paper are summarizedasfollows. 1),afractionalorderPIDcontrollerisdevelopedwiththe purposetomitigatedccomponentinjectionintothegrid. 2)A particle swarm optimization algorithm is utilized to perform the optimal design for the proposed Fractional orderPID(FOPID)controller 3)A second order generalized integrator (SOGI) based dc component estimation is proposed, which does not introduceadditionaltimedelayasitdoesn'trequiremultiple timeintegrationcomparedwithpre existedsoftware based dcextractionmethods. Thispaperisorganizedasfollows.Insection2,modellingof a three phase LCL type grid connected inverter is demonstrated. In section 3, the proposed dc component suppression control strategy is introduced. The fractional calculus and the design of the proposed Particle Swarm Optimization(PSO FOPID)controllerisintroducedinsection

MATHEMATICAL MODEL OF LCL GCC

AccordingtotheKCLandKVLlaws,themathematicalmodel ofathree phaseinvertercanbeobtainedas(1).

Compared to the AC component, the DC component in the grid current is very small. Thus, the accuracy of the DC componentextractiondeterminesthesuppressioneffect.As statedinIEEEStandard1547 2000,thedccomponentneeds tobeminimizedwithin0.5%oftheratedoutputcurrent[4]. In[19],theauthorproposedareal timesoftware basedDC injection detection method, which is called the sliding windowdoubleintegralmethod(SWDIM).Similarly,based onthisidea,in[20],JiangandYuanproposedamethodcalled Moving Average Filter (MAF) to detect the dc component basedonthemultipleintegrationmethods.Comparedtolow passfilter(hardware based),software basedmethodshave much higher accuracy in filtering and faster dynamic response. However, these methods are hard to match betweentheintegrationnumberandthedynamicresponse. Moreover, they will introduce additional time delay. To overcometheaboveissuesandmeetIEEEStandard1547 2000 on dc current injection requirement, a second order generalized integrator (SOGI) dc component estimation approach,whichdoesn'trequiremultipletimeintegration,is proposed.AgeneralSOGIestimatorstructureisshowninFig. 2where ig, ε and k representtheinputsignal,theerrorsignal andthedampingfactor,respectively.FromFig.2,theclosed looptransferfunctionsofthegeneralSOGIcanbeobtainedas

Let'sassumetheoutputgridcurrentsignal ig(t),comprisesof both ac and dc components. Then the grid current can be describedas: (1) Where idc and iac are the dc and ac component in the grid current, respectively, and A0, is the amplitude of dc component. Beside A1, ωs and φs are the amplitude, frequency,andphase angleofaccomponents,respectively. Ins domain, ig(s) canbeexpressedby(4) Therefore, iac(s) can be derived from (2) and (4) ApplyingtheinverseLaplacetransformto(5),thesteady stateoutputof iac(t) canbeobtainedas: Therefore, the dc component and harmonics can be determined by simply subtracting iac, from grid current. Accordingto[26],thedampingfactorkin(2)canbesimply determinedbydecidinganappropriatevalueforthesettling time ts. In which stability is guaranteed for all k > 0. The lower value of k, the better filtering effect of G(s). But the stronger dependence on the resonant frequency ω0 and a verylowvalueof k degradesthedynamicperformanceofthe SOGI. Inthispaper,basedontheanalysisoftheSOGI'sbode

3.1 DC Component Extraction

3.3 Particle Swarm Optimization Algorithm

3.2

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The block diagram of the proposed control scheme is showninFig.3,whichiscomposedofthreeparts:ASecond OrderGeneralizedIntegrator(SOGI),PSO FOPIDcontroller, andQPRcontroller.TheSOGIwillestimatedccomponentsin thegridcurrent,andthePSO FOPIDcontrollerrealizeszero steady stateerrorforthedcsuppressionloop.Inthiswork, the QPR controller is adopted for the inner loop current control which, has better steady state performance and ensuresthehigh powerqualityofthesystemoutputcurrent, comparedwiththeconventionalPIorPIDcontroller.

Recently,PIandPIDcontrollershavebeenwidelyusedin mostdccomponentcompensationmethodsbecauseoftheir simplestructureandrobustperformanceinawiderangeof operating conditions. However, in addition to difficulty tuning the gains of PID controllers properly, the PID controllercannotprovideaperfectcontrolperformancefor the highly nonlinear and uncertain controlled plant. Therefore,itishighlydesirabletoincreasethecapabilitiesof thePIDcontrollerbeyondintegralapplicationbycombining themeritsoffractionalordercalculationandoptimization algorithm. Fractional order PID controller has two extra parameters corresponding to the integral and differential terms of Integer order PID controller, which handles the system dynamics and nonlinearities with robustness and increasestheflexibilityforbetterdesignofcontrolsystem. Furthermore,weemployedaParticleSwarmOptimization (PSO) algorithm based FOPID controller, which has the advantagesofstrongadaptation,self learningcapabilityand onlineparameterregulationcapabilitycombinedwithFOPID controllerforminimizationofdccomponentinjectioninto theThegrid.PSOalgorithmadjuststhecontrolparameters (kp,ki,kd, λ and μ ) ofthe controllerbytrackingdccomponent erroratthesamplingtimepointandeliminatingtheseerrors in a very short finite time. As mentioned earlier, the PSO algorithmisaimedtoachieveaminimumdccurrenterrorin thenextsamplingperiod. Forthispurpose,itisnecessarytofirstgetthedccurrent error. The error is defined as the absolute difference between the reference dc current and the obtained dc component extracted from the grid current. Then, a cost functionF(s)isappliedtotheobtaineddccurrenterror.The costfunctionisdefinedin equation(21).BecausethePSO method is an excellent optimization methodology and promisingapproachforobtainingoptimalFOPIDcontroller parametersproblem;therefore,thisstudydevelopsthePSO FOPID to search optimal FOPID parameters. And this controlleriscalledthePSO fractionalorderPIDcontroller, whichweappliedfordccurrentsuppression.

DC Component Suppression with PSO-FPID Controller

PSOisoneofthemostpowerfuloptimizationalgorithm methods, especially for achieving the best solutions for nonlinear systems. This technique is an evolutionary algorithmthatisbasedonthenaturalbehaviorsofschoolsof fishesandflocksofbirdsthatmovearoundinagroupataD dimensionalspace[28].Eachmemberofthepopulationsin PSOisonesolutioncandidateinthedomainofsearchspace. InthePSOalgorithm,membersofthegroupcanlearnfrom the experiences of each other, which directs members towardthebestsolutioninthesearchspace.PSOalgorithm principles mainly depend on two factors, velocity and positionofeachcandidateinthesearchspace.InPSO,each member uses its own past memory and the knowledge of neighborstofindthebestsolution(pbest). pbest isthebest solution of a particle amongst its own past iterations, as expressedbyitshighestfitnessvalue.Amongstallindividual pbest valuesthebestfitnessvalueiscalledtheglobalbest (gbest). gbest isconsidered asa solutioncandidate,italso guides the other particle member to move toward its neighbor'sbestglobalsolutionsinthenextiterations,and thus,cancausetheparticlestotrapinthelocaloptimums.In thePSOalgorithmatthebeginning,itinitializestheswarm byassigningarandomvalueintheproblemsearchspacefor each candidate solution. The position of the ith particle is givenby Xi= Xi1, Xi2 ,…, Xid] anditsvelocityisgivenby Vi=[ Vi1, Vi2 ,…, Vid].Theoptimalpositionofeachparticleisgiven by Pi= Pi1,Pi2 ,…, Pid] andthebestglobalpositionisgivenby [Pg= Pg1, Pg2 ,…, Pgd].

plots, considering the tradeoff between the transient responsespeedandfilteringperformance,theparameterof k ischosenas 0.1 idc ω0 kεε + + + k EstimatorSOGI ω0 ig iac ig Fig 2:Blockdiagramstructureforadccurrent componentextractionbasedonSOGI.

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Fig 3:TheblockdiagramoftheproposedPSO PI controllerforthree phaseinverterdccomponent suppression.

Initializes swarm with a random value Represent each swarm as kp andki. XN = {kp, ki} Evaluatefitness function foreach X(i) in the swarm. Updatepersonal and global best of Swarm Population. Updatevelocity and position ofeach Swarm OutputOptimum value (Ki, and Kp) Xbest = [kp, ki]

4. FRACTIONAL ORDER PID CONTROLLER

4.1 Basic of Fractional Order Calculus

TheRiemannLiouville(RL)definitionavoidsusinglimit andsum,insteadusesinteger orderderivativeand integral,whichispresentedasfollows:

StartCriteria

Stopping

Thevalueof thevelocityof eachmemberisupdated by usingequations(9)ineverysearchiterationaccordingtoits own pbest and gbest. where( =1,2,....,m),nistheiterationnumber, , are randomnumbersbetween(0,1). and ,arethesocial rate and the cognitive rate, respectively. ω is the inertia weight, and denotethevelocitiesofthenewandold particles,respectively.Thepositionisupdatedby Withmoreiteration,thebestsolutioncanbeobtainedas SetPSO parameters

YES NO TheOptimal Outputvalues were assigned to PI controller. Fig-4:FlowchartofthePSOalgorithmforthedc componentsuppressionloopcontroller.

There are many definitions of FOC; the three widely used definitions of Fractional order calculus are, Riemann Liouville,Grunwald Letnikov,andCaputoapproach[22 25]. Grunwald Letnikov'sdefinitionispresentedasfollows: where h stands for the time step, , ,isintegerpart,and areupperandlower limitsoftheoperator,respectively.Thebinomialcoefficient isevaluatedbygammafunctionasinequation(x)

The third commonly used definition of fractional order derivative is proposed by M.Caputo and defined by the followingequation: WiththedevelopmentofFOCapplicationsinthecontroller, newareasofcontroltheoryareappeared,namelyfractional theory and fractional controller. Fractional order control theoryisbuiltupbasedonfractionalcalculustheory.Recent research studies have shown that Fractional order controllers could perform better than integer order controllersintermsofsystemperformanceandrobustness.

Thefractional ordercalculus(FOC)isoneofthepopular andnewlyemergingmathematicsbranches,whichprovides anefficienttoolformanyrealsituationsrelatedtoinfinite memory,fractionaldimensions,andchaoticbehavior.

Thefractional orderdifferentiatorcanbedescribedasa continuousdifferential integratoroperator,whichisgiven byw(9)here, is the order of the differentiation and is constantrelatedtoinitialcondition.Laplacetransformisthe most commonly used tool to describe a fractional order system, which transforms from the time domain to the frequencydomain. order( )derivativeofasignal at isgivenby(x): Let assume and , the fractionalcalculusequationcanbeobtainedasfollows:

4.2 Fractional Order PID Control

Then by assuming initial conditions are zero, the transfer functionofthefractionalequationcanbeobtainedas In this paper, a Fractional order PID control system is proposedandintegratedintotheDCsuppressionloop.The proposedfractional order controller,fordccurrent suppressionloop,isshowninFig.6,where, istheerror signal, isthe transferfunctionof SOGI, isthe transferfunctionof controller. Gs(s) Gp(s) ig idc +e(t) + idcref =0

Fig 5: BlockDiagramofPI^λD^μController.

Fig 6:BlockDiagramofsimplifieddccurrentsuppression loop.ThetransferfunctionofaconventionalPIDcontrolleris showninequation(xx)withthreeparameters. TheFractional orderPIDcontrollerintroducestwomore adjustable parameters and than the conventional PID controller,asshowninfig.2.Thedifferentialequationofthe Fractional order the controller is given as the

Thefollowing:transferfunctionisgivenas: Where , ,and ,aretheproportional,integral,and derivativegain,respectively.Atthesametime, and are

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Fig. 10 and Fig. 11 shows DC current generated due to disparitiesofPowerTransistorsandDCcurrentgenerated duetotheunbalancedgridvoltage.Fig.10(c)andFig.11(c) The waveform of grid current with the proposed method. FFTanalysisresultofthegrid connectedcurrentisshownin

4.3

ThetuningprocessoftheFOPIDcontrollerisdoneusing theparticleswarmoptimization(PSO)method. Theblock diagraminFig.7representstheuseofthePSOalgorithmto design the proposed fractional order Controller. J represents an objective function to be minimized for dc current suppression loop controller to find the optimum fractional order , controller's parameters giving satisfactoryresponses.Jisformulatedasanintegraloftime multipliedabsoluteerror(ITAE)betweenreferenceanddc componentextractedfromgridcurrent.

In Loop (HIL) test that could offer the most complex model baseddesignforinteractingwiththereal timeplatform.RT LAB (OP4050) was used as the Real Time Simulator for powerstageemulation.Fig.8showstheexperimentalsetup, and the parameter specifications are given in Table I and TableII. Desk RT I/O Fig 8: ConfigurationoftheHILexperimentalplatform. Table 1: PHASELCL voltage 700V Gridvoltage 500 Fundamentalfrequency 220V Fundamentalfrequencyofthegrid 50 Parasiticresistanceof 1 ParasiticresistanceofL2 1 Inverterinductance 2 Filtercapacitance 2.2 Grid sideinductance 25

Symbol PARAMETER Values

The proposed PSO FOPID methods have been verified throughsimulationandExperiments.Thesimulationmodel is set up in the MATLAB/Simulink environment, and experimentalverificationisperformedusingaHardware

5. EXPERIMENTAL RESULTS

Numberofpopulations 50 MaximumNoofIteration 100 Weightcoefficient1 2 Weightcoefficient2 2 InertiaConstant 1

Todemonstratehowourproposedmethodsuppressesdc components, dc components of 3A in phase A, 1.5A in phase B,and 1.5Ainphase Careinjectedintothereference current.Atthetimepointt=0.2s,thedcsuppressionloopof thePSO FOPIDcontrollerstartstooperate.FromFig.9 b,it isclearthattheproposedmethodhasasmoothandsteady statesinusoidalgridcurrentwaveformafteronecycle. This shows the output DC component of current is almost reducedtozero,whichfullydemonstratestheeffectiveness oftheproposedmethod.

GCCS Symbol PARAMETER Values Input

Where istheabsolutevalueoftheerror(theerror between referenceanddccomponent extracted from grid current), isatime,and ,isthemaximumtime. Gs(s) Gp(s) ig idc +e(t) + idcref =0 PSO J

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Parameter Tuning of Fractional Order PID Controller

Control

LAB dSPACE RT LAB AnalogOP4050I/ODigital

Fig-7: PSO basedfractionalPIDcontrollerdesign

Table 2: PARAMETERSPECIFICATIONSOFPSO ALGORITHM

the two non integer orders of the integral and derivative constants,respectively.

PARAMETERSPECIFICATIONSOFTHREE

Fig.12, which shows the THD of the grid current is only 4.00% that meets the harmonic requirement of grid connectedinverters(THD<5%).

International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056

CaseI:DCCurrentDuetoDisparitiesofPowerTransistors (d)(b)(a)(c)

The comparison results of the proposed second order generalized integrator (SOGI), and sliding window double integralmethod(SWDIM)ofdccurrentdetectionisshownin Fig.13.At0.2s,adccurrentofstepsignalof3AinphaseAis addedinreferencecurrent.TheSWDIMmethodstakeabout 0.035stoestimatethedccurrent,whiletheproposedSOGI methodstakeonly0.025s,whichshowstheadvantageofthe quickdynamicresponseoftheproposedmethod. Fig.14showstheresultsof thecomparative simulation analysis of the DC compensation scheme of the proposed method with the virtual capacitor concept and BP PID approach.AsshowninFig.10(a),atthetimepointt=0.2s, thedccomponentof 3Aisinjectedinto phase A.Itcan be seenthatwiththevirtualcapacitorconcept[12]andtheBP PIDmethod [19],theDCcomponentinthe grid current is suppressedbelow0.5%oftheratedcurrentatt=0.286sand t=0.33s,respectively.However,withtheproposedmethod, theDCcomponentinthegridcurrentissuppressedtoless than 0.5% of the rated current at t= 0.243s (which only required 0.043s). Moreover, the overshoot for DC componentsuppressionwiththeproposedmethodismuch smallerthanthevirtualcapacitorandBP PIDmethod.The (b)(a)(c)

Journal | Page

(d) Fig 9: Thewaveformofgridcurrentwithandwithoutthe proposedmethod.(a)Thesteady statewaveformofgrid currentunderoriginalQPRcontrolstrategy.(b)The waveformofgridcurrentwithouttheproposedmethod. (c)Thewaveformofgridcurrentwiththeproposed method.(d)dccomponentextractedfromgridcurrent.

Fig 12: THDandharmonicspectrumoftheinverter outputcurrentwiththeProposedMethod. Fig-13: Comparisonofdccomponentdetectionmethods. Fig-14: ComparisonofDCcomponentsuppressionresults undertheconditionofinjecting3ADCcomponentintothe powergrid.

This paper presents an effective dc current compensation techniqueforathree phasegrid connectedtransformerless inverter. The SOGIs were employed for dc component extractionfromgridcurrentandmitigatedusingdccurrent suppression loop. An optimization technique based on

Fig 10: DCcurrentgeneratedduetodisparitiesofPower Transistors.(a)Thesteady statewaveformofgridcurrent underoriginalQPRcontrolstrategy.(b)Thewaveformof gridcurrentwithouttheproposedmethod.(c)The waveformofgridcurrentwiththeproposedmethod.

6 CONCLUSIONS

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Fig 11: DCcurrentgeneratedduetogridvoltage distortion.(a)Thesteady statewaveformofgridcurrent underoriginalQPRcontrolstrategy.(b)Thewaveformof gridcurrentwithouttheproposedmethod.(c)The waveformofgridcurrentwiththeproposedmethod.

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CaseII:DCcurrentduetotheunbalancedgridvoltage: (d)(b)(a)(c)

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Journal

[7] T.Shimizu,O.HashimotoandG.Kimura,"Anovelhigh performance utility interactive photovoltaic inverter system,"inIEEETransactionsonPowerElectronics,vol. 18, no. 2, pp. 704 711, March 2003, doi: 10.1109/TPEL.2003.809375.

[4] "IEEE Recommended Practice for Utility Interface of Photovoltaic(PV)Systems,"inIEEEStd929 2000,vol., no.,pp.i ,2000,doi:10.1109/IEEESTD.2000.91304.

[3] B.Long,M.Zhang,Y.Liao,L.HuangandK.T.Chong,"An Overview of DC Component Generation, Detection and SuppressionforGrid ConnectedConverterSystems,"in IEEE Access, vol. 7, pp. 110426 110438, 2019, doi: 10.1109/ACCESS.2019.2934175.

[5] W. M. Blewitt, D. J. Atkinson, J. Kelly, and R. A. Lakin, "Approach to low cost prevention of DC injection in transformerless grid connected inverters," IET Power Electron.,vol.3,no.1,pp.111 119,Jan.2010.

[14] M. Armstrong, D. J. Atkinson, C. M. Johnson, and T. D. Abeyasekera,"Auto CalibratingDCLinkCurrentSensing TechniqueforTransformerless,GridConnected,HBridge Inverter Systems," IEEE Transactions on Power Electronics, vol.21,no.5,pp.1385 1393,2006.

natural behaviors of schools of fish (PSO algorithms) is proposedfortuningparametersofFOPIDcontrollers,which has the advantage of robustness, and global convergence capability to achieve fast and high accuracy parameter estimation. The objective function was chosen as the absolute error between the actual and estimated values, whichisminimizedbysearchingfortheoptimalvalueusing thePSOalgorithm.Theproposeddcsuppressiontechnique enables robust suppression of dc injection into the utility gridunderawiderangeofdcuncertainties.Thefeasibility and effectiveness of the proposed scheme has been confirmedthroughsimulationandexperimentaltests.

[18] S. N. Vukosavić and L. S. Perić, "High Precision Active Suppression of DC Bias in AC Grids by Grid Connected Power Converters," in IEEE Transactions on Industrial Electronics, vol. 64, no. 1, pp. 857 865, Jan. 2017, doi: 10.1109/TIE.2016.2542126.

REFERENCES

[20] J. Jiang and X. Yuan, ‘‘Differential DC component suppression in three phase non isolated connected

[2] M. N. H. Khan, M. Forouzesh, Y. P. Siwakoti, L. Li, T. Kerekes and F. Blaabjerg, "Transformerless Inverter Topologies for Single Phase Photovoltaic Systems: A ComparativeReview,"inIEEEJournalofEmergingand Selected Topics in Power Electronics, vol. 8, no. 1, pp. 805 835, March 2020, doi: 10.1109/JESTPE.2019.2908672.

International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 09 Issue: 02 | Feb 2022 www.irjet.net p ISSN: 2395 0072 © 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified |

[19] L.Bo,L.Huang,Y.Dai,Y.Lu,andK.ToChong,"Mitigation of DC Components Using Adaptive BP PID Control in Transformless Three Phase Grid Connected Inverters," Energies,vol.11,no.8,2018.

[11] M. Armstrong, D. J. Atkinson, C. M. Johnson, and T. D. Abeyasekera,"Auto CalibratingDCLinkCurrentSensing TechniqueforTransformerless,GridConnected,HBridge Inverter Systems," IEEE Transactions on Power Electronics, vol.21,no.5,pp.1385 1393,2006.

[1] H.Xiao,"OverviewofTransformerlessPhotovoltaicGrid Connected Inverters," in IEEE Transactions on Power Electronics, vol. 36, no. 1, pp. 533 548, Jan. 2021, doi: 10.1109/TPEL.2020.3003721.

[16] B.Guoetal.,"Cost EffectiveDCCurrentSuppressionfor Single Phase Grid Connected PV Inverter," in IEEE Journal of Emerging and Selected Topics in Power Electronics,vol.9,no.2,pp.1808 1823,April2021,doi: 10.1109/JESTPE.2020.3029393.

[12] B. Long et al., "Design and implementation of a virtual connectedcapacitorbasedDCcurrentsuppressionmethodforgridinverters," ISA Transactions, vol.92,pp.257 272,2019.

Page982

[8] R. Sharma, "Removal of DC offset current from transformerless PV inverters connected to utility," presentedatthe40thInternationalUniversitiesPower EngineeringConference,Cork,Ireland,2005,technique for transformerless, grid connected, H bridge inverter systems,"IEEETrans.PowerElectron.,vol.21,no.5,pp. 1385 1393.

[10] L.BowtellandA.Ahfock,"Directcurrentoffsetcontroller for transformerless single phase photovoltaic grid connectedinverters," IET Renewable Power Generation, vol. 4, no. 5, pp. 428 437, 2010, doi: 10.1049/iet rpg.2009.0043.

[13] Q.N.Trinh,P.Wang,Y.TangandF.H.Choo,"Mitigationof DC and Harmonic Currents Generated by Voltage Measurement Errors and Grid Voltage Distortions in Transformerless Grid Connected Inverters," in IEEE Transactions on Energy Conversion, vol. 33, no. 2, pp. 801 813,June2018,doi:10.1109/TEC.2017.2763240.

[15] C.Lu,B.Zhou,J.LeiandJ.Shan,"MainsCurrentDistortion Suppression for Third Harmonic Injection Two Stage Matrix Converter," in IEEE Transactions on Power Electronics,vol.36,no.6,pp.7202 7211,June2021,doi: 10.1109/TPEL.2020.3039596.

[17] T. Mannen, I. Fukasawa and H. Fujita, "A New Control Methodof SuppressingDCCapacitorVoltageRipples Caused by Third Order Harmonic Compensation in Three PhaseActivePowerFilters,"inIEEETransactions onIndustryApplications,vol.54,no.6,pp.6149 6158, Nov. Dec.2018,doi:10.1109/TIA.2018.2849751.

[9] M.Chen,D.Xu,T.Zhang,K.Shi,G.HeandK.Rajashekara, "ANovel DCCurrentInjectionSuppressionMethod for Three Phase Grid Connected Inverter Without the Isolation Transformer," in IEEE Transactions on IndustrialElectronics,vol.65,no.11,pp.8656 8666,Nov. 2018,doi:10.1109/TIE.2018.2808916.

[6] R. Gonzalez, J. Lopez, P. Sanchis and L. Marroyo, "TransformerlessInverterforSingle PhasePhotovoltaic Systems,"inIEEETransactionsonPowerElectronics,vol. 22, no. 2, pp. 693 697, March 2007, doi: 10.1109/TPEL.2007.892120.

[21] J.Z.Shi,"AFractional Order General Type 2FuzzyPID ControllerDesignAlgorithm,"inIEEEAccess,vol.8,pp. 52151 52172, 2020, doi: 10.1109/ACCESS.2020.2980686.

inverter,’’ Power Capacitor Reactive Power Compensation,vol.39,no.1,pp.132 137,2018.

[22] F.Meng,S.Liu,A.PangandK.Liu,"FractionalOrderPID Parameter Tuning for Solar Collector System Based on FrequencyDomainAnalysis,"inIEEEAccess,vol.8,pp. 148980 148988, 2020, doi: 10.1109/ACCESS.2020.3016063.

[24] S. Seo and H. H. Choi, "Digital Implementation of Fractional Order PID Type Controller for Boost DC DC Converter," in IEEE Access, vol. 7, pp. 142652 142662, 2019,doi:10.1109/ACCESS.2019.2945065.

[25] F.Meng,S.LiuandK.Liu,"DesignofanOptimalFractional OrderPIDforConstantTensionControlSystem,"inIEEE Access, vol. 8, pp. 58933 58939, 2020, doi: 10.1109/ACCESS.2020.2983059.

[27] M.A.AkhtarandS.Saha,"AnAdaptiveFrequency Fixed Second OrderGeneralizedIntegrator QuadratureSignal Generator Using Fractional Order Conformal Mapping Based Approach," in IEEE Transactions on Power Electronics,vol.35,no.6,pp.5548 5552,June2020,doi: 10.1109/TPEL.2019.2951427.

Journal | Page983

[26] A.K.Mishra,S.R.Das,P.K.Ray,R.K.Mallick,A.Mohanty andD.K.Mishra,"PSO GWOOptimizedFractionalOrder PIDBasedHybridShuntActivePowerFilterforPower QualityImprovements,"inIEEEAccess,vol.8,pp.74497 74512,2020,doi:10.1109/ACCESS.2020.2988611.

[28] L. Jia and X. Zhao, "An Improved Particle Swarm Optimization(PSO)OptimizedIntegralSeparationPID anditsApplicationonCentralPositionControlSystem," inIEEESensorsJournal,vol.19,no.16,pp.7064 7071, 15Aug.15,2019,doi:10.1109/JSEN.2019.2912849.

[23] B.Hekimoğlu,"OptimalTuningofFractionalOrderPID ControllerforDCMotorSpeedControlviaChaoticAtom SearchOptimizationAlgorithm,"inIEEEAccess,vol.7,pp. 38100 38114, 2019, doi: 10.1109/ACCESS.2019.2905961.

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