International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.netp-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1382 A Review of Sliding Mode Control Of DC-DC ConvertersBetcy Mariam David1, Sreeja K.K.2 1 M.Tech Student, Applied Electronics and Instrumentation Engineering, LMCST, Kerala, India 2 Asst. Professor, Applied Electronics and Instrumentation Engineering , LMCST, Kerala, India ---------------------------------------------------------------------***---------------------------------------------------------------------Abstract - DCDC converter convert DC voltage signal from high level to low level signal or it can be vise versa dependingonthetypeofconverterusedinsystem.DC-DCconvertersarewidelyusedinavarietyof applications,rangingfromcomputertomedical electronicsystems,adaptersofconsumerelectronic devices,spacecraftpowersystemsand telecommunicationequipments.Thepaperdealswith theofperformanceofDC-DCbuckconverterusing SlidingModeControl(SMC).DC/DCconvertersare widelyusedinmanyindustrialandelectricalsystems. DC-DCconvertersshowedahighpotentialfor improvingthedynamicperformancebyapplying SlidingModeControl.Thisnonlinearcontrolschemeis especiallywellsuitedforVariableStructureSystem (VSS)likeDC-DCconverters.Themainadvantageof SMCovercommonlinearcontrolschemesisitshigh robustness against line, load and parameter variations. KeyWords:DCDCconverter,SlidingModeControl (SMC), Buck Power Converter 1. INTRODUCTION DC-DCconvertersarewidelyusedpowerelectronics componentsinindustrialarealikeswitchingmodepower supply(SMPS),personalcomputer,dcmotordrives,etc. The input of the dc-dc converters is unregulated dc voltage obtainedbytherectifyingline-voltageandaconverter convertsthisinputintoaregulateddcoutputvoltageata desiredlevel.Sincedc-dcconvertershavepowerdevices, effectof switchingandpassivecomponentslikeinductors andcapacitors,theyarenon-linearsystems[1],[2]. Therefore, control methods used to control the converters directlyaffecttheperformanceof theconverter.DCtoDC powerconverterscanbeusedassuitablecontrolled electronicstartersforanyDCmachineTherearemany typesofdc-dcconverterwhichisbuck(stepdown converter),boost(step-up)converter,andbuck-boost (stepup-step-down)convertor[3],[4].Theseconverters have received an increasing deal of interest in many areas. Thisisduetotheirwideapplicationslikepowersupplies forpersonalcomputers,officeequipment,appliance control,telecommunicationequipment,DCmotordrives, automotive, aircraft, etc. Differentcontrolalgorithmsareappliedtoregulatedc-dc converterstoachievearobustoutputvoltage.Asdc-dc convertersarenonlinearandtimevariantsystems,the applicationoflinearcontroltechniquesforthecontrolof theseconvertersarenotsuit-able.Inordertodesigna linearcontrolsystemusingclassicallinearcontrol techniques,thesmallsignalmodelisderivedby linearizationaroundapreciseoperatingpointfromthe statespaceaveragemodel[5].Thecontrollersbasedon thesetechniquesaresimpletoimplementhow-ever,itis difficulttoaccountthevariationofsystemparameters, becauseofthedependenceofsmallsignalmodel parametersontheconverteroperatingpoint[6]. Variationsofsystemparametersandlargesignal transientssuchasthoseproducedinthestartupor againstchangesintheload,cannotbedealtwiththese techniques.Multiloopcontroltechniques,suchascurrent modecontrol,havegreatlyimprovedthedynamic behavior,butthecontroldesignre-mainsdifficult especially for higher order converter topologies. Acontroltechniquesuitablefordc-dcconvertersmust copewiththeirintrinsicnonlinearityandwideinputvolt-age and load variations, ensuring stability in any operating conditionwhileprovidingfasttransientresponse.Since switchingconvertersconstituteacaseofvariable structuresystems, the sliding mode control technique can be a possible option to control this kind of circuits [7]. The slidingmodecontrolisanonlinearsystem,itisderived fromvariablestructuresystem.Itiswellknownfortheir stabilityandrobustnessagainstparameters,lineandload variation.Theflexibilityisthedesignchoice.Theuseof slidingmodecontrolenablestoimproveandeven overcomethedeficiencyofthecontrolmethodbasedon smallsignalmodels.Inparticular,slidingmodecontrol improvesthedynamicbehaviorofthesystem,and becomesveryusefulwhenthesystemisrequiredto operateinthepresenceofsignificantunknown disturbances and plant uncertainties [8].International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.netp-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1383 Inordertoobtainthedesiredresponse,theslidingmode techniquechangesthestructureofthecontrollerin responsetothechangingstateofthesystem.Thisis realizedbytheuseofahighspeedswitchingcontrol forcing the trajectory of the system to move to and stay in apredeterminedsurfacewhichiscalledslidingsurface. Theregimeofacontrolsystemintheslidingsurfaceis calledSlidingMode.Inslidingmodeasystemsresponse remainsinsensitivetoparametervariationsand disturbances[9].Unlikeotherrobustschemes,whichare computationallyintensivelinearmethods,analogue implementations or digital computation of sliding modeis simple.ImplementingofSMcontrollerisrelativelyeasy when compare with the other controllers. 2. DC - DC POWER CONVERTERS Dc-dcpowerconvertersareemployedinavarietyof applications,includingpowersuppliesforpersonal computers,officeequipment,spacecraftpowersystems, laptopcomputers,andtelecommunicationsequipment,as wellasdcmotordrives.Theinputtoadc-dcconverteris anunregulateddcvoltageVg.Theconverterproducesa regulatedoutputvoltageV,havingamagnitude(and possibly polarity) that differs from Vg. 2.1 Buck Converter Buck converter is a step down DC-DC converter. Due to its attractivefeatureslikecompactsizeandhighefficiency, theseconvertersarecommonlyusedinvariouscontrol applications [10]. Fig.1 shows basic Buck converter circuit. Fig -1: Basic Buck Converter Circuit Fig -2:The two circuit configurations of a buck converter: On-state and Off-state. Thebasicoperationof thebuckconverterhasthecurrent inan inductor controlledbytwoswitches(usuallya transistor anda diode).Intheidealizedconverter,allthe componentsareconsideredtobeperfect.Specifically,the switch and the diode have zero voltage drop when on and zerocurrentflowwhenoffandtheinductorhaszero series resistance. Further, it is assumed that the input and outputvoltagesdonotchangeoverthecourseofacycle (this would imply the output capacitance as being infinite). Fig -3:(a) Continuous conduction (b) Discontinuous conduction, operating modes of Buck converter Basedoninductorcurrentabuckconverteroperationcanbe categorizedintwomodes.Wheninductorcurrentneverfalls tozero,buckconverterissaidtobeoperatingincontinuous conductionmode(CCM).Ontheotherhandifinductor currentfallstozeroatsomeinstance,itiscalled discontinuousconductionmode(DCM).Theseareshownin Fig.3(a and b). 2.2 Boost Converter Boostconverterisastepupconverter.Theboost converter will produce an output voltage ranging from the same voltage as theinput, to a level much higherthanthe input i.e., it is a voltage elevator. Boost converters are used inbatterypowereddevices,wherethecircuitrequiresa higheroperatingvoltagethanthebatterycansupply,e.g. laptops, mobile phones, camera flashes & battery powered vehicles. The function of boost converter is like during ON time of switch inductance is charged with energy & during theOFF time of the switch this energy istransferred from theinductorthroughthediodetotheoutputcapacitor. Control of this type of converter is more difficult than buck converter,whereoutputvoltageissmallerthaninput voltage.Controlofboostconverterisdifficultduetotheir non minimum phase structure, since control input appears in voltage as well as current equations [11]. Fig -4: Boost Converter Circuit International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.netp-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1384 TheboostconverterisshowninFig.4.Whenthecontrol signal Q is 1, the circuit is shown in Fig. 5(a). The inductor LisbeingchargedbytheinputvoltageVg,andthe capacitorCisbeingdischargedthroughtheresistorR. WhenQis0,thecircuitisshowninFig.5(b).VgandL chargeC.Theoutput(load)voltageisvandibethe inductor current. Fig -5:(a). Boost converter when Q is ON Fig -5: (b). Boost converter when Q is OFF. Fig -6: Waveforms of source current (i) Inthiscase,theoutputvoltageishigherthantheinput voltage,ascontrastedwiththepreviouscaseofbuck converter(dc-dc).So,thisiscalledboostconverter(dc-dc),whenaself-commutateddeviceisusedasaswitch. Instead,ifthyristorisusedinitsplace,thisistermedas step-upchopper.Thevariation(range)oftheoutput voltage can be easily computed. 2.3 Buck-Boost Converter Buck-boostconvertersareatypicaltypeofpower conditioningdevicesduetoitssimplestructureand practicalfunctionalityofdroppingorliftingtheoutput voltagewithrespecttoaninputvoltage.Buck-boost converterprovides an output voltagewhich canbe higher orlowerthantheinputvoltage.Theoutputvoltage polarity is opposite to that of the input voltage. Buck-boost convertercanbeobtainedbythecascadeconnectionof thetwobasicconverterswhicharethestepdown converterandstepupconverter.Thesetwoconverters canbecombinedintothesinglebuck-inputprovides energy to the inductor and the diode is reverse biased. Fig -7: Buck-boost Converter Circuit Thebuck-boostconverterisshowninFig.7.Itconsistsof aninputvoltagesourceVg,atransistorswitchQ,adiode D,acapacitorC,aninductorLandaloadresistorR[12]. Theinductorcurrentisi.Theoutputvoltageacrossthe resistor is v. The absolute value ofv can be greater or less thanVg.visoppositetoVginpolarity.WhenQison,the circuitisshowninFig.8(a).ThevoltagesourceVg suppliesenergytotheinductorLandthecapacitorC suppliesenergytotheloadresistorR.WhenQisoff,the circuitisshowninFig.8(b).Theconnectionofthediode maybenoted,ascomparedwithitsconnectioninaboost converter. The inductor, L is connected in parallel after the switchandbeforethediode.Theloadisofthesametype as given earlier. A capacitor, C is connected in parallel with theload.Thepolarityoftheoutputvoltageisoppositeto that of input voltage here. Fig. 8: (a). Buck-boost converter when Q is ON International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.netp-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1385 Fig. 8: (b). Buck-boost converter when Q is OFF Fig. 9:Inductor current (i) waveform Thepathof thecurrentisthroughL,parallelcombination of load & C, and diode D, during the time interval, TOFF. The output voltage remains nearly constant, as the capacitor is connected across the load. 3. SLIDING MODE CONTROL Linearcontrollerscouldnotresolvethecontrolissuesin DC-DCconverters.Thereforenon-linearcontrollersare beinginvestigatedforefficientoperationofsuch converters.Slidingmodecontroller(SMC)isversatile controltechniquethatprovidesrobustnesstovariable structuresystems(VSS)underparametervariationsand externaldisturbances[13-17].Ascomparedtoother nonlinearcontrollers,SMCiseasiertoimplementand showshigherdegreeofdesignflexibility.Itsapproachis systematicandstabilityismaintained.Variationinsupply andloadwillcausethegrainstoswitchfromonepointto anotherbetweentwofixedvalues.SMCwilldrivethese variationsinnonlinearplantsstatetrajectoryonauser chosensurfacecalledswitchingsurface.Tocontrolthe converterFeedbackpathwillhavedifferentgainswhen planttrajectoryisbeloworabovesurface.Proper switching rule is then defined by the surface (called sliding surface). Once the process is started, switched control will maintaintheplantsstatetrajectoryontheslidingsurface forallsubsequenttimeintervals.Stability,regulationand tracking etc are achieved for variable structure systems by properlydesignedslidingsurface.SMCrequiresthe knowledgeofparametervariationrangeforitsdesign insteadofaccuratemathematicalmodels.Irrespectiveof the order of system to be controlled, SMC will be designed tohavefirst-orderresponse.Properslidingsurface selectionwillensurethateventheworst-casedynamics wouldbehandled.Mattavelliet.al,proposedageneral slidingmodecontrollerforalltypesofDC/DCconverters [18]. Fig.10: Block Diagram of Sliding Mode Control The basic principle behind the SMC controlled system is to drive the converter to the steady surface called the sliding surface and maintain the stability of the system thus giving the regulatedoutput voltage for any variations in the load or switching frequency [19]. 4. CONCLUSION AreviewofslidingmodecontrolofDC-DCconverterhas beenpresented.SMCprovidesseveraladvantagesover other control methods: Robustness, stability foreven very large line and load variations, good dynamic response and simpleimplementation.ThestudyshowsthatBuck convertersaremostwidelyuseddcdcconvertersinthe worldbecausenoothertopologyisassimple.Their applications range from low-power regulators to very high power step-down converters, which are characterized by a lownumberofcomponents,lowcontrolcomplexity,and no insulation. REFERENCES [1]D.M.M.S.Prabha,S.P.Kumar,andG.G.Devadhas, "An optimum setting of controller for a dc-dc converter usingbacterialintelligencetechnique,"inProc.PES InnovativeSmartGridTechnologiesConf.,2011,pp. 204-210.[2] M.Namnabat,M.B.Poudeh,andS.Eshtehardiha, "Comparisonthecontrolmethodsinimprovementthe performanceoftheDC-DCconverter,"inProc.Power Electronics Conf., 2007, pp. 246-251 [3]R.W.Erickson,FundamentalsofPowerElectronics, New York: Chapman and Hall, 1997. 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[13] VUtkin,JGuldner,JXShi.SlidingModeControlin ElectromechanicalSystemsLondonUK.Taylorand Francis 1999 [14] V Utkin. Sliding Modes in Control Optimization, Berlin: Springer-Verlag 1992 [15] CEdwards,SKSpurgeron.SlidingModeControl: TheoryandApplicationsLondon,U.K.:Taylorand Francis. 1998. [16] WPerruquetti,JPBarbot.SlidingModeControlin Engineering. New York, NY: Marcel Dekker 2002. [17] JJESlotine,WLi,SlidingControl,Ch.7,Applied NonlinearControl.EnglewoodCliffs,N.J.:Prentice- Hall, Inc. 1991 [18] MattavelliP,RossettoL,SpiazziG,TentiP,General-PurposeSlidingModeControllerforDC/DCConverter Applications,24thIEEEPowerElectronicsSpecialist ConferenceSeattle,WA,pp.609-615,20-24April 1993 [19] CEdwards,SKSpurgeron.SlidingModeControl: TheoryandApplicationsLondon,U.K.:Taylorand Francis. 1998 BIOGRAPHIES BetcyMariamDavid receivedB.Techdegreein AppliedElectronicsand Instrumentationfrom MahatmaGandhiUniversity,atMarBaseliosChristian CollegeofEngineeringand Technology-Peermadein 2012 . Currently she is doing herM.Techdegreeunder Keralauniversity,Keralain LourdesMathaCollegeOf ScienceAndTechnology-Thiruvananthapuram. SreejaK.KreceivedM.Tech DegreeinApplied Electronics& Instrumentation from Kerala University,Keralaand B.TechDegreein Instrumentation&Control EngineeringfromCalicut University,Keralaand Currently,isanAssistant ProfessorintheDepartment ofElectronics& CommunicationEngineering at the Lourdes matha College ofscience&Technology, Kerala University.