International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1321 Modular Multilevel DC-DC Converters In Hybrid Electric Vehicle Jyothi.V1, Anitha.P2 1 Student, Electrical and Electronics, Adi Shankara Institute of Engg. And Technology, Kerala, India, 2Assistant Professor, Electrical and Electronics, Adi Shankara Institute of Engg. And technology, Kerala, India, ---------------------------------------------------------------------***---------------------------------------------------------------------Abstract: By having an eye on present scenario of our earth,ithasbeenseenthatglobalwarminghasbeen increasingdangerouslyanditaffectsourenvironment inhazardousways.Themajorreasonforthesameis duetotheblinddependencyonnon-renewableenergy sources.Hybridelectricvehicleareoneofthemost practicalusablesystemwhichwillreducethe dependencyondieselandpetrol,whicharemajornon renewableresources.Soherewearegoingtodiscuss thebestconvertersuitableforHEVandconduct experiment of the same. KeyWords:DC-DCConverter,modularmultilevel converter(MMDC),highpowerapplications,hybrid electric vehicle (HEV). 1. INTRODUCTION. Theusageofvehiclesisincreasingdaybyday.Asthe vehiclesarefedbyfossilfuelssuchaspetrolanddiesel whichcauseairpollutionleadingtoglobalwarmingand relatedissues.Moreoverfossilfuelsarenolongera reliablesourceofenergyastheyarefastlyexhausting.So herecomestheroleofhybridelectricvehicleswhichuse lessamountoffuelconsumptioncomparedto conventional vehicles [16][17]. HybridelectricvehicleconsistofaconventionalIC engine and an electric motor part. For the electric part we make use of a converter, electric motor and a battery. Both theICengineandelectricmotorcanbeusedalternatively andhenceitcanreducethedependencyonfuel.Electric motorcanbechargedfromandelectricsupply. Dependencyonelectricitywhichisproducedfrom renewableresourcesaremuchadvantageousthannon renewableenergysources.Thisshowstheimportanceof HEV.So the main advantage of hybrid electric vehicle is that it reducesthedependencyonfuelandenvironmentimpact. Simpleblockdiagramofhybridelectricvehicleisgiven below. Fig 1: Block diagram of hybrid electric vehicle. 2.DC DC CONVERTERS. Thedc-dcconverterinhybridvehicleisusedto interfacetheelementsinelectricvehiclebtboostingor chopping the voltage levels. For the better efficiency if the systemthepowerconvertershouldbereliable,light weight,smallvolume.Andthenonlytheelectricvehicle can achieve high performance. Theimportanceofusingdc-dcconvertersinhybrid electric vehicles can be describes as given below: Atleastonedc/dcconverterisnecessaryto interface the system. A bidirectional dc/dc converter is needed to make use of regenerative breaking. Thepowerflowcanbecontrolledbyvaryingthe duty ratio of the converter. Soassaidbeforeweshouldhaveaconverterwith propertiessuchaslightweight,highefficiency,small volume, low electromagnetic interface, low ripple current, better power flow control etc. 3. PROPOSED SYSTEM. Inliteraturevariousconverterssuchasbuck,boost, buck-boostconverters,interleavedconvertersetcare proposedforlowpowerapplications.Inthispaperanew topologyisproposedwhichcanbeusedinhighpower applications such as hybrid electric vehicles, hvdc systems etc. International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1322 Chart-1:Graphwhichshowstheresearchestakingplace in conventional converter and MMDC on the basis of year Sothispaperpresentsanewtopologynamedmodular multilevelDC-DC(MMDC)convertersthatcanbeusedin highpowerapplications.Andfromtheliteraturesurveyit wasidentifiedtatmoreresearcheshavebeendoneinthe field of modular multilevel DC-DC converters compared to otherconventionalconverters.Chart-1showsthe comparative study of the researches carried out in field of conventional converters and MMDC. The main feature of converter that can be used in electric vehicleisthepropertyofbidirectionalconversionsothat itcanmakeuseoftheregenerativebraking.Someofthe otherfeaturesthatareabsentintheconventional convertersareMMDCis(i)Modularinnature. (ii)Transformer-less operation. (iii) Redundancy. (iv)Fault tolerantoperation.(v)Faultbypassingcapacity.(vi)Easy switchingscheme.Andalsointheproposedsystemitis possibletotransferpowerfromhighvoltagebatteryto lowvoltagebatteryandviceversa, thedirectionof power flow depends upon the voltages at the both end.

Fig -1:Five Level Modular Multilevel Dc-Dc Converter. Thenewconvertertopologyismodularinnature.A moduleconsistsof2mosfetsand1capacitor.IfNisthe numberoflevelsthatistobeobtainedthennumberof modules is equal to (N-1).The main advantageof this new topologyisthatregardlessofthenumberoflevelsonly2 operatingstatesisneeded.Mosfets(SR1-SR7)operate togetherandMosfets(SB1-SB6)operatesimultaneously. Astheswitchingissimple,theoperationwillbespeedy. Fromthesteadystateanalysisitwasobtainedthatthe valuesofeachcapacitorsusedineachmodulesaresame in value. Toobtaintheswitchingscheme,itisinitiallyassumed thattheconverterwillperformitsoperationin5 operationsor5subintervalswhichisbasedonthe chargingofcapacitors.InfirstsubintervalC5ischarged fromthebatterysourceanddischargesthroughoutput circuit.InsecondsubintervalC5transferitschargetoC4 throughtheoutputcircuit.InthethirdsubintervalC4 released its charge to C3 through output circuit and at the sametimeC5getschargesthroughinputcircuit.Inthe fourth subinterval in addition to C3 transfers charge to C2 throughoutputcircuit,secondsubintervaloperationalso takesplace.Infifthsubinterval,3operationstakeplaceie C5isagainchargedfromtheinputcircuit,C4transfersits energytoC3andalsoC2transfersitsenergytooutput circuit.Thelasttwosubintervalsarerepeatedagainand againandthetwooperationsandtakenasstate1and state2operations.Lasttwooperationsarethesteady stateoperationsandtherestareconsideredasthe initialization step. Sotheswitchingschemeforthisoperationcanbe obtained easily. The operation of SR1-SR7 is considered as thestate1operationandtheoperationofSB1-SB6is consideredasthestate2operation.Thisismuchmore simplex than the conventional converters. Fault by passing capacityisverygoodasitiseasilypossibletoeliminate thefaultedmodule.Andalsoitcanincreaseitsnumberof levelsbyjustincreasingitsnumberofblocks.Duetoso manyadvantagesitisverymuchadvantageoustousein high power applications. 3. MODELLING OF HYBRID ELECTRIC VEHICLE. AtypicalHEVconsistofanICengine,apowersplitter, synchronousgenerator,synchronousmotor,rechargeable battery and a power management system. TheICengineisdirectlyconnectedtothecarrierofthe planetarygearwhichsplitsthemechanicalpowertothe generator.Thepowermanagementsystemisthebrainof hybridelectricvehiclewhichcontrolstheHEVworkingin differentmodes.Itisalsousedtocontrolmotorspeedor International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1323 torque. The battery provides the power at lower speeds or assiststheengineduringsuddenacceleration.Italsoacts asgeneratingmodeduringdecelerationwhichrecovers the kinetic energy as electrical energy. 3.1 Synchronous Motor/Generator. Even through various modes of generators are available, all of them take the detailed physics into account. Here the mostimportantapplicationforgeneratoristhatthe outputfrequencyisdeterminedbyinputshaftspeedand amplitude of output can be controlled. Fig -2:Synchronous Generator Modeling System. 3.2 Power Management System. Theentirecontrolalgorithmforthehybridelectric vehicle is controlled by power management system. Speed control,Torquecontrol,Batterychargecontrol,Over-currentprotection,Under-voltageprotectionaresomeof the main functions of the power management systems. Thespeedcontrolandbatterychargecontrolofthe system can be shown as: Enginespeedcontrollerisusedforthedemandsbelow the idle speed of 800 rpm the speed demand is set to zero. ThelimiterinthebatterychargerisusedbecauseIfthe batteryhasmorethanrequiredamperehour,thenno generationisrequired.Linearlyramptousing20%of engine torque for charging between the ranges needed Fig -3:Speed Controlling System The battery control for the system is given by: Fig -4:Battery Control System. Thecontrolsystemofthedrivecalculatesfromtheflux andtorquereferencesgivenbythedrive'sspeedcontrol thecorrespondingcurrentcomponentreferences. Typically proportional-integral (PI) controllers are used to keep the measured currentcomponents at their reference values. International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1324 Fig -5 :Vector Flux Control. 4. SIMULATION RESULT. After simulation of the MMDC converter alone, it is then simulated with hybrid electric vehicle with various control suchasspeedcontrol,torquecontrol,vectorcontrol,and alsothemainimportantparti.e.thepowermanagement system.Theconvertersideandthevehiclesideare interfaced with the help of converter which converters the dc output from MMDC to an AC input to the vehicle side. Fig -6 :Five level MMDC with HEV From the experiment done the obtained result was as given below. Fig -7: Output Waveforms. Current,RotorSpeed,ElectromagneticTorque,Dcbus Voltage,Fluxofthevehicleisareplottedandthegraphs shows the proper working of the system. 5. CONCLUSION. The proposed new topology is modular in nature. As it ismodularthefaultbypassingcapacityisgood.Ifany faultwasidentifiedinthesystemthatmodulecanbe easilyremovedorbypassedsothatothermodulescan workproperly.Duetothesamevaluedcapacitorsused inMMDC,thevoltagestressacrosstheswitchesis reducedandhencetheripplevoltageandcurrentwill getreduced.Sowecanconcludethattheconverteris modular,havehighfrequencyoperation,bidirectional powermanagement,faultbypassingandduetothe absenceofinductorincircuittheharmonicswillbe less.hustheconvertercanbeusedinvarious applicationstoestablishbidirectionalpower management such as in hybrid electric vehicles. International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1325 6.REFERENCES [1]Ying-ChunChuang,High-efficiencyZCSbuck converter for rechargeable batteries, IEEE Trans. Ind.Electron, Vol. 57, No. 7, pp. 2463-2472, July 2010. 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Mechatronics, vol. 4, no. 3, pp. 246257, 1999. [14] X. He and J. W. Hodgeson, B Modeling and simulation forhybridelectricvehicles,I.Modeling,IEEETrans. Intelligent Transportation Syst., vol. 3, no. 4, pp. 235243. BIOGRAPHIES Jyothi.VwasborninKerala, Indiain1991.Shereceivedher B.TechinElectricaland ElectronicsEngineeringin2013 fromNSScollegeofEngineering, Palakkad, Kerala.. She is currently pursuing Master of Technology in PowerElectronicsandPower SystemfromAdiShankara InstituteofEngineeringand Technology,Cochin.Hercurrent researchinterestsincludePower ElectronicsandRenewable energy systems. Anitha P was born in Kerala in1969.ShegraduatedfromMA collegeofengineeringin Electrical&Electronics Engineeringintheyear1991.She tookherMTechinIndustrial drives&controlfromRajagiri SchoolofEngineering& TechnologyunderMGuniversity SheisworkingasAsst.Professor inthedepartmentofElectrical& ElectronicsEngineringatAdi Shankara Institute of Engineering & Technology Kalady from 2001. Photo