Seite - 217 - in Emerging Technologies for Electric and Hybrid Vehicles

energies Article DevelopmentofaNovelBidirectionalDC/DC ConverterTopologywithHighVoltageConversion RatioforElectricVehiclesandDC-Microgrids Ching-MingLai DepartmentofVehicleEngineering,NationalTaipeiUniversityofTechnology,1,Sec. 3,Chung-HsiaoE.Rd., Taipei106,Taiwan;pecmlai@gmail.com;Tel.:+886-2-2771-2171 (ext. 3612);Fax:+886-2-2731-4990 AcademicEditor:NevilleWatson Received: 3February2016;Accepted: 19May2016;Published: 26May2016 Abstract:Themainobjectiveof thispaperwas tostudyabidirectionaldirect current todirect current converter (BDC) topologywith ahighvoltage conversion ratio for electric vehicle (EV)batteries connectedtoadc-microgridsystem. Inthisstudy,anunregulatedlevelconverter (ULC)cascaded witha two-phase interleavedbuck-boostcharge-pumpconverter (IBCPC) is introducedtoachieve a high conversion ratiowith a simpler control circuit. In discharge state, the topology acts as a two-stagevoltage-doublerboostconverter toachievehighstep-upconversionratio (48Vto385V). Inchargestate, theconverteractsas twocascadedvoltage-dividerbuckconverters toachievehigh voltagestep-downconversionratio (385Vto48V).Thefeatures,operationprinciples, steady-state analysis, simulation andexperimental results aremade toverify theperformanceof the studied novel BDC. Finally, a 500Wratingprototype system is constructed for verifying the validity of theoperationprinciple. Experimental resultsshowthathighestefficienciesof96%and95%canbe achieved, respectively, inchargeanddischargestates. Keywords: bidirectionaldc/dcconverter (BDC); electricvehicle (EV);dc-microgrid;highvoltage conversionratio 1. Introduction In recent years, to reduce fossil energy consumption, the development of environmentally friendlydc-microgrid technologieshavegradually receivedattention [1–7]. As shown inFigure1, a typicaldc-microgrid structure includesa lotofpowerelectronics interfaces suchasbidirectional grid-connectedconverters (GCCs),PV/winddistributedgenerations (DGs),batteryenergysystems (BES), electricvehicles (EVs), andsoon[4]. Theyconnect togetherwithahigh-voltagedc-bus, so that dchomeappliancescandrawpowerdirectly fromthedc-bus. In this system, themain functionof GCCsis tomaintainthedc-busvoltageconstant,while inordertoensurethereliabilityofoperationfor dc-microgrids,amassofBEScanusuallybeaccessed into thesystem.Electricvehicles (EVs)canalso provideauxiliarypowerservices fordc-microgrids,whichmakescleanandefficientbattery-powered conveyance possible by allowing EVs to power and be powered by the electric utility. Usually, indc-microgrid systems,when thevoltagedifferencebetween theEVbattery, BESand thedc-bus is large, a bidirectionaldc/dc converter (BDC)withahighvoltage conversion ratio for bothbuck andboost operations is required [4,7]. In the previous literatures, BDCs circuit topologies of the isolated[8–10]andnon-isolatedtype[11–23]havebeendescribedforavarietyofsystemapplications. IsolatedBDCsusethetransformertoimplementthegalvanic isolationandtocomplywiththedifferent standards. Personnel safety,noisereductionandcorrectoperationofprotectionsystemsare themain reasonsbehindgalvanic isolation. Incontrastwith isolatedBDCs,non-isolatedBDCs lack thegalvanic isolationbetweentwosides,however, theyoffer thebenefitsofsmallervolume,highreliability, etc., so theyhavebeenwidelyusedforhybridpowersystem[24,25]. Energies 2016,9, 410;doi:10.3390/en9060410 www.mdpi.com/journal/energies217