Seite - 226 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 410 3. Steady-StateAnalysis 3.1.VoltageConversionRatio Inchargestate,VH is the inputandVL is theoutput.AccordingtoEquations (1)–(5)andbasedon thevoltage-secondbalanceprinciple inL1 andL2, thevoltageconversionratioMd inchargestatecan bederivedas: Md “ VLVH “ Dd 4 (11) InEquation(11),Dd is thedutycycleof theactiveswitchesQ1 andQ2.Ascanbeseen, thevoltage conversion ratio in charge state is one-fourthof thatof the conventionalbuckconverter. Similarly, indischargestate,VL is the inputandVH is theoutput.AccordingtoEquations (6)–(10)andbasedon thevoltage-secondbalanceprinciple inL1 andL2, thevoltageconversionratioMb indischargestate canbederivedas: Mb “ VHVL “ 4 1´Db (12) whereDb is thedutycycleof theactiveswitchesQ3 andQ4.Ascanbeseen, thevoltageconversion ratio indischargestate is four timesof thatof theconventionalboostconverter. Figure 11 shows that the studiedBDCdemands a smaller duty cycle for the active switches toproduce the samevoltage conversion ratio, or canproduceahighervoltage conversion ratio at the sameduty cyclewhen comparedwith the traditional BDC [18] and thepreviousBDC in [22]. Furthermore, thevoltageconversionratioof studiedBDCishigher than thatof theBDCproposed in[23],underareasonablerangeof25%~75%dutycycles. Figure 11. Comparisonof voltage conversion ratiosproducedby the studiedBDC, the converters introducedin[18,22,23]. 3.2.VoltageStressof theSwitches Whenever theULCworks as abackor front-end stage, theopen circuit voltage stress on the switchesS1~S4 ofULCisequal to the low-side inputvoltageVL, as follows: VS1,max “VS2,max “VS3,max “VS4,max “VL (13) Theparticular inherent featureof theULCbenefits the lowconduction lossescanbeachievedby adoptingthe low-voltageMOSFETs. As to thehigh-sidestageof thestudiedBDC,basedontheaforementionedoperationanalyzes in Section2, theopencircuitvoltagestressofswitchesQ1~Q4 canbeobtaineddirectlyas: 226