Seite - 314 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 10 ȱ (a)ȱ (b) Figure7.Equivalentcircuitsofq-Zsource inshoot-throughstate (a) andnon-shoot-throughstate (b). Theoperatingmodeof theq-Zsource iscontrolledbythecascadeHBridge.WhentheHBridge works in the traditionalphaseshiftingstate,novoltageboostingphenomenonhappens,butwhenthe systemchargingpowerneeds tobe increased,makingeitherof thebridgearmstobeshoot-through, thevoltageboostingphenomenonhappens. Theoutputof theq-Zsource is shortedbytheHBridge in theshoot-throughstate,andL2 is chargedbyC2,L1 is chargedbyC1 andVS,whereas theHBridge becomesanequivalentcurrentsource in thenon-shoot-throughstateasshowninFigure7b,C2 and L2 providetheoutputvoltage together,C1,L1 andVSprovidetheoutputvoltage together. Thisalso explainswhythewithstandvoltageacrossC1 reduces. Bycontrolling theratiobetweenshoot-through timeandnon-shoot-throughtime, theoutputvoltageof theq-Zsourcecanbeadjusted. FromFigure7a, wehave: VS`VC1 “VL1, VC2 “VL2 (11) Similarly, fromFigure7b,wehave: VS`VL1`VC1 “VO, VS`VL1 “VC2, VC1 “VL2, VC1`VC2 “VO (12) Normally,L1 equalsL2, andthecurrentsflowingthroughthemare thesame, thusonehas: VL1 “VL2 (13) Since thevolt-secondsof the inductorshouldbe identical in thesteadystate,wecanget: pVC1`VSq¨TS “pVO´VC1´VSq¨TN (14) TS represents theshoot-throughtimeandTN represents thenon-shoot-throughtime, thesumof those is thewholecycle timeT.ThensubstitutingEquations (11)–(13) intoEquation(14),wehave: VO “ TTN´TS ¨VS “ 1 1´2D ¨VS “BF ¨VS (15) D=TS/T is thedutycycle,BF is theboost factorproducedbytheshoot-throughstate,andit is alwaysgreater thanorequal to1.Additionally,wecanalsoobtain thevoltagesacross thecapacitorC1 andC2: VC1 “ VO´VS2 “ TS TN´TS ¨VS “ D 1´2D ¨VS (16) VC2 “ VO`VS2 “ TN TN´TS ¨VS “ 1´D 1´2D ¨VS (17) 314