Seite - 258 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 616 andflexible,whichmightreduce theswitchingfrequenciesof inverterdevices. Thetotal switching frequencyofdevices increasedafter shifting fromthe lowswitching frequencymethodto thehigh powerdifferencemethodat0.4s; the total switchingfrequency increasedevenmoreafterswitching themajorpowersource frompowersource1 topowersource2,a lowervoltagepowersource,at0.5s, which indicatedthatsettingahighervoltagepowersourceas themajorpowersourcecouldreducethe switchingfrequenciesofdevices. Inaddition, the total switchingfrequencyofdevices insteadystate was lower thanthat in transientstateanditwashigherwhenthemotorspeedwasdecreasingthan whenmotorspeedwas increasing.Under theproposedcontrolmethod, total switchingfrequency is far lowerthaninthecontrastingmodel,especially intheperiodofstarandtrianglemode. InFigure9b, the switching lossof inverterswasproportional to the total switching frequencyofdevicesand in mostcircumstances theshareofswitching lossesof inverterswasunder30%,whichwas ideal. Inputpowercurvesofboth invertersareshowninFigure10. Itwasevident thatbefore0.5s,powersource1wasthemajorpowersource; in thisperiod, star modeand trianglemodewereall poweredbypower source 1andall inputpowerwasgenerated byinverter1;after0.5s,powersource2wasthemajorpowersource. In thisperiod, starmodeand trianglemodeweresuppliedbypowersource2andall inputpowerwasgeneratedbyinverter2.When in independentmode, bothpower sourcesprovidedpower. After shifting fromthe lowswitching frequencymethodto thehighpowerdifferencemethodat0.4 s, thepowerdifferencebetweentwo inverters increased;afterswitchingthemajorpowersource frompowersource1 topowersource2 at0.5s, inverter2’spowerwashigher thaninverter1’s,becomingthemajorpoweroutput inverter; nevertheless,becauseof thevoltageofpowersource2being lower thanthatofpowersource1,after switching themajorpower source topower source 2, thepowerdifferencebetween two inverters decreased,which indicated that thepowerdifference of the inverterswas affectedby thevoltage differenceof thepowersources. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 time (s) -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 10 4 input power of inverter 1 input power of inverter 2 total input power Figure10.Curvesof inputpowerofboth inverters. AnefficiencyMAPof thedrivesystemwithswitchedwindingmodesandmulti-level current hysteresis modulation is shown in Figure 11a; that of the contrasting drive system is shown in Figure11b. 258