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Energies 2017,10, 616
3.2. CurrentModulationMethod in IndependentMode
Different from star and trianglemodes, independentmode is powered by two sources and
controlledbytwoinverters,whichmeanseachwindingâselectricpotential is controlledbybothof the
twoinvertersâbridgesandhas fourstatuses: (10), (01), (11), and(00).
The ïŹrst number of switching status stands for the electric potential of inverter 1âs bridge.
Thesecondnumberofswitchingstatusstandsfortheelectricpotentialof inverter2âsbridge. Thestatus
of the inverter bridge upper arm (on) and lower arm (off) obtained high potential, which was
substitutedwith number â1â. The status of the inverter bridge upper arm (off) and lower arm
(on)obtainedlowpotential,whichwassubstitutedwithnumberâ0â. Because the twosourceswere
insulated, themid-point voltage difference of the two sources unm variedwith different inverter
switching statuses, which brought about diverse phase voltages in different switching statuses,
especiallywhenVdc1 =Vdc2.Whenthemid-pointvoltageof the twosourceswasunm=0, thephase
voltagewasthemid-pointphasevoltage.Whentheswitchingstatuseswere (10), (01), (11), and(00),
thecorrespondingmid-pointphasevoltageswere (Vdc1+Vdc2)/2,â(Vdc1+Vdc2)/2, (Vdc1âVdc2)/2,
andâ(Vdc1âVdc2)/2. Hence, whenVdc1 = Vdc2, we could get fourmid-point voltages via dual
invertersâ control. WhenVdc1 = Vdc2, we could get threemid-point voltages and themid-point
voltageswithswitchingstatuses (11)and(00)werebothzero.
Thetraditionalhysteresiscurrentmodulationalgorithmhas twopotentialsandcorresponding
twotriggerareas:Îiâ„ handÎiâ€âh.WhenVdc1 =Vdc2, thereare fourpotentials in independent
modeof thehysteresis currentmodulationalgorithm.Apart fromtwotriggerareasusedforactivating
switchingstatuses (01)and(10), twointermediate trigger lineswereneededforactivatingswitching
statuses (00) and (11)âtwo intermediate potentials. Provided the two intermediate trigger lines
wereÎi= dandÎi=âd,withdas the linear currentdeviationof the intermediate line,wecould
getEquation (23) basedon theprinciple thatmid-pointvoltage isproportional to current errorÎi
whentriggered:
h : Vdc1+Vdc2
2 = d : Vdc1âVdc2
2 . (23)
Equation(23)couldbe transformedto:
d= Vdc1âVdc2
Vdc1+Vdc2 h. (24)
Itwasobvious thatwhenVdc1>Vdc2,d> 0;whenVdc1<Vdc2,d< 0;whenVdc1=Vdc2,d= 0,
andat this time, two intermediate trigger linescoincidedatÎi= 0. Ithas tobepointedout that in
eachwindingâs fourpotentials in independentmode, twoboundarypotentials are triggeredbyÎi
being in thecorrespondingarea toensure thatÎi candepart fromthat triggeredareaswiftly in the
relativelygreaterphasevoltagegeneratedbyboundarypotentialsas longasÎi is in thecorresponding
areaandrestrictedtohysteresisband [âh,h]. Twointermediatepotentialswere triggeredbycrossing
thecorrespondingintermediate trigger lineswithoutconsideringthecrossingdirection; thiscontrol
logicmainlymatteredinslowingïŹuctuationsofÎidowntoloadsmallervoltage.Arathersmallphase
voltagewouldbe loadedifÎi is close to thecenter line (Îi=0) toavoiddrasticïŹuctuations frequently
hitting thehysteresis boundary if constantly loadedwith largephasevoltage. Whenappliedwith
thismodulationmethod, the changing ratewoulddecreaseafterÎi crosses the control lineÎi= d
orÎi=âduntil ithits theboundaryagain. Twoadditionalpotentialswouldeffectively retard the
ïŹuctuationspeedofÎi tomakecurrentchangesmilderandreduce the invertersâ switchingfrequency.
Twoimprovedmulti-levelhysteresismodulationmethodswereproposedonthefoundationof
theabovemulti-levelhysteresiscurrentmodulationstrategy. Theywere the lowswitchingfrequency
methodandhighpowerdifferencemethod. These twomethodswereachievedbyaddingthe trigger
conditionsof inverterbridgesâ switchingstatuses (00)and(11) in independentmode.
Due to independentmode being powered by two sources, power distribution between two
sourceswas involved. Thus,amajorpowersourcewasproposedandwasexpectedtohavegreater
252
Emerging Technologies for Electric and Hybrid Vehicles
- Title
- Emerging Technologies for Electric and Hybrid Vehicles
- Editor
- MDPI
- Location
- Basel
- Date
- 2017
- Language
- English
- License
- CC BY-NC-ND 4.0
- ISBN
- 978-3-03897-191-7
- Size
- 17.0 x 24.4 cm
- Pages
- 376
- Keywords
- electric vehicle, plug-in hybrid electric vehicle (PHEV), energy sources, energy management strategy, energy-storage system, charging technologies, control algorithms, battery, operating scenario, wireless power transfer (WPT)
- Category
- Technik