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Energies 2017,10, 616
3.1. CurrentModulationMethod inStarandTriangleModes
Starmoderequiredendsof three-phasestatorwindingsconnectedtoonepoint,whichcouldbe
accomplishedbymakingall lowerarmsof the idle inverterâsbridges turnedonat thesametimein
dual invertersconïŹgurationwhile theother inverterwasworkingtocontrol the three-phasecurrent.
BasedonexpectedtorqueTâe ,wecouldgetcontrolvariables iâd and i â
q throughtheabovementioned
MTPAandïŹux-weakeningstrategy. Then,withdq0toABCcoordinationtransformation,expected
phase currents iâA, i â
B and i â
C were obtained;meanwhile, actual phase currents iA, iB, and iC were
acquiredvia thecurrent sensor. Phasecurrenterror representedthedifferencebetweeneachphase
expectedcurrentandtheactualcurrent,which isdemonstratedbyfollowingformula:
ÎiA= iAâ iâA,ÎiB= iBâ iâB,ÎiC= iCâ iâC. (20)
Fromeachphasecurrentâserror,wecouldcontrol the three-phasecurrent.Giventhehalf-width
of thecurrentâshysteresisband, theacceptablecurrenterror ish.WhenonephasecurrenterrorÎiâ„ h,
theupperarmof thisphaseâs inverterbridgewasturnedoffandthe lowerarmwasturnedon,making
themidpointvoltageof thisphaseâVdc/2, a lowervoltage, and thephase current errorÎiof this
phasedecreasing.WhenphasecurrenterrorÎiâ€âh, theupperarmof thisphaseâs inverterbridge
wasturnedonandthe lowerarmwasturnedoff,makingthemidpointvoltageof thisphaseVdc/2,
a lowervoltage,andthephasecurrenterrorÎiof thisphase increasing.
Trianglemode requires theheads and tails of three-phase statorwindings tobe connected in
a circle, which is completed by shutting downone power source and turning on triangle circuit
switch. Theother sideâs inverterwasworking to control themotorâs current. Whatwasdifferent
fromstarmodewasthat trianglemode, insteadofcontrolling themotorâsphasecurrent iA, iB, and
iC directly, controlledmotorâs line current i1, i2, and i3 to controlmotorâs phase current indirectly.
The relationshipof trianglemodeâsphase current and line current is shown inEquation (3). With
Equation(3),wecantransformphasecurrentâsexpectedvalue iâA, i â
B, and i â
C to linecurrentâsexpected
value iâ1, i â
2, and i â
3, thendetermine line currentâs errorÎi1,Îi2, andÎi3 to have each line current
hysteresiscontrolledrespectively.
If ignoringzero-sequencecurrent in trianglecircuit,wegot iA+ iB+ iC=0,andthenwecould
get thephasecurrentexpression, representedbythe linecurrentasEquation(21)viaEquation(3):
iA=(i1â i2)/3, iB=(i2â i3)/3, iC=(i3â i1)/3. (21)
If theacceptable linecurrenterrorwashl, thehalf-widthof thehysteresisbandof i1, i2washl,
andtheacceptableerrorof i1â i2was2hl, thenwecouldcalculate theacceptableerrorofphasecurrent
iA = (i1â i2)/3as 2hl/3. Thus, itwas clear that if the acceptable error ofphase current stayedat
h, the line currenthysteresis comparatorâs acceptable current errorwas required tobe set at 3h/2,
sowehad:
hl=3h/2. (22)
At thispoint, if ignoring thezero-sequence current, the trackingerrorof thephase current in
trianglemodewasthesameas that instarmode.However,note that the topologyof trianglemode
is different from that of starmode andDCbusvoltagewasdirectly loadedon thephase current.
Ineverycombinationof inverterswitchingstates, thereareïŹvepossiblephasevoltages instarmode:
â2Vdc/3,âVdc/3, 0,Vdc/3, 2Vdc/3. In trianglemode, there are threepossiblephasevoltageswith
higheramplitude:âVdc, 0,Vdc. Therefore, if thehalf-widthof thehysteresisbandwasdetermined
accordingtoEquation(22), eventhoughtheacceptable trackingerrorof thecurrent in trianglemode
wasthesameas that instarmode, thecurrentsawtoothïŹuctuation in trianglemodeismoredrastic
than that in starmodeand the switching frequencyof inverters, alongwith the core lossofmotor,
wouldbegreater thanthose instarmode.
251
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