7_ Inverter operated induction machines.pdf

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1、7.7.InverteroperatedinductionmachinesInverteroperatedinductionmachinesSource:SiemensAG,GermanyDARMSTADTDept.ofElectricalEnergyConversionUNIVERSITYOF7/1TECHNOLOGYProf.A.BinderInverter-fedinductionmachine•Frequencyconverter(inverter)generatesthree-phasevoltagesystemwithvariable

2、frequencyfandvariableamplitudeU(rms).Hencesynchronousspeediscontinuouslyssvariable.Withthatinductionmachineiscontinuouslyvariableinspeed.•Reversalofspeed=Changingoftwophasesofstatorwinding.Changingofenergyflow(motor/generator)bydecreasing/increasingphaseshiftbetweenvoltageand

3、current:motorϕπ/2•VoltageamplitudeUmustbechangedinproportiontoftokeepthefluxinthessmachineconstant.Thustorquewillstayconstant,ifthethesamecurrentisused.ForR=0:Us=jωsLsσIs+jωsLh(Is+I′r)sUs=jLI+jL(I+I′)=j(ˆ+ˆ)/2=jˆ/2=const.sshsrΨsΨhΨsσσωsU~ωRuleforcontrollingthei

4、nverter:ssωω•Slip:s=f/f=ω/ω⇒Ω=s−rrsrsmppCurveM(n)=M(Ω)asCurveM(ω)forvaryingωisshiftedinparallel!eemersDARMSTADTDept.ofElectricalEnergyConversionUNIVERSITYOF7/2TECHNOLOGYProf.A.BinderM(n)-Characteristicforinverter-fedinductionmachine•R=0:sKLOSSformula:2M2MbbM==essωω+brrb+sbsωr

5、bωr22msUs11−σmspUs1−σBreakdowntorqueMb:Mb=⋅⋅=⋅⋅=const.ωs/pXs2σ2ωsσLsR′(ω/ω)⋅R′ωRr′Breakdownslip:s/s=r=srr=rbwithωrb=Slipfrequencyb′⋅′σL′sσXσωLωrrsrrDARMSTADTDept.ofElectricalEnergyConversionUNIVERSITYOF7/3TECHNOLOGYProf.A.BinderInfluenceofstatorwindingresistanceRs•Vol

6、tagedropatstatorresistanceinstatorvoltageequationMUSTNOTbeneglectedatsmallangularfrequencyωsU=RI+jωLI+jωL(I+I′)sssssσsshsr•Example:Inductionmachine:R0.06Ωsf=50Hz:==0.02Rateddata:f=50Hz,U=230V:ssNsNωL3.0ΩssNOTE:AtsmallfresistanceRmustnotbeneglected.ssR6sf=5Hz:==0.2sωL5ss⋅30050

7、•VoltagedropatstatorresistancereducesatconstantstatorphasevoltageUtheinternalvoltageU.Henceshbreakdowntorquedecreaseswithsquareofinternalvoltage!•ByincreasingofUbyRIinternalvoltageUssshmustbekeptconstantforconstantM.bDARMSTADTDept.ofElectricalEnergyConversionUNIVERSITYOF7/4TE

8、CHNOLOGYProf.A.BinderInverterwithvoltagesixstepoperation•Bridgerecti