电机拖动 第二章 直流电机Motor dragdc motor.docx

电机拖动 第二章 直流电机Motor dragdc motor.docx

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电机拖动第二章直流电机Motordragdcmotor

03电机拖动第二章直流电机3（Motordrag2dcmotor3）

Fundamentalsofelectricalengineeringandtraction

Fundamentalsofelectricalengineeringandtraction

Schoolofautomation,ChongqingUniversity

One

Fundamentalsofelectricalengineeringandtraction

Thesecondchapter:

DCmotor

Two

primarycoverage

First,theworkingprincipleandstructureofDCmotor

Fundamentalsofelectricalengineeringandtraction

TheoperatingprincipleofseventhDCmotorcalculationsectionsixthDCmotorexcitationwindingsfourthDCmotornameplatedatasectionthirdsectionsecondDCmotorDCmotorandthefifthmagneticfieldinducedelectromotiveforceandtheelectromagnetictorqueofthereversing

Three

Sixthquarter

One

Fundamentalsofelectricalengineeringandtraction

TheoperatingprincipleofDCmotor

ThebasicequationofDCmotormotor?

Inenergyconversion,musthaveitsmotionequationintheenergyconversion,musthaveitsmotionequationtodescribetheinternalprocessofelectromagneticelectromagneticprocessandtype,characterizedbyitsinternalelectromagneticprocessandelectromechanicalprocess?

（a）electromotiveforcebalanceequation（two）torquebalance?

Equation（three）thepowerbalanceequation?

Four

（1）electromotiveforcebalanceequation

Takeexcitationforexample

Fundamentalsofelectricalengineeringandtraction

Thedirectionofeachmotorisspecified:

thedirectionofeachmotorisspecified:

ThearmatureelectromotiveforceEandthecurrentIarmatureelectromotiveforceEaandthecurrentIadirectionopposite,theelectromagnetictorqueTandthespeedndirectionaresame,theelectromagnetictorqueTeandthespeedndirectionissame,isthedrivetorque

Positivedirectionofgenerator:

regulationofpositivedirectioningenerator:

ThearmatureelectromotiveforceEandthecurrentIarmatureelectromotiveforceEaandthecurrentIadirectionareconsistent,theelectromagnetictorqueTandthespeedndirectionareopposite,theelectromagnetictorqueTeandthespeedndirectionopposite,isthebrakingtorque

Five

（1）electromotiveforcebalanceequation

Forsteady-stateoperation,formotors:

steadyrunning,formotors:

Fundamentalsofelectricalengineeringandtraction

U=U,a=Ea+Ra,I,a

U=U,f=（RF+r=）=I,f=R,F,I,f

Importantspeedformula:

importantspeedformula:

U,Ra,I,a,n=,Ce,Phi

Steadystateoperationforgenerator:

steadystateoperation,forgenerator:

Ea=U+Ra,I,a

U=Rf,I,f

Six

（two）torquebalanceequation

Formotors:

formotors:

Fundamentalsofelectricalengineeringandtraction

D=Te=T2+,T0+,TJ=T2+,T0+,J,DT

T2-loadbrakingtorqueT0-no-loadlosstorqueTJ-inertiatorque

Insteadystateoperation,themotorrotatesataconstantangularspeed,andthemotorrotatesataconstantangularspeedinsteadystateoperation:

Te=T2+T0

T2+T0Ia=CTPhi

Corollary:

corollary:

?

Ifthetotalbrakingdiameterunchanged,unchanged,unchangedIawasstableafter?

Theactualload,Ia=0

Forgenerators:

forgenerators:

T1=Te+T0

T1primemoverdragtorque

Seven

（three）powerbalanceequation

Formotors:

formotors:

InputelectricpowerP1inputelectricpowerP

Fundamentalsofelectricalengineeringandtraction

P=UI=U（I,F+I,a）1=UI,F+（I,a,Ra+2,U,C+,Ea）I,a=pCuf+,pCua+,PC+Pe

ElectromagneticpowerPe,electromagneticpowerP,no-loadlossP0,no-loadlossp

Pe=Ea,I,a=Te==（T0+T2）=P0+P2,P0=pFe+pmech+P?

OutputmechanicalpowerP2P2=T2outputmechanicalpowerP

Powerbalancetype:

powerbalancetype:

P=P2+,pCuf+,pCua+,PC+,pFe+,pmech+,P=P2+sigma,p1

Efficiency:

efficiency:

P2P）*100%=sigmaETA=（1x100%PP2+p1sigma?

Eight

（three）powerbalanceequation

Forgenerators:

forgenerators:

InputmechanicalpowerP1P1=T1==（Te+T0）=Pe+P0inputmechanicalpowerP

Fundamentalsofelectricalengineeringandtraction

=Pe+pFe+pmech+P?

ElectromagneticpowerPeelectromagneticpowerP

Pe=Ea,I,a=（U+,I,a,Ra+2,U,c）I,a

2=UI,a+,I,a,Ra+2,I,a,U,C=2+UI,F+I,a,Ra+2,I,UI,a,U,C

=P2+pCuf+pCua+PC

OutputelectricpowerP2outputelectricpowerP

P2=UI

Powerbalancetype:

powerbalancetype:

P=P2+,pCuf+,pCua+,PC+,pFe+,pmech+,P=P2+sigma,p1

Nine

Powerdiagram

Fundamentalsofelectricalengineeringandtraction

Ten

Two

WorkingcharacteristicsofDCmotor

Workcharacteristics:

referstotheU=UN,withoutthearmaturecircuitresistance,externalcharacteristics:

referstotheU=Uinexternalarmaturecircuitresistance,electromagnetictorqueandspeednTefficiencyIf=IfN,nspeed,electromagnetictorqueTeandefficiencyofthreeandtherelationshipbetweenthetransmissionpowerofP.TherelationbetweenoutputpowerandP2.Namely:

machine

Fundamentalsoflearninganddragging

N=f（P2,Te）=f（P2）,ETA=f（P2）

Inactualoperation,Iacanbedirectlymeasured,andtheincreaseofIawithP2andtheactualoperation,canbedirectlymeasured,bothincreased,theincreasingtrendissimilar,bothincreased,theincreasingtrendisnotmuch,sooftenworkcharacteristicsexpressedas:

characteristicsexpressedas:

N=f（I,a）Te=f（I,a）=f（Ia）.

Eleven

（1）shunt（separatelyexcited）motorspeedcharacteristicandshunt（separatelyexcited）

U=UN,R,=0,If=IfN,n=（Ia）,=0,n=f（I）relationshipcurveforspeedcharacteristics,speedcharacteristics.Therelationcurveisspeedcharacteristic.

Fundamentalsofelectricalengineeringandtraction

Accordingtotheformulaofspeed:

accordingtotheformulaofspeed:

theformulaofspeed

U,N,Ra,I,a,Ra,n==N0,Ia,Ce,Ce,phi,Phi

UN,N0=idealno-loadspeedideal,no-loadspeedCePhi

Ifthearmaturereactionisnotdecreased,ifthearmaturereactionisnotconsidered,ifthearmaturereactionistakenintoaccount,thearmaturereactionmaybeincreasedifthearmaturereactionisconsidered,

Twelve

（two）shunt（separatelyexcited）torquecharacteristicofmotorandshunt（separatelyexcited）

WhenU=UNandIf=IfN,therelationcurveofTe=f（Ia）istorquecharacteristic.Torquecharacteristic.（I'srelationshipcurveistorquecharacteristic

Fundamentalsofelectricalengineeringandtraction

Accordingtothetorqueformula:

accordingtothetorqueformula:

torqueformula

Te=CTphiIa

Ifthearmaturereactionisnotconsidered,thelineisclosetothestraightline.Ifthearmaturereactionisnotconsidered,ifthearmaturereactionisconsidered,thedecreaseisnotenough,ifthearmaturereactionistakenintoaccount,

Thirteen

（three）theefficiencycharacteristicofshunt（separatelyexcited）motorandshunt（separatelyexcited）

U=UN,If=IfN,=f（Ia）curveforefficiencycharacteristics.Efficiencycharacteristics.（I'srelationcurveisefficiencycharacteristic

Fundamentalsofelectricalengineeringandtraction

P2P）*100%=sigmaETA=1x100%（P=11?

P（1?

2pCuf+pFe+pmech+P++IaRa+2IaUC?

UN（Ia+I,f）

*100%

Amongthem,amongthem,

PCuf+pFe+pmech+Pisinvarianttoloss

2,pCua=I,a,Ra,PC=2,I,a,U,C

Variableloss

Fourteen

TherearetwotimestherelationshipbetweenETAandIa,oneofthemostefficiencycurveexistsbetweenthetwo,therearetwolargevaluenegligibleexcitationcurrent;electric?

DuetoIfN<

Fundamentalsoflearninganddragging

迪一

2pcuf+生活+PMech=我一个RA

结论：

当电动机在某负载下不变损耗等于可变损结论：

耗时，此时效率最高。

耗时，此时效率最高。

？

推论：

1）额定运行时总损耗推论：

2，P=2inRA∑

2）可从额定数据来估算电枢回路总电阻？

上述结论和推论具有普遍性

1美元？

pn=？

22

十五

（四）串励直流电动机的工作特性

基本方程式：

基本方程式：

电机学及拖动基础电动势平衡方程式U=CeΦN+1个（RA+RFC）电动势公式转矩平衡方程式转矩公式转速公

EaceΦN=CN′

TE=T2+T0

′TE=CTΦ我=我A

u？

我A（RA）u1N==？

RA′CEΦCA′我Ca

′为串励绕组电阻，（RFC为串励绕组电阻，RA′=RA+RFCCA′=CeKFCT=CTKF）

十六

结论：

结论：

转速特性：

1）随负载增大迅速转速特性：

电降低；空载时有飞速危险，降低；2）空载时有飞速危险，机学不允许在空载或负载很小情况及下运行。

下运行。

拖动基础

并励电动机

转矩特性：

以高于电流一次方转矩特性：

的比例增加，的比例增加，保证在同样大小的起动电流下得到比并励电动机更大的起动转矩。

机更大的起动转矩。

？

效率特性：

与并励相似效率特性：

与并励相似。

串励电动机

十七

（五）复励直流电动机的工作特性

结论：

结论：

工作特性介于并励与串励的特性之间；？

工作特性介于并励与串励的特性之间；？

若并励磁动势为主，则接近并励特性；若并励磁动势为主，则接近并励特性；？

若串励磁动势为主，则接近串励特性；若串励磁动势为主，则接近串励特性；？

由于有并励磁动势存在，空载时没有飞速由于有并励磁动势存在，的危险。

的危险。

1并励电动机并励电动机2积复励电动机积复励电动机3串励电动机串励电动机

十八

电机学及拖动基础

一台他励直流电动机的额定数据为：

[例2-1】一台他励直流电动机的额定数据为：

PN=1325kwUn=750v我n=1930aNN=200r/min电机电枢绕组的电阻Ra＝0.0161？

电刷接触压降学2？

u＝2伏

及拖动基础

设电动机原来在额定转速和额定负载下运行，在负设电动机原来在额定转速和额定负载下运行，载的总制动转矩（包括损耗转矩）载的总制动转矩（包括损耗转矩）保持不变的情况下，试求

（1）在电枢回路中突然串入电阻=0.0743，求串）在电枢回路中突然串入电阻R入电阻最初瞬间和达到稳定时的电枢电流和转速分别是多少？

别是多少？

十九

（2）减少电动机的励磁电流，使磁通减少）减少电动机的励磁电流，使磁通Φ减少10%，当达到稳定时的电枢电流和转速分别是多少到稳定时的电枢电流和转速分别是多少？

当达到稳定时的电枢电流和转速分别是多少

电解EA=u？

我是RA？

2？

=（750？

1930×0。

0161?

2）V=717V

（1）inthearmaturecircuitresistanceintothefirstmoment）onsuddenlysuddenlyinthearmaturecircuitresistanceRandEaonI=717Va=U?

Ea?

U2?

C=750?

717?

2A=343ARa+0.0161R+0.0743Isteadydraga=1930AEa=U'I?

A（Ra+R）?

2?

UC.=[750?

1930x（0.0161+0.0743）2]V=574V?

N'=n'Ea574=（200*）R/min=160r/minEa717

Twenty

Electric''Ia=（1930/0.9）A=2145Areducedto0.9oftheoriginal

（2）fluxreducedtotheoriginalmachine'''）'Ea=U?

IaRa?

2?

U（C=750x0.0161?

2145?

2）V=713VandEa''Phi7131'n'=n=200*r/min=221r/mindragEaPhi''7170.9basic

Twenty-one

Two

?

?

?

Characteristicsofadirectcurrentgenerator

FourbasicphysicalquantitiesofDCgenerator:

fourbasicphysicalquantitiesU,I,If,nDCgenerator:

DCgeneratorbymotordrive,usuallyn=nDCgeneratorbymotordrive,usuallyn=nNremainedunchangedasthepowersupply,theprimaryconcernisthecharacteristicsoftheterminalvoltageasthepowersupply,theprimaryproblemattentionisthecommoncharacter