Closed Loop Control of DC Drives

Lecture notes on Closed Loop Control of DC Drives.

Electrical Drives, B.Tech. (Electrical) Rajasthan Technical University

Contents:
● Control structure of DC drive
● Inner current loop and outer speed loop
● Dynamic model of dc motor – dynamic equations and transfer
functions
● Modeling of chopper as gain with switching delay, Plant
transfer function for controller design
● Current controller specification and design, Speed controller
specification and design

1. Electrical Drives
Unit-4
Closed Loop Control of DC Drives
Syllabus:
●Control structure of DC drive
●Inner current loop and outer speed loop
●Dynamic model of dc motor –dynamic equations and transfer
functions
●Modelingof chopper as gain with switching delay, Plant
transfer function for controller design
●Current controller specification and design, Speed controller
specification and design
Prepared by:
Rohan Sharma
Assistant Professor EE
Arya Institute of Engineering Technology &
Management, Jaipur
Rohan Sharma

2. Introduction to DC Drives
●
DCdrivesareusedforcontrollingthe
speedandtorqueofDCmotorsin
industrialapplications.
●
Closed-loopcontrolisapopular
techniqueusedtoimprovethe
performanceofDCdrives.
Rohan Sharma

3. Control Structure of DC Drive
●
Aclosed-loopcontrolsystemforaDC
drivetypicallyinvolvesusingfeedback
fromasensortoadjustthevoltageor
currentsuppliedtotheDCmotor.
●
Thebasiccomponentsofsuchasystem
are:
●
Sensor
●
Controller
●
Poweramplifier
●
DCmotor
Rohan Sharma

4. Control Structure of DC Drive
●
Sensor:Asensorisusedtomeasurethespeedorpositionof
themotorshaft,whichisusedasfeedbackforthecontrol
system.
●
Controller:Thecontrollercomparestheactualspeedor
positionofthemotorwiththedesiredspeedorposition,and
generatesacontrolsignaltoadjustthevoltageorcurrent
suppliedtothemotor.
Rohan Sharma

5. Control Structure of DC Drive
●
Poweramplifier:Thepoweramplifiertakesthecontrolsignal
fromthecontrollerandamplifiesittoalevelthatcandrivethe
motor.
●
DCmotor:TheDCmotorconvertstheelectricalenergysupplied
toitintomechanicalenergytoperformthedesiredtask.
Rohan Sharma

6. Control Structure of DC Drive
●
Theclosed-loopcontrolsystemforaDCdriveworksbycontinuously
monitoringthemotorspeedorpositionusingthesensor,comparingitwiththe
desiredspeedorposition,andadjustingthevoltageorcurrentsuppliedtothe
motorusingthecontrollerandpoweramplifier.
●
Thisfeedbackloopensuresthatanydisturbancesorchangesintheloadonthe
motorarecompensatedfor,andthemotoroperatesatthedesiredspeedor
position.
●
Theclosed-loopcontrolsystemforaDCdrivecanbeimplementedusing
variouscontroltechniquessuchasproportional-integral-derivative(PID)
control,adaptivecontrol,ormodel-basedcontrol.Thechoiceofcontrol
techniquedependsonthespecificapplicationrequirements,andthesystem's
desiredperformancecharacteristicssuchasaccuracy,stability,andresponse
time.
Rohan Sharma

7. Inner Current Loop and Outer Speed
Loop
●
Inclosed-loopcontrolofDCdrives,there
aretypicallytwofeedbackloopsthat
worktogethertocontrolthemotor's
speedandtorque:
●
theinnercurrentloop
●
theouterspeedloop
Rohan Sharma

8. Inner Current Loop
●
Theinnercurrentloopcontrolsthecurrent
suppliedtothemotorbyadjustingthe
voltageappliedtoit.Thisloopis
responsibleforensuringthatthemotor
currentremainsconstantdespitechanges
intheloadorsupplyvoltage.Itoperatesat
afasterratethantheouterspeedloopand
isresponsibleforprovidingfastand
accuratecurrentcontrol.
Rohan Sharma

9. Inner Current Loop
●
Thecomponentsoftheinnercurrentloop
includeacurrentsensor,acurrent
controller,andapoweramplifier.The
currentsensormeasurestheactual
currentsuppliedtothemotor,whichis
comparedtothedesiredcurrentbythe
currentcontroller.Thecurrentcontroller
thengeneratesacontrolsignalthat
adjuststhevoltageappliedtothemotor
throughthepoweramplifier.
Rohan Sharma

10. Outer speed loop:
●
Theouterspeedloopcontrolsthespeed
ofthemotorbyadjustingthecurrent
suppliedtoit.Itisresponsibleforensuring
thatthemotoroperatesatthedesired
speeddespitechangesintheloadorother
externalfactors.Thisloopoperatesata
slowerratethantheinnercurrentloopand
isresponsibleforprovidingstableand
accuratespeedcontrol.
Rohan Sharma

11. Outer speed loop:
●
Thecomponentsoftheouterspeedloop
includeaspeedsensor,aspeedcontroller,
andacurrentreferencegenerator.The
speedsensormeasurestheactualspeed
ofthemotor,whichiscomparedtothe
desiredspeedbythespeedcontroller.The
speedcontrollerthengeneratesacontrol
signalthatadjuststhecurrentsuppliedto
themotorthroughthecurrentreference
generator.
Rohan Sharma

12. Inner Current Loop and Outer Speed Loop
●
Theinnercurrentloopandouterspeed
loopworktogethertoprovidepreciseand
stablecontroloftheDCmotor.
●
Thecurrentloopprovidesfastand
accuratecurrentcontrol,whilethespeed
loopprovidesstableandaccuratespeed
control.
●
Theinteractionbetweenthetwoloopsis
essentialtoachievethedesired
performanceofthemotor.
Rohan Sharma

13. Current Limit Control
●
Thisschemeisusedtolimittheconverterandmotorcurrent
belowasafelimitduringthetransientoperation.Thesystem
hasacurrentfeedbackloopwithathresholdlogiccircuit.
Rohan Sharma

14. Closed-Loop Torque Control
●
Suchtypesofloopareusedinbatterypoweredvehicles,rails,
andelectrictrains.ThereferencetorqueT*issetthroughthe
accelerator,andthisT*followsbytheloopcontrollerandthe
motor.Thespeedofthedriveiscontrolledbyputtingpressure
ontheaccelerator.
Rohan Sharma

15. Closed-Loop Speed Control
●
Theblockdiagramoftheclosedloopspeedcontrolsystemis
showninthefigurebelow.Thissystemusedaninnercontrol
loopwithinanouterspeedloop.Theinnercontrolloopcontrols
themotorcurrentandmotortorquebelowasafelimit.
Rohan Sharma

16. Closed-Loop Speed Control of Multi Motor Drives
Rohan Sharma

17. Closed Loop Speed Control of DC Motor
Theconverters(rectifiersand
choppers)arebuiltusing
semiconductordevices,whichhave
verylowthermalcapacity.
Consequentlytheirtransientand
steadystatecurrentratingsare
same.Thedcmotorscancarry2to
3.5timestheratedcurrentduring
transientoperationsofshort
duration’s,suchasstarting,braking
andreversing.Higherthecurrent,
higheristhetorqueandfasteris
thetransientresponse.
Rohan Sharma

18. Dynamic Model of DC Motor
●
ThedynamicmodelofaDCmotordescribeshowthemotor
respondstochangesinitsinputs(voltageandcurrent)and
outputs(speedandtorque).
●
ThebasicdynamicmodelofaDCmotorcanbeexpressed
usingthefollowingequations:
●
Electricalequation
●
Mechanicalequation
●
Speedequation
●
BackEMFequation
Rohan Sharma

19. Dynamic Model of DC Motor
Electricalequation:
V = E + RI + L(di/dt)
whereVistheappliedvoltage,EisthebackEMF(electromotive
force)generatedbythemotor,Ristheresistanceofthemotor's
armature,Iisthearmaturecurrent,Listheinductanceofthe
armature,anddi/dtisthetimederivativeofthearmature
current.
Rohan Sharma

20. Dynamic Model of DC Motor
Mechanicalequation:
T = kΦI
whereTisthetorquegeneratedbythemotor,kisaconstant
thatrelatesthemotor'smagneticfieldstrengthtoitstorque,Φis
themagneticfluxproducedbythemotor,andIisthearmature
current.
Rohan Sharma

21. Dynamic Model of DC Motor
Speedequation:
ω = (V -E)/kΦ-(b/J)ω
whereωisthemotorspeed,bisthemotor'sfrictioncoefficient,
Jisthemotor'smomentofinertia,andthesecondtermonthe
right-handsiderepresentsthedampingduetofriction.
Rohan Sharma

22. Dynamic Model of DC Motor
BackEMFequation:
E = kΦω
wherekΦisthemotor'sbackEMFconstant.
TheseequationscanbeusedtosimulatethebehaviorofaDC
motorunderdifferentoperatingconditionsandtodesigncontrol
systemsthatregulatethemotor'sspeedandtorque.The
dynamicmodelcanalsobeusedtoanalyzethemotor's
performance,suchasitsresponsetostepchangesinvoltageor
load.
Rohan Sharma

23. Dynamic Model of DC Motor
Rohan Sharma

24. Dynamic Model of DC Motor
Rohan Sharma

25. Dynamic Model of DC Motor
Rohan Sharma

26. Dynamic Model of DC Motor
Rohan Sharma

27. Dynamic Model of DC Motor
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28. Dynamic Model of DC Motor
Rohan Sharma

29. Dynamic Model of DC Motor
Rohan Sharma

30. Rohan Sharma

31. Modelingof Chopper
●
ThechopperinaDC
driveismodeledasa
gainwithswitching
delay.
●
Themodelisusedto
derivetheplant
transferfunctionfor
controllerdesign.
Rohan Sharma

32. Modelingof Chopper
Rohan Sharma

33. Modelingof Chopper
Rohan Sharma

34. Current Controller Specification and Design
●
Inclosed-loopcontrolofaDCdrive,thecurrentcontrolleris
animportantcomponentofthecontrolsystem.The
specificationanddesignofthecurrentcontrollerdependon
themotor'scharacteristicsandthedesiredperformance
requirements.
●
Herearesomegeneralstepsinvolvedinthespecificationand
designofacurrentcontrollerforaclosed-loopDCdrive:
●
Determinethemotorparameters:Thefirststepistomeasureor
calculatethemotor'sparameters,suchasitsresistance,
inductance,andback-EMFconstant.
Rohan Sharma

35. Current Controller Specification and Design
●
Choosethecontrolstrategy:Differentcontrolstrategies
maybeused,suchasPIcontrol,wherethecontroller
adjuststhecurrentbasedonthedifferencebetweenthe
desiredcurrentandtheactualcurrent.
●
Determinethecontrollerparameters:Thecontroller
parameters,suchastheproportionalandintegralgains,
aredeterminedbasedonthedesiredresponsetimeand
stabilityrequirementsofthesystem.Theseparameters
canbedeterminedusingsimulationtoolsortrial-and-
errortuningmethods.
Rohan Sharma

36. Current Controller Specification and Design
●
Implementthecontroller:Thecontrollercanbe
implementedusinganalogordigitalcircuits,depending
onthespecificapplication.
●
Testandtunethecontroller:Thecontroller's
performancecanbetestedusingsimulationsor
experiments,andthecontrollerparameterscanbe
adjustedtooptimizetheperformanceofthesystem.
Rohan Sharma

37. Advantages of Closed-Loop Control
●
Increasedaccuracy:Closed-loopcontrolallowsformore
accuratecontrolofthemotor'sspeedandtorque,whichcan
improvetheperformanceofthedriveandreducewearandtear
onthemotor.
●
Improvedresponse:Closed-loopcontrolallowsforfaster
responsetochangesintheloadoroperatingconditions,which
canimprovethedrive'sperformanceandefficiency.
●
Disturbancerejection:Closed-loopcontrolallowsforbetter
rejectionofdisturbances,suchaschangesintheloadorsupply
voltage,whichcanimprovethedrive'sstabilityandreliability.
Rohan Sharma

38. Advantages of Closed-Loop Control
●
Flexibility:Closed-loopcontrolallowsformoreflexible
operationofthedrive,asitcanadapttochangesintheloador
operatingconditionswithoutrequiringmanualadjustments.
●
Protection:Closed-loopcontrolcanprovideprotectiontothe
motorbylimitingthecurrentorvoltagetopreventdamagedue
tooverloadingorotheroperatingconditions.
Rohan Sharma

39. Applications of Closed-Loop Control
●
Industrialautomation:Closed-loopcontroliswidelyusedin
industrialautomationapplications,suchasmanufacturing
processes,assemblylines,androbotics.
●
Aerospaceanddefense:Closed-loopcontrolisusedinaircraft
controlsystems,missileguidancesystems,andunmanned
aerialvehicles(UAVs).
●
Automotive:Closed-loopcontrolisusedinautomotive
systems,suchasenginecontrol,anti-lockbrakingsystems
(ABS),andelectronicstabilitycontrol(ESC).
Rohan Sharma

40. Applications of Closed-Loop Control
●
Medicaldevices:Closed-loopcontrolisusedinmedical
devices,suchasinfusionpumps,ventilators,andanesthesia
machines.
●
Powersystems:Closed-loopcontrolisusedinpowersystems,
suchasvoltageregulation,frequencycontrol,andpowerfactor
correction.
Rohan Sharma

41. Conclusion
●Inconclusion,closed-loopcontrolofDC
drivesiswidelyusedinvariousapplications
whereprecisecontrolofmotorspeedand
torqueisrequiredforefficientandreliable
operation.
●Theuseofclosed-loopcontrolallowsfor
improvedperformance,accuracy,and
stabilityoftheDCdrive,leadingtoincreased
efficiencyandreducedwearandtearonthe
motor.
Rohan Sharma