Chapter 1 DC Drives Part1

8/9/2019 Chapter 1 DC Drives Part1

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DC DrivesDC Drives


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Learning Objectives

At the end of this Chapter, you should be able to :

Analyze the operation and characteristics of

various types of DC motors

Analyze the operation and characteristics of DC

motor in four quadrants


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3

Review of D.C. motors: operation, characteristics and

modes of control

Degree of Control applied: quadrants of control,

implications on power electronic requirements

Converters: principles, single and three phase bridge

configurations, controllability and protection,

implications on a.c. supply power factor and

harmonics!

"ulse #idth $odulated Chopper amplifiers:

principles, single%four quadrant bridge configurations,

losses, controllability and protection, supply

implications capacitor, cho&e, regeneration!


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4

'ypes of (lectric $otors'ypes of (lectric $otors

$otors are categori)ed on the basis of input

supply, construction and operation principles

Classification of $otors

(lectric $otors

*lternating Current

*C! $otors

Direct Current DC!

$otors

+ynchronous nduction

'hree%"hase+ingle%"hase

+elf (-cited+eparately

(-cited

+eries +huntCompound


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5

DC $otorsDC $otors

ield pole /orth pole and south pole

Receive electricity to formmagnetic field

*rmature Cylinder between the poles

(lectromagnet when current goes through

0in&ed to drive shaft to drive the load

Commutator

1verturns current direction in armature

DC $otors 2 Components

(Direct Industry, 1!"


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6

DC $otorsDC $otors

+peed control without impact of

power supply quality

Changing armature voltage

Changing field current

Restricted use

ew low3medium speed applications

Clean, non%ha)ardous areas

(-pensive compared to *C motors


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ield winding parallel

with armature winding 0ine Current 4 field

current 5 armature

current

+peed constant

independent of load

up to certain torque

+peed control:

insert resistance

in armature or

field circuit

DC motors

Self-excited DC motor: shunt motor

ia

Ra

La

ea

n

Ka

if

vf

Va

Field current supplied from aseparate source

Separately-excited DC motor:


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+elf%e-cited DC motor: series motor

DC motors

ield winding in serieswith armature winding

ield current 4

armature current

+peed restricted to6777 R"$

*void running with

no load: speed

uncontrolled

+uitable for

high startingtorque: cranes,

hoists


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Electric drives are used for a

wide range of different loads.

Some common load

characteristics are shown along

with their associated equations.

It is desirable that the load

torque and the motor torque

characteristics are orthogonalor

nearly so. his will improve

speed regulation.

S!eed" #

orque" L

L

$ %&

' %(#

Eg." )oist


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10

m#$torque,Developed%m,#$torque,&oad%

sradspeed,'

tcoefficien(riction),m*+Inertia,ofoment-

%')dt

d'-%

&

1.

/

&

==

=

==

++=

Dynamic torque equation for a motor

Dynamic voltage equation for a DC motor

aa

aaaa edt

di&0iv ++=


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11

Relationship between speed, field

flu- and armature voltage

Ea= Z!"#$%&' Define (a= Z!"#$%&'

DC motors

Back electromotive force: Ea= KaN Volts

!ere Ka= Volts"r#m

$f s#ee% is eresse% as = ' N"60 ra%(sec)1

Back electromotive force: Ea= Ka1

!ere Ka1

= Volts" ra%(sec)1= Kv

= ZP/(2 A)

Ea= Kv Volts* !ere emf co+sta+t Kv= Volts" ra%(sec)1

(a4 electromotive force developed at armature terminals volts!

4 field flu- which is directly proportional to field current

/ 4 speed in R"$ revolutions per minute!

= speed inradians"sec


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1'

!o)er developed* !a= Ea+a ,atts

orque developed = !a" Nm

orque: , = Ea$a" Nm

DC motors

8asic equations for average ($ and

average 'orque developed by motor

*verage ($, Ea= (a. = (v/olts

= (a. +a m Define (a.= Z!"#0 &'

&verage orque* = (+a m*

+a= armature current

= speed* rad1 sec-.

(v= /olts"rad1 sec-.* E2F constant

(= m"&* torque constant


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13

ia

Ra

La

ea

n

Ka

if

vf

Va

aa i2% =

1

A3

%v

a

v

a

v

aa

v

a

v

aaa

%A3a

1

v

aaa

vaaaaaa

a%aa1A3

va1aa

secrad%22

0

2

3

20I

23

20I3

24%Ias

torque,ofin terms56pressin+

secrad2

0I3

20I50I3

constantisflu6ifspeed,Avera+e

I2I2%

developed%orqueAvera+e

22or$25

=

==

=

=

+=+=

==

==

n12e aa =

aa

aaaa edt

di&0iv ++=

7eparately.e6cited motor:

Avera+e induced volta+e:

Dynamic 3olta+e and torque equations


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14

1

A3

%v

a

v

a

v

aa

v

a

v

aaa

%A3a

1

v

aaa

vaaaaaa

a%aa1A3

va1aa

secrad%

22

0

2

3

2

0I

2

3

2

0I324%Ias

torque,ofin terms56pressin+

secrad2

0I320I50I3


I2I2%

developed%orqueAvera+e22or$25

=

=

=

=

=

+=+=

==

==

1

A3

%v

a

v

a

1

v

aaa

a%A3

va

secrad%22

0

2

3

secrad2

0I3


I2%

developed%orqueAvera+e

25

volta+earmatureAvear+e

=

=

=

=

Self-excited Shunt Motor:

Avera+e induced volta+e:


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15

Ra'Rf

La

ea

n

Ka

Va L

f

if$ i

a

/afaA3

afaa

I22%

developed%orqueAvera+e$I225

=

=

/afaaa

afaa

f

aa

i22i12%

developed%orque

ni22e

i21

n12e

equationsDynamic

a

==

=

=

=

aI22

"0(0I3$

$,7peedAvera+e

5"0(0I3

edt

di

"&(&"0(0iv

fa

faaa

afaaa

a

a

fafaaa

+=

++=++++=

Series Excited Motor:

Avera+e induced volta+e

Dynamic 3olta+e equations


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16

320I3 += aaa

aI2% %=

$m4A"(2"sec3olts4rad(2constant,isIIf

secrad7peed,8

Acurrent,ArmatureI

33olta+e,Applied3

$m4Aconstant,%orque2

sec3olts4radconstant,f#m#e)ac*29here

%

1

3f

1.

a

a

%

1

3

=

==

=

=

=

=


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17*current"+ield+ullI

,required-*current"+ieldI

secradS!eed"

*current"*rmatureI

VVoltage"*!!lied V

#m/*constant"orqueK

secVolts/radconstant"f.m.e0ac%Kwhere

fo

f

(1

a

a

(V

=

+=

;f

f

%

;f

f

3

I

I2I%

I

I20I3

a

aaa


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18

1.

foao

fa

a

%

1

3

secrad7peed,8

Acurrent,ieldullIAcurrent,ArmatureullI

(required"Acurrent,ieldIAcurrent,ArmatureI

33olta+e,Applied3



==

===

===

=

=

=

=

+=

;

%

;

3

I

I2I%

I

I20I3

a

a

a

a

a

aaa


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19

Acurrent,ieldullI

(required"Acurrent,ieldI

secrad7peed,8

Acurrent,ArmatureI

33olta+e,Applied3



fo

f

1.

a

a

%

1

3

=

=

==

=

=

=

=

=

+=

;f

f%

;f

f3

I

I2I%

I

I20I3

a

aaa


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!ro3lem:.

- fi&e% fiel% ./ motor %rives a com#ressor a+%!as t!e folloi+ c!aracteristics:

Back emf co+sta+t 0(17' V"r#m

,or2e co+sta+t 1(64 N(m"--rmat2re resista+ce 0('5

+%er t!e most severe co+%itio+s* t!e com#ressor+ee%s to e %rive+ at 8'5 r#m it! a tor2e of 50Nm( .etermi+e t!e ma&im2m c2rre+t a+% voltaere2ire% for t!e motor(


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31


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- ./ tractio+ motor !as t!e folloi+c!aracteristics:

Back emf co+sta+t ' V"ra%(s)1 2ll

fl2&e%,or2e co+sta+t 3 Nm"- 2ll fl2&e%-rmat2re fiel% resista+ces 0(3 -rmat2re i+%2cta+ce ' m;

,!e motor is to #rovi%e a ma&im2m tor2e of 600N(m at a s#ee% of 1500 r#m(

.etermi+e t!e armat2re voltae* V%(

!ro3lem:0


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2otor s!eed $1;@#1!@

=;

1!;;/

=;

/ === rads

N

3?@


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'4

The

-T plane with motor's shaft cross sectional area is shown.

ElectricalElectrical 2ech2ech

For)ardFor)ard

2otoring2otoring4ve4ve

4ve4ve

2ech2ech ElectricalElectrical

For)ardFor)ard

5ra6ing5ra6ing -ve-ve

4ve4ve

ElectricalElectrical 2ech2ech

7everse7everse

2otoring2otoring -ve-ve -ve-ve

7everse7everse

5ra6ing5ra6ing4ve4ve -ve-ve

2ech2ech ElectricalElectrical

2otor2otorElectricalElectrical 2echanical2echanical

! = +/! = +/ ! =! =

,hen accelerating,hen accelerating

8enerator8enerator

ElectricalElectrical

! = +/! = +/ ! =! =

,hen 3ra6ing,hen 3ra6ing

2echanical2echanical


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'5

The positive orforward speed isarbitrarily chosen

The positivepositivetorquetorqueis in thedirection that will

produceproduceacceleration inacceleration inforward speedforward speed,as shown above.

For)ard

7everse

< $< $$

< $$$ < $V


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'6

Both torque and speed are positivetorque and speed are positive- themotor rotates in forward directionforward direction, which is in

the same direction as the motor torquethe same direction as the motor torque.

The power of the motor is the product of the

speed and torque ! " T#, therefore the

power of the motor is positive.

$nergy$nergyis converted from electrical form toelectrical form tomechanical formmechanical form, which is used to rotate theused to rotate the

motormotor.

The mode of operation is %nown as forwardforward

motorin.motorin.

Ea #ositive

$a #ositive


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'7

The speed is in forward directionspeed is in forward directionbut the motormotortorque is in oppositetorque is in oppositedirection or negative value.

The torque producedtorque producedby the motor is used to &bra%eused to &bra%e&the forward rotationthe forward rotationof the motor.

The mechanical energy during the bra%ing, ismechanical energy during the bra%ing, isconverted to electrical energyconverted to electrical energy- thus the 'ow ofenergy is from the mechanical system to theelectrical system.

The product of the torque and speed is negativeproduct of the torque and speed is negativethusthe power is negative, implying that the motorimplying that the motoroperates in bra%ing modeoperates in bra%ing mode.

The mode of operation is %nown as forwardforward!ra"in.!ra"in.

Ea #ositive

$a +eative


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'8

The speed and the torque of the motor are inspeed and the torque of the motor are inthe same direction but are both negativethe same direction but are both negative.

The reverse electrical torque is used to rotatereverse electrical torque is used to rotate

the motor in reverse directionthe motor in reverse direction. The power, i.e. the product of the torque andproduct of the torque and

speed, is positive implying that the motorspeed, is positive implying that the motoroperates in motoring modeoperates in motoring mode.

The energy is converted fromelectrical formelectrical form

to mechanical formto mechanical form. This mode of operation is %nown as reversereverse

motorinmotorin.

Ea +eative

$a +eative


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'9

The speed is in reverse direction but the torque ispositive.

The motor torque is used to &bra%e& the reversemotor torque is used to &bra%e& the reverse

rotation of the motorrotation of the motor. The mechanical energy gained during the bra%ing ismechanical energy gained during the bra%ing is

converted to electrical formconverted to electrical form- thus power 'ow fromthe mechanical system to the electrical system.

The product of the speed and torque is negativeproduct of the speed and torque is negative

implying that the motor operates in bra%ing modeimplying that the motor operates in bra%ing mode. This mode of operation is %nown as reversereverse

!ra"in.!ra"in.

Ea +eative

$a #ositive


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30

,or2e"s#ee% c!aracteristics of variale s#ee% %rive

,!e o#eratio+ of a %rive ofte+ e&te+%s o2tsi%e o+e 2a%ra+ta+% are ofte+ eresse% as a four-quadrant torque/speedra#!( ,!e 2se of 2a%ra+t c!arts to re#rese+t commo+state c!a+es are as s!o+(

ypically motor control systems )ill operate in either +* ++or +/ of thesee quadrants1

Note:9uadrant ++ and +/ have the potential forregeneration1

S!eed" #

orque"

III

III IV

e.g." Locomotive

S!eed" #

orque"

III

III IV

e.g." Electric carS!eed" #

orque"

III

III IV

e.g." 3rane


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- oo%s> elevator is to e 2se% to lift !eav loa%s etee+floors i+ a ma+2fact2ri+ com#le& as s!o+ i+ F+87E .($t is to e #oere% a ./ motor it! co+sta+t e&citatio+(

,!e %etails elo %efi+e t!e c!aracteristics for t!e motor:?otor: ,or2e co+sta+t 0(8 Nm"-

Back emf co+sta+t 0(8 V"ra% s)1-rmat2re resista+ce 0(03

a ,!e elevator is to carr loa%s it! ma&im2m ei!t of 800k( ,!e ei!t of t!e lift is 300 k( ,!e 2il%i+ !as 5 floorsa+% t!e averae !ei!t of eac! floor is 8 m( ,!e mi+im2mtime for t!e elevator to move from ro2+% floor to to# floor is

33 s( se t!e acceleratio+ %2e to ravit at sea level* g= 9(81ms)'( /alc2late i t!e mi+im2m #oer re2ireme+t for t!emotor a+% ii t!e tor2e !e+ t!e motor is r2++i+ at as#ee% of 900 r#m( .etermi+e t!e motor armat2re c2rre+t a+% t!e armat2revoltae(

!ro3lem:;


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4 metres

+loor (

o! +loor

DC motor

u!

down

5nd +loor

F+87E .


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33

) metres

+loor (

o! +loor

DC motor

u!

down

5nd +loor

,otal mass* m = @ A = 1100 k

,otal !ei!t of floors = ; & = 40 mVelocit of t!e lift* v = ; & " = 1(' m"sorce to lift t!e loa%* = m a = m & 9(81 = 10791 k(m"s'Coer re2ire%* C = , = v = 13057 @atts

D = 94('5 ra%"s,or2e %evelo#e%* , = C" = 138(54 N(m

ei!t of loa% = @ k(ei!t of t!e lift = k(!ei!t of eac! floor = ; mNo( of floors = ,ime take+ = sec

a

ol2tio+:


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Torque constant " (.)*m+

Bac% emf constant " (.)+rad s-

rmature resistance " (.(/

3=#>;;#;?61@?#1@3

A1@#1@?>#;

!

I2%%orque,

20I3

a%

3

=+=

==

=

+=

a

a

aaa

I


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- a+tr cra+e is to e #oere% a ./ motorit! co+sta+t e&citatio+( ,!e ./ motor is toraise a+% loer a loa% it! ma&im2m ei!t of1500 k( -s s!o+ i+ F+87E 0* t!e motorit! t!e #arameters liste% elo* is ei+ 2se%it! a 50:1 re%2ctio+ earo& a+% a %r2m of%iameter 0(3 m( ,!e %etails elo %efi+e t!ec!aracteristics for t!e motor a+% %c)%cco+verter(

?otor: ,or2e co+sta+t = 0(6 Nm"- Back emf co+sta+t =0(6 V"ra% s)1

-rmat2re resista+ce = 0('

!ro3lem:pen-loop control:

#ee% co+trol of motors is carrie% o2t i+ eit!er o#e+

or close% loo#(


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?@=ER

3@#R@LLER2@@R L@*A

?ower

InRequireds!eed

acho

*ctuals!eed

$+ close% loo# s#ee% co+trol sstem* t!e o2t#2t s#ee%is com#are% it! t!e re2ire% s#ee% to %etermi+e t!e

error(,!e i+#2t #oer is t!e+ a%F2ste% to re%2ce t!e error(,!e close% loo# a##roac! !as ma+ a%va+taes* 2tt!e e&tra ee+se a+% com#le&it is +ot F2stifie% ifs#ee% re2latio+ is 2+im#orta+t(

Closed-loop control:

Chapter 1 DC Drives Part1

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Transcript of Chapter 1 DC Drives Part1