chapter 1 dc drives part1
TRANSCRIPT
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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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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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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
constantisflu6ifspeed,Avera+e
I2I2%
developed%orqueAvera+e22or$25
=
=
=
=
=
+=+=
==
==
1
A3
%v
a
v
a
1
v
aaa
a%A3
va
secrad%22
0
2
3
secrad2
0I3
constantisflu6ifspeed,Avera+e
I2%
developed%orqueAvera+e
25
volta+earmatureAvear+e
=
=
=
=
Self-excited Shunt Motor:
Avera+e induced volta+e:
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15
Ra'Rf
La
ea
n
Ka
Va L
f
if$ 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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1.
foao
fa
a
%
1
3
secrad7peed,8
Acurrent,ieldullIAcurrent,ArmatureullI
(required"Acurrent,ieldIAcurrent,ArmatureI
33olta+e,Applied3
$m4Aconstant,%orque2
sec3olts4radconstant,f#m#e)ac*29here
==
===
===
=
=
=
=
+=
;
%
;
3
I
I2I%
I
I20I3
a
a
a
a
a
aaa
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Acurrent,ieldullI
(required"Acurrent,ieldI
secrad7peed,8
Acurrent,ArmatureI
33olta+e,Applied3
$m4Aconstant,%orque2
sec3olts4radconstant,f#m#e)ac*29here
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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- ./ 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: