Chopper Controlled Dc Drive: INSTRUCTED BY: Dr. Buddhika

CHOPPER CONTROLLED DC DRIVE

INSTRUCTED INSTRUCTE D BY: Dr. Buddhika

NAME : D.K.Pathirana INDE NO : !"!##$P %ROUP : D%& DATE O' PER : ()*!#*$!($ DATE O' SUB : #!*!+*$!($

OBSERVATION SHEET NAME : D.K.Pathirana INDE NO : !"!##$P %ROUP : D%& DATE O' PER : ()*!#*$!($ DATE O' SUB : #!*!+*$!($ INSTRUCTED BY : Dr. Buddhika

O,-r/ati0n(b) Measurement of chopper performance with non back emf load S1..d2In1ut P0t.nti06.t.r S.ttin7

VL 3V4

IL 3A4

5

0

7.6

0.3

0.021

1

7.6

0.3

0.021

2

9.6

0.36

0.02

3

16.6

0.62

0.0!"



23.6

0.9

0.1"

"

29

1.12

0.19

6

37

1.

0.26

7

"

1.72

0.30

!

"3

2.02

0.36

9

61

2.32

0.

10

62

2.3!

0."

#hopper input $# %olta&e ' 131.! (c) Measurement of $# motor speed control characteristics S1d2In1ut P0tnti06tr Sttin7

S1d 3r164

0

20!

1

200

2

193

3

3"1



"26

"

706

6

932

7

1106

!

13"2

9

1"90

10

1616

rmature olta&e and rmature #urrent wa%eforms correspondin& to step 7

*ield olta&e and *ield #urrent wa%eforms correspondin& to step 7

(d) +tud, of control circuit operation -ate wa%eform of /2

+aw tooth wa%eform

#omparator control input wa%eform

#omparator output wa%eform

-ate wa%eform of /1

CALCULATIONS (b) Measurement of chopper performance with non back emf load VL = δ. V dc

/ere Vdc = 131.8V

S1d2In1ut P0tnti06tr Sttin7

5

Ca89u8atd VL 3V4

Pra9ti9a8 VL 3V4

0

0.021

2.76

7.6

1

0.021

2.76

7.6

2

0.02

"."3

9.6

3

0.0!"

11.20

16.6



0.1"

19.77

23.6

"

0.19

2".0

29

6

0.26

3.26

37

7

0.30

39."

"

!

0.36

7."

"3

9

0.

"7.99

61

10

0."

"9.31

62

Di-9u--i0n (1) 0plain wh, there is a %olta&e at the load e%en when the speedinput potentiometer at minimum. n the /145 time period a %olta&e is applied to the motor terminal because the armature is connected to the source. $urin& this period an increasin& current flows throu&h the armature. hen the /14** motor current freewheels throu&h diode named as $ f . $urin& this period the ener&, stored in the armature inductance flows throu&h the freewheelin& diode and a 8ero %olta&e appears across the armature. nd also the motor current is decreases. f the current decreases to 8ero %alue before the net /145 state discontinuous current conduction occurs. $urin& this period back emf of the armature windin& due to the field flu will appear across the armature. t is the reason for a %olta&e to be appeared across the armature e%en at the speed potentiometer is at minimum. (2) h, the speedinput potentiometer in the first few steps did not respond to the motor speed how the problem can possibl, be eliminated n the first few steps the onperiod of /1 is %er, small. his result in a small a%era&e %olta&e applied across the motor. herefore the a%era&e power of the motor becomes small. his results in lower  speeds. 0%en if there is a small increase in the speed it is not fairl, reflected when the speed le%el is low. /owe%er after the few first steps of the potentiometer settin&s a fair speed %ariation can be identified. his is due to the increased onperiod and hence increased a%era&e power. he motor is operatin& accordin& to the :M output &i%en b, /1. his problem can be eliminated b, settin& the si&nal ran&e set potentiometer input to a lower %alue at the be&innin&. (3) +tate wh, field current wa%eform contains less ripples compared with the field %olta&e wa%eform. *rom the obser%ation it can be seen that the field current wa%e form is almost constant and has less ripples while the %olta&e possesses hu&e ripples. he field windin& has a hi&h inductance and this hi&h inductance will not allow sudden rapid chan&es in the field current. +o it shows a fairl, constant (a%era&e) %alue. ;ut this is not the case in the field %olta&e wa%eform. () #omment on the shape of armature %olta&e and current wa%eforms of part(#) th

he output %olta&e consists of se%eral harmonics some times up to 9  harmonic. his is a alternatin& s ($) he reference for the obser%ation of the control circuit wa%eforms is the pulse &enerator output.-ate wa%eform of /2 (#3) is a s
(6) he functions of potentiometers ?1 ?2 ?3 ? and ?" n dc dri%es speed can be sensed without a tachometer when field current is held constant. @se is made of the fact that the back emf is directl, proportional to speed when the flu is held constant. he  back emf is measured b, deductin& from motor terminal %olta&e a si&nal e