# JNTU Kakinada B-Tech 3-2 RT32026 I POWER SEMICONDUCTOR DRIVES R13 April 2018 Question Paper

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026

5 a) Draw the speed-torque characteristics of with constant supply voltage and variable
frequency based Induction motor drive? Describe the disadvantages of this drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 400 V, 925 rpm squirrel cage induction
motor is having , 5 . 0 , 3 . 0 , 2 . 0 ? ? ? ? ? ?
s r s
X R R and . 1 . 1 ? ?
r
X The motor is
operated from voltage source inverter with constant V/f ratio form 0 to 50 Hz and
having the constant voltage of 400 V above 50 Hz frequency, calculate (i) speed for
a frequency of 35 Hz with half full load torque (ii) torque for a frequency of 35 Hz
for a speed of 650 rpm.
[8M]
6 a) Explain with neat diagram and equations about the static Scherbius system of slip
power recovery scheme?
[8M]
b) A static Kramer drive is used for the speed control of a 6-pole slip ring induction
motor fed from 415 V, 50 Hz supply. The inverter is connected directly to the
supply. If the motor is required to operate at 800 rpm, find the firing advance angle
of the inverter. Voltage across the open-circuited slip rings at stand-still is 600 V.
Allow a voltage drop of 0.7 V and 1.5 V across each of the diodes and thyristors
respectively. Inductor drop is neglected?
[8M]
7 a) Show that the torque of synchronous motor is independent of speed when it
operates in current control mode?
[8M]
b) Explain the synchronous motor drive self-control operation with power factor
improvement?
[8M]

*****

2 of 2
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026

5 a) Draw the speed-torque characteristics of with constant supply voltage and variable
frequency based Induction motor drive? Describe the disadvantages of this drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 400 V, 925 rpm squirrel cage induction
motor is having , 5 . 0 , 3 . 0 , 2 . 0 ? ? ? ? ? ?
s r s
X R R and . 1 . 1 ? ?
r
X The motor is
operated from voltage source inverter with constant V/f ratio form 0 to 50 Hz and
having the constant voltage of 400 V above 50 Hz frequency, calculate (i) speed for
a frequency of 35 Hz with half full load torque (ii) torque for a frequency of 35 Hz
for a speed of 650 rpm.
[8M]
6 a) Explain with neat diagram and equations about the static Scherbius system of slip
power recovery scheme?
[8M]
b) A static Kramer drive is used for the speed control of a 6-pole slip ring induction
motor fed from 415 V, 50 Hz supply. The inverter is connected directly to the
supply. If the motor is required to operate at 800 rpm, find the firing advance angle
of the inverter. Voltage across the open-circuited slip rings at stand-still is 600 V.
Allow a voltage drop of 0.7 V and 1.5 V across each of the diodes and thyristors
respectively. Inductor drop is neglected?
[8M]
7 a) Show that the torque of synchronous motor is independent of speed when it
operates in current control mode?
[8M]
b) Explain the synchronous motor drive self-control operation with power factor
improvement?
[8M]

*****

2 of 2
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) What are the different load torque components, how they are approximated in
deriving the torque equation of motor-load system?
[4M]
b) When discontinuous mode of operation is occurs in the operation of converter fed
DC drives?
[4M]
c) How do you control DC series motor in the second-quadrant? [4M]
d) Why it is required to maintain the ratio of V/f is constant in the control of
induction motor?
[4M]
e) What are the two types of static Scherbius system? [3M]
f) What are the advantages of self-control of synchronous motor? [3M]
PART -B
2 a) Discuss the different modes of operation of electric drive with suitable examples? [8M]
b) A 220V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m.
Determine the speed at which the motor can hold the load by regenerative
braking.
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase semi-converter and describe the effect of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited DC motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by ?? ?? = 400 –
0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a three phase
full controlled rectifier with AC source voltage (phase) of 220 V, 50 Hz and field
is fed from a full controlled single phase rectifier with a single phase source
voltage of 220 V, 50Hz. Drive operates in continuous conduction. Calculate the
firing angles for speeds of 600 rpm and 1200 rpm.
[8M]
4 a) Draw a neat sketch of a four-quadrant DC-DC converter for a variable speed
reversible drive of DC series motor and discuss its operation?
[8M]
b) A 230 V separately excited DC motor takes 50 A at a speed of 800 rpm. It has
armature resistance of 0.4 ?. This motor is controlled by type-C chopper with an
input voltage of 230 V and frequency of 800 Hz. Assuming the continuous
conduction mode, calculate speed-torque characteristics for (i) motoring
operation for duty ratios of 0.3 and 0.6 (ii) regenerative braking operation for
duty ratios of 0.7 and 0.4

1 of 2
[8M]
R13
SET – 2

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026

5 a) Draw the speed-torque characteristics of with constant supply voltage and variable
frequency based Induction motor drive? Describe the disadvantages of this drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 400 V, 925 rpm squirrel cage induction
motor is having , 5 . 0 , 3 . 0 , 2 . 0 ? ? ? ? ? ?
s r s
X R R and . 1 . 1 ? ?
r
X The motor is
operated from voltage source inverter with constant V/f ratio form 0 to 50 Hz and
having the constant voltage of 400 V above 50 Hz frequency, calculate (i) speed for
a frequency of 35 Hz with half full load torque (ii) torque for a frequency of 35 Hz
for a speed of 650 rpm.
[8M]
6 a) Explain with neat diagram and equations about the static Scherbius system of slip
power recovery scheme?
[8M]
b) A static Kramer drive is used for the speed control of a 6-pole slip ring induction
motor fed from 415 V, 50 Hz supply. The inverter is connected directly to the
supply. If the motor is required to operate at 800 rpm, find the firing advance angle
of the inverter. Voltage across the open-circuited slip rings at stand-still is 600 V.
Allow a voltage drop of 0.7 V and 1.5 V across each of the diodes and thyristors
respectively. Inductor drop is neglected?
[8M]
7 a) Show that the torque of synchronous motor is independent of speed when it
operates in current control mode?
[8M]
b) Explain the synchronous motor drive self-control operation with power factor
improvement?
[8M]

*****

2 of 2
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) What are the different load torque components, how they are approximated in
deriving the torque equation of motor-load system?
[4M]
b) When discontinuous mode of operation is occurs in the operation of converter fed
DC drives?
[4M]
c) How do you control DC series motor in the second-quadrant? [4M]
d) Why it is required to maintain the ratio of V/f is constant in the control of
induction motor?
[4M]
e) What are the two types of static Scherbius system? [3M]
f) What are the advantages of self-control of synchronous motor? [3M]
PART -B
2 a) Discuss the different modes of operation of electric drive with suitable examples? [8M]
b) A 220V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m.
Determine the speed at which the motor can hold the load by regenerative
braking.
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase semi-converter and describe the effect of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited DC motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by ?? ?? = 400 –
0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a three phase
full controlled rectifier with AC source voltage (phase) of 220 V, 50 Hz and field
is fed from a full controlled single phase rectifier with a single phase source
voltage of 220 V, 50Hz. Drive operates in continuous conduction. Calculate the
firing angles for speeds of 600 rpm and 1200 rpm.
[8M]
4 a) Draw a neat sketch of a four-quadrant DC-DC converter for a variable speed
reversible drive of DC series motor and discuss its operation?
[8M]
b) A 230 V separately excited DC motor takes 50 A at a speed of 800 rpm. It has
armature resistance of 0.4 ?. This motor is controlled by type-C chopper with an
input voltage of 230 V and frequency of 800 Hz. Assuming the continuous
conduction mode, calculate speed-torque characteristics for (i) motoring
operation for duty ratios of 0.3 and 0.6 (ii) regenerative braking operation for
duty ratios of 0.7 and 0.4

1 of 2
[8M]
R13
SET – 2

Code No: RT32026

5 a) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O , ?? ?? = 0.3 O , ?? ?? = 0.5 O , and
?? ?? = 1.1 O. The motor is operated from voltage source inverter with constant
V/f ratio form 0 to 50 Hz and having the constant voltage of 440 V above 50 Hz
frequency, calculate
i) Speed for a frequency of 25 Hz with half full load torque
ii) Torque for a frequency of 25 Hz for a speed of 600 rpm.
[8M]
b) Explain the closed loop operation of induction motor drive including both current
and speed loop with the help of block diagram?
[8M]
6 a) Explain the operation of induction motor speed control using rotor resistance
variation?
[8M]
b) A three phase, 415 V, 4 pole, 50 Hz star connected slip ring induction motor has
its speed controlled by means of GTO chopper in its rotor circuit. The effective
phase turns ratio from rotor to stator is 0.8. The filter inductor makes the inductor
current ripple free. Losses in the rectifier, inductor, GTO chopper and no load
losses of the motor are neglected. Assume that load torque is proportional to
square of the speed equal to 450 N-m at 1415 rpm. i) For a minimum motor speed
of 1000 rpm, calculate the value of chopper resistance R. ii) For the value of R
obtained in part (i), if the speed is raised to 1300 rpm, calculate inductor current.
iii) Duty cycle of the chopper. iv) Rectified output voltage.
[8M]
7 a) Describe the advantages of self-controlled variable speed synchronous motor
drive over the separate controlled drive?
[8M]
b) Describe the open-loop and closed loop methods of speed control of synchronous
motor fed from VSI?
[8M]

*****

2 of 2

R13
SET – 2

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026

5 a) Draw the speed-torque characteristics of with constant supply voltage and variable
frequency based Induction motor drive? Describe the disadvantages of this drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 400 V, 925 rpm squirrel cage induction
motor is having , 5 . 0 , 3 . 0 , 2 . 0 ? ? ? ? ? ?
s r s
X R R and . 1 . 1 ? ?
r
X The motor is
operated from voltage source inverter with constant V/f ratio form 0 to 50 Hz and
having the constant voltage of 400 V above 50 Hz frequency, calculate (i) speed for
a frequency of 35 Hz with half full load torque (ii) torque for a frequency of 35 Hz
for a speed of 650 rpm.
[8M]
6 a) Explain with neat diagram and equations about the static Scherbius system of slip
power recovery scheme?
[8M]
b) A static Kramer drive is used for the speed control of a 6-pole slip ring induction
motor fed from 415 V, 50 Hz supply. The inverter is connected directly to the
supply. If the motor is required to operate at 800 rpm, find the firing advance angle
of the inverter. Voltage across the open-circuited slip rings at stand-still is 600 V.
Allow a voltage drop of 0.7 V and 1.5 V across each of the diodes and thyristors
respectively. Inductor drop is neglected?
[8M]
7 a) Show that the torque of synchronous motor is independent of speed when it
operates in current control mode?
[8M]
b) Explain the synchronous motor drive self-control operation with power factor
improvement?
[8M]

*****

2 of 2
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) What are the different load torque components, how they are approximated in
deriving the torque equation of motor-load system?
[4M]
b) When discontinuous mode of operation is occurs in the operation of converter fed
DC drives?
[4M]
c) How do you control DC series motor in the second-quadrant? [4M]
d) Why it is required to maintain the ratio of V/f is constant in the control of
induction motor?
[4M]
e) What are the two types of static Scherbius system? [3M]
f) What are the advantages of self-control of synchronous motor? [3M]
PART -B
2 a) Discuss the different modes of operation of electric drive with suitable examples? [8M]
b) A 220V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m.
Determine the speed at which the motor can hold the load by regenerative
braking.
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase semi-converter and describe the effect of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited DC motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by ?? ?? = 400 –
0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a three phase
full controlled rectifier with AC source voltage (phase) of 220 V, 50 Hz and field
is fed from a full controlled single phase rectifier with a single phase source
voltage of 220 V, 50Hz. Drive operates in continuous conduction. Calculate the
firing angles for speeds of 600 rpm and 1200 rpm.
[8M]
4 a) Draw a neat sketch of a four-quadrant DC-DC converter for a variable speed
reversible drive of DC series motor and discuss its operation?
[8M]
b) A 230 V separately excited DC motor takes 50 A at a speed of 800 rpm. It has
armature resistance of 0.4 ?. This motor is controlled by type-C chopper with an
input voltage of 230 V and frequency of 800 Hz. Assuming the continuous
conduction mode, calculate speed-torque characteristics for (i) motoring
operation for duty ratios of 0.3 and 0.6 (ii) regenerative braking operation for
duty ratios of 0.7 and 0.4

1 of 2
[8M]
R13
SET – 2

Code No: RT32026

5 a) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O , ?? ?? = 0.3 O , ?? ?? = 0.5 O , and
?? ?? = 1.1 O. The motor is operated from voltage source inverter with constant
V/f ratio form 0 to 50 Hz and having the constant voltage of 440 V above 50 Hz
frequency, calculate
i) Speed for a frequency of 25 Hz with half full load torque
ii) Torque for a frequency of 25 Hz for a speed of 600 rpm.
[8M]
b) Explain the closed loop operation of induction motor drive including both current
and speed loop with the help of block diagram?
[8M]
6 a) Explain the operation of induction motor speed control using rotor resistance
variation?
[8M]
b) A three phase, 415 V, 4 pole, 50 Hz star connected slip ring induction motor has
its speed controlled by means of GTO chopper in its rotor circuit. The effective
phase turns ratio from rotor to stator is 0.8. The filter inductor makes the inductor
current ripple free. Losses in the rectifier, inductor, GTO chopper and no load
losses of the motor are neglected. Assume that load torque is proportional to
square of the speed equal to 450 N-m at 1415 rpm. i) For a minimum motor speed
of 1000 rpm, calculate the value of chopper resistance R. ii) For the value of R
obtained in part (i), if the speed is raised to 1300 rpm, calculate inductor current.
iii) Duty cycle of the chopper. iv) Rectified output voltage.
[8M]
7 a) Describe the advantages of self-controlled variable speed synchronous motor
drive over the separate controlled drive?
[8M]
b) Describe the open-loop and closed loop methods of speed control of synchronous
motor fed from VSI?
[8M]

*****

2 of 2

R13
SET – 2

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Enumerate all the conditions to be satisfied for regenerative braking operation
takes place?
[4M]
b) Describe the draw backs if armature current in a DC motor is discontinuous? [4M]
c) What are the advantages of DC-DC converter fed drives compared to converter
fed drives?
[4M]
d) What is the effect on power factor at starting when an induction motor is operated
with reduced voltage and frequency operation?
[4M]
e) In the static Kramer drive a diode bridge is replaced by thyristor bridge, what is
speed range possible?
[3M]
f) In self-control of synchronous motor how the frequency is is controlled? [3M]
PART -B
2 a) Explain briefly, what are the factors involved in the selection of drives? [8M]
b) A 220 V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m. If the
motor is to be operated by dynamic braking, calculate the value of external
resistance to be connected across the armature when the motor should carry the
[8M]
3 a) Explain the operation of DC series motor operated with 3-phase semi converter?
Describe its speed control characteristics with respect to change of firing angle?
[8M]
b) A 250 V separately excited dc motor has an armature resistance of 2.5 ?. When
driving a load at 600 rpm with constant torque, the armature takes 40 A. This
motor is controlled by a three phase full converter circuit a phase input voltage of
250 V with continuous current. What should be the value of firing angle to reduce
the speed from 600 to 400 rpm, with the load torque maintained constant?
[8M]
converters?
[8M]
b) A 220 V, 900 rpm, 30 A separately excited DC motor has an armature resistance
of 0.7 O and inductance of 50mH. The motor is controlled in regenerative braking
by a chopper operating at a frequency of 800 Hz from a DC source of 220 V.
Assuming continuous conduction, (i) Calculate duty ratio of chopper for rated
torque and speed of 600 rpm. (ii) What will be the motor speed for duty ratio of
0.6 and rated motor torque (iii) What will be the maximum allowable speed of the
motor, if the chopper has a maximum duty ratio of 0.9 and maximum allowable
motor current is twice the rated current?
1 of 2
[8M]
R13
SET – 3

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026

5 a) Draw the speed-torque characteristics of with constant supply voltage and variable
frequency based Induction motor drive? Describe the disadvantages of this drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 400 V, 925 rpm squirrel cage induction
motor is having , 5 . 0 , 3 . 0 , 2 . 0 ? ? ? ? ? ?
s r s
X R R and . 1 . 1 ? ?
r
X The motor is
operated from voltage source inverter with constant V/f ratio form 0 to 50 Hz and
having the constant voltage of 400 V above 50 Hz frequency, calculate (i) speed for
a frequency of 35 Hz with half full load torque (ii) torque for a frequency of 35 Hz
for a speed of 650 rpm.
[8M]
6 a) Explain with neat diagram and equations about the static Scherbius system of slip
power recovery scheme?
[8M]
b) A static Kramer drive is used for the speed control of a 6-pole slip ring induction
motor fed from 415 V, 50 Hz supply. The inverter is connected directly to the
supply. If the motor is required to operate at 800 rpm, find the firing advance angle
of the inverter. Voltage across the open-circuited slip rings at stand-still is 600 V.
Allow a voltage drop of 0.7 V and 1.5 V across each of the diodes and thyristors
respectively. Inductor drop is neglected?
[8M]
7 a) Show that the torque of synchronous motor is independent of speed when it
operates in current control mode?
[8M]
b) Explain the synchronous motor drive self-control operation with power factor
improvement?
[8M]

*****

2 of 2
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) What are the different load torque components, how they are approximated in
deriving the torque equation of motor-load system?
[4M]
b) When discontinuous mode of operation is occurs in the operation of converter fed
DC drives?
[4M]
c) How do you control DC series motor in the second-quadrant? [4M]
d) Why it is required to maintain the ratio of V/f is constant in the control of
induction motor?
[4M]
e) What are the two types of static Scherbius system? [3M]
f) What are the advantages of self-control of synchronous motor? [3M]
PART -B
2 a) Discuss the different modes of operation of electric drive with suitable examples? [8M]
b) A 220V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m.
Determine the speed at which the motor can hold the load by regenerative
braking.
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase semi-converter and describe the effect of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited DC motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by ?? ?? = 400 –
0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a three phase
full controlled rectifier with AC source voltage (phase) of 220 V, 50 Hz and field
is fed from a full controlled single phase rectifier with a single phase source
voltage of 220 V, 50Hz. Drive operates in continuous conduction. Calculate the
firing angles for speeds of 600 rpm and 1200 rpm.
[8M]
4 a) Draw a neat sketch of a four-quadrant DC-DC converter for a variable speed
reversible drive of DC series motor and discuss its operation?
[8M]
b) A 230 V separately excited DC motor takes 50 A at a speed of 800 rpm. It has
armature resistance of 0.4 ?. This motor is controlled by type-C chopper with an
input voltage of 230 V and frequency of 800 Hz. Assuming the continuous
conduction mode, calculate speed-torque characteristics for (i) motoring
operation for duty ratios of 0.3 and 0.6 (ii) regenerative braking operation for
duty ratios of 0.7 and 0.4

1 of 2
[8M]
R13
SET – 2

Code No: RT32026

5 a) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O , ?? ?? = 0.3 O , ?? ?? = 0.5 O , and
?? ?? = 1.1 O. The motor is operated from voltage source inverter with constant
V/f ratio form 0 to 50 Hz and having the constant voltage of 440 V above 50 Hz
frequency, calculate
i) Speed for a frequency of 25 Hz with half full load torque
ii) Torque for a frequency of 25 Hz for a speed of 600 rpm.
[8M]
b) Explain the closed loop operation of induction motor drive including both current
and speed loop with the help of block diagram?
[8M]
6 a) Explain the operation of induction motor speed control using rotor resistance
variation?
[8M]
b) A three phase, 415 V, 4 pole, 50 Hz star connected slip ring induction motor has
its speed controlled by means of GTO chopper in its rotor circuit. The effective
phase turns ratio from rotor to stator is 0.8. The filter inductor makes the inductor
current ripple free. Losses in the rectifier, inductor, GTO chopper and no load
losses of the motor are neglected. Assume that load torque is proportional to
square of the speed equal to 450 N-m at 1415 rpm. i) For a minimum motor speed
of 1000 rpm, calculate the value of chopper resistance R. ii) For the value of R
obtained in part (i), if the speed is raised to 1300 rpm, calculate inductor current.
iii) Duty cycle of the chopper. iv) Rectified output voltage.
[8M]
7 a) Describe the advantages of self-controlled variable speed synchronous motor
drive over the separate controlled drive?
[8M]
b) Describe the open-loop and closed loop methods of speed control of synchronous
motor fed from VSI?
[8M]

*****

2 of 2

R13
SET – 2

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Enumerate all the conditions to be satisfied for regenerative braking operation
takes place?
[4M]
b) Describe the draw backs if armature current in a DC motor is discontinuous? [4M]
c) What are the advantages of DC-DC converter fed drives compared to converter
fed drives?
[4M]
d) What is the effect on power factor at starting when an induction motor is operated
with reduced voltage and frequency operation?
[4M]
e) In the static Kramer drive a diode bridge is replaced by thyristor bridge, what is
speed range possible?
[3M]
f) In self-control of synchronous motor how the frequency is is controlled? [3M]
PART -B
2 a) Explain briefly, what are the factors involved in the selection of drives? [8M]
b) A 220 V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m. If the
motor is to be operated by dynamic braking, calculate the value of external
resistance to be connected across the armature when the motor should carry the
[8M]
3 a) Explain the operation of DC series motor operated with 3-phase semi converter?
Describe its speed control characteristics with respect to change of firing angle?
[8M]
b) A 250 V separately excited dc motor has an armature resistance of 2.5 ?. When
driving a load at 600 rpm with constant torque, the armature takes 40 A. This
motor is controlled by a three phase full converter circuit a phase input voltage of
250 V with continuous current. What should be the value of firing angle to reduce
the speed from 600 to 400 rpm, with the load torque maintained constant?
[8M]
converters?
[8M]
b) A 220 V, 900 rpm, 30 A separately excited DC motor has an armature resistance
of 0.7 O and inductance of 50mH. The motor is controlled in regenerative braking
by a chopper operating at a frequency of 800 Hz from a DC source of 220 V.
Assuming continuous conduction, (i) Calculate duty ratio of chopper for rated
torque and speed of 600 rpm. (ii) What will be the motor speed for duty ratio of
0.6 and rated motor torque (iii) What will be the maximum allowable speed of the
motor, if the chopper has a maximum duty ratio of 0.9 and maximum allowable
motor current is twice the rated current?
1 of 2
[8M]
R13
SET – 3

Code No: RT32026

5 a) With necessary diagrams and theoretical principles explain stator
voltage/frequency control of induction motor?
[8M]
b) A 3 phase, 4 pole, 50 Hz squirrel cage Induction motor has the following circuit
parameters: ?? 1
= 0.05 O, ?? 2
= 0.09 O, ?? 1
+ ?? 2
= 0.55 O . The motor is star
connected and rated voltage is 440V. It drives a load whose torqueis proportional
to the speed and is given as ?? ?? = 0.05 ?? N-m. Determine the speed and torque of
the motor for a firing angle of 60
0
of the AC Voltage Controller on a 440V, 50 Hz
supply?
[8M]
6 a) With relevant circuit and characteristics, explain the operation of static Scherbius
drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O ,?? ?? ‘
= 0.3 O , ?? ?? = ?? ?? ‘
= 1.2 O , and
?? ?? = 50 O. The stator to rotor turns ratio is 4. The motor is controlled by static
rotor resistance control. Find the external resistance to be connected such that
break down torque is produced at slip equal to 2, now the motor connections are
changed from motoring to single phase AC dynamic braking with three
connections (i.e. one phase is in series with other two phase in parallel). Calculate
the braking current and torque for a speed of 600 rpm?
[8M]
7 a) Describe separate control mode of operation of a synchronous motor drive in
detail?
[8M]
b) Draw the block diagram of closed loop synchronous drive fed from VSI and
explain its operation?
[8M]

*****

2 of 2
R13
SET – 3

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026

5 a) Draw the speed-torque characteristics of with constant supply voltage and variable
frequency based Induction motor drive? Describe the disadvantages of this drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 400 V, 925 rpm squirrel cage induction
motor is having , 5 . 0 , 3 . 0 , 2 . 0 ? ? ? ? ? ?
s r s
X R R and . 1 . 1 ? ?
r
X The motor is
operated from voltage source inverter with constant V/f ratio form 0 to 50 Hz and
having the constant voltage of 400 V above 50 Hz frequency, calculate (i) speed for
a frequency of 35 Hz with half full load torque (ii) torque for a frequency of 35 Hz
for a speed of 650 rpm.
[8M]
6 a) Explain with neat diagram and equations about the static Scherbius system of slip
power recovery scheme?
[8M]
b) A static Kramer drive is used for the speed control of a 6-pole slip ring induction
motor fed from 415 V, 50 Hz supply. The inverter is connected directly to the
supply. If the motor is required to operate at 800 rpm, find the firing advance angle
of the inverter. Voltage across the open-circuited slip rings at stand-still is 600 V.
Allow a voltage drop of 0.7 V and 1.5 V across each of the diodes and thyristors
respectively. Inductor drop is neglected?
[8M]
7 a) Show that the torque of synchronous motor is independent of speed when it
operates in current control mode?
[8M]
b) Explain the synchronous motor drive self-control operation with power factor
improvement?
[8M]

*****

2 of 2
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) What are the different load torque components, how they are approximated in
deriving the torque equation of motor-load system?
[4M]
b) When discontinuous mode of operation is occurs in the operation of converter fed
DC drives?
[4M]
c) How do you control DC series motor in the second-quadrant? [4M]
d) Why it is required to maintain the ratio of V/f is constant in the control of
induction motor?
[4M]
e) What are the two types of static Scherbius system? [3M]
f) What are the advantages of self-control of synchronous motor? [3M]
PART -B
2 a) Discuss the different modes of operation of electric drive with suitable examples? [8M]
b) A 220V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m.
Determine the speed at which the motor can hold the load by regenerative
braking.
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase semi-converter and describe the effect of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited DC motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by ?? ?? = 400 –
0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a three phase
full controlled rectifier with AC source voltage (phase) of 220 V, 50 Hz and field
is fed from a full controlled single phase rectifier with a single phase source
voltage of 220 V, 50Hz. Drive operates in continuous conduction. Calculate the
firing angles for speeds of 600 rpm and 1200 rpm.
[8M]
4 a) Draw a neat sketch of a four-quadrant DC-DC converter for a variable speed
reversible drive of DC series motor and discuss its operation?
[8M]
b) A 230 V separately excited DC motor takes 50 A at a speed of 800 rpm. It has
armature resistance of 0.4 ?. This motor is controlled by type-C chopper with an
input voltage of 230 V and frequency of 800 Hz. Assuming the continuous
conduction mode, calculate speed-torque characteristics for (i) motoring
operation for duty ratios of 0.3 and 0.6 (ii) regenerative braking operation for
duty ratios of 0.7 and 0.4

1 of 2
[8M]
R13
SET – 2

Code No: RT32026

5 a) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O , ?? ?? = 0.3 O , ?? ?? = 0.5 O , and
?? ?? = 1.1 O. The motor is operated from voltage source inverter with constant
V/f ratio form 0 to 50 Hz and having the constant voltage of 440 V above 50 Hz
frequency, calculate
i) Speed for a frequency of 25 Hz with half full load torque
ii) Torque for a frequency of 25 Hz for a speed of 600 rpm.
[8M]
b) Explain the closed loop operation of induction motor drive including both current
and speed loop with the help of block diagram?
[8M]
6 a) Explain the operation of induction motor speed control using rotor resistance
variation?
[8M]
b) A three phase, 415 V, 4 pole, 50 Hz star connected slip ring induction motor has
its speed controlled by means of GTO chopper in its rotor circuit. The effective
phase turns ratio from rotor to stator is 0.8. The filter inductor makes the inductor
current ripple free. Losses in the rectifier, inductor, GTO chopper and no load
losses of the motor are neglected. Assume that load torque is proportional to
square of the speed equal to 450 N-m at 1415 rpm. i) For a minimum motor speed
of 1000 rpm, calculate the value of chopper resistance R. ii) For the value of R
obtained in part (i), if the speed is raised to 1300 rpm, calculate inductor current.
iii) Duty cycle of the chopper. iv) Rectified output voltage.
[8M]
7 a) Describe the advantages of self-controlled variable speed synchronous motor
drive over the separate controlled drive?
[8M]
b) Describe the open-loop and closed loop methods of speed control of synchronous
motor fed from VSI?
[8M]

*****

2 of 2

R13
SET – 2

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Enumerate all the conditions to be satisfied for regenerative braking operation
takes place?
[4M]
b) Describe the draw backs if armature current in a DC motor is discontinuous? [4M]
c) What are the advantages of DC-DC converter fed drives compared to converter
fed drives?
[4M]
d) What is the effect on power factor at starting when an induction motor is operated
with reduced voltage and frequency operation?
[4M]
e) In the static Kramer drive a diode bridge is replaced by thyristor bridge, what is
speed range possible?
[3M]
f) In self-control of synchronous motor how the frequency is is controlled? [3M]
PART -B
2 a) Explain briefly, what are the factors involved in the selection of drives? [8M]
b) A 220 V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m. If the
motor is to be operated by dynamic braking, calculate the value of external
resistance to be connected across the armature when the motor should carry the
[8M]
3 a) Explain the operation of DC series motor operated with 3-phase semi converter?
Describe its speed control characteristics with respect to change of firing angle?
[8M]
b) A 250 V separately excited dc motor has an armature resistance of 2.5 ?. When
driving a load at 600 rpm with constant torque, the armature takes 40 A. This
motor is controlled by a three phase full converter circuit a phase input voltage of
250 V with continuous current. What should be the value of firing angle to reduce
the speed from 600 to 400 rpm, with the load torque maintained constant?
[8M]
converters?
[8M]
b) A 220 V, 900 rpm, 30 A separately excited DC motor has an armature resistance
of 0.7 O and inductance of 50mH. The motor is controlled in regenerative braking
by a chopper operating at a frequency of 800 Hz from a DC source of 220 V.
Assuming continuous conduction, (i) Calculate duty ratio of chopper for rated
torque and speed of 600 rpm. (ii) What will be the motor speed for duty ratio of
0.6 and rated motor torque (iii) What will be the maximum allowable speed of the
motor, if the chopper has a maximum duty ratio of 0.9 and maximum allowable
motor current is twice the rated current?
1 of 2
[8M]
R13
SET – 3

Code No: RT32026

5 a) With necessary diagrams and theoretical principles explain stator
voltage/frequency control of induction motor?
[8M]
b) A 3 phase, 4 pole, 50 Hz squirrel cage Induction motor has the following circuit
parameters: ?? 1
= 0.05 O, ?? 2
= 0.09 O, ?? 1
+ ?? 2
= 0.55 O . The motor is star
connected and rated voltage is 440V. It drives a load whose torqueis proportional
to the speed and is given as ?? ?? = 0.05 ?? N-m. Determine the speed and torque of
the motor for a firing angle of 60
0
of the AC Voltage Controller on a 440V, 50 Hz
supply?
[8M]
6 a) With relevant circuit and characteristics, explain the operation of static Scherbius
drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O ,?? ?? ‘
= 0.3 O , ?? ?? = ?? ?? ‘
= 1.2 O , and
?? ?? = 50 O. The stator to rotor turns ratio is 4. The motor is controlled by static
rotor resistance control. Find the external resistance to be connected such that
break down torque is produced at slip equal to 2, now the motor connections are
changed from motoring to single phase AC dynamic braking with three
connections (i.e. one phase is in series with other two phase in parallel). Calculate
the braking current and torque for a speed of 600 rpm?
[8M]
7 a) Describe separate control mode of operation of a synchronous motor drive in
detail?
[8M]
b) Draw the block diagram of closed loop synchronous drive fed from VSI and
explain its operation?
[8M]

*****

2 of 2
R13
SET – 3

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by
deceleration mode of the electric drive?
[4M]
b) What are the advantages of continuous current conduction mode of operation DC
motor?
[4M]
c) What are the advantages of four-quadrant DC-DC converter fed DC drives? [4M]
d) What are disadvantages of AC voltage controller fed induction motor drive? [4M]
e) In the static Kramer drive a diode bridge and DC motor are used, what is speed
range possible?
[3M]
f) In separate control of synchronous motor how the frequency of the supply to
motor is is changed?
[3M]
PART -B
2 a) Explain the multi-quadrant operation of an electric motor with relevant
characteristics when the motor is driving a hoist load?
[8M]
b) The electric motor drive develops a torque expressed by ?? ?? = ?? ?? + ?? where ??
and ?? are positive constants, the motor is supposed to drive the load torque which
is given by ?? ?? = ?? ?? 2
+ ?? where ?? and ?? are other positive constants, The total
inertia of the rotating masses is ?? , Determine the relation among the among
?? , ?? , ?? and ?? in order to start the motor and load together and have an equilibrium
operating speed and also calculate this equilibrium operating speed?
[8M]
3 a) Explain the operation of DC series motor operated with 3-phase full converter?
Describe its speed control characteristics with respect to change of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by
?? ?? = 400 – 0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a
three phase semi controlled rectifier with AC source voltage (phase) of 220 V, 50
Hz and field is fed from a full controlled single phase rectifier with a single phase
source voltage of 220 V, 50Hz. Drive operates in continuous conduction.
Calculate the firing angles for speeds of 700 rpm and 1500 rpm.

1 of 2

[8M]
R13
SET – 4

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by acceleration
mode of the electric drive?
[4M]
b) Describe the various drawbacks of rectifier controlled dc series motor drive? [4M]
c) How do you control separately excited DC motor in the fourth-quadrant? [4M]
d) Draw the speed-torque characteristics of induction motor with variable supply
voltage and constant frequency?
[4M]
e) What are the advantages of Kramer drive compared to the Scherbius drive? [3M]
f) When can be a synchronous motor is load commutated? [3M]
PART -B
2 a)The electric motor drive develops a torque expressed by b a T
m
? ? ? where ?? and
?? are positive constants, the motor is supposed to drive the load torque which is
given by d c T
L
? ?
2
? where c and d are other positive constants, The total inertia
of the rotating masses is J, Determine the relation among the a, b, c and d in order
to start the motor and load together and have an equilibrium operating speed and
also calculate this equilibrium operating speed?
[8M]
b) Develop a criterion for finding the steady state stability of an electric drive?
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase full converter and describe the effect of firing angle?
[8M]
b) A separately excited DC motor is operating from a three phase semi converter at a
speed of 1400 rpm, with phase input voltage of 330 V (peak-to-peak), and back
emf of 120 V. The converter is fired symmetrically with . 30
0
? ? The armature
resistance of 0.5 ?. Calculate average current and the motor developed torque?

[8M]
4 a) Explain the operation of two-quadrant, type-D chopper drive with necessary
equivalent circuits and waveforms?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 400 V, armature resistance is 0.25 O,
. sec/ 2 . 1 rad V K
m
? ? The average armature current during regenerative braking is
kept constant at 200 A. For a duty cycle of 60% of chopper, determine the
following: (i) power fed back to the supply. (ii) Minimum and maximum braking
speeds. (iii) Speed during regenerative braking.

1 of 2
[8M]
R13
SET – 1

Code No: RT32026

5 a) Draw the speed-torque characteristics of with constant supply voltage and variable
frequency based Induction motor drive? Describe the disadvantages of this drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 400 V, 925 rpm squirrel cage induction
motor is having , 5 . 0 , 3 . 0 , 2 . 0 ? ? ? ? ? ?
s r s
X R R and . 1 . 1 ? ?
r
X The motor is
operated from voltage source inverter with constant V/f ratio form 0 to 50 Hz and
having the constant voltage of 400 V above 50 Hz frequency, calculate (i) speed for
a frequency of 35 Hz with half full load torque (ii) torque for a frequency of 35 Hz
for a speed of 650 rpm.
[8M]
6 a) Explain with neat diagram and equations about the static Scherbius system of slip
power recovery scheme?
[8M]
b) A static Kramer drive is used for the speed control of a 6-pole slip ring induction
motor fed from 415 V, 50 Hz supply. The inverter is connected directly to the
supply. If the motor is required to operate at 800 rpm, find the firing advance angle
of the inverter. Voltage across the open-circuited slip rings at stand-still is 600 V.
Allow a voltage drop of 0.7 V and 1.5 V across each of the diodes and thyristors
respectively. Inductor drop is neglected?
[8M]
7 a) Show that the torque of synchronous motor is independent of speed when it
operates in current control mode?
[8M]
b) Explain the synchronous motor drive self-control operation with power factor
improvement?
[8M]

*****

2 of 2
R13
SET – 1

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) What are the different load torque components, how they are approximated in
deriving the torque equation of motor-load system?
[4M]
b) When discontinuous mode of operation is occurs in the operation of converter fed
DC drives?
[4M]
c) How do you control DC series motor in the second-quadrant? [4M]
d) Why it is required to maintain the ratio of V/f is constant in the control of
induction motor?
[4M]
e) What are the two types of static Scherbius system? [3M]
f) What are the advantages of self-control of synchronous motor? [3M]
PART -B
2 a) Discuss the different modes of operation of electric drive with suitable examples? [8M]
b) A 220V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m.
Determine the speed at which the motor can hold the load by regenerative
braking.
[8M]
3 a) Obtain the speed-torque characteristics of separately excited DC motor operated
with 3-phase semi-converter and describe the effect of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited DC motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by ?? ?? = 400 –
0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a three phase
full controlled rectifier with AC source voltage (phase) of 220 V, 50 Hz and field
is fed from a full controlled single phase rectifier with a single phase source
voltage of 220 V, 50Hz. Drive operates in continuous conduction. Calculate the
firing angles for speeds of 600 rpm and 1200 rpm.
[8M]
4 a) Draw a neat sketch of a four-quadrant DC-DC converter for a variable speed
reversible drive of DC series motor and discuss its operation?
[8M]
b) A 230 V separately excited DC motor takes 50 A at a speed of 800 rpm. It has
armature resistance of 0.4 ?. This motor is controlled by type-C chopper with an
input voltage of 230 V and frequency of 800 Hz. Assuming the continuous
conduction mode, calculate speed-torque characteristics for (i) motoring
operation for duty ratios of 0.3 and 0.6 (ii) regenerative braking operation for
duty ratios of 0.7 and 0.4

1 of 2
[8M]
R13
SET – 2

Code No: RT32026

5 a) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O , ?? ?? = 0.3 O , ?? ?? = 0.5 O , and
?? ?? = 1.1 O. The motor is operated from voltage source inverter with constant
V/f ratio form 0 to 50 Hz and having the constant voltage of 440 V above 50 Hz
frequency, calculate
i) Speed for a frequency of 25 Hz with half full load torque
ii) Torque for a frequency of 25 Hz for a speed of 600 rpm.
[8M]
b) Explain the closed loop operation of induction motor drive including both current
and speed loop with the help of block diagram?
[8M]
6 a) Explain the operation of induction motor speed control using rotor resistance
variation?
[8M]
b) A three phase, 415 V, 4 pole, 50 Hz star connected slip ring induction motor has
its speed controlled by means of GTO chopper in its rotor circuit. The effective
phase turns ratio from rotor to stator is 0.8. The filter inductor makes the inductor
current ripple free. Losses in the rectifier, inductor, GTO chopper and no load
losses of the motor are neglected. Assume that load torque is proportional to
square of the speed equal to 450 N-m at 1415 rpm. i) For a minimum motor speed
of 1000 rpm, calculate the value of chopper resistance R. ii) For the value of R
obtained in part (i), if the speed is raised to 1300 rpm, calculate inductor current.
iii) Duty cycle of the chopper. iv) Rectified output voltage.
[8M]
7 a) Describe the advantages of self-controlled variable speed synchronous motor
drive over the separate controlled drive?
[8M]
b) Describe the open-loop and closed loop methods of speed control of synchronous
motor fed from VSI?
[8M]

*****

2 of 2

R13
SET – 2

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Enumerate all the conditions to be satisfied for regenerative braking operation
takes place?
[4M]
b) Describe the draw backs if armature current in a DC motor is discontinuous? [4M]
c) What are the advantages of DC-DC converter fed drives compared to converter
fed drives?
[4M]
d) What is the effect on power factor at starting when an induction motor is operated
with reduced voltage and frequency operation?
[4M]
e) In the static Kramer drive a diode bridge is replaced by thyristor bridge, what is
speed range possible?
[3M]
f) In self-control of synchronous motor how the frequency is is controlled? [3M]
PART -B
2 a) Explain briefly, what are the factors involved in the selection of drives? [8M]
b) A 220 V, 900 rpm, 70 A DC separately excited motor has an armature resistance
of 0.05 ?. It is coupled to an overhauling load with a torque of 200 N-m. If the
motor is to be operated by dynamic braking, calculate the value of external
resistance to be connected across the armature when the motor should carry the
[8M]
3 a) Explain the operation of DC series motor operated with 3-phase semi converter?
Describe its speed control characteristics with respect to change of firing angle?
[8M]
b) A 250 V separately excited dc motor has an armature resistance of 2.5 ?. When
driving a load at 600 rpm with constant torque, the armature takes 40 A. This
motor is controlled by a three phase full converter circuit a phase input voltage of
250 V with continuous current. What should be the value of firing angle to reduce
the speed from 600 to 400 rpm, with the load torque maintained constant?
[8M]
converters?
[8M]
b) A 220 V, 900 rpm, 30 A separately excited DC motor has an armature resistance
of 0.7 O and inductance of 50mH. The motor is controlled in regenerative braking
by a chopper operating at a frequency of 800 Hz from a DC source of 220 V.
Assuming continuous conduction, (i) Calculate duty ratio of chopper for rated
torque and speed of 600 rpm. (ii) What will be the motor speed for duty ratio of
0.6 and rated motor torque (iii) What will be the maximum allowable speed of the
motor, if the chopper has a maximum duty ratio of 0.9 and maximum allowable
motor current is twice the rated current?
1 of 2
[8M]
R13
SET – 3

Code No: RT32026

5 a) With necessary diagrams and theoretical principles explain stator
voltage/frequency control of induction motor?
[8M]
b) A 3 phase, 4 pole, 50 Hz squirrel cage Induction motor has the following circuit
parameters: ?? 1
= 0.05 O, ?? 2
= 0.09 O, ?? 1
+ ?? 2
= 0.55 O . The motor is star
connected and rated voltage is 440V. It drives a load whose torqueis proportional
to the speed and is given as ?? ?? = 0.05 ?? N-m. Determine the speed and torque of
the motor for a firing angle of 60
0
of the AC Voltage Controller on a 440V, 50 Hz
supply?
[8M]
6 a) With relevant circuit and characteristics, explain the operation of static Scherbius
drive?
[8M]
b) For a 3-phase delta connected 6-pole 50 Hz 440 V, 905 rpm squirrel cage
induction motor is having ?? ?? = 0.2 O ,?? ?? ‘
= 0.3 O , ?? ?? = ?? ?? ‘
= 1.2 O , and
?? ?? = 50 O. The stator to rotor turns ratio is 4. The motor is controlled by static
rotor resistance control. Find the external resistance to be connected such that
break down torque is produced at slip equal to 2, now the motor connections are
changed from motoring to single phase AC dynamic braking with three
connections (i.e. one phase is in series with other two phase in parallel). Calculate
the braking current and torque for a speed of 600 rpm?
[8M]
7 a) Describe separate control mode of operation of a synchronous motor drive in
detail?
[8M]
b) Draw the block diagram of closed loop synchronous drive fed from VSI and
explain its operation?
[8M]

*****

2 of 2
R13
SET – 3

Code No: RT32026
III B. Tech II Semester Regular/Supplementary Examinations, April-2018
POWER SEMICONDUCTOR DRIVES
(Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B)2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
*****
PART ?A
1 a) Write the torque equation of the motor-load system? What is meant by
deceleration mode of the electric drive?
[4M]
b) What are the advantages of continuous current conduction mode of operation DC
motor?
[4M]
c) What are the advantages of four-quadrant DC-DC converter fed DC drives? [4M]
d) What are disadvantages of AC voltage controller fed induction motor drive? [4M]
e) In the static Kramer drive a diode bridge and DC motor are used, what is speed
range possible?
[3M]
f) In separate control of synchronous motor how the frequency of the supply to
motor is is changed?
[3M]
PART -B
2 a) Explain the multi-quadrant operation of an electric motor with relevant
characteristics when the motor is driving a hoist load?
[8M]
b) The electric motor drive develops a torque expressed by ?? ?? = ?? ?? + ?? where ??
and ?? are positive constants, the motor is supposed to drive the load torque which
is given by ?? ?? = ?? ?? 2
+ ?? where ?? and ?? are other positive constants, The total
inertia of the rotating masses is ?? , Determine the relation among the among
?? , ?? , ?? and ?? in order to start the motor and load together and have an equilibrium
operating speed and also calculate this equilibrium operating speed?
[8M]
3 a) Explain the operation of DC series motor operated with 3-phase full converter?
Describe its speed control characteristics with respect to change of firing angle?
[8M]
b) A 250 V, 900 rpm, 100 A separately excited motor has armature and field
resistances of 0.05 and 200 ? respectively. Load torque is given by
?? ?? = 400 – 0.25 ?? N-m. Where ? ?? ? is the speed in rpm. Armature is fed from a
three phase semi controlled rectifier with AC source voltage (phase) of 220 V, 50
Hz and field is fed from a full controlled single phase rectifier with a single phase
source voltage of 220 V, 50Hz. Drive operates in continuous conduction.
Calculate the firing angles for speeds of 700 rpm and 1500 rpm.

1 of 2

[8M]
R13
SET – 4

Code No: RT32026

4 a) Discuss the closed loop operation of DC series motor drive fed with suitable DC-
DC converter?
[8M]
b) A DC chopper is used for regenerative braking of a separately excited DC motor.
The supply input voltage is 250 V, armature resistance is 0.4 O,
?? ?? = 1.2 ?? – ?? ?? ?? /?? ?? ?? . The average armature current during regenerative
braking is kept constant at 100 A. For a duty cycle of 60% of chopper, determine
the following:
i) Power fed back to the supply.
ii) Minimum and maximum braking speeds.
iii) Speed during regenerative braking.
[8M]
5 a) With necessary diagrams and theoretical principles explain the control induction
motor with stator constant voltage and variable frequency for below and above
rated speeds?
[8M]
b) A 3 phase, star connected, 50 Hz, 4-pole induction motor has the following
parameters in ohms per phase referred to the stator:
?? ?? = ?? ?? ‘
= 0.034 O , ?? ?? = ?? ?? ‘
= 0.15 O . The motor is controlled by variable
frequency control with a constant (V/f). Determine the following for an operating
frequency of 25 Hz
i) The breakdown torque as a ratio of its value at the rated frequency for motoring
and braking.
ii) The starting torque and rotor current in terms of their values at the rated
frequency.
[8M]
6 a) Draw the speed-torque characteristics of rotor resistance controlled induction
motor and explain the effect of rotor resistance?
[6M]
b) A 415V, 50 Hz, 6 Pole star connected slip ring induction motor is controlled by
static Kramer drive. The effective phase turns ratio from rotor to stator is 0.7, the
transformer turns ratio from l.v side to h.v side is 0.4. The load torque is
proportional to the square of the speed and it is equal to 250 N-m at 870 rpm. To
operate at 750 rpm calculate (i) rotor rectifier voltage (ii) delay angle of the
inverter (iii) efficiency, if the inductor resistance is 0.02 ?, stator and rotor
resistances are 0.01 ? and 0.03 ? respectively. Assume losses in diode rectifier,
inductor and transformer are negligible.

[10M]
7 a) Explain the working of synchronous motor operating in self-controlled mode? [8M]
b) Explain the closed loop control of PWM fed synchronous motor drive employing
variable frequency control?
[8M]
*****
R13
SET – 4

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