Download File

EE 2352 — SOLID STATE DRIVES
UNIT-I
PART-A
1.
Write the fundamental torque equation of motor load system.
2.
Write the factors to be considered to select a motor to drive the load.
3.
What are the disadvantages of DC motors?
4.
What are the various types of load torques?
5.
What is meant by dynamic torque?
6.
When does an equilibrium point be stable in speed-torque plane of motor-load system?
7.
Define – Steady State Stability in drive characteristics
8.
What are the three modes of operation for electrical drive?
9.
What is meant by regenerative braking?
10. What are all the conditions to be satisfied for the regenerative braking operation to take
place?
PART-B
1. A motor drives two loads. One has rotational motion. It is coupled to the motor through
a reduction gear with a = 0.1 and efficiency of 90%. The load has a moment of inertia of
10 kg-m2 and a torque of 10 N-m. Other load has translational motion and consists of
1000 kg weight to be lifted up at a uniform speed of 1.5 m/s, coupling between this load
and the motor has an efficiency of 85%. Motor has inertia of 0.2 kg-m2 and runs at a
constant speed of 1420 rpm. Determine equivalent inertia referred to the motor shaft and
power developed by the motor.
(16)
2. Derive and explain the equations governing motor load.
(16)
3. State the essential parts of electrical drive. What are the functions of power modulator?
(8)
4. A drive has the following parameters: J=10 kg-m2, T = 100-0.1 N,N-m. Passive load
torque T1 = 0.05 N,N-m where N is the speed in rpm. Initially the drive is operating in
steady state. Now it is to be reversed. For this motor characteristic is changed to
T = -100-0.1 N,N-m. Calculate the time of reversal.
(8)
5. Derive the mathematical condition for the steady state stability analysis of equilibrium
operating point.
(16)
6. Explain in detail, the multi quadrant operation of low speed hoist in speed torque plane.
(16)
7. Describe the various modes of operation of an electrical drive.
(16)
8. Explain in detail, the principle of regenerative braking used in the four quadrant industrial
drives.
(16)
9. Derive the equations for the equivalent moment of inertia and load torque of loads with
translational motion.
(8)
10. Explain the concept of steady state stability conditions in industrial drives.
(8)
UNIT II
PART-A
1. Why does the armature voltage control is not preferred for the speeds above the rated
value in dc motors?
2. Draw the characteristics of torque and power limitations of dc drives operating with
combined armature of field control.
3. What is meant by continuous and discontinuous operations?
4. What is the difference between continuous and discontinuous conduction modes?
5. Write the conditions under which the DC motor operates under continuous current mode.
6. What is CLC in chopper fed dc drives?
7. What is meant by TRC?
8. What are applications of chopper fed DC drives?
9. What are the merits of four quadrant operation of a converter?
10. List out the drawbacks of ac-dc converter fed DC drive.
PART-B
1. Explain in detail, the operation of a three phase fully controlled converter fed separately
excited DC motor.
(16)
2. Explain in detail, the operation of a single phase fully controlled converter fed separately
excited DC motor.
(16)
3. Explain in detail, the operation of 3 phase fully controlled converter fed DC drive with
neat waveforms for X = 30° and X = 140°.
(16)
4. Explain in detail, the steady state analysis of single phase fully controlled converter fed
separately excited DC motor drive in continuous and discontinuous conduction modes.
(16)
5. Speed of a separately excited DC motor is controlled by means of two 3 phase full
converters one in the armature circuit and the other in the field circuit and both are fed
from 3 phase, 400 V, 50 Hz supply. Resistances of the armature and field circuits are
0.2 Ω and 320 Ω respectively. The motor torque constant is 0.5 V.S/A-rad. Field converter
has zero degree firing angle delay. Armature and field currents have negligible ripple.
For rated load torque of 60 N-rn at 2000 rpm, calculate the rated armature current. (8)
6. A chopper used for ON and OFF control of a dc separately excited motor has supply
voltage of 230 V, TON = 10 ms, TOFF = 15 ms. Neglecting armature inductance and
assuming continuous conduction of motor current. Calculate the average load current
when the motor speed is 1500 rpm, has a voltage constant K = 0.5 V/rad/sec. The
armature resistance is 2 Ω.
7. Explain in detail, the two methods of time ratio control.
(8)
8. Explain in detail, the chopper control of DC series motor.
(8)
9. Explain in detail, the different control strategies of chopper.
(8)
10. Explain in detail, the power circuit the working of a single phase semi converter fed
separately excited motor drive.
(16)
11. Explain in detail, the motoring mode operation of chopper fed DC motor.
(8)
12. Derive the expression for critical speed which separates the continuous conduction mode
from discontinuous conduction mode of operation of single phase fully controlled
rectifier fed separately excited DC motor.
(8)
UNIT III
DESIGN OF CONTROLLERS FOR DRIVES
PARTA
1.
2.
3.
4.
5.
6.
7.
What is mechanical time constant of DC machine?
Write the transfer function of converter.
What is the role of current limiter in the closed loop control of DC drives?
What is meant by speed feedback?
What are the advantages of closed loop speed control?
What is meant by field weakening mode control?
Draw the characteristics of maximum torque and power limitations of DC drives
operating with combined armature voltage and field control.
8. How is speed feedback achieved in speed controller design?
9. What is the function of inner current control loop closed loop speed control system?
10. List out the simulation software packages that can be used for electrical drives.
PARTB
1. Derive the transfer function of DC motor-load system with converter fed armature
voltage control.
(16)
2. Derive the closed loop transfer function of converter fed separately excited DC motor.
(16)
3. A 50 kW, 240 V, 1700 rpm separately excited dc motor is controlled by a converter. The
field current is maintained at If = 1.4 A and the machine back emf constant is
Kv = 0.91 V/A rad/s. The armature resistance is Rm = 0.1 Q and the viscous friction
Constant is B = 0.3 Nm/rad/s. The amplification of the speed sensor is Kl = 95 m V/rad/s
and the gain of the power controller is K2= 100. (i) Determine the reference voltage Vr
to drive the motor at the rated speed (ii) If the reference voltage is kept unchanged,
determine the speed at which the motor develops rated torque.
(16)
4. Explain in detail, the operation of a closed loop scheme for speed control of a DC motor,
below and above the base speed.
(16)
5. Derive the transfer function of an armature controlled DC motor.
(8)
6. Explain in detail, the closed loop operation of armature voltage control method with field
weakening mode control in detail.
(16)
7. Explain in detail, the design procedure of current controller in detail.
8. Explain the converter selection and characteristics.
(16)
(8)
UNIT-IV
INDUCTION MOTOR DRIVE
PART A
1. List out the merits and demerits of stator voltage control.
2. What are the drawbacks of stator voltage control method?
3. What are the various applications of stator voltage control scheme?
4. What is meant by constant volt/frequency control?
5. Why is the speed control of a 3 phase induction motor with constant supply voltage and
reduced supply frequency not preferred?
6. Write the consequences of increasing the frequency of induction motor without a change
in the terminal voltage.
7. What are the three regions in the speed-torque characteristics of the induction motor?
8. Compare CSI fed drives with VSI fed drives.
9. Define – Vector Control
10. Write the advantages of vector control technique.
11. What is meant by slip power recovery scheme?
12. What is meant by super synchronous operation?
PART B
1. Explain the speed control scheme of induction motor drive with stator voltage control
and also state the disadvantages of this method.
(8)
2. A 2.8 kW, 400 V, 50 Hz, 4 pole, 1370 rpm, delta connected squirrel cage induction motor
has following parameters referred to the stator: Rs = 20 Ω, Rr = 5 Ω, Xs =Xr = 5 Ω,
Xm = 80 Ω. Motor speed is controlled by stator voltage control. When driving a fan load,
it runs at rated speed at rated voltage. Calculate motor terminal voltage, current and torque
at l200 rpm.
(16)
3. Explain in detail, the v/f control of induction motor drives.
(16)
4. Explain in detail, the principle of operation and drive strategy of constant air gap flux
control of induction motors.
(8)
5. A 3 phase, 56 kW, 4000 rpm, 460 V, 60 Hz, 2 pole star connected induction motor has
the following parameters: Rs = 0, Rr = 0.28 Ω, Xs = 0.23 Ω, Xr = 0.23 Ω and
Xm = 11 Ω. The motor is controlled by varying the supply frequency. If the break down
torque requirement is 70 Nm. Calculate the supply frequency and the speed ωm at the
maximum torque.
(8)
6. A 3 phase star connected, 60 Hz, 4 pole induction motor has the following parameters for
the per phase equivalent circuit. Rs = Rr = 0.024 Ω and Xs = Xr = 0.12 Ω. The motor is
controlled by the variable frequency control with a constant (v/f) ratio. For an operating
frequency of 12 Hz, calculate the breakdown torque as a ratio of its value at the rated
frequency for both motoring and braking.
(8)
7. Compare CSI drive with VSI drives.
(8)
8. Explain in detail, the vector control of Induction motor drives.
(16)
9. Explain in detail, the principle of operation of Scherbius system.
(16)
10. Explain in detail, the closed loop speed control of VSI fed and CSI fed induction motor
drives.
(16)
UNIT 5
Part-A
1. When is a synchronous motor said to be self-controlled?
2. Why self-controlled synchronous motor is free from hunting operations?
3. Define – Self-control Technique of synchronous motor
4. Which type of control can be used for constant torque operation in synchronous motor?
5. What are the different types of controls used in Synchronous motor drives?
6. What are the characteristics of self-controlled mode operated synchronous motor?
7. What are the different modes of control that exist in a synchronous motor on a variable
frequency supply?
8. What is meant by margin angle of commutation in the control of synchronous motors?
9. What are the advantages of PMSM?
10. List out the different types of permanent magnet synchronous motor.
Part-B
1. Describe the open loop v/f control of VSI fed synchronous motor drives.
(8)
2. Explain in detail, the open loop control of synchronous motor with constant v/f ratio. (16)
3. Draw the open loop V/f speed control of multiple PM synchronous motors and V/f speed
control characteristics in torque-speed plane.
(l6)
4. Explain margin angle control in synchronous motor.
(8)
5. Explain in detail, the self-control of synchronous motor drive operated with constant
margin angle control.
(16)
6. Explain the power factor control of synchronous motor.
(8)
7. Explain in detail, the working of a permanent magnet synchronous motor.
(8)
8. Explain in detail, the closed loop control of synchronous motor.
(16)