EX-802-B Special Machine - May 2022 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aExplain how to control load angle in Stepper Motor.
   How to answer

   • Define load angle in stepper motor
   • Relation of load angle to holding torque and rotor position
   • Methods to control: excitation current, switching sequence, microstepping
   • Effect on stability and pull-out torque
2. 7 Marks
   bDifferentiate between permanent and hybrid stepper motor.
   How to answer

   • Construction of permanent magnet stepper motor
   • Construction of hybrid stepper motor
   • Comparison of torque, resolution, cost
   • Applications of each type
3. 14 Marks
   Describe operating principle of switched reluctance motor. Also explain torque development with angle torque characteristics.
   How to answer

   • Construction and doubly salient structure of SRM
   • Principle of variable reluctance and sequential excitation
   • Torque production vs rotor position
   • Angle-torque characteristics diagram
4. 14 Marks
   Discuss the construction and working principle of permanent magnet brushless DC motor. Also draw its torque speed characteristics.
   How to answer

   • Stator with windings and rotor with permanent magnets
   • Electronic commutation and position sensing
   • Working principle with trapezoidal / sinusoidal drive
   • Torque-speed characteristics diagram
5. 7 Marks
   aExplain commutation and armature reaction in the PMBLDC motor.
   How to answer

   • Need for electronic commutation in PMBLDC
   • Commutation sequence and inverter action
   • Armature reaction effect on air-gap flux
   • Compensation / mitigation effects
6. 7 Marks
   bGive details of sensor less control of PM synchronous motor.
   How to answer

   • Concept of sensorless control and rotor position estimation
   • Back-EMF, observer and saliency methods
   • Block diagram of sensorless drive
   • Advantages and limitations
7. 7 Marks
   aExplain series and parallel winding pattern of Brushless DC motor.
   How to answer

   • Series winding connection pattern
   • Parallel winding connection pattern
   • Current, voltage and torque implications
   • Diagram of winding connections
8. 7 Marks
   bGive application of permanent magnet synchronous motor.
   How to answer

   • High efficiency and power density applications
   • Industrial, traction and appliance uses
   • Robotics and aerospace uses
   • Reason for selection in each application
9. 7 Marks
   aExplain advantages and disadvantages of Solid Rotor.
   How to answer

   • Solid rotor construction
   • Advantages: robustness, high speed, low cost
   • Disadvantages: losses, low efficiency, heating
   • Comparison with laminated rotor
10. 7 Marks
    bList the important features of stepper motors.
    How to answer

    • Discrete step motion and holding torque
    • Open-loop control and resolution
    • Types and excitation modes
    • High torque at low speed features
11. 7 Marks
    aDescribe the methods to reduce the torque pulsation in the PM synchronous motor.
    How to answer

    • Sources of torque pulsation: cogging, ripple
    • Skewing, magnet shaping and winding design
    • Control techniques: current profiling
    • Comparison of effectiveness
12. 7 Marks
    bExplain speed control methods of PM Synchronous Motor.
    How to answer

    • V/f and vector control principles
    • Field weakening for speed above base speed
    • Inverter frequency and voltage control
    • Block diagram of speed control scheme
13. 7 Marks
    aExplain the shaft position sensor in the Switched Reluctance Motor.
    How to answer

    • Need for rotor position feedback in SRM
    • Optical, Hall and inductive sensors
    • Placement and output waveforms
    • Role in phase excitation control
14. 7 Marks
    bDiscuss speed control methods of Stepper Motor.
    How to answer

    • Pulse frequency control of stepping rate
    • Voltage, chopper and microstepping control
    • Open-loop vs closed-loop speed control
    • Torque-speed considerations