EX-802-B Special Machine - May 2023 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
   aList the important features of stepper motor.
   How to answer

   • Define stepper motor and its positioning function
   • List features: brushless, open-loop control, discrete steps, holding torque
   • High torque at low speed, precise positioning and repeatability
   • No brushes, robust and maintenance requirements
2. 7 Marks
   bDiscuss Speed control methods of Stepper Motor.
   How to answer

   • Define speed control need in stepper motor
   • Pulse frequency / stepping rate control method
   • Voltage and chopper / current control and microstepping
   • Closed-loop vs open-loop speed regulation
3. 7 Marks
   aBriefly describe how to control load angle in Stepper Motor.
   How to answer

   • Define load angle / torque angle in stepper motor
   • Relation of developed torque to load angle
   • Control via stator current / excitation and stepping sequence
   • Stability limit and pull-out torque consideration
4. 7 Marks
   bA hybrid variable reluctance motor has 8 main poles which have been castellated to have 5 teeth. Calculate the stepping angle if rotor has 50 teeth.
   How to answer

   • State hybrid stepper stepping angle formula
   • Compute total stator teeth = main poles x teeth per pole
   • Substitute $N_r = 50$ and stator teeth to find step angle
   • Obtain stepping angle value in degrees
5. 7 Marks
   aGive details of sensorless control of PM synchronous motor.
   How to answer

   • Define PMSM sensorless control need
   • Back-EMF / observer based position estimation methods
   • Block diagram of sensorless drive
   • Advantages and limitations
6. 7 Marks
   bExplain advantages and disadvantages of Solid Rotor.
   How to answer

   • Define solid rotor construction
   • Advantages: rugged, high speed, low cost
   • Disadvantages: high losses, poor power factor, heating
   • Suitable applications conclusion
7. 7 Marks
   aExplain series and parallel winding pattern of brushless DC motor.
   How to answer

   • Define BLDC winding arrangement
   • Series winding pattern connection and features
   • Parallel winding pattern connection and features
   • Comparison of current / voltage ratings
8. 7 Marks
   bExplain commutation and armature reaction in PMBLDC motor.
   How to answer

   • Define electronic commutation in PMBLDC motor
   • Role of Hall sensors and inverter switching sequence
   • Armature reaction effect in PM machines
   • Impact on torque and commutation angle
9. 7 Marks
   aDiscuss the construction and working principle of permanent magnet brushless DC motor.
   How to answer

   • Stator, rotor PM and Hall sensor construction
   • Electronic commutation working principle
   • Voltage and torque equations
   • Diagram of BLDC drive
10. 7 Marks
    bGive application of permanent magnet synchronous motor.
    How to answer

    • Define permanent magnet synchronous motor
    • List industrial and traction applications
    • High efficiency and servo drive uses
    • EV, robotics and renewable examples
11. 7 Marks
    aWith necessary diagrams, discuss about various power controllers used for PMSM.
    How to answer

    • Define PMSM power controller / inverter need
    • VSI, CSI and PWM controller types with diagrams
    • Vector / field oriented control scheme
    • Applications and selection criteria
12. 7 Marks
    bExplain the operation of single stack and multi stack stepper motor with a neat diagram.
    How to answer

    • Define single stack stepper construction and operation
    • Define multi stack stepper construction and operation
    • Neat cross-sectional diagrams of both types
    • Comparison of step angle and torque
13. 7 Marks
    aDifferentiate between permanent and hybrid stepper motor.
    How to answer

    • Construction: PM rotor vs hybrid rotor with PM + teeth
    • Working: excitation and detent torque differences
    • Tabular comparison of step angle, torque, cost
    • Applications of each type
14. 7 Marks
    bExplain speed control methods of PM Synchronous Motor.
    How to answer

    • V/f and voltage control of PMSM
    • Field oriented / vector control method
    • Direct torque and flux weakening control
    • Speed-torque characteristics
15. 14 Marks
    Write a short note on (any two):

    1. a)PV Fed Water Pumping
    2. b)DC Brushed Motors
    3. c)Torque development in Brushless DC motor
    4. d)Case Study: Electric Vehicles
    How to answer

    • Select any two topics from four options
    • Definition, construction / working and key equations for each
    • Relevant diagram and applications
    • Advantages and limitations conclusion