Anna University ME Power Electronics and Drives Previous Year Question Papers: Set-7

Anna University ME Power Electronics and Drives Previous Year Question Papers

In this post we had collected some of the Previous Year Anna University ME Exam Questions. Instead of giving entire question paper, we had focused on special motor drives.
This approach will be useful for you to get refresh in one particular topic.
In addition to the exam questions we had added few basic questions to understand the subject easily. Please share your thoughts about it...

[1] What is step angle in stepper motor? [ Anna Univ. may-2007]
Step angle is defined as the angle through which the stepper motor shaft rotates for each command pulse.
It is denoted beta.

[2] What is stepper motor?
A stepper motor is a digital actuator whose input is in the form of programmed energization of the stator windings and whose output is in the form of discrete angular rotation.

[3] What is slewing in stepper motor?
A stepper motor operates at high speeds is called as slewing.

[4] Define resolution in stepper motor?
It is defined as the number of steps needed to complete one revolution of the rotor shaft.
Resolution = No of steps/ Revolution

[5] State some applications of stepper motor? [ Anna Univ jan 2008]

  • Floppy disk drives
  • Camera shutter operation
  • Machine tool application
  • Robotics
  • Dot matrix and line printers
  • Quartz watches

[6] What are the advantages and disadvantages of the stepper motor? [Anna Univ. May-2009]


  1. It is mechanically simple.
  2. It requires less maintenance.
  3. It can be driven in open loop without feedback
  4. As it responds directly to digital control signals, stepper motors are natural choice for digital computer controls.


  1. Low efficiency with ordinary controller.
  2. Limited power output and sizes available
  3. Low efficiency with ordinary controller.
  4. Fixed step angle

[7] What are the different types of stepping motors? [Anna Univ. Dec-2008]

  • Variable reluctance stepper motor
  • Permanent magnet stepper motor
  • Hybrid stepper motor

[8] What are the different modes of excitation in a stepper motor? [ Anna Univ. May-2003,2006]

  • 1-Phase on or full-step operation
  • 2-phase on mode
  • Half step operation ( alternate 1-phase on and 2-phase on mode)
  • Micro stepping operation

[9] What is meant by half-step operation? [Anna Univ. Dec-2002,2006, Anna univ (ME(PED)) 2008]
It is the alternate one-phase on and 2-phase on mode operation.
Here, the rotor rotate an each angle is half of the full step angle.

[10] What is meant by full-step operation? [Anna Univ. ME(PED)2008, 2006]

  • It is one-phase on mode operation.
  • It means, at that time only one winding is energized.
  • By energizing one stator winding, the rotor rotates some angle.
  • It is the full-step operation.

[11] What is meant by micro stepping in stepper motor? [Anna Univ. ME(PED)2008,2004,2007]

  • Micro stepping means, the step angle of the VR stepper motor is very small.
  • It is also called mini-stepping.
  • It can be achieved by two phases simultaneously as in 2-phase on mode but with the two currents deliberately made unequal.

[12] What is the main application of the micro stepping VR stepper motor?

  • The micro stepping is mainly used where very fine resolution is required.
  • The applications are printing and photo type setting.
  • A VR stepper motor with micro stepping provides very smooth low-speed operation and high-resolution.

[13] What are the advantages and disadvantages of VR stepper motor?


  1. Low rotor inertia
  2. Less weight
  3. Freewheeling capability
  4. High stepping rate capability
  5. High torque to inertia ratio


  1. Normally available in 3.6deg to 30 step angles
  2. No detente torque available with windings de-energized.

[14] What is a multi-stack VR stepper motor?
Micro stepping of VR stepper motor can be achieved by using multistack VR stepper motor.
It has 3 separate magnetically isolated sections or stacks. Here the stator and rotor teeths are equal.

[15] What are the advantages and disadvantages of permanent magnet stepper motor?


  1. Requires low power
  2. High detente torque as compared to VR motor.
  3. Rotor do not require external exciting current.
  4. It produces more torque per ampere stator current.

You may also like to read:
Power Electronics Basic Interview Questions : Set-4
Power Electronics Interview Questions: Set-1
Power Electronics Technical Interview Questions: Set-2

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