Power Electronics Interview Questions and Answers: Set-8
Power Electronics Interview Questions and Answers
 Why self commutated devices are preferred over thyristors for chopper circuits?
Self commutated devices such as power MOSFETs, power Transistors, IGBTs, GTOs and IGCTs are preferred over thyristors for building choppers because they can be commutated by a low power control signal and don't need commutation circuit.
 Why thyristors are not preferred now a days for chopper fed DC drives? [AU -2000]
Since it requires commutation circuit, thyristors are not preferred now a days for chopper fed DC drives. The commutation circuit is complex for chopper circuits.
 What is function of a free wheeling diode in a phase controlled rectifier? [MKU-2000]
- Input power factor is improved
- Make the load current continuous
 What causes poor input power factor in phase controlled DC drives?
The input power factor in the phase controlled rectifier is low when the output voltage is less than the maximum, that is when the firing angle is large. When the firing angle increases, the converter draws more lagging reactive power. So the input power is low.
 What are the advantages of three-phase drives over single phase drives? [AU/PED-2004]
- Reducing the armature ripple current
- The filtering requirement is less
- Armature current is mostly continuous
- Motor performance is better
 What are the various control strategies for varying duty cycle of the chopper [AU/ME(PED) -2004]
- Time Ratio Control (TRC)
- Current Limit Control (CLC)
 What are the different methods of speed control of induction motors?
- Stator voltage control
- Supply frequency control
- Rotor resistance control
- Slip power recovery control
 What are the advantages in operation of choppers at high frequency?
The operation at a high frequency improves motor performance by reducing current ripple and eliminating discontinuous conduction.
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