Anna University Previous Year Question Papers for EEE: Set-1
Anna University Previous Year Question Papers from Power Electronics and Drives Paper
 What is full converter? What is dual converter? (Nov-2004)
When positive as well as negative half cycles of the supply are rectified, it is called full converter.
When the polarities of output voltage as well as current can be reversed then it is said to be dual converter. It operates in all the four quadrants of the VO – IO plain.
 What are the advantages and disadvantages of buck/boost regulator? ( Apr-2005)
- Provides inverted output
- Both buck/boost operations achieved simultaneously
- High efficiency
- Short circuit protection can be easily implemented
- Output voltage polarity opposite to that of input
- Voltage stress on switching device in the chopper is high
 What is the function of free wheeling diode in semiconverter? (Nov-2004)
- When the load is inductive, the load current circulates through free wheeling diode.
- Actually, the semiconverter have the inherent freewheeling.
- This freewheeling can take place through one SCR and one diode.
- But if separate freewheeling diode is used, then freewheeling takes place through that free wheeling diode itself. This reduces losses that takes place in SCR and diode.
 List the merits and demerits of AC voltage controller (Nov-2004)
- They use line commutation, hence no extra commutation circuits are required
- They have high efficiencies, since device losses are reduced.
- large ripple and harmonics are present in the output
- Output waveforms are not sinusoidal.
 Define the delay angle of phase controlled rectifier (Nov-2003)
The angle at which thyristors are triggered after zero crossing is called the delay angle. After zero crossing of supply voltage, one pair of thyristors is forward biased. After delay angle (alpha), these SCRs are triggered
 What the two types of AC voltage controllers? which one these is preferred and why? (Nov-2003)
Types of AC voltage controllers:
- ON-OFF type AC voltage Controller
- Phase angle type AC voltage controller
In this type of controller, the full input voltage is applied to output for some number of cycles and no voltage is applied to output for some number of cycles. In this control, output voltage waveform is discontinuous and contains large ripple.
Phase angle control:
In phase angle control, each half cycle of the source voltage is applied partially or fully to the load. Firing angle of the SCRs is charged to control output voltage. Output voltage waveform is continuous but phase controlled.
The type of AC controller which is highly preferred is Phase angle control, because it contains less ripple and discontinuities in output.
 What are the effects of load inductance on the performance of an AC voltage controller? (Nov-2005)
- The load inductance makes the output current to flow continuously.
- With load inductance, the commutation becomes difficult if TRIAC switches are used
- The control fails sometimes due to high inductive load
 what are the advantages of GTO over BJT (Nov-2004)
- Higher voltage blocking capability
- It is majority carrier device
- High ratio of peak surge current to average current
- Operates as a switch always hence on state losses are reduced
 Define holding current of an SCR (apr-2005)
Holding current is the minimum forward current that flows through the SCR to keep it in forward conduction mode. When forward current reduces below holding current, SCR turns off.
 Define string efficiency of SCRs connected in series (Apr-2005)
String efficiency is given as
η = [VS / nVDI ] x 100
It indicates the amount by which the sting is utilized.
Read More Anna University Previous Year Question Papers for EEE
Electrical drives Interview Questions with Answers: Set-1
Electrical drives Interview Questions with Answers: Set-2
Electrical drives Interview Questions with Answers: Set-3
Anna University Previous Year Question Papers for EEE 7th Sem Power Electronics
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