# Power Electronics Questions and Answers – Single Phase VSI-2

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “Single Phase VSI-2”.

1. What is the voltage across the R load when only T2 is conducting? a) Vs
b) Vs/2
c) 2Vs
d) Zero

Explanation: Considering T2 as an ideal switch, the load is directly connected to the lower voltage source when T2 is on.

2. The voltage in a single phase half wave inverter varies between
a) Vs and 0
b) Vs/2 and 0
c) Vs/2 and –Vs/2
d) Vs and –Vs

Explanation: It varies between –Vs/2 and Vs/2 as the upper and lower thyristors/IGBTs are fired in sequence.

3. Below given is a a) SCR based inverter
b) MOSFET based inverter
c) IGBT based inverter
d) None of the mentioned

Explanation: It is a half wave inverter with MOSFET switches. The diodes are used to bypass the negative current.

4. The output of a single-phase half bridge inverter on R load is ideally
a) a sine wave
b) a square wave
c) a triangular wave
d) constant dc

Explanation: Due to rapid switching on and off of the devices, it seems to be a square wave. But practically it is a B-wave.

5. In the below given circuit, T1 is fired at 0,T and so on and T2 at T/2, 3T/2 etc. What is the frequency of the alternating voltage obtained? a) 50 Hz
b) T Hz
c) 1/T Hz
d) T/2 Hz

Explanation: T1 conducts from 0 to T/2 and T2 from T/2 to T. Hence, 1 cycle is completed in T time. f = 1/T Hz.
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6. In the below circuit, if Vs/2 = 50 V. Find, the rms AC voltage that would be ideally obtained. a) 50 V
b) 100 V
c) 0.707 x 50 V
d) 0.707 x 100 V

Explanation: Peak value would be = 50 V
RMS = Peak/√2 = Peak x 0.707 V.

7. Find the conduction time of the diodes if the SCRs are fired at 0 and T/2 respectively in a single phase half wave inverter with R load.
a) 0
b) T/2
c) 2/T
d) insufficient data

Explanation: With R load, the diodes do not come into play.

8. The output current wave of a single-phase full bridge inverter on RL load is
a) a sine wave
b) a square wave
c) a triangular wave
d) constant dc

Explanation: On RL load, the SCRs are revised biased due to the voltage drops across the diodes and negative current flows.

9. Single-phase full bridge inverters requires
a) 4 SCRs and 2 diodes
b) 4 SCRs and 4 diodes
c) 2 SCRs and 4 diodes
d) 2 SCRs and 2 diodes

Explanation: Full bridge inverters require 4 SCR and 4 diodes along with a two wire dc source.

10. Identify the circuit given below. a) Full wave series inverter
b) Half wave series inverter
c) Full wave bridge inverter
d) Full wave parallel inverter

Explanation: It is a full wave bridge inverter using 4 diodes and 4 SCRs.

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