# Power Electronics Questions and Answers – Single Phase VSI-3

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “Single Phase VSI-3”.

1. The output voltage from a single phase full wave bridge inverter varies from
a) Vs to –Vs
b) Vs to zero
c) Vs/2 to zero
d) –Vs/2 to Vs/2

Explanation: The output from a full wave bridge inverter varies from Vs to –Vs.

2. In a single phase full wave bridge inverter, when the output is Vs or –Vs
a) one SCR and one diode are conducting
b) four SCRs are conducting
c) two SCRs are conducting
d) two diodes are conducting

Explanation: When two SCRs are conducting, T1-T2 or T3-T4, the output voltage magnitude is Vs. When the diodes are conducting, freewheeling action is taking place and voltage is zero.

3. In the following circuit, the diodes D1 to D4 are used to

a) reduce the switching losses
b) send current back to the dc source when SCRs are off
c) send current back to the load when SCRs are off
d) send current back to the dc source when SCRs are conducting

4. For a full wave bridge inverter, the output voltage (Vo)
a) Vo = Vs/2 for 0 < t < T/2
b) Vo = Vs for 0 < t <T/2
c) Vo = Vs for T/2< t < T
d) Vo = -Vs for T/2< t < 3T/2

Explanation: For the first half cycle, Vo = Vs and for the second half cycle Vo = -Vs.

5. For a half wave bridge inverter, the output voltage
a) Vo = – Vs/2 for 0 < t < T/2
b) Vo = – Vs/2 for T/2< t<T
c) Vo = – Vs for 0 < t < T/2
d) Vo = Vs/2 for T/2< t < T

Explanation: In case of a half wave inverter, for the first half cycle, Vo = Vs/2 and for the second half cycle Vo = -Vs/2.

6. The fundamental component of output voltage for a half wave bridge inverter is given by
a) (4Vs/π) sinωt
b) (2Vs/π) sinωt
c) (Vs/2π) sinωt
d) (Vs)

Explanation: The fourier analysis of half wave inverter gives,

Put n = 1 for the fundamental component.

7. The fundamental component of output voltage for a full wave bridge inverter is given by
a) (2Vs/π) sinωt
b) (4Vs/π) sinωt
c) (Vs/2π) sinωt
d) (Vs)

Explanation: The fourier analysis of full wave inverter gives,
Vo =

Put n = 1 for the fundamental component.

8. A single phase half bridge inverter has a dc voltage source Vs/2 = 115 V. Find the rms value of the fundamental component of output voltage.
a) 510 V
b) 103.5 V
c) 120 V
d) 96 V

Explanation: The fundamental component of voltage = (2Vs/π) sinωt.
Peak value Vm = 2Vs/π
Rms value = 2Vs/π√2 = 103.552 V.

9. A single phase half bridge inverter has load R = 2 Ω and a dc voltage source Vs/2 = 115 V. Find the rms value of the fundamental load current.
a) 10.25 A
b) 51.7 A
c) 86 A
d) 24.8 A

Explanation: Peak value Vm = 2Vs/π
Rms value = 2Vs/π√2 = 103.552 V
Io = Vo/R = 103.552/2 = 51.776 A.

10. A single phase half bridge inverter has load R = 2 Ω and a dc voltage source Vs/2 = 115 V. Find the power delivered to the load due to the fundamental component.
a) 536 kW
b) 53.61 kW
c) 5.361 kW
d) 536 W

Explanation: Peak value Vm = 2Vs/π
Rms value = 2Vs/π√2 = 103.552 V
Io = Vo/R = 103.552/2 = 51.776 A
P = Io2 x R = 5361.5 Watts.

Sanfoundry Global Education & Learning Series – Power Electronics.

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