Power Electronics Questions and Answers – 3-Phase Bridge Inverters-3

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

1. The 120° mode of operation of a three phase bridge inverter requires ___________ number of steps.
a) 2
b) 4
c) 6
d) 8
View Answer

Answer: c
Explanation: Like the 180 mode, the 120° mode also requires six steps, each of 60° duration.

2. In case of the 120° mode of operation, __________ devices conduct at a time.
a) 2
b) 3
c) 4
d) none of the mentioned
View Answer

Answer: a
Explanation: Unlike the 180° mode, in the 120° mode one 2 devices are conducting at a time as each conduct for 120°.

3. Safe commutation can be achieved in case of the ____________ operating mode.
a) 180°
b) 120°
c) 360°
d) none of the mentioned
View Answer

Answer: b
Explanation: In the 120 mode of operation, there is a 60° interval between turning off of T1 and turning on of T4 (or any two SCRs belonging to the same leg), hence SCRs are commutated safely.
advertisement

4. What is the R phase voltage when only T1 and T2 are conducting from 60° to 120°. Consider star connected R load.
Find the R phase voltage when only T1 & T2 are conducting from 60° to 120°
a) Vs
b) Vs/2
c) –Vs/2
d) 0
View Answer

Answer: b
Explanation: As only 2 SCRs are conducting at a time, it is 120 mode.
When T1 and T2 are conducting, R phase is connected to the positive bus through the T1 SCR and B phase is connected to the negative bus through the T2 SCR.
Considering that the load is a balanced R load.
VRN = Vs/2
VYN = -Vs/2.

5. If T1 is gated at 0 °, T3 and T5 will start conducting at _______ and _________ respectively.
a) 180°, 270°
b) 120°, 240°
c) 180°, 300°
d) 240°, 360°
View Answer

Answer: b
Explanation: As T1 is gated at 0, T3 will be gated after 120° and T5 after 120+120 = 240°.

Devices T1 T1 0 T4 T4 0 T1 T1 0
T6 0 T3 T3 0 T6 T6 0 T3
0 T2 T2 0 T5 T5 0 T2 T2
Free 30-Day Python Certification Bootcamp is Live. Join Now!

6. What is the B phase voltage when only T1 and T2 are conducting from 60° to 120°. Consider star connected R load.
Find the R phase voltage when only T1 & T2 are conducting from 60° to 120°
a) Vs
b) Vs/2
c) –Vs/2
d) 0
View Answer

Answer: c
Explanation: When T1 and T2 are conducting, R phase is connected to the positive bus through the T1 SCR and B phase is connected to the negative bus through the T2 SCR. Considering that the load is a balanced R load.

Devices T1 T1 0 T4 T4 0 T1 T1 0
T6 0 T3 T3 0 T6 T6 0 T3
0 T2 T2 0 T5 T5 0 T2 T2

VRN = Vs/2
VBN = -Vs/2.

7. What is the R phase voltage and Y phase voltage when only T3 and T4 are conducting? Consider a star connected balanced R load.
Find the R phase voltage when only T1 & T2 are conducting from 60° to 120°
a) Vs, -Vs
b) Vs/2, -Vs/2
c) –Vs/2, Vs/2
d) –Vs, Vs
View Answer

Answer: c
Explanation: When T3 and T4 are conducting, R phase is connected to the negative bus through the T4 SCR and the Y phase is connected to the positive bus through the T3 SCR. Considering that the load is a balanced R load.

Devices T1 T1 0 T4 T4 0 T1 T1 0
T6 0 T3 T3 0 T6 T6 0 T3
0 T2 T2 0 T5 T5 0 T2 T2

VYN = Vs/2
VRN = -Vs/2.

advertisement

8. If the SCR T1 is gated at 0°, then for 120° mode of operation, from ωt = 240° to 300° __________ devices would conduct.
Find the R phase voltage when only T1 & T2 are conducting from 60° to 120°
a) T3, T4
b) T4, T5
c) T1, T6
d) T5, T6
View Answer

Answer: b
Explanation:

Devices T1 T1 0 T4 T4 0 T1 T1 0
T6 0 T3 T3 0 T6 T6 0 T3
0 T2 T2 0 T5 T5 0 T2 T2

ωt = 240° to 300°, would form the 5th step.

9. Find the line voltage VYR when only T3 and T4 are conducting? Consider a star connected balanced R load.
Find the R phase voltage when only T1 & T2 are conducting from 60° to 120°
a) 2Vs/3
b) Vs/2
c) Vs
d) –Vs
View Answer

Answer: c
Explanation: When T3 and T4 are conducting, R phase is connected to the negative bus through the T4 SCR and the Y phase is connected to the positive bus through the T3 SCR. Considering that the load is a balanced R load.
VYN = Vs/2
VRN = -Vs/2.
VYR = VYN – VRN = Vs.

10. The peak value of the line voltage in case of 120° mode of operation of a three-phase bridge inverter is
a) Vs/2
b) 3Vs/2
c) Vs/√2
d) Vs
View Answer

Answer: d
Explanation: The peak value for 120° mode is Vs. The line voltage waveform is a sine wave with a peak value of Vs ( = supply voltage).

Sanfoundry Global Education & Learning Series – Power Electronics.

To practice all areas of Power Electronics, here is complete set of 1000+ Multiple Choice Questions and Answers.

advertisement
advertisement
Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

Youtube | Telegram | LinkedIn | Instagram | Facebook | Twitter | Pinterest
Manish Bhojasia - Founder & CTO at Sanfoundry
I’m Manish - Founder and CTO at Sanfoundry. I’ve been working in tech for over 25 years, with deep focus on Linux kernel, SAN technologies, Advanced C, Full Stack and Scalable website designs.

You can connect with me on LinkedIn, watch my Youtube Masterclasses, or join my Telegram tech discussions.

If you’re in your 40s–60s and exploring new directions in your career, I also offer mentoring. Learn more here.