# Electric Drives Questions and Answers – Solid-State Switching Circuits – DC/AC Conversion

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This set of Electric Drives Multiple Choice Questions & Answers (MCQs) focuses on “Solid-State Switching Circuits – DC/AC Conversion”.

1. Inverters are used to convert DC power into variable AC power.
a) True
b) False

Explanation: Inverters are used to convert DC power into variable AC power. The variable AC power means variable frequency and variable voltage level.

2. Short circuit problem is severe in case of Voltage source inverter.
a) True
b) False

Explanation: Short-circuit problem is severe in case of voltage source inverter. The output voltage of VSI is fixed but the output current depends upon the load. When Z=0, I=V÷Z=∞.

3. Switches used in VSI are ___________
a) Unipolar & Unidirectional
b) Bipolar & Bidirectional
c) Unipolar & Bidirectional
d) Unidirectional

Explanation: Switches used in VSI are unipolar and bidirectional in nature. MOSFET, BJT are the examples of switches used in VSI. The output voltage of VSI is fixed but the output current depends upon the load.

4. Switches used in CSI are ____________
a) Bipolar & Unidirectional
b) Bipolar & Bidirectional
c) Unipolar & Unidirectional
d) Bidirectional

Explanation: Switches used in CSI are bipolar and unidirectional in nature. GTO, thyristors are the examples of switches used in CSI. The output voltage of CSI is variable but the output current is fixed.

5. Full form of VSI is ___________
a) Voltage source inverter
b) Volume source inverter
c) Voltage severe inverter
d) Voltage source inserter

Explanation: VSI stands for Voltage source inverter. The output voltage of VSI is fixed but the output current depends upon the load. Switches used in VSI are unipolar and bidirectional in nature.

6. Full form of CSI is ___________
a) Counter source inverter
b) Counter severe inverter
c) Current source inverter
d) Current severe inverter

Explanation: CSI stands for Current source inverter. The output voltage of CSI is variable but the output current is fixed.

7. Number of switches turned on in 3-phase 180° VSI at a single time are __________
a) 3
b) 2
c) 1
d) 4

Explanation: In 3-phase 180° VSI each phase conducts for 180° and only two switches from different phases conduct at a single time.

8. Number of switches turned on in 3-phase 120° VSI at a single time are __________
a) 2
b) 4
c) 5
d) 3

Explanation: In 3-phase 120° VSI each phase conducts for 120° and only three switches from different phases conduct at a single time.

9. Calculate the phase voltage for 3-∅ 180° VSI if the value of DC supply is 20 V.
a) 9.40 V
b) 9.42 V
c) 9.18 V
d) 9.78 V

Explanation: The phase voltage for 3-∅ 180° VSI is (√2÷3)×VDC=.471×20=9.42 V. In 3-phase 180° VSI each phase conducts for 180° and only two switches from different phases conduct at a single time.

10. Calculate the line voltage for 3-∅ 180° VSI if the value of DC supply is 22 V.
a) 18.52 V
b) 18.12 V
c) 17.96 V
d) 15.48 V

Explanation: The line voltage for 3-∅ 180° VSI is (√2÷√3)×VDC=.81×22=17.96 V. In 3-phase 180° VSI each phase conducts for 180° and only two switches from different phases conduct at a single time.

11. Calculate the line voltage for 3-∅ 120° VSI if the value of DC supply is 24 V.
a) 16.52 V
b) 16.97 V
c) 12.96 V
d) 12.48 V

Explanation: The line voltage for 3-∅ 120° VSI is (VDC÷√2)=.707×24=16.97 V. In 3-phase 120° VSI each phase conducts for 120° and only three switches from different phases conduct at a single time.

12. Calculate the phase voltage for 3-∅ 120° VSI if the value of DC supply is 26 V.
a) 10.52 V
b) 10.97 V
c) 10.96 V
d) 10.61 V

Explanation: The line voltage for 3-∅ 120° VSI is (VDC÷√6)=10.61 V. In 3-phase 120° VSI each phase conducts for 120° and only three switches from different phases conduct at a single time.

13. Calculate power absorbed by 5 Ω load in 3-∅ 120° VSI if the value of DC supply is 16 V.
a) 17.06 W
b) 15.15 W
c) 18.25 W
d) 19.26 W

Explanation: The power absorbed by 5 Ω load in 3-∅ 120° VSI if the value of DC supply is 16 V is Vph2÷R=(16÷√3)2÷5=17.06 W.

14. Calculate power absorbed by 10 Ω load in 3-∅ 180° VSI if the value of DC supply is 36 V.
a) 20.6 W
b) 24.5 W
c) 26.4 W
d) 28.8 W

Explanation: The power absorbed by 10 Ω load in 3-∅ 180° VSI if the value of DC supply is 36 V is Vph2÷R=(22.6÷3)2÷10=28.8 W.

15. T.H.D value for 3-∅ 180° VSI is ________________
a) 36 %
b) 31 %
c) 39 %
d) 46 %

Explanation: T.H.D value for 3-∅ 180° VSI is 31 %. Triplen harmonics are absent in 3-∅ 180° VSI and 3-∅ 120° VSI. Only 6k±1 harmonics are present.

Sanfoundry Global Education & Learning Series – Electric Drives.

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