Electric Drives Questions and Answers – Solid-State Switching Circuits – Current Source Inverter

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This set of Electric Drives Multiple Choice Questions & Answers (MCQs) focuses on “Solid-State Switching Circuits – Current Source Inverter”.

1. The use of inductor in CSI is to make source current constant.
a) True
b) False

Explanation: The inductor in CSI is used to make the source current constant. The input current of CSI should be constant.

2. The output voltage of CSI depends upon the load.
a) True
b) False

Explanation: The output voltage of CSI depends upon the load. The output current of CSI is fixed as the input source current is fixed.

3. Which one of the element is used to make R load commutating?
a) Inductor
b) Capacitor
c) Resistor
d) Coil

Explanation: Capacitor is used to make the R load commutating. It is used in parallel with the resistive load.

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4. Calculate the minimum time period for ASCI using the data: R=12 kΩ, C=45 μF.
a) 2.58 sec
b) 2.16 sec
c) 2.23 sec
d) 2.48 sec

Explanation: The minimum time period for ASCI is a 4×R×C = 4×12×45×.001 = 2.16 sec. The total time is the sum of charging and discharging time.

5. Full form of ASCI is ___________
a) Auto sequential commutated inverter
b) Auto starter commutated inverter
c) Auto sequential current inverter
d) Auto sequential current inserter

Explanation: ASCI stands for Auto sequential commutated inverter. No external forced commutation is required for ASCI. The capacitor itself works as a load commutated inverter.

6. Calculate the maximum frequency for ASCI using the data: R=15 kΩ, C=5 μF.
a) 3.51 Hz
b) 3.69 Hz
c) 3.33 Hz
d) 3.98 Hz

Explanation: The maximum frequency for ASCI is a 1÷(4×R×C) = 1÷(4×15×5×.001) = 3.33 Hz. The total frequency is the sum of charging and discharging frequency.

7. The output current waveform for R load in CSI is ___________
a) Square
b) Triangular
c) Constant
d) Vertical

Explanation: The output current of CSI for R load is square in nature. The amplitude of the output current varies from I to -I.

8. T.H.D value for CSI is ________________
a) 48.43 %
b) 41.15 %
c) 39.15 %
d) 46.48 %

Explanation: T.H.D value for VSI is 48.43 %. Triplen harmonics are present in CSI due to which harmonic content increases.

9. What is the distortion factor value in CSI?
a) .85
b) .90
c) .95
d) .88

Explanation: The distortion value in CSI is .90. The r.m.s value of the fundamental current is 2√2I÷π and r.m.s value of the output current is I. The distortion factor is (2√2I÷π)÷I = .90.

10. Number of switches turned on in CSI at a single time are __________
a) 2
b) 4
c) 5
d) 3

Explanation: In CSI two switches conduct at a single time. The common switch used in CSI is thyristor. Thyristors are unidirectional, bipolar in nature.

11. Calculate the r.m.s value of the output current having an amplitude of 2 A for CSI.
a) 3 A
b) 4 A
c) 2 A
d) 1 A

Explanation: The r.m.s value of the output current having an amplitude of 2 A for CSI is 2A. The waveform for output current is a square wave. The r.m.s value of the square wave is its amplitude.

12. Calculate the r.m.s value of the fundamental component of the output current having an amplitude of 3 A for CSI.
a) 2.80 A
b) 2.70 A
c) 2.54 A
d) 3.48 A

Explanation: The r.m.s value of the fundamental component of the output current is 2√2I÷π=8.48÷3.14=2.70 A. The r.m.s value of the output current is I.

13. Calculate the string efficiency if the de-rating factor is .76.
a) 24 %
b) 25 %
c) 26 %
d) 27 %

Explanation: The string efficiency is calculated for series and parallel connection of SCRs. The value of string efficiency is 1-(De-rating factor)=1-.76=24 %.

14. 20 V rated 8 SCRs are connected in series. The operation voltage of the string is 50. Calculate the De-rating factor.
a) .67
b) .68
c) .69
d) .70

Explanation: The string efficiency can be calculated using the formula operation voltage÷(Number of SCRs×Rated voltage)=50÷(20×8)=.31. The De-rating factor value is 1-.31=.68.

15. Forced commutated CSI require _________
a) Diode
b) Resistor
c) Inductor
d) Capacitor

Explanation: Forced commutated CSI requires a capacitor. The capacitor acts as a commutating element. It is connected in parallel with the load.

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