# Power Electronics Questions and Answers – Current Source Inverters

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “Current Source Inverters”.

1. In voltage source inverters (VSIs), the amplitude of the output voltage is
c) dependent only on L loads
d) none of the mentioned

Explanation: In VSIs the input voltage is maintained at a constant value and the amplitude of the output voltage does not depend on the load conditions. However, the waveform of the load current as well as its magnitude depends upon the nature of the load impedance.

2. In voltage source inverters (VSIs), the output currents _____________
a) amplitude depends upon the load impedance
b) waveform depends upon the load impedance
c) amplitude as well as the nature of the waveform depends on the load
d) both amplitude and waveform are independent of the load impedance

Explanation: In VSIs the input voltage is maintained at a constant value and the amplitude of the output voltage does not depend on the load conditions. However, the waveform of the load current as well as its magnitude depends upon the nature of the load impedance.

3. In current source inverters (CSIs)
a) the amplitude of the output current is independent of the load
b) the amplitude of the output current dependents on the load
c) the amplitude of the output voltage is independent of the load
d) none of the mentioned

Explanation: In CSIs, the amplitude of the output current is independent on the load impedance, as the input current (to the CSI) is kept constant.

4. In current source inverters (CSIs), the output voltage’s
a) amplitude depends upon the load impedance
b) waveform depends upon the load impedance
c) amplitude as well as the nature of the waveform depends on the load
d) both amplitude and waveform are independent of the load impedance

Explanation: In CSIs, the amplitude of the output current is independent on the load impedance, as the input current (to the CSI) is kept constant. However, the magnitude of output voltage and its waveform depends upon the nature of the load impedance.

5. In current source inverters
a) L filter is used after the CSI (load side)
b) L filter is used before the CSI (input side)
c) C filter is used after the CSI (load side)
d) C filter is used before the CSI (input side)

Explanation: In order that the current input to the CSI must remain ripple free an constant, L-filter is used before the CSI (in series with the energy source).
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6. A CSI converters
a) the input dc current to an an current at output
b) the input ac current to dc current at output
c) the input dc current to amplified dc current at the output
d) the input ac current to amplified ac current at the output

Explanation: CSI converts the input dc current to an ac current at its output terminals.

7. In the below shown, the ideal single-phase CSI circuit has constant input source current of I amps. The output current waveform varies from a) 2I to – 2I
b) I/2 to –I/2
c) I to –I
d) none of the mentioned

Explanation: Considering the SCRs as ideal voltage sources, when T1, T2 are on the load current is = I. When T3, T4 conduct, the load current is negative with respect to the previous value and = -I.

8. T1, T2 are triggered at 0 and T3, T4 at T/2. If both the pairs of SCRs conduct for equal duration and the load consists of a capacitor. Then a) the load current waveform is a square wave
b) the load voltage waveform is a square wave
c) the load current is constant dc
d) the load voltage is constant dc

Explanation: The load current waveform is a square wave with frequency = 1/T. As the load consists of a capacitor, dv/dt must be constant over every half cycle. This slope is positive from zero to T/2 and negative from T/2 to T.

9. In a 3-phase VSI operating in square-wave mode, the output line voltage is free from
a) 3rd harmonic
b) 7th harmonic
c) 11th harmonic
d) 13th harmonic

Explanation: The line voltage is the difference of two phase voltages, the 3rd harmonic gets cancelled out, though it is present in the phase voltages.

10. Force-commutated CSIs need
a) capacitors for their commutation
b) inductors for their commutation
c) diodes for their commutation
d) none of the mentioned

Explanation: All the CSIs need capacitors for their commutation if force commutation is required. Force commutation is essential for lagging power factors.

Sanfoundry Global Education & Learning Series – Power Electronics.

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