Question 11 : In pulse width modulation
1. the output voltage is modulated
2. the input voltage is modulated
3. the gating pulses are modulated
4. none of the mentioned
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Question 12 : In single-phase modulation of PWM inverters, the 5th order harmonic can be eliminated if the pulse width is made equal to ___________
1. 30°
2. 36°
3. 72°
4. None of the mentioned
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Question 13 : In a 3-phase VSI operating in square-wave mode, the output line voltage is free from
1. 3rd harmonic
2. 7th harmonic
3. 11th harmonic
4. 13th harmonic
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Question 14 : Several equidistant pulses per half cycle are used in ___________ type of modulation technique.
1. single-pulse
2. multiple-pulse
3. sine-pulse
4. equidistant-pulse
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Question 15 : In voltage fed thyristor inverters __________ commutation is required.
1. load
2. forced
3. self
4. any commutation technique can be used
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Question 16 : In the single-pulse width modulation method, the Fourier coefficient b_n is given by
1. (Vs/π) [ sin(nπ/2) sin(nd) ].
2. 0
3. (4Vs/nπ) [sin(nπ/2) sin(n
4. ].d) (2Vs/nπ) [sin(nπ/2) sin(nd)].
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Question 17 : The output of a single-phase half bridge inverter on R load is ideally
1. a sine wave
2. a square wave
3. a triangular wave
4. constant dc
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Question 18 : The Total Harmonic Distortion (THD) is the ratio of
1. rms value of all the harmonic components to the rms value of the fundamental component
2. average value of all the harmonic components to the rms value of the fundamental component
3. rms value of all the third harmonic component to the rms value of the fundamental component
4. rms value of all the fundamental component to the rms value of all the harmonic components
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Question 19 : In pulse width modulated inverters, the output voltage is controlled by controlling the
1. input frequency
2. modulating index
3. amplification factor
4. none of the mentioned
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Question 20 : 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.
1. 510 V
2. 103.5 V
3. 120 V
4. 96 V
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