Power Electronics Questions and Answers – PWM Inverters-2

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “PWM Inverters – 2”.

1. In case of a single-pulse width modulation with the pulse width = 2d, to eliminate the 5th harmonic from the output voltage waveform, the value of the pulse width (2d) must be equal to
a) 72°
b) 86°
c) 91°
d) 5°
View Answer

Answer: c
Explanation: To eliminate the nth harmonic, nd = π.
Therefore, d = π/n = π/5 = 36°
Hence, 2d = 72°.

2. Several equidistant pulses per half cycle are used in ___________ type of modulation technique.
a) single-pulse
b) multiple-pulse
c) sine-pulse
d) equidistant-pulse
View Answer

Answer: b
Explanation: In MPM, several equidistant pulses per half cycle are used.

3. In the multiple-pulse width modulation method, the Fourier coefficient an is
a) (Vs/π) [ cos(nπ/2) cos(nd) ].
b) 0
c) (4Vs/nπ) [sin(nπ/2) sin(nd)].
d) (2Vs/nπ) [sin(nπ/2) sin(nd)].
View Answer

Answer: b
Explanation: As the positive and the negative half cycles are identical the coefficient an = 0.
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4. In the multiple-pulse width modulation method with two pulses per half cycle of width = d each and ɣ as the distance between the first pulse and ωt=0, has the Fourier coefficient bn =
a) (8Vs/π) [ cos(ɣπ/2) cos(nd/2) ].
b) 0
c) (4Vs/nπ) [sin(nɣ) sin(nd/2)].
d) (8Vs/nπ) [sin(nɣ) sin(nd/2)].
View Answer

Answer: d
Explanation: The Fourier analysis is as under:
bn = (4/π) ∫ Vs sin⁡ nωt .d(ωt) , Where the integration would run from (ɣ + d/2) to (ɣ – d/2)
bn = (8Vs/nπ) [sin(nɣ) sin(nd/2)].

5. The amplitude of the nth harmonic of the two-pulse MPM waveform is given by __________
Let d be the width of a single pulse and ɣ be the distance from 0 to the centre of the first pulse.
a) (8Vs/nπ) sin(nɣ) sin(nd/2)
b) (4Vs/nπ) sin(nɣ) sin(nd/2)
c) (8Vs/nπ) sin(nπ) sin(nd/2)
d) (8Vs/nπ) sin(nɣ/2) sin(nd/2)
View Answer

Answer: a
Explanation: The Fourier series representation of such a wave will be given by
The Fourier series representation of a wave
bn = (8Vs/nπ) [sin(nɣ) sin(nd/2)] an = 0
Therefore,
Hence, the amplitude is the term excluding the sin nωt factor.
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6. In case of MPM with two pulses per half cycle of width = d each and ɣ as the distance between the first pulse and ωt=0, for eliminating the nth harmonic from the output voltage, which of the following condition must be satisfied?
a) d = 2π
b) d = π
c) d = n°
d) d = 2π/n
View Answer

Answer: d
Explanation:
The Fourier series representation of a wave
If d = 2π/n, sin (π) = 0 and the whole term is eliminated.

7. In case of MPM with two pulses per half cycle of width = d each and ɣ as the distance between the first pulse and ωt=0, for eliminating the nth harmonic from the output voltage, the value of gamma (ɣ) must be equal to
a) 0
b) π
c) π/n
d) d/n
View Answer

Answer: c
Explanation:
power-electronics-questions-answers-pwm-inverters-2-q5
If gamma = π/n , the whole nth output voltage comes becomes zero.
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8. Find the peak value of the fundamental component of voltage with MPM with two pulses having pulse width = 36° and ɣ = 54°. The Fourier representation of the waveform is as follows.
The Fourier series representation of a wave
a) 0.7484 x Vs
b) 1.414 x Vs
c) 0.637 x Vs
d) 2.54 x Vs
View Answer

Answer: c
Explanation: For the fundamental component put n = 1.
n = 36° and ɣ = 54° . . . (given)
Vo1 = 8Vs/π x sin54 x sin18 = 0.637 Vs.

9. In the MPM method, the comparator is given _______ and _______ types of waveform at its input.
a) square, sine
b) square, quasi-square
c) sine, triangular
d) square, triangular
View Answer

Answer: d
Explanation: To generate the modulated waves of equal width, square wave which is the reference signal is compared with the triangular wave which is the carrier signal wave.
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10. In MPM, the square wave is the ________ signal whereas the triangular wave is the ________ signal.
a) reference, carrier
b) base, reference
c) carrier, reference
d) none of the mentioned
View Answer

Answer: a
Explanation: To generate the modulated waves of equal width, square wave which is the reference signal is compared with the triangular wave which is the carrier signal wave.

Sanfoundry Global Education & Learning Series – Power Electronics.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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