250+ TOP MCQs on PWM Inverters-2 and Answers

Power Electronics Multiple Choice Questions 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°
Answer: C
Clarification: 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
Answer: B
Clarification: In MPM, several equidistant pulses per half cycle are used.

3. In the multiple-pulse width modulation method, the Fourier coefficient a_n 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.].
Answer: B
Clarification: As the positive and the negative half cycles are identical the coefficient a_n = 0.

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 b_n =
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)].
Answer: D
Clarification: The Fourier analysis is as under:
b_n = (4/π) ∫ Vs sin⁡ nωt .d(ωt) , Where the integration would run from (ɣ + d/2) to (ɣ – d/2)
b_n = (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)
Answer: A
Clarification: The Fourier series representation of such a wave will be given by

b_n = (8Vs/nπ) [sin(nɣ) sin(nd/2)]
a_n = 0
Therefore,
Hence, the amplitude is the term excluding the sin nωt factor.