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    250+ TOP MCQs on PWM Inverters

    Power Electronics Multiple Choice Questions on “PWM Inverters-1”. 1. In the single-pulse width modulation method, the output voltage waveform is

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    250+ TOP MCQs on PWM Inverters-1 and Answers

    Power Electronics Multiple Choice Questions on “PWM Inverters-1”.

    1. In the single-pulse width modulation method, the output voltage waveform is symmetrical about __________

    A. π B. 2π C. π/2 D. π/4 Answer: C

    Clarification: The waveform is a positive in the first half cycle and symmetrical about π/2 in the first half.

    2. In the single-pulse width modulation method, the output voltage waveform is symmetrical about ____________ in the negative half cycle.

    A. 2π B. 3π/2 C. π/2 D. 3π/4 Answer: B

    Clarification: In the negative half the wave is symmetrical about 3π/2.

    3. The shape of the output voltage waveform in a single PWM is

    A. square wave B. triangular wave

    C. quasi-square wave

    D. sine wave Answer: C

    Clarification: Positive and the negative half cycles of the output voltage are symmetrical about π/2 and 3π/2 respectively. The shape of the waveform obtained is called as quasi-square wave.

    4. In the single-pulse width modulation method, the Fourier coefficient bn is given by

    A. (Vs/π) [ sin(nπ/2) sin(nD. ].

    B. 0

    C. (4Vs/nπ) [sin(nπ/2) sin(nD.].

    D. (2Vs/nπ) [sin(nπ/2) sin(nD.].

    Answer: C

    Clarification: The Fourier analysis is as under:

    bn = (2/π) ∫ Vs sin⁡ nωt .d(ωt) , Where the integration would run from (π/2 + D. to (π/2 – D.

    2d is the width of the pulse.

    5. In the single-pulse width modulation method, the Fourier coefficient an is given by

    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 an = 0.

    6. In the single-pulse width modulation method, when the pulse width of 2d is equal to its maximum value of π radians, then the fundamental component of output voltage is given by

    A. Vs B. 4Vs/π C. 0 D. 2Vs/π Answer: B

    Clarification: The Fourier representation of the output voltage is given by

    Put 2d = π & n = 1.

    7. In case of a single-pulse width modulation with the pulse width = 2d, the peak value of the fundamental component of voltage is given by the expression

    A. 4Vs/π B. Vs C. (4Vs/π) sin 2d D. (4Vs/π) sin d Answer: D

    Clarification: For the fundamental component put n = 1.

    Vo = (4Vs/π) sin (D. sin (ωt)

    Hence the peak value is (4Vs/π) sin d.

    8. In case of a single-pulse width modulation with the pulse width = 2d, to eliminate the nth harmonic from the output voltage

    A. d = π B. 2d = π C. nd = π D. nd = 2π Answer: C

    Clarification: To eliminate, the nth harmonic, nd is made equal to π radians, or d = π/n.

    From the below expression,

    when nd = π. sin nd = 0 hence, that output voltage harmonic is eliminated.

    स्रोत : engineeringinterviewquestions.com

    [Solved] In a single

    Single-pulse modulation: It consists of a pulse width of 2d located symmetrically about π/2 and another pulse located at symmetrically about 3π/2. The

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    In a single-phase inverter using single pulse modulation for control of output voltage, Harmonics of the order ‘n’ can be eliminated by making the pulse width equal to

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    4π/n 2π/n π/n π/2n

    Answer (Detailed Solution Below)

    Option 2 : 2π/n

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    Detailed Solution

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    Single-pulse modulation:

    It consists of a pulse width of 2d located symmetrically about π/2 and another pulse located at symmetrically about 3π/2. The range of pulse width varies from 0 to π.

    The output voltage is controlled by varying pulse width.

    To eliminate nth harmonic, ‘nd’ should be made equal to π.

    This method of voltage control, a great deal of harmonic content is introduced in the output voltage, particularly at low output voltage levels.

    The output voltage waveform of a single-phase full-bridge inverter is represented as below.

    v0=∑n=1,3,5∞⁡4Vsnπsin⁡nπ2sin⁡ndsin⁡nωt

    v0=4Vsπ[sin⁡dsin⁡ωt−13sin⁡3dsin⁡3ωt+15sin⁡5dsin⁡5ωt]

    If nd is equal to π or

    d=πn

    or if pulse width is made equal to

    2d=2πn

    , it shows that nth harmonic is eliminated from the inverter output voltage.

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    More Pulse Width Modulated Inverters Questions

    Q1. A 3-phase grid-connected voltage source converter with DC link voltage of 1000 V is switched using sinusoidal Pulse Width Modulation (PWM) technique. If the grid phase current is 10 A and the 3-phase complex power supplied by the converter is given by (−4000 − j3000) VA, then the modulation index used in sinusoidal PWM is ___________. (round off to two decimal places)Q2. A single-phase full-bridge inverter fed by a 325 V DC produces a symmetric quasi-square waveform across 'ab' as shown. To achieve a modulation index of 0.8, the angle θ expressed in degrees should be ______. (Round off to 2 decimal places.) (Modulation index is defined as the ratio of the peak of the fundamental component of Vab to the applied DC value.)Q3. In single pulse modulated PWM inverter, third harmonic is eliminated by making pulse width equal to 120°. To eliminate fifth harmonic the pulse width will beQ4. For the speed control of AC drive the preferred method using thyristor is:Q5. A PWM switching scheme is used with three phase inverter toQ6. Direction: The following item consists of two statements, one labelled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below: Statement (I): In sinusoidal pulse width modulation, width of each pulse is varied in proportion to amplitude of a sine-wave evaluated at the centre of the same pulse. Statement (II): The rms value of output voltage can be varied by varying the modulation index.Q7. In the sinusoidal pulse-width modulation scheme, if the zero of the triangular wave coincides with the zero of the reference sinusoidal, then the number of pulses per half cycle isQ8. In single pulse modulation PWM inverter third harmonics can be eliminate if the pulse – width is made equal to

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    PWM Inverters

    This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “PWM Inverters-1”. 1. In the single-pulse width modulation method, the output voltage waveform is symmetrical about __________ a) π b) 2π c) π/2 d) π/4 2. In the single-pulse width modulation method, the output voltage waveform is symmetrical about ____________ in the ... Read more

    Power Electronics Questions and Answers – PWM Inverters-1

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    This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “PWM Inverters-1”.

    1. In the single-pulse width modulation method, the output voltage waveform is symmetrical about __________

    a) π b) 2π c) π/2 d) π/4 View Answer

    2. In the single-pulse width modulation method, the output voltage waveform is symmetrical about ____________ in the negative half cycle.

    a) 2π b) 3π/2 c) π/2 d) 3π/4 View Answer

    3. The shape of the output voltage waveform in a single PWM is

    a) square wave b) triangular wave

    c) quasi-square wave

    d) sine wave View Answer

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    4. In the single-pulse width modulation method, the Fourier coefficient bn is given by

    a) (Vs/π) [ sin(nπ/2) sin(nd) ].

    b) 0

    c) (4Vs/nπ) [sin(nπ/2) sin(nd)].

    d) (2Vs/nπ) [sin(nπ/2) sin(nd)].

    View Answer

    5. In the single-pulse width modulation method, the Fourier coefficient an is given by

    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

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    6. In the single-pulse width modulation method, when the pulse width of 2d is equal to its maximum value of π radians, then the fundamental component of output voltage is given by

    a) Vs b) 4Vs/π c) 0 d) 2Vs/π View Answer

    7. In case of a single-pulse width modulation with the pulse width = 2d, the peak value of the fundamental component of voltage is given by the expression

    a) 4Vs/π b) Vs c) (4Vs/π) sin 2d d) (4Vs/π) sin d View Answer advertisement

    8. In case of a single-pulse width modulation with the pulse width = 2d, to eliminate the nth harmonic from the output voltage

    a) d = π b) 2d = π c) nd = π d) nd = 2π View Answer

    9. Find the peak value of the fundamental component of voltage with a pulse width of 2d = 90 and Vs = 240 V for single-pulse modulation in a full wave bridge inverter.

    a) 305 V b) 216 V c) 0 V d) 610 V View Answer advertisement

    10. In case of a single-pulse width modulation with the pulse width = 2d, to eliminate the 3rd harmonic from the output voltage waveform, the value of the pulse width (2d) must be

    a) 0° b) 60° c) 120° d) 180° View Answer

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