GATE EE 2025 Set 1 — Question 46
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Power Electronics → Inverters → Sinusoidal PWM
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Question
The 3-phase modulating waveforms (, and ), used in sinusoidal PWM in a Voltage Source Inverter (VSI) arewhere is the fundamental frequency. The modulating waveforms are compared with a 10 kHz triangular carrier whose magnitude varies between +1 and −1. The VSI has a DC link voltage of 600 V and feeds a star connected motor. The per phase fundamental RMS motor voltage, in volts, is closest to
Correct answer
(A) 169.71
Solution
In a three-phase Voltage Source Inverter (VSI) using sinusoidal pulse width modulation (SPWM), the peak value of the fundamental component of the phase (line-to-neutral) voltage is determined by the modulation index and the DC link voltage.
Peak of modulating signal,
Peak of triangular carrier, (since it varies between and )
Given ,
The value is closest to . Thus, option (A) is correct.
1.Determine the amplitude modulation index ():
The modulation index is the ratio of the peak amplitude of the control (modulating) signal to the peak amplitude of the carrier signal.Peak of modulating signal,
Peak of triangular carrier, (since it varies between and )
2.Calculate the peak phase voltage ():
For linear modulation (), the peak of the fundamental component of the phase voltage is:Given ,
3.Calculate the RMS phase voltage ():
The RMS value of the fundamental component is:The value is closest to . Thus, option (A) is correct.
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