GATE 2021 EE – Question 65
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 $\theta$ 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 $v_{ab}$ to the applied DC value.)
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Correct answer: 50.00 to 52.00
Explanation
For a quasi-square wave with zero intervals of width $\theta$ at the start of each half-cycle, the fundamental peak is $\frac{4V_{dc}}{\pi}\cos\theta$. So $m=\frac4\pi\cos\theta=0.8$, giving $\cos\theta=0.628$ and $\theta=51.0^\circ$.