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GATE 2016 EE – Question 60

Power Electronics · Single-phase and three-phase voltage and current source inverters, sinusoidal pulse width modulation · 2 marks · Multiple choice

A single-phase full-bridge voltage source inverter (VSI) is fed from a 300 V battery. A pulse of 120° duration is used to trigger the appropriate devices in each half-cycle. The rms value of the fundamental component of the output voltage, in volts, is

  1. 234
  2. 245
  3. 300
  4. 331

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Correct answer: (A) 234

Explanation

For a quasi-square wave with a pulse width $\sigma$ from a full bridge, the rms fundamental is $\frac{4V_{dc}}{\pi\sqrt{2}}\sin\frac{\sigma}{2}$. With $V_{dc} = 300$ and $\sigma = 120°$ this is $\frac{4 \times 300}{\pi\sqrt{2}} \times \sin 60° = 270.1 \times 0.866 = 234$ V.