Discussion
In the single pulse modulation of a PWM inverter, if the pulse width is \(72^\circ\), the ______ harmonic can be eliminated.
Answer: B
In single pulse width modulation of an inverter, one pulse of width \(2d\) is placed symmetrically in each half cycle. The Fourier series of the output has the harmonic amplitudes proportional to \(\sin(n d)\), so the \(n\)th harmonic is eliminated when \(\sin(nd) = 0\), that is when the pulse width equals \(360^\circ / n\) (or a multiple of it).
\[ 2d = 72^\circ = \frac{360^\circ}{5} \]
So the fifth harmonic is eliminated. For the third harmonic the width would be \(120^\circ\), for the seventh about \(51.4^\circ\) and for the eleventh about \(32.7^\circ\). The answer is the 5th, option B.
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