Question

In case of sinusoidal pulse width modulation with MI < 1, if the number of pulses per half cycle (N) = 6, then

(a) harmonics of order 7 and 9 become significant

(b) harmonics of order 7 and 9 are eliminated

(c) harmonics of order 11 and 13 become significant

(d) harmonics of order 11 and 13 are eliminated

I had been asked this question in an internship interview.

This intriguing question comes from PWM Inverters-4 topic in chapter Inverters of Power Electronics

Answer 1

Correct choice is (c) harmonics of order 11 and 13 become significant

Best explanation: For MI less than one, largest harmonic amplitudes in the output voltage are associated with harmonics of order 2N (+/-) 1. Thus, by increasing the number of pulses per half cycle (N), the order of the dominate harmonic can be raised, which can be filtered out easily.