
DC–AC Converters 14-11
e frequency modulation index is useful to know where the harmonic content of the switched or
PWM waveform are located in the corresponding spectrum, as shown in Figure 14.9. Note that for the
qualitative case illustrated in Figure 14.9, the carrier signal has 15 cycles compared to the reference,
hence m
f
= 15. erefore, the main or strongest harmonic component is located at n = 15. Each main
harmonic is accompanied by a group of sideband harmonics located at m
f
± 2 and m
f
± 4, therefore in
the spectrum of Figure 14.9b, some lower order harmonics located at n = 11 and n = 13 are visible. ese
harmonics appear due to