In the example of FIG. 5A, the time intervals during which the modulating signal Vfm lies below the half-amplitude value, i.e., during which the frequency of the modulated signal falls between the value around which the modulation is performed and the highest (maximum) frequency value are longer than the time intervals during which the modulating signal Vfm lies above the half-amplitude value, i.e., for which the frequency of the modulated signal falls between the value around which the modulation is performed and the lowest (minimum) frequency value.
The aim of the foregoing is to shift the harmonic content where the weighting coefficient is low, seeking to remain in the higher part of the spectrum as long as possible.
It has been noted that the adoption of a non-uniform modulation profile distributes the spectrum differently so as to concentrate more energy where the energy has a lower weight.
The diagram of FIG. 6 represents a possible FFT resulting from the application of the FM-PWM criteria exemplified in FIGS. 5A and 5B (which also in this case is a non-uniform spread-spectrum modulation technique) facilitates achievement of an SVM value further reduced as compared to the uniform spectrum-spread modulation exemplified in FIGS. 3A and 3B.
