Performance and Characterization of Optimal Harmonic Dispersion Effect in Double Frequency-Band Random PWM Strategy

In the traditional random switching frequency pulsewidth modulation (RSFPWM), the frequency range should be set large enough to make the harmonics evenly distributed without spikes, which may also disperse the harmonics to the lower frequency band that is hard to be filtered. To avoid the low-frequency harmonics induced by widening the frequency range, a double frequency-band random pulsewidth modulation (DFB-RPWM) strategy is proposed in this article, to form a more uniform harmonic distribution in a narrower frequency range. In this strategy, each harmonic cluster is divided into two harmonic peaks, and the relative position of the two harmonic peaks influences the harmonic dispersion effect. By adopting the harmonic dispersion theory of the frequency spectrum, the condition that makes lower harmonic amplitudes and more uniform harmonic distribution can be determined. The simulation and experiment are conducted to verify the effectiveness of the DFB-RPWM, showing a better performance than the RSFPWM.