Reconfigurable Periodic Bifrequency DPWM With Custom Harmonic Reduction in DC–DC Converters

Majority of spectral spreading techniques employ chaos-based pulsewidth-modulation (PWM) schemes in a switching dc-dc converter, in which neither dynamic performance nor ripple parameter can be correctly predicted so as for efficiency. Periodic frequency modulation using a triangular carrier wave can achieve custom spectral spreading and harmonic reduction. This paper proposes a periodic bifrequency digital PWM (BF-DPWM) technique in a dc-dc converter, which uses two discrete frequencies f
₁
and f
₂
as guided by a modulating signal f
_m
. Fourier analysis shows that f
₁
and f
₂
do not exist; however, they contribute to power spectrum of f
_m
. This method achieves considerable harmonic reduction and improved DPWM resolution with an insignificant ripple impact, compared to a dither-based periodic modulation scheme. Design guidelines using simulation study are presented. A buck converter prototype has been made, and different control schemes are implemented using a field-programmable gate array device. Test results show that the BF-DPWM has insignificant impacts on transient performance. Finally, the proposed scheme is extended to the triangular-wave modulation scheme, which results in further harmonic reduction.