Low-frequency oscillation of continuous conduction mode buck converter with pulse skipped modulation

Abstract

Low-frequency oscillation phenomenon in pulse skipped modulation (PSM) buck converter operating in continuous conduction mode (CCM) is reported in this paper. Energy transfer difference between the PSM-controlled buck converter operating in discontinuous conduction mode (DCM) and that in CCM is studied. The mechanism of low-frequency phenomenon in PSM-controlled CCM buck converter is revealed, and a discrete-time model of PSM-controlled buck converter operating in CCM is established. Based on this model, the border collision bifurcation with variations of the ESR is studied; meanwhile, the inhibition effect of output capacitor equivalent series resistance (ESR) on low-frequency oscillation is presented. Based on the above analysis, a capacitor current pulse skipped modulation (CC-PSM) technology is proposed; the energy transfer principle of CC-PSM controlled buck converter is analyzed. The control pulse of CC-PSM is generated by the comparison between the sampled capacitor current and preset peak reference current, and thus the range of inductor current ripple is limited. Results show that CC-PSM effectively eliminates the low-frequency oscillation in CCM buck converter under classical PSM when the ESR is low. Finally, the experimental results validate the correctness of theory and simulation analysis