The Methods On Suppressing Low Frequency Oscillation Of Pulse Train Controlled Switching DC-DC Converter

Pulse train control is a kind of discrete control technique for switching DC-DC converter,which applies different combination of high or low power control pulses to regulate output voltage according to relative inferiority of output and reference voltage.When working in continuous conduction mode,the phases of capacitor voltage and inductor current are closel occur if the equivalent series resistance is small,which causes that output voltage can’t be regulated strictly by pulse combinations.It will enhance the ripple of output voltage and drastically reduce performance of converter.As for now,solutions to inhibit low-frequency oscillation can be classified to three types which are increasing equivalent series resistance of output capacitor,improving control method and changing circuit structure.Though increasing equivalent series resistance of output capacitor could narrow the gap between output voltage and inductor current and suppress low-frequency oscillation,it will also enlarge switching ripples of output voltage.Capacitor current pulse train control technique is able to inhibit low-frequency oscillation in some specific working circumtances.When the duty ratio is over 0.5,low-frequency oscillation still occurs.This occurance mechanism delved into and a modified control technique,hysteretic capacitor current pulse train(HCC-PT)is proposed in this paper,which can effectively inhibit low-frequency oscillation in the circumstance where duty ratio is over 0.5.The principle of HCC-PT controlled Buck converter is presented and its energy transforming model and working characteristic are analysed in this paper.Based on the analysis on the fact that there is no low-frequency oscillation happening in PT controlled DCM Buck converter,circuit structure is changed and a new control technique is proposed,which can make Buck converter work in pseudo-continuous conduction mode(PCCM).Platform of pulse train controlled PCCM Buck converter based on capacitor current is established.The experimental results show that low-frequency oscillation is inhibited and this converter has outstanding transient responding.Discrete phase shifted(DPS)controlled full-bridge converter intended for high power applications still has the problem of low-frequency oscillation.A generalized equivalent circuit for PT controlled Buck-type converter is founded and DPS controlled PCCM full-bridge converter is proposed in this paper.The experimental results show that PT controlled PCCM switching DC-DC converter can suppress low-frequency oscillation and has excellent portability.