Study On Pulse Train Controlled DC/DC Converter

Pulse Train(PT)control is a new control method proposed in recent years.It selects the pulse signal with different duty ratios according to the comparison result of the output voltage and the reference voltage to realize the adjustment of the output voltage of the DC/DC converter.The PT controlled DC/DC converter has the advantages such as simple structure,fast dynamic response,no compensation network,etc.When the converter operates in the Discontinuous Conduction Mode(DCM)of the inductor current,the control effect of the PT control is good.However,when switching converter operates at Continuous Conduction Mode(CCM),the output voltage will generate low frequency oscillation,which will have a serious impact on the steady-state performance of converters.Aiming at the phenomenon of output voltage low-frequency oscillation existing in PT controlled CCM converter,the traditional PT control method has been improved to suppress the low frequency oscillation phenomenon.In this paper,the causes of the low-frequency oscillation of the traditional PT-controlled CCM converter are studied.Based on this,a new method of Capacitor Current Pulse Train(CC-PT)control is proposed.By comparing the comparison result of the capacitor current with the current reference value and the comparison result of the output voltage with the voltage reference value,the condition of the selection pulse signal is obtained.The working principle of CC-PT control and the suppression mechanism of low-frequency oscillation are analyzed,and verified by simulation and experiment.A valley Current Regulation Pulse Train(VCR-PT)control method is designed,and the basic principle of VCR-PT control is described.According to its working mode,approximate discrete-time model and energy-iterative model of VCR-PT controlled Buck circuit are deduced.The situation of different periodic states under specific load conditions is analyzed,which has been verified by simulation and experiment.According to the cause of low-frequency oscillation,this paper designs a Restrictive Continuous Pulse Train(RC-PT)control method,introduces the working principle of RC-PT control,and describes the mechanism of suppressing the low frequency oscillation.Finally,a simulation circuit and an experimental circuit are built.The results show that the proposed RC-PT control method can effectivelysuppress low-frequency oscillation.