Modeling And Control Technique Of Switching Converter Operating In Pseudo Continuous Conduction Mode

Pseudo continuous conduction mode(PCCM)of the inductor current is a special operating mode of switching converter,which takes into account the advantages of continuous conduction mode(CCM)and discontinuous conduction mode(DCM)and is suitable for wide load or wide power range.What's more,PCCM switching converter has the characteristics of decoupling control and reducing cross-regulation.Therefore,it is of great significance to study the PCCM switching converter.In order to improve the light load efficiency of the PCCM switching converter,a novel control technique,named as fixed off time(FOT)control technique,for PCCM switching converter is proposed in this paper.Firstly,the working principle of PCCM buck converter with FOT control is studied.Then,the steady state performance,transient performance and efficiency in a wide load range of the constant reference current(CRC)controlled and FOT controlled PCCM buck converters are analyzed and compared through simulation analysis.Considering the voltage-voltage(V~2)control technique of switching-mode power supply has a fast load transient response,a V~2 fixed freewheeling-time(V~2-FFT)control technique for PCCM switching converters is proposed.The working principle of PCCM buck converter with V~2-CRC control and V~2-FFT control is studied,and the small signal models and the corresponding "control to output","input to output","output impedance" transfer functions of PCCM buck converters with V~2-CRC control and V~2-FFT control are established using the average switching models.The frequency domain performances of V~2-CRC controlled and V~2-FFT controlled PCCM buck converters are analyzed and compared by frequency domain simulation,whose correctness is verified by time domain simulation.In order to analyze the dynamic characteristics of PCCM buck converter,the discrete-map model of PCCM buck converter is established.On the basis of the model,the dynamical behaviors of the PCCM buck converter with the variations of circuit parameters are analyzed,including load resistance,equivalent series resistance(ESR)of inductor,inductance,capacitance,reference current,and input voltage.In addition,the corresponding time domain model is established.The time domain waveforms of the output voltage and inductor current of the converter under the corresponding parameters are obtained,which verifies the correctness of the discrete modeling.The conclusions are of great significance for the research and control of PCCM buck converters.Finally,the experimental platform of PCCM buck converter with different control is built,and the correctness of the theoretical analysis and simulation analysis is verified by experimental results.