Research On Control Technology Of Single-Inductor Dual-Output Buck Converter In Pseudo-Continuous Conduction Mode

Under the background of increasingly development of electronic device such as portable equipment and LED lighting,single-inductor multiple-output switching converter have received more and more attention because of their advantages such as small size,high power density,and controllable multiple outputs.Due to the mutual coupling between the output branches,a load change of one branch will have a cross-regulation effect on other branches.Due to the limitation of the operation mode,the load range of the single-inductor multipleoutput converter is limited.Therefore,it is of great significance to study the cross-regulation and load range of single-inductor multiple-output switching converter.In this thesis,the single-inductor dual-output(SIDO)buck converter operating in pseudocontinuous conduction mode(PCCM)is studied,and the circuit topology and operation principle of the converter are analyzed.On this basis,the main power circuit of the PCCM SIDO buck converter is modeled by using the time averaging equivalent circuit modeling method;the DC voltage gains of the two outputs of the PCCM SIDO buck converter are obtained from the DC steady state analysis,and the essential reason for the cross-regulation of the converter is explained;the transfer function of control-output,output impedance and cross-regulation impedance are derived from AC small signal analysis.Finally,the correctness of power stage modeling is verified by simulation.The operation principle and operation sequence of the voltage-type-based constant freewheeling control PCCM SIDO buck converter are analyzed,and the small-signal modeling of the voltage-type-based constant freewheeling control loop is carried out.Combined with the power stage model,the closed-loop small-signal model of the converter with voltage-typebased constant freewheeling control is established,and the transfer function of closed-loop output impedance and cross-regulation impedance of the two output branches are deduced.The transient performance and cross-regulation effects of the converter under different freewheeling values are analyzed.The load range of the PCCM SIDO buck converter with voltage-type-based constant freewheeling control is analyzed,the mathematical expressions for the load range of the two output branches are derived,and the losses and efficiency of the converter are studied.The research results show that increasing the freewheeling value can widen the load range of the converter;the efficiency of the converter varies with the power,and the lower the power,the more severe the reduction in efficiency,and reducing the freewheeling value can improve the efficiency of the converter.Finally,the correctness of the theoretical analysis is proved by experimental results.In order to widen the load range of the PCCM SIDO buck converter,improve the efficiency and transient performance of the converter,and reduce the cross-regulation between the output branches,the voltage-ripple-based dynamic freewheeling(VR-DF)control technology and its realization scheme are proposed.The VR-DF control principle is analyzed,the small signal model of VR-DF control converter is established,the closed-loop output impedance and cross-regulation impedance of the system are deduced,and the compensation network design of the converter is carried out.The intrinsic causes of sub-harmonic oscillation produced by VR-DF control are analyzed,and a feasible slope compensation control is proposed.The results show that VR-DF control has superior transient performance,wider load range,higher efficiency,and also no cross-regulation problem compared with voltage type constant renewal control in four aspects: load range,efficiency,transient performance and cross influence characteristics.Finally,the correctness of the theoretical analysis is verified by experiments.