Research On Dynamic Freewheeling Control Technique Of Hybrid Conduction Mode Single Inductor Dual Output Switching Converter

In recent years,with the increasing requirements for integration of portable electronic products,the number of internal functional modules is gradually increasing,which usually needs different levels of voltage source power supply for various modules.Single-inductor multiple-output(SIMO)switching converter uses one inductor,adopts time-sharing multiplexing principle,and supplies power for each branch separately.It has the advantages of small size,low cost and high efficiency,and well meets the demand of such electronic products.Because each branch has independent sampling feedback,the output voltage of each branch has high regulation precision.However,due to sharing a single inductor,there is obvious cross-regulation among the output branches.Therefore,the study of SIMO switching converter with low cross-regulation,fast transient response and high efficiency has important research value and practical significance.In this thesis,the operating principle of hybrid conduction mode(HCM)single-inductor dual-output(SIDO)converter is analyzed in detail.The duty cycle expression in the main power circuit of the converter is derived,which is proved to be a good solution to the unbalanced load problem.The time-average equivalent circuit is established,the voltage gain expressions of the two output branches are calculated,and the control-output transfer function,control-inductor current transfer function,cross-regulation impedance and output impedance are obtained.The root cause of cross-regulation in hybrid conduction mode is revealed from two perspectives of DC steady state and AC small signal model.Based on the transfer function of the main power circuit,the small signal model of voltage-mode constant freewheeling control is established.In order to improve transient performance and suppress cross-regulation,dynamic freewheeling control is introduced,and the small signal model of voltage-mode dynamic freewheeling controlled HCM SIDO switching converter is established.The closed-loop output impedance and cross-regulation impedance of each output branch under the two control methods are derived,and the cross-regulation characteristics and transient performance of the two control methods are compared.Under the sampling coefficient of different output branch load current,the cross-regulation and transient performance of output branch in voltage-mode dynamic freewheeling control are analyzed,and the voltage-mode dynamic freewheeling controlled HCM SIDO switching converter with minimum cross-regulation is presented.To solve the problems of poor transient performance of voltage-mode control and cross-regulation of output branches,a V~2 dynamic freewheeling control is proposed,which not only improves the transient performance of HCM SIDO switching converter,but also suppresses the cross-regulation,and effectively improves the working efficiency and load range.Considering the parasitic parameters of components in the main power circuit,the losses of constant freewheeling controlled HCM SIDO switching converter,constant freewheeling controlled PCCM SIDO switching converter and dynamic freewheeling controlled HCM SIDO switching converter are calculated respectively,and the losses and efficiency of the above three converters under different load conditions are compared and analyzed.The relation between load and duty cycle under dynamic freewheeling control and constant freewheeling control is deduced,and their working ranges are compared.The results show that the V~2 dynamic freewheeling controlled HCM SIDO switching converter can ensure the small cross-regulation and good transient performance,and improve the load range and work efficiency of the converter.