Analysis Of Non-Minimum Phase Characteristics And Control Strategies For Single-Inductor Dual-Output Buck-Boost Converters

Single-Inductor Dual-Output(SIDO)Buck-Boost converter with one inductor can achieve two voltage outputs,with the advantages of high conversion efficiency,low production cost and buck-voltage characteristics,and has become a research hotspot at home and abroad in recent years.However,the output of the converter not only has a crossover effect,and one of the branches of the control-output transient mathematical model contains the Right Half Plane Zero(RHPZ),so that the converter presents non-minimum phase characteristics,resulting in poor transient performance of the converter and control difficulties and other problems.In order to improve the transient performance of the non-minimum phase SIDO Buck-Boost converter,a transient mathematical model of the control-output of the converter operating in the inductor current continuous conduction mode is established.thus showing the minimum phase characteristic.The transient transition process of the converter with sudden duty cycle change is analysed and it is found that the output voltage of the pilot branch of the converter is negatively regulated,while the output voltage of the rear pilot branch is not negatively regulated,which is consistent with the transient mathematical model.Based on this transient mathematical model,the influence of the converter circuit parameters on the non-minimum phase characteristics of the system is analysed,which provides a theoretical basis for the design of the converter circuit parameters to suppress the negative regulation.To address the problems of serious cross influence and poor control performance at the output of the traditional voltage-based control SIDO Buck-Boost converter,a mathematical model of the internal dynamics of the branch containing RHPZ is established,pointing out that when the output voltage of the branch containing RHPZ is selected as the feedback variable,the system zero dynamics is unstable;when the inductor current is selected as the feedback variable,the system zero dynamics is stable.Based on this,a double closed-loop control with an inner loop of current and an outer loop of voltage is used for the branch containing RHPZ,and a conventional voltage-based control is used for the branch without RHPZ.The simulation results verify the feasibility of the control method.At the same time,the stability of the SIDO Buck-Boost converter is analysed in detail.A uniform discrete iterative model of the converter is established and the bifurcation behaviour of the system with different values of parameters is analysed by means of phase diagrams.The closed-loop characteristic equations of the SIDO Buck-Boost converter are further developed and a range of stable parameter values is obtained according to the Rouse-Helwitz criterion.The simulation results verify the correctness of the stability analysis.In order to further optimise the transient and steady-state performance of the system and to suppress crossover effects at the output of the converter,the sensitivity theory of the characteristic root is applied in the stable parameter domain to quantitatively analyse the degree and trend of the influence on the stability of the system when the converter parameters are taken at different values.The critical inductance and output ripple voltage of the converter are analysed in detail,and then the parameter design method of the inductor and capacitor is obtained based on the principle of negative regulation voltage suppression.The experimental results show that the proposed control method has better transient performance than traditional voltage control and effectively suppresses the crossover effects between output branches.