Discrete Modeling And Stability Characteristics Of Digital-controlled Cascaded Dual-buck Grid-connected Inverter

In power electronic systems,there are a large number of switching power devices.Therefore,the power electronic system is a typical nonlinear system.Under certain working conditions,the system will exhibit instability such as bifurcation and oscillation,which seriously affects the safety and stability of the system.Therefore,the study of the stability characteristics of power electronic systems has become a research hot spot in power electronics in recent years.In this paper,the cascaded dual-buck grid-connected inverter is taken as the research object,and the digital control is used as the research method to deeply analyze the bifurcation instability phenomenon and oscillation phenomenon.In order to analyze the stable operating range of the digitally controlled cascaded dual-buck grid-connected inverter(CDB-GCI)and the oscillation phenomenon during the unstable operation of the CDB-GCI system,first of all,the basic principle and working mode of the system of the digitally controlled CDB-GCI was analyzed.In view of the problem of a switching cycle delay between the duty cycle and inductor current caused by the digitally controlled,it is proposed to use the delayed inductor current as a new state variable.And the mathematical model of the CDB-GCI system is established by the segment integration method.Secondly,the stability of the CDB-GCI system is analyzed by the Jacobian matrix local stability analysis method,and the stability domain of the CDB-GCI system is deduced.Studies have shown that when the CDB-GCI system is unstable,there is oscillations in the CDB-GCI system,and the mathematical expression of the oscillation frequency is derived.Then,based on the Matlab / Simulink platform,a simulation model of the digitally controlled CDB-GCI system is built,and the simulation results verify the correctness of the theoretical derivation which is about the stability domain and the mathematical expression of the oscillation frequency.At the same time,the simulation studies are used to verify the influence of the filter inductance and switching frequency on the stable domain and oscillation frequency of the CDB-GCI system.Finally,a hardware experiment platform is built to validate theoretical research and simulation.The experimental results verify that the theoretical research and design scheme are correct and feasible,and have certain practicability.