Research On Modeling And Nonlinear Bifurcation Characteristics Of Dual Input DC Converter

In the new energy combined power generation system,the multi-input DC converter is used as the connection hub between the new energy input unit and the load.Its nonlinear instability determines the system performance and reliable operation.In the study of nonlinear dynamic behavior,the simplicity of the analysis method and the effectiveness of the results are closely related to the established mathematical model.It is very important to study the nonlinear dynamic behavior of multi-input DC converter to establish a mathematical model that can characterize the nonlinear behavior.In this paper,the dual-input Buck/Buck-Boost DC converter is taken as the research object.The multi-frequency modeling of the PWM modulator,decoupling control,nonlinear bifurcation behavior and differential frequency oscillation in the output voltage v0 are mainly studied.Fist,the topology characteristics of the dual input Buck/Buck-Boost DC/DC converter are analyzed,the overall control strategy of the system is introduced,and the identification method and numerical analysis method of nonlinear bifurcation in power electronic converter are analyzed.Secondly,the mathematical model of the main circuit corresponding to the three working modes of the converter is established,and the decoupling control and control parameter design of the working mode I are carried out by using the decoupling idea;On the basis of considering the side band effect of the PWM modulator,the multi-frequency small-signal model of the PWM modulator of the Buck-Boost input unit and the multi-frequency loop gain transfer function are derived and approximated.The correctness of the multi frequency model is verified by simulation.Then,the average model of the system in working model I and its Jacobian matrix are established,and the reference current value IL0_ref of current loop is selected as the bifurcation parameter,and the bifurcation diagram of the output voltage v0 that decreases with IL0_ref is obtained.The existence of the bifurcation is verified by the phase diagram and the time domain simulation diagram.According to the change of the characteristic root of the Jacobian matrix of the system with IL0_ref,the occurrence of bifurcation is identified and the bifurcation mechanism is explained.For the unstable behavior of differential frequency oscillation in working model I,the mechanism of its generation is described by using the established multi-frequency model,and the guiding theory to avoid the phenomenon of differential frequency oscillation in the system is given.Finally,an experimental prototype of a dual-input Buck/Buck-Boost DC converter with a rated power of 150W was built.The experimental results show that the designed hardware system can realize stable operation of three working modes,and verify the existence of Hopf bifurcation in working mode I,which is consistent with the theoretical and simulation results.