Stability Analysis Of Cascaded Converter System For New Energy Vehicles

In the new energy vehicle power system,A variety of internal converter are cascaded as a system.The DC-DC converter is a typical nonlinear system,which has a very rich linear and nonlinear dynamic behavior,So the stability analysis becomes more complicated.In the complex dynamic system of new energy vehicles,the stability determines whether the DC-DC converter of the whole cascade system can run stably,the stability analysis is to obtain the stability condition of the DC-DC converter in the steady state,and to get the steady state of the system in the unstable state.So,it is very important to analyze the stability of DC-DC converter.In this paper,we focus on the stability of cascaded converter,and propose a new impedance ratio criterion.Firstly,this paper introduces the research background and significance of cascade system,and its research status of stability analysis;Then,in the CCM(Continuous Conduction Mode,continuous conduction mode)mode,the state space average method is used to establish the mathematical model of the DC-DC converter system.Using this method,the Buck and Boost converters are modeled respectively,and the loop gain of the two converters and the input and output impedance expressions are obtained;Based on the average model,the dynamic model of the converter is analyzed.And based on the established model,Using the Simulink module of MATLAB software,the compensation of the Buck and Boost converter are analyzed,and then set up two kinds of converter in stable and unstable state with two kinds of compensation parameters,and the Bode diagram and simulation waveform of each state are obtained.The results show that the small signal model can only be used to analyze the stability of the system when the signal is small,and cannot be used to analyze the stability of the system in the large signal state.Finally,based on the improved impedance ratio criterion proposed by the previous scholars,this paper proposes a new impedance ratio criterion.As long as the cascade system satisfies the three conditions required by the criterion,we can use this new impedance ratio.And finally,the three groups of control simulation experiments are used to prove the correctness and applicability of the new impedance ratio criterion.