The Mathmatical Modelling And Control Of Isolated Bidirectional DC/DC Converter

With the rapid development of productivity and economy,the consumption of traditional energy such as fossil fuel is increasing.In response to the call for energy conservation and emission reduction,more and more attention has been paid to the development of new energy sources,such as photovoltaic and wind power.Then,new energy sources such as photovoltaic and wind power are insufficient in the continuity and stability of energy supply,so power electronic conversion device is needed to achieve stable output of voltage or current.For the isolated bidirectional DC/DC converter,its main features are that it can realize the two-way flow of power and ensure the electrical isolation between the input side and the output side.The isolated bidirectional DC/DC converter is mainly used in new energy electric vehicles,photovoltaic power generation,uninterrupted power supply system,wind power and DC power amplifier.The research object of this paper is the dual-active bridge DC/DC converter with symmetrical circuit structure.It is not only easy to realize the ZVS(Zero-Voltage-Switching)of the switching tube,but also has the advantages of high power density,bidirectional energy transmission and simple control method.First of all,the research background and significance of this research topic are introduced,and the topology,control strategy and model establishment method of the dual-active bridge DC/DC converter at home and abroad are expounded respectively.Secondly,the basic principle of the DAB converter is analyzed in detail,and the waveforms of voltage and current at key nodes during the steady-state operation of the converter are plotted through the detailed description of each switch mode in a switching cycle.The main basic characteristics of DAB converter are analyzed theoretically,including transmission power,reflux power and soft switching characteristics.The relationship between the transmitted power and the duty ratio of the control variable,the relationship between the back-flow power and the control strategy,and the working scope of soft switch implementation are obtained respectively.Then,around the dual active bridge DC/DC converter modeling,according to the state variables of the DAB converter capacitor voltage and inductor current column state equation,the method of using Fourier decomposition,the switching function with a series of harmonic superposition,the switching function model,using phasor analysis,get the time-domain expression of the state variables in the steady state equation on the basis of applying small disturbance,get small signal model for describing the dynamic characteristics of DAB converter.Based on the small signal model,the design criteria of the closed-loop feedback controller is carried out,and the design method of the procedural controller is proposed and verified.Finally,relevant simulation test experiments were designed to test the controller system of the designed bi-directional DC/DC converter,and relevant software such as MATLAB was used to plot and analyze the experimental data.The performance index of the controller is analyzed in detail,the research work of the subject is summarized,and the prospect of future research work is given.