| The “dual carbon” strategic goal points out the direction for energy development in the new era and promotes the development of energy storage systems,DC microgrid,electric vehicles and so on.In the energy storage systems and DC microgrids,bi-directional isolated dual active bridge(DAB)DC converter has played an important role.DAB converter has the advantages of bidirectional power flow,soft switching characteristics,high power density and symmetrical structure.It has great application prospects and research values.In spite of these advantages,with the role of DAB converter becoming more and more important,the better steady-state accuracy,dynamic performance and robustness of output voltage is required in practical applications.In this thesis,the output voltage control of DAB converter is investigated.Firstly,the DAB converter and sliding mode control are introduced.Secondly,the switching state and operation principles of the DAB converter are analyzed in detail under the single phase shift control.The dynamic model of output voltage is derived by Fourier decomposition of switching function.Aiming at the shortcomings of traditional PI control method,the single-integral sliding mode control(SISMC)is proposed in this thesis.Based on the dynamic model of output voltage,sliding mode control with integral terms is applied to the voltage controller and voltage single closed loop control is designed.Better output voltage accuracy and robustness are obtained.Finally,the advantages of the proposed control method are verified in the MATLAB/Simulink.However,adopting the single-integral sliding mode control scheme based on dynamic model of output voltage has the inconvenience of collecting the information of load current considered as disturbance.The nonlinear disturbance observer is applied to the sliding mode controller and the single-integral sliding mode control method based on a nonlinear disturbance observer(SISMC-NDO)is proposed in this thesis.Applying the nonlinear disturbance observer to estimate the load current considered as disturbance,the output voltage control is realized without collecting the information of load current.Finally,the simulation models are built in the MATLAB/Simulink.Meanwhile,the simulation experiments of proposed method have been carried out from different aspects and the advantages and validity of the proposed control method are verified. |
