There can be bus voltage fluctuation caused by the power fluctuation of the distributed generation, and by the frequent switching of the loads and the uncertainty disturbance in a DC microgrid system. Thus an improved sliding mode and active disturbance rejection control based on flatness theory is proposed with the bi-directional DC-DC converter of a DC microgrid energy storage unit as the research object. The method adopts the double closed-loop control structure, in which the current inner loop adopts differential flatness-based control to improve the dynamic response speed of the system. Considering the system immunity performance and the influence of high-frequency noise, the total disturbance of the outer loop model is estimated using an increased-order filter extended state observer. The improved sliding mode and active disturbance rejection controller of the voltage outer loop is designed based on the estimation information of state and disturbance quantities to further improve the robustness of the system. Finally, the results of simulation built by Matlab/Simulink demonstrate the validity and superiority of the proposed control scheme.

This work is supported by the National Natural Science Foundation of China (No. 51777167).