Microgrid Secondary Control Design Based on Second-Order Sliding Mode Algorithm

In this paper, an improved distributed secondary control scheme for DC microgrids based on a sliding mode controller is proposed to address the shortcomings of common secondary control methods. The scheme employs a second-order Super-Twisting (ST) sliding mode control algorithm, which is highly robust. When the load is connected at the output end, it can ensure that the voltage deviation caused by droop control is eliminated and the current sharing accuracy is guaranteed in the case of frequent load changes, so as to improve the control performance of the system under complex working conditions. Each distributed secondary controller only collects the output voltage and its calculated average value and the output current and its calculated average value signals of the neighboring converters, and then uses their average values as the control objects of the voltage and current in the secondary controller, respectively, and adopts the voltage-shifting-based method to ensure that each of the converters involved in the control has an equal equivalent output impedance. In addition, this control strategy also improves the transient response of the DC voltage when applied to the converter control due to its robustness to external load variations. In simulation, the robustness of the proposed control strategy is tested by providing different load steps in a short period of time, and the optimization of the transient response by the control strategy is verified by comparing the results with those of the traditional secondary control strategy based on PI controller. The simulation results verify the effectiveness and advantage of the proposed algorithm.