Research On Hierarchical Control Strategy Of DC Microgrid

In order to accept distributed generation (DG) and meet the growing needs of the DC load, DC microgrid connecting DG, energy storage device and load cell through DC line and connecting AC power grid through the controllable interface is becoming the new direction of research on microgrid in the future. Compared with AC microgrid, the frequency and synchronization problems do not exist in DC microgird, so DC microgrid is more suitable for variety of DC to access. In addition, the proportion of load use DC power directly increases, DC microgrid can cut down the number of conveters and reduce power loss. However, with various components, complicated operation conditions and flexible control mode in DC microgrid, how to coordinate the control of each unit to work in variety of operation modes and reach the goal of reliable and efficient for the load power supply is the problem need to solve.The structure and mathematical model of DC microgrid with photovoltaic unit and hybrid energy storage system (HESS) contain battery cell and super capacitor is built in this paper, the model of each component and converter is also established. Based on these models, the hierarchical coordination control strategy contains system layer and converter layer control of DC microgrid is established. The operation condition is divided according to grid-connection status, the DC bus voltage and battery state of charge (SOC) parameters, so the control strategy of each layer is identified. Finally, the hierarchical control strategy of DC microgrid is verified through software simulation analysis. The simulation results show that the operation control strategy can achieve the control target to maintain the power balance of DC microgrid and the stability of DC bus voltage, and the hierarchical control strategy proved to be scientific and effective.