Coordinated control strategy for a DC microgrid with two-level bus voltage

In order to meet the requirement of different voltage levels of DC loads, the coordination control strategy of a DC microgrid with two-level bus voltage is presented in this paper. The proposed system consists of two DC microgrids with different voltage levels, and the two sub-microgrids are connected through a bidirectional Buck/Boost converter. Hybrid energy storage systems (HESS) together with its control strategy are developed to smooth voltage ripple in the system. According to the droop characteristics of sub-microgrids, a droop control strategy of the bidirectional Buck/Boost converter is designed in detail to keep power balance of the two sub-micrigrids. Moreover, the bus voltage stability can be maintained by the control strategy. Besides, the whole system operation can be optimized and the HESS life can be prolonged. Finally, the availability of the control strategy is verified by experiments.