Coordination control strategy of DC microgrid with two DC buses based on power pool

In order to integrate DC micro sources and loads of different voltage levels to DC microgrids, a novel DC sub-microgrid and its coordination control strategy are proposed in this paper. The DC microgrid consists of two sub-microgrids with different voltage levels through a power pool. A lithium battery pack is set as the energy backup of the power pool. Droop control is designed for the power pool to compensate the unbalanced power in the microgrid. The lithium battery pack is controlled by sampling the voltage of the power pool to avoid energy shortage of the power pool and smooth the current of the battery. The system is divided into nine operations region to coordinate the units in the sub-microgrid. Finally, simulation results show that the proposed control strategy can not only stabilize the DC bus voltages, but also realize low frequency power exchanges among the two sub-microgrids and the lithium battery pack. Furthermore, system loss could be reduced and the battery life can be prolonged.