Hierarchical Control Strategy of Hybrid Energy Storage System in Bipolar-type DC Micro-grid

In order to stabilize the power fluctuation caused by distributed energy in the bipolar-type DC micro-grid, a new hybrid energy storage system (HESS) coordination control strategy is proposed in this paper. First, in order to take advantage of lithium battery and super capacitor complementary performances, a cascade structure of the lithium battery and the super capacitor is adopted. Meanwhile, voltage balancer is cooperated with the hybrid energy storage to achieve multi energy complementary between double DC buses. Second, a hierarchical droop control method is designed. And the hybrid energy storage system operation is divided into three modes according to the super capacitor voltage. Finally, the simulation results verify that different voltage levels in bipolar-type DC micro-grid can be maintained stable. The proposed control strategy is flexible and effective.