An Adaptive Droop Control Strategy of Storage Energy Units in Flexibly Interconnected Microgrid Clusters Considering the Balance of Charge State

The flexible interconnection based on flexible interconnection device (FID) has considered as a promising solution to interconnect microgrid clusters (MGC) due to its flexibility, reliability and resilience. In the flexibly interconnected MGC, energy storage units (ESUs) are usually equipped to stabilize the power fluctuation from both of renewable energies and loads, maintaining the stability of the DC bus voltage of SOP. Due to the difference of line impedance among ESUs, the sudden power fluctuation would result in the inconsistent transient currents of ESU as well as unbalanced state of charge (SOC). In this paper, a double quadrant-based adaptive droop control for ESUs in MGC is proposed for the improved dynamic performance and SOC balance. Firstly, the bi-directional DC-DC converter is executed upon the dual-quadrant mode, avoiding the excessive charging or discharging of individual energy storages; Secondly, a I-SOC based adaptive droop control is used to change the droop coefficient in real time according to the weight of the SOC and current in different states of system operation, which can achieve SOC and current balance concurrently; Finally, the effectiveness of the proposed method are fully demonstrated by the simulation verification of the flexibly interconnected MGC.