Power Control of Distributed Energy Storage System in Bipolar DC Microgrid

Distributed energy storage system plays an important role in stabilizing energy fluctuation and maintaining power balance in bipolar DC microgrid. The energy storage system is used to stabilize the bipolar DC bus voltage and ensure that the positive and negative bus voltages are equal. For achieving the above control objectives, the control strategy of single energy storage converter is studied, and the regulation ability of the strategy is analyzed. However, the single energy storage unit (ESU) is usually difficult to meet the large -capacity requirements of the microgrid system., so multiple ESUs can be connected in parallel to DC bus to form a distributed energy storage system for the expansion of system capacity. In this paper, an improved state of charge (SOC) droop control strategy is proposed. By constructing a new exponential function relationship between droop coefficient and SOC of ESU, the output or input power of each ESU can be adjusted in real time according to its own SOC during charging or discharging. Therefore, the balance of power and SOCs can be achieved among parallel ESUs, and the reasonable distribution of load power can be realized. Finally, the feasibility of the proposed control strategy is verified by experiments.