Distributed cooperative control of battery energy storage system in AC microgrid applications

• Cooperative control approach for distributed BESS with different SoC.
• Proposed a decentralized control strategy considering SoC of each BESS.
• Modified P/f droop control method to balance the SoC in discharging process.
• Setting the droop coefficients inversely proportional with the rate of SoC.

The approach to optimal control for distributed battery energy storage systems (BESS) has recently been closely investigated and implemented by numerous experts. The management of the power balance based on the dischargeable energy of each battery is the main issue in this type of BESS control. In this regard, the performance of power sharing between Battery Energy Storage Units (BESUs) with different States of Charge (SoC) can be enhanced. Based on the traditional droop control, the sharing of power between different BESUs is based on power capacities, rather than on energy levels; it thus causes some limitations for the ideal injection and absorption of energy by the energy storage system. In this paper, a decentralized control method for SoC is proposed, based on a modified droop control method in which the SoC of each BESU is balanced during the discharge process. The droop coefficients should be set to be inversely proportional to the SoC of each BESU. Using this control strategy, the storage unit with the highest SoC provides more power to support the load, while the unit with lower SoC provides less power. Thus, the output power of each converter will be proportional to each SoC. The method is validated using simulation results from PSCAD/EMTDC software.