State of Charge Balance of Distributed Batteries in DC Shipboard Microgrids

Electric ships have become popular for the purpose of reducing greenhouse gas emissions and improving energy efficiency. The DC shipboard microgrid (SMG) provides a good solution to integrate the battery energy storage system (BESS), generators, electric propulsion system, and shipboard loads. In order to avoid over-discharging and over-charging of batteries and prolong the battery lifetime, it is necessary to balance the battery state-of-charge (SoC). This paper proposes a decentralized SoC balance method based on droop control in the DC SMG. The battery SoC balancing speed is regulated by an exponent parameter n, and larger n leads to faster SoC balance. In addition, the voltage drop caused by the proposed SoC-based droop control can be ensured within the allowed value in the entire SoC range. Verification of the proposed method is implemented in Matlab/Simulink model, which consists of two batteries. The simulation results verify the effectiveness of the proposed method.