Factors Affecting Battery Unit Contributions to Fault Currents in Grid-connected Battery Storage Systems

This paper investigates factors affecting the contributions of battery units to fault currents in grid-connected battery storage systems (BSSs). The work in this paper is intended to examine effects of the state-of-charge (SOC) on battery currents that are drawn due to faults. This paper also examines impacts of charger controller actions on the currents drawn from battery units to faults in grid-connected BSSs. The impacts of the SOC and charger controller on battery currents due to faults, are examined for the Lead-Acid, Lithium-Ion, and Nickle-Cadmium battery units. Examination results show that the battery currents due to faults are directly dependent on the SOC. Moreover, these results show that actions of charger controller can support the battery terminal voltage, thus preventing the fast reduction of the SOC. The support of the battery terminal voltage helps in limiting the currents drawn from battery units during faults. The effects of the SOC and charger controller are verified using a 1 MW, 3ϕ grid-connected BSS, which has Lead-Acid battery units. Several faults have been created during charging and discharging operations, and at different values of SOC. Test results confirm the direct dependence of battery currents (due to faults) on the SOC. In addition, obtained results demonstrate the ability of charger controller to limit the currents drawn from battery units due to faults in different parts of a grid-connected BSS.