Optimal sizing of battery energy storage systems in unbalanced distribution feeders

This paper presents a mathematical model for optimal sizing of battery energy storage systems (BESS) in an unbalanced distribution system. The vanadium radox (VR) and sodium sulfur (NaS) based batteries are considered in this study. Detailed life-cycle cost analysis is carried out to first identify the long-term cost of the batteries, which is then included in the proposed model. Two case studies are carried out: first the effect of the local distribution company (LDC) savings on the battery size is examined, and second the optimal size of the battery is determined by solving a comprehensive optimization problem. The proposed model seeks to maximize the savings of the LDC accrued from BESS operation, i.e., maximize the difference of discharging and charging cost of the BESS, while the investment cost is minimized. The IEEE 13-node test feeder is used to test the proposed model.