Decentralized BESS charging and discharging control method for avoiding pole transformer overcapacity

This paper proposes a decentralized charging and discharging control method of a battery energy storage system (BESS) to prevent the over-capacity of a pole transformer (Pole-Tr) in low-voltage (LV) distribution systems due to reverse power flow from the photovoltaic generation (PV) system. A distribution system operator (DSO) provides the charging/discharging parameters determined by using only the LV-distribution system configuration and the PV/BESS capacity to the customers and each BESS automatically controls the charging/discharging power according to the provided parameters. The charging parameter is defined in the relationship between the state-of-charge (SoC) and the charging threshold ϵ as the SoC-ϵ curve, and a total of three SoC-ϵ curves for the different objectives are prepared. In the charging phase, the BESS selects one SoC-ϵ curve every minute and determines the charging power based on the charging threshold ϵ and the present SoC. In the discharging phase, the BESS operates in the load-following discharging and SoC control discharging to adjust the SoC for the prevention of the over-capacity of Pole-Tr. The proposed method is tested on several types of LV-distribution systems, and the numerical simulation results demonstrate that the proposed method can prevent the over-capacity of Pole-Tr and maintain the high charging amount of BESSs.