Energy storage system and method for operating the same

An energy storage system of the present disclosure includes: a battery configured to store a received electrical energy in a form of direct current, 5 or to output the stored electrical energy; and a battery management system configured to control the battery, wherein the battery management system includes: a sensing unit comprising a plurality of sensors for measuring voltage, current, and temperature 10 of the battery; a memory configured to store an open circuit voltage table and an internal resistance table; and a microcomputer unit configured to determine an internal resistance of the battery from the internal resistance table by using data detected by the sensing 15 unit, to calculate a battery real voltage reflecting a voltage drop due to the internal resistance of the battery, and to determine a state of charge (SOC) by using the battery real voltage. GridDicagn Charging - icagn --0 1 3132 Load 31 a Control PMS -command PCS Supervision Control l1 1a CO 0 001 - =0 3 L _ _ Battery