The scott transformer changes three-phase power to two single-phase power. However, this method causes unbalance and fluctuation of voltage by the change of electric railload. Recently, the AC railway system based on $3{Phi}/1{Phi}$ back-to-back (BTB) voltage source converter (VSC) has been proposed to solve these problems. Meanwhile, battery energy storage system (BESS) is used to compensate voltage instantaneously in power system. In this paper, BESS application to the AC railway system based on $3{Phi}/1{Phi}$ BTB VSC is suggested to compensate voltage instantaneously. The application effect is shown through simulation using MATLAB/SIMULINK.