Along with the augmentation of energy storage systems'capacity， energy storage devices can be connected to the 10 kV and above networks. The increasing power quality requirement of urban network along with the space and noise of the industrial frequency transformers are the limiting factors to the large scale energy storage system applications in the urban network. To address these issues， this paper proposes a new topology of cascaded battery energy storage system based on a common DC bus. Several dual active bridge DC/DC converters are applied to substitute the industrial frequency transformers， and the energy storage modules are connected to a common DC bus through separate interfacing circuits. The system is more modular and easy to be extended. They also provide easy access for different kinds of batteries. The main circuit of the new energy storage system is designed， with proper mathematical models and control system. The EMTDC simulation results verify the effectiveness of the proposed system.