Abstract: With the development of the electrified railway in the direction of high-speed and high-power, the power quality of the electric traction grid becomes more and more serious. For the purpose of the three-phase current balance of electric traction grids, a double star bridge cells based railway power conditioner（DSBC-RPC） with the advantages of both high-voltage and large-capacity was studied. The DSBC-RPC was characterized by the modular and high voltage cascade structure, consisting of four H-Bridge links and corresponding output filter inductors, which could be directly connected to the voltage class of 27.5 k V. This conditioner could be used for different types of traction transformers, especially suited to the active power transfer of Scott transformer electric traction systems with a co-phase supply mode. Based on the analysis of the topology structure, the equivalent model and the energy balance of DSBC-RPC, the hierarchical control strategy was put forward aiming to balancing the sub-module capacitance voltage, which ensured the safety and stability of the system. Finally, the proposed structure and its control strategy effectiveness are verified by the simulations and experiments.