In order to control the railway system power quality problems

a multilevel railway power conditioner(MRPC)composed of cascaded H-bridge cells is studied. It can be connected to the traction feeders directly without isolating transformers in the co-phase supply system. The equivalent circuit diagram is derived according to the topology of the MRPC

and mathematical modeling is performed. On this basis

a Euler-Lagrange mathematical model in dq frame is developed by Park transformation(αβ/dq). Furthermore

the passivity of the system is analyzed

and a passivity-based control method is proposed by injecting damping items into the system. Simulation and experimental results show that the proposed control method with its strong robustness can improve the power quality of the traction system.