Design and Research of Variable Frequency Direct Feed Power Supply for Urban Rail Transit

This paper presents a variable frequency direct feed power supply system based on the cascade topology of ZVS three-level Buck+LLC resonant converter. The system takes power directly from the overhead line, and the three-level buck depresses the input voltage with a wide fluctuation range to obtain stable DC power to the LLC converter in the rear stage. This scheme can realize the ZVS of all power switching tubes without adding any auxiliary devices. The key conditions of realizing ZVS of three-level Buck, the working principle of LLC and the control strategy of cascade topology are analyzed and studied. To verify the feasibility and effectiveness of the design scheme, a simulation model is built. It provides theoretical support for the development of a new type of variable frequency direct feed power supply system, so as to optimize the architecture of the auxiliary power supply system of urban rail and improve system efficiency.