Half Bridge Sub-module Based Modular Multilevel Converter in 50Hz/50Hz Railway Continuous Co-phase Power Supply Application

This paper proposes a system configuration of the half-bridge submodule based modular multilevel converter (HBSM-MMC) combined with SCOTT transformer, which can be applied in the 50Hz three-phase to 50Hz single-phase conversion for railway supply. Three AC terminals of MMC are respectively connected to the public- and railway- grids. The railway and SCOTT transformer are grounded together to provide circuit path for the catenary current. A control strategy based on fundamental-frequency zero-sequence voltage injection is proposed, to implement separate control of public-and railway- grids. Simulation results verify the validation of the proposed system and control strategy. The proposed system can eliminate the imbalance of public grid, and MMC arm output voltages are fully and evenly used. It is economical advantageous due to the reduction in converter capacity, capacitor requirement, and converter loss. In addition, the bulky transformers and filters can be avoided.