Novel high speed railway uninterruptible flexible connector based on modular multilevel converter structure

Phase sequence commutating method among traction feeders results in a neutral section without power supply between two feeders in traction substation of electrified railway. Electric locomotives suffer from a no-power time of more than 100 millisecond when going through the neutral section, during which the power failure and restoration process causes serious over-voltage and over-current problems. A novel railway uninterruptible flexible connector based on two-phase modular multilevel converter structure(MMC-UFC) is proposed in this paper, which can completely eliminate power supply dead zone. System utilization and operational principle are analyzed. Mathematical model of MMC-UFC is built to derive the difference between MMC-UFC. Double close-loop control strategies are given and close-loop control of both upper arm current and lower arm current for MMC converter is proposed to ensure the quality of output current. PSCAD/EMTDC simulations and experiment are carried out to prove the effectiveness of proposed MMC-UFC and its control system.