The invention relates to a flexible DC
system starting method and device based on a modular multi-level current converter. The device comprises the following steps: S1, after the current converter
station uncontrolled charging is finished, newly adding a sub-module for conducting a T2 tube for each bridge arm, thereby gradually adding the number of the submodule of each bypass; charging residual sub-modules to the charging
voltage threshold through
transformer valve side line
voltage, and executing sub-module dynamic
voltage-sharing control under a condition of maintaining unchanged total number of the submodule of each bridge arm bypass; S2, when receiving an unlocking instruction, stepping the
DC voltage to a rated modulation ratio corresponding numerical value; and S3, after the
DC voltage is stabilized, ramping the
DC voltage to a DC voltage instruction value, thereby realizing the smooth starting of the flexible DC
system. after the uncontrolled charging of the current converter
station is finished, the effective voltage-sharing of the current conversion valve submodule at any time slot can be realized, the time for dispatching the unlocking instruction is unlimited, and the AC
system impact and heavy
harmonic problem caused by low DC voltage at unlocking early stage of the current converter
station can be effectively avoided.