Method for starting flexible high-voltage direct-current (HVDC) system of modularized multi-level converter

The invention provides a method for starting a flexible HVDC (high-voltage direct-current) system of a modularized multi-level converter, which is utilized to control a switch, a breaker, a converter and the like, so that the submodule voltage and DC voltage are ensured to reach rated values; and control strategies are formulated properly to restrain impulse currents generated in a charging process. By using the method, a charging control method is simplified, a modulation algorithm is optimized, the problem that a far-end converter submodule is short of capacitor voltages when an alternating-current system at one end charges two stations is solved, and the problem of the charging of a DC line is solved as well.