Cyclic modulation method and system of modular multilevel DC converter, and medium

The invention discloses a cyclic modulation method and system for a modular multi-level direct current converter and a medium, and the method comprises the steps: determining the number N of operating sub-modules in a single stack in the modular multi-level direct current converter, a modulation coefficient K, and the starting angle and duty ratio of a square wave driving pulse of a tube on each sub-module, and N is a positive integer greater than or equal to 1; determining a matrix PN * N in a preset mode; judging whether the greatest common divisor of N and K is equal to 1; if the largest common divisor of N and K is not equal to 1, a matrix R is obtained through calculation in a preset mode; controlling the sub-modules in the stack according to the combination sequence in the matrix R and circulating; and if the greatest common divisor of N and K is equal to 1, controlling the sub-modules in the stack according to the combination sequence in the matrix P and circulating. According to the invention, the pro