The flexible low-frequency transmission system based on the modular multilevel matrix converter (M3C) has great application potential in the fields of long distance and large capacity transmission

urban power grid and offshore wind power transmission

and has received extensive attention in recent years. At present

the research on the startup control strategy of the flexible low-frequency transmission system based on M3C is less and

on this purpose

the relevant research in this field is performed in this paper. First

the structure of the flexible low-frequency transmission system and the basic principle of M3C are studied

and the problems to be faced in the startup process are analyzed. Then

a reasonable charging strategy is designed for M3C based on the characteristics of full bridge sub-module. And a reasonable startup logic is designed for the dual terminals M3C flexible low-frequency transmission system to ensure that the low-frequency circuit breaker can be closed without impact and the M3C stations can be connected without disturbance during the startup process. At the same time

the current impact can be reduced in the process of M3C deblocking and low-frequency voltage establishment. Finally

the correctness and feasibility of the proposed startup control strategy are verified by setting up a simulation model under the PSCAD/EMTDC simulation software. The startup control strategy proposed in this paper is safe

reliable and easy to implement and has high engineering application.