Based on modular multilevel matrix converter (M3C)

low-frequency transmission system for offshore wind power (LFTS) faces the problem of insufficient sensitivity of differential protection for transmission lines due to weak feedback from dual power sources

and insufficient response speed of differential protection due to frequency reduction. In response to the above issues

based on the control characteristics of M3C and wind turbine converters

the coupling relationship between various sequence currents during asymmetric faults in the transmission line is analyzed. It is verified that there is a significant difference in the amplitude of negative sequence currents between the two sides of the fault line in the area. Based on this feature

a new principle of flexible low-frequency transmission line sampling value current accumulation protection based on the difference in negative sequence control characteristics is proposed. The new method can use accumulation operation to quickly amplify the different characteristics of negative sequence currents on both sides when asymmetric faults occur in flexible low-frequency transmission lines

greatly improving the speed of line protection action and ensuring reliability in external faults. Finally

an electromagnetic transient model of the wind farm transmission system via M3C is built in PSCAD

and the operational performance of the proposed protection method is verified by combining it with actual fault recordings on site. The results show that the proposed protection can quickly identify different types of internal and external faults

and the identification time of metal short circuit faults is less than 3 ms

with a maximum tolerance to 200 Ω for transition resistance.