Abstract：Aiming at the problem of large switching loss of modular multilevel converter（MMC），starting

from the switching frequency optimization strategy，the existing switching frequency optimization strategy was

improved，and the accurate analytical formula of sub-module capacitor voltage based on the real-time value of

MMC transmission power was derived，so as to calculate the fluctuation range of the mean value of capacitor

voltage. The dynamic retention factor was obtained by using the margin between the mean value of capacitor

voltage and the engineering constraint，and the final output switching instruction was realized by the main flow of

the equalization strategy. The PSCAD/EMTDC model was built based on the offshore wind power flexible

engineering parameters to verify and compare the proposed strategy with the traditional strategy. The simulation

results show that under the premise of meeting the requirements of the project on the fluctuation range and the

imbalance index，the switching frequency of the proposed strategy is reduced by 49%~58% compared with the

traditional strategy under each steady-state condition，and the switching loss is reduced by 63%~90% under each

steady-state condition，and the expected loss reduction effect is achieved.

      Key words：modular multilevel converter（MMC）；valve power loss；switching frequency；voltage balancing；switching losses