The fluctuation of the capacitor voltage of the modular multilevel converter(MMC)sub-module capacitor makes it difficult to reduce the capacitance value

which hinders the development of the light-weight MMC converter valve. Based on the consideration of the second and fourth inter-phase circulation

this paper analyzes the mechanism of interaction effect between that the sub-module capacitance voltage and the bridge arm current. In order to reduce the fluctuation level of the sub-module capacitor voltage

a control method for switching the bridge reactor in the form of submodule is proposed. The mechanism of capacitor voltage fluctuation of sub-module is analyzed. The principle of the reactor sub-module switching method is analyzed

and the control strategy of the method is designed. Finally

a two-terminal MMC based high-voltage direct current(MMC-HVDC)model is built under the PSCAD/EMTDC simulation environment to verify the effectiveness of the strategy proposed and compared with the existing circulation suppression strategy.