First

the basic control strategy of a modular multilevel converter(MMC)based high voltage direct current(MMC-HVDC)transmission system is studied. Then

the characteristics of the back-to-back MMC-HVDC transmission system is analyzed

which can provide synchronous control signal sharing between sending and receiving ends so as to realize delay-free sharing of control signal at two sides of the converter. On this basis

according to the application requirements of MMC based back-to-back high voltage direct current transmission system

a control strategy is proposed. Finally

the effectiveness of the control strategy is verified by digital simulation via PSCAD/EMTDC. This work is supported by State Grid Corporation of China(No. 2014GW-05).