Modular Multi-level Converters (MMCs) are considered as one of the promising multilevel converter topologies specially in high voltage applications such as HVDC transmission systems. The idea behmd MMC is to use floating capacitors as a voltage sources along with a switchmg circuit (chopper cell) to form what is called “submodules”. These submodules are inserted or bypassed according to the required output voltage level. To ensure a stable operation, submodule capacitor voltages should be kept m the same level, total converter energy should be uniformly distributed between the three phases. This can be achieved by controlling the current that circulates between the three phases. In this paper a grid connected three phase MMC is considered. An analytical study has been done, operating principles, mathematical model and control system have been described. Also, the system performance has been verified usmg shnulation with Matiab-Shnulink.