The continuous growing of energy market prompt for energy sources every time more distant to energy consumption centres. In this scenario, high voltage DC systems have proved to be the best alternative to transmit power over long distances. Among the different converter topologies used in HVDC systems, the modular multilevel converter provides the highest modularity, reliability, availability and power quality. These converters usually have a complex control scheme, due to the coupled currents and the DC voltage balance. This paper is focused on the control of currents and average voltage proposing a decoupled control of output, input and circulating current components which simplifies drastically the control scheme. Simulation results using a MMC with 200 cells per arm show the performance of the proposed scheme.