Modular multilevel converter (MMC) becomes furthermost promising topologies especially for medium or high voltage (HV) applications. A typical application of MMC is to control the active power as well as reactive power. This paper presents the design of decoupled current controller for a grid connected MMC. The proposed controller gives an efficient and decoupled control of active power and reactive power then substantially improves MMC dynamic response. However, the performance of MMC depends on the controller’s parameters. The tuning of controller’s parameters depends on the desired output for disturbance applied to the input. The effectiveness of MMC is evaluated by transient simulation with decoupled current controller parameters. The transient simulation is done by MATLAB/Simulink using three-phase detailed model. © 2020, World Academy of Research in Science and Engineering. All rights reserved.