In a grid connected photovoltaic (PV) system, dynamic control strategy is essential to use the solar energy efficiently as well as for an energy optimization. This paper presents a decoupled control of grid connected photovoltaic system using Fractional Order Proportional–Integral (FO-PI) controller. In the proposed system, closed loop high gain multilevel DC/DC converter is also implemented to meet the regulated DC link voltage at the inverter input. The decoupled control strategy allows independent control of real power (P) and reactive power (Q) according to the power generated by photovoltaic systems and the power consumed by the utility grid. A complete study of the dynamic behavior of the grid connected PV system is presented using Matlab/Simulink. Simulation results are presented to validate the system response during disturbance with FO-PI controller, power factor control at the grid and the Total Harmonic Distortion (THD) of grid current for any solar irradiation. © 2016 Faculty of Engineering, Ain Shams University