In this paper, a robust nonlinear control for a three-phase Photovoltaic system (PV), connected to the grid, is proposed. The control objectives targeted are the extraction of the maximum PV panel power by regulating the DC voltage of the intermediate bus and controlling the current injected into the grid, to ensure the best Power Factor Correction (PFC). In order to ensure these objectives, a nonlinear control structure, based on an adaptive Backstepping technique, which uses cascade control loops with unknown parameter estimation, has been proposed. The global stability of this system is based on the development of the Control Lyapunov Function (CLF), by using the unknown parameters of the system, which are estimated by the adaptation laws. The efficiency and the validity of the proposed control system are based on a comparison with a nonlinear Backstepping controller and tested using variable operating conditions in MATLAB/Simulink software. The simulation results have showed a robust control in terms of improving the quality of the energy injected into the grid.