This paper proposes a new control strategy to track the maximum power point of a photovoltaic pumping system. The system includes a photovoltaic (PV) array, a DC/DC boost converter and a DC motor pump. The proposed strategy is based on the robust integral backstepping control design to be applied to the DC/DC converter in order to achieve an optimal PV array output power, it allows a direct control of power converter. The integral action is introduced in order to improve the robust properties of the nonlinear controller, the stability of the control algorithm is demonstrated by means of Lyapunov analysis. The performances of the developed approach has been analyzed trough computer simulations to illustrate the validity of the designed control method under various climatic conditions.