This work is oriented to research performance in terms of optimal transfer of energy from a photovoltaic generator to a permeant magnet synchronous motor type used as a centrifuge pump driver. The performance improvement is done using a variable structure controller with sliding mode as a maximum power point tracker (MPPT). A stability analysis for the proposed MPPT is developed for a photovoltaic (PV) pumping system. The global stability of the variable structure algorithm is demonstrated by means of Lyapunov’s approach. The tracking algorithm leads the PV generator coordinates to the maximum power point by changing the pulse width modulation (PWM) signal frequency of the boost converter. The steady-state behaviour of the PV pumping system with variable structure control is characterized by a stable oscillation around the maximum power point. The effectiveness of the proposed MPPT scheme is demonstrated under internal and external disturbances.