This paper presents a nonlinear control strategy based on variable gain super-twisting algorithm (VGSTA) assisted with a fuzzy logic controller (FLC) to maximize the extracted power of a wind energy conversion system (WECS). The studied system in this paper is composed by: a wind turbine, a permanent magnet synchronous generator, a controlled bridge rectifier connected to a permanent-magnet DC motor used to drive a centrifugal pump. Unlike the most studied standalone wind energy conversion systems in literature, that use a resistive load, this work consider a nonlinear load represented by a motor-pump group. The proposed Field Oriented Control (FOC) based on Fuzzy-Variable Gain Super Twisting Algorithm, allows dealing with the non-linearity of the wind turbine and load characteristics, adding to that the different perturbations and disturbances that such system can occurs. The obtained results show high tracking performances with very small error, without chattering phenomenon and a high stability and robustness against wind speed change.