In this paper, a super-twisting integral sliding mode controller (ST-ISMC) is proposed to enhance the performance of grid-tied Photovoltaic (PV) system based on voltage-oriented control (VOC). The three-phase two-stage grid connected voltage source inverter (VSI) based PV source is considered in this study. The ST-ISMC controller is designed and implemented at dc-link of the inverter to ensure better regulation of the capacitor voltage. Furthermore, two ST-ISMC controllers are implemented at the ac side to generate the control vectors for space vector modulation (SVM), while ensuring a lower total harmonic distortion (THD). Extensive simulation studies are carried out using MATLAB/Simulink software to evaluate the performance of the proposed controllers. The obtained results show the superiority of STISMC in term of dc-link voltage regulation and power quality improvement under different operating conditions.