In this study, a two-stage grid-connected inverter is proposed for photovoltaic (PV) systems. The proposed system consist of a single-ended primary-inductor converter (SEPIC) converter which tracks the maximum power point of the PV system and a three-phase voltage source inverter (VSI) with LCL filter to export the PV supplied energy to the grid. The incremental conductance (IC) method with novel variable step algorithm is used as maximum power point tracking algorithm. Thus, tracking speed and accuracy is improved. A sliding-mode control (SMC) strategy is used to control the inverter stage. Obtained simulation results show that proposed system tracks the maximum power point of the PV system and injects sinusoidal currents to the grid.