When the grid experiences unbalanced voltages sag, the output power of the grid-connected inverter will have second harmonics. The objective of this thesis is to propose a new control scheme based on Lagrange multiplier method to calculate the current commands for the Photovoltaic (PV) inverter with the low-voltage ride-through (LVRT) capability. The current commands can control the second harmonics in the output power of the grid-connected inverter. The proposed method can combine with the maximum current amplitude control (MCAC) strategy. Computer simulations are shown to verify the performance of the proposed control scheme.