Distributed Generation (DG) systems, such as renewable energy sources and fuel cells are widely used for standalone microgrids to complement fossil fuel generators. However, these systems still suffer from various problems such as dynamics uncertainties, external disturbances, and imprecision of the system parameters. In this paper, we present a new Integral super-twisting Terminal Sliding Mode Control incorporating Time Delay Estimation (STA-TDE) applied to Three-Phase Inverter for Standalone Distributed Generation System with dynamics uncertainties and unknown bounded disturbances. Unlike conventional adaptive approaches, the proposed Time Delay Estimation uses delayed one step only of the control input and outputs of the system to approximate the uncertain dynamics. A finite time of both selected sliding surface and estimation error simultaneous is achieved using an appropriate Lyapunov function. Numerical simulation results found to confirm the effectiveness of the proposed control.