This paper proposes a nonlinear reduced-order model of a grid-connected AC Microgrid as seen from the point of common coupling (PCC) to the grid. The model is based on the dynamics of a single droop-control generator and aims to reproduce the behavior of the low-voltage grid with a minimum set of parameters. The model is first derived considering an infinite bus at the PCC, showing the fundamental procedure and the physical meaning of the parameters of the model. A large-scale real-world scenario with sixty households and ten distributed generators is presented, including simulations and comparisons for the case of a non-stiff medium voltage grid.