Power plants employing renewable energy sources connected to large power systems continue increasing their number and size. PV and wind farms are a clear example of this trend. They employ power electronics in order to inject power in the grid and in most cases the interaction does not take into account the power system needs. However, as their size increases, these plants should support the grid with ancillary services and it is necessary to analyze their impact on the grid. Despite large conventional power plants usually comprise a small amount of synchronous generators in the range of 100 MW, large power plants using power electronics are formed by a relevant number of individual generating units in the 1 MW range, which introduces additional complexity in the analysis of power systems. Therefore, it is necessary to develop aggregated models of distributed power plants. This paper presents the control of a 20 MW PV power plant and an equivalent model, which is validated through simulation.