This article describes a simulator for the Automatic Generation Control function (AGC) which is useful to decide the generators to be controlled by AGC. The main components of the simulator are: the physical model, a technical analyzer, and an economic analyzer. The physical model: a) considers that AGC function is only applied to restore the frequency; b) does not consider the transmission grid; c) computes the evolution of the frequency each 4 seconds, from the demand forecasting and the power for each generator. The generated power is estimated by considering the production plan, the primary regulation, the secondary regulation, the economic dispatch (manual and automatic), and the startup and shutdown processes of each unit. The effect of the frequency on the demand is considered. The technical analyzer is based on performance indexes which are computed from the frequency obtained by the physical model. The economic analyzer compares the total production costs for the different analyzed scenarios. These scenarios are different sets of generators to be controlled by AGC, which have been considered as feasible solutions by the technical analysis.