An electric power system includes an electric power generator, a first converter, an electric energy storage device, and a first converter controller. The first converter controller is to correct a target output of the electric power generator based on a charging margin so as to control an output of the electric power generator via the first converter so that an input electric power to the electric energy storage device does not exceed an input electric power threshold of the electric energy storage device or to correct the target output of the electric power generator based on a discharging margin so as to control the output of the electric power generator via the first converter so that an output electric power from the electric energy storage device does not exceed an output electric power threshold of the electric energy storage device.