NOVELTY - The apparatus (200) has a sensing part (220) for sensing voltage value and current value of a secondary battery (121) that is charged with charge voltage. A power control unit (210) outputs a compensation charge control signal and a discharge control signal to a power net (140). The voltage value of the secondary battery is less than pre-set reference voltage value. An electric power production part (110) is provided with a generator that produces electricity using renewable energy. The electric power production part supplies the electricity to the power net.    USE - Apparatus for controlling charging and discharging of a secondary battery of an electric power generation system (claimed). Uses include but are not limited to a solar power generation system, a wind power generation system, a geothermal power generation system, a neogenesis energy generation system, a hydro-electric power generation system, a tidal power generation system and an ocean temperature difference energy generation system.    ADVANTAGE - The apparatus effectively compensates charged capacity of the secondary battery when the voltage value of the secondary battery reaches the pre-set reference voltage value so as to increase rechargeable cycle of the secondary battery, thus preventing reduction of charged capacity of the secondary battery. The apparatus enhances operating performance of an electric power generation system based on state of the secondary battery by reducing degeneration speed of the secondary battery.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) an electric power generating system    (2) a method for controlling charging and discharging of a secondary battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of an apparatus for controlling charging and discharging of a secondary battery.'(Drawing includes non-English language text)'    Electric power production part (110)    Secondary battery (121)    Power net (140)    Apparatus for controlling charging and discharging of secondary battery (200)    Power control unit (210)    Sensing part (220)