Abstract: There is provided a secondary battery system which converts direct current power supplied from secondary batteries into alternating current power by power converters, and supplies the converted power to an electric power system on a load side, the secondary battery system including a control apparatus that stops operating the operating the power converter and starts operating the stopped the power converter when a residual stored power level of the secondary battery corresponding to operating the power converter becomes to be not greater than a predetermined rate of a residual stored power level of the secondary battery corresponding to stopped the power converter.

Abstract: An output-power control apparatus is provided in an electric power system connecting a secondary battery system and a power generator in parallel, and controls output power of the electric power system. The output-power control apparatus detects output power of the power generator, and controls output voltage of the secondary battery system, based on a value obtained by subtracting the detected output power of the power generator from an output power instruction for controlling the output power.