A pumped storage system comprising: a reversible pump turbine; a synchronous motor generator directly coupled to a runner shaft of the reversible pump turbine; a frequency converter comprising: a first power conversion unit performing bidirectional AC/DC conversion and connected to a grid; a second power conversion unit performing bidirectional AC/DC conversion and connected to the synchronous motor generator; and a storage battery connected between the first power conversion unit and the second power conversion unit; a calculation device configured to calculate an actual reactive power and an actual active power based on a current and a voltage between the first power conversion unit and the grid; a governor configured to adjust a guide vane opening of the reversible pump turbine; and a control device configured to control the first power conversion unit, the second power conversion unit and the governor, depending on a power generation operation and a pumping operation, wherein the control device comprises: a first frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the first power conversion unit such that the calculated actual reactive power and actual active power respectively coincide with a reactive power command and an active power command that are input externally; and a second frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the second power conversion unit such that a voltage of the storage battery is maintained at a constant value. a reversible pump turbine; a synchronous motor generator directly coupled to a runner shaft of the reversible pump turbine; a frequency converter comprising: a first power conversion unit performing bidirectional AC/DC conversion and connected to a grid; a second power conversion unit performing bidirectional AC/DC conversion and connected to the synchronous motor generator; and a storage battery connected between the first power conversion unit and the second power conversion unit; a calculation device configured to calculate an actual reactive power and an actual active power based on a current and a voltage between the first power conversion unit and the grid; a governor configured to adjust a guide vane opening of the reversible pump turbine; and a control device configured to control the first power conversion unit, the second power conversion unit and the governor, depending on a power generation operation and a pumping operation, wherein the control device comprises: a first frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the first power conversion unit such that the calculated actual reactive power and actual active power respectively coincide with a reactive power command and an active power command that are input externally; and a second frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the second power conversion unit such that a voltage of the storage battery is maintained at a constant value. a first power conversion unit performing bidirectional AC/DC conversion and connected to a grid; a second power conversion unit performing bidirectional AC/DC conversion and connected to the synchronous motor generator; and a storage battery connected between the first power conversion unit and the second power conversion unit; a calculation device configured to calculate an actual reactive power and an actual active power based on a current and a voltage between the first power conversion unit and the grid; a governor configured to adjust a guide vane opening of the reversible pump turbine; and a control device configured to control the first power conversion unit, the second power conversion unit and the governor, depending on a power generation operation and a pumping operation, wherein the control device comprises: a first frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the first power conversion unit such that the calculated actual reactive power and actual active power respectively coincide with a reactive power command and an active power command that are input externally; and a second frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the second power conversion unit such that a voltage of the storage battery is maintained at a constant value. a first frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the first power conversion unit such that the calculated actual reactive power and actual active power respectively coincide with a reactive power command and an active power command that are input externally; and a second frequency converter control unit configured to control, in each of the power generation operation and the pumping operation, the second power conversion unit such that a voltage of the storage battery is maintained at a constant value.