Uninterruptible power supply system

1. An uninterruptible power supply system, comprising:

a plurality of uninterruptible power supply devices which are connected in parallel with respect to a load, and switch between power supplies supplying power to said load depending on states of said power supplies;

a control circuit controlling an operation of switching between said power supplies by the plurality of said uninterruptible power supply devices; and

a storage battery connected to the plurality of said uninterruptible power supply devices in common,

at least one of the plurality of said uninterruptible power supply devices including

a conversion circuit to convert a first AC power of an AC power supply into a first DC power,

a switching circuit connected to the conversion circuit and the storage battery and configured to switch between the first DC power and a second DC power input from said storage battery, and

an inversion circuit having a same configuration as the conversion circuit and being configured to invert the first DC power or the second DC power, based on a setting of the switching circuit, into second AC power and to supply the second AC power to said load, and

in the case where a total power amount required for said load is smaller than a total power output by a plurality of inversion circuits of the plurality of said uninterruptible power supply devices, said control circuit deactivates an uninterruptible power supply device that does not contribute to a power amount required by the load by deactivating an inversion circuit of the uninterruptible power supply device while maintaining a conversion circuit and a switching circuit of the uninterruptible power supply device active.

2. The uninterruptible power supply system according to claim 1 , wherein

said control circuit activates all of the plurality of said inversion circuits,

said control circuit determines said total power amount required for said load,

said control circuit compares said total power amount required for said load with a total rated power amount output by the plurality of said activated inversion circuits, and

when said total power amount is smaller than said total rated power amount, said control circuit deactivates at least one of the plurality of said activated inversion circuits.

3. The uninterruptible power supply system according to claim 1 , wherein

said control circuit activates a predetermined number of the plurality of said inversion circuits, the predetermined number being not less than two, and a rest of the plurality of said inversion circuits being kept deactivated,

said control circuit determines said total power amount required for said load,

said control circuit compares said total power amount required for said load with a first total rated power amount output by the predetermined number of the plurality of said activated inversion circuits,

when said total power amount is not less than said first total rated power amount, said control circuit activates said rest of the plurality of said inversion circuits being kept deactivated one by one until said total power amount becomes smaller than said first total rated power amount,

when said total power amount is smaller than said first total rated power amount, said control circuit compares said total power amount with a second total rated power amount output, when at least one of the plurality of said activated inversion circuits is deactivated, by currently activated inversion circuits, and

when said total power amount is smaller than said second total rated power amount, said control circuit deactivates at least one of the plurality of said currently activated inversion circuits.

4. The uninterruptible power supply system according to claim 3 , wherein said control circuit sets said predetermined number of the plurality of said inversion circuits to be activated to half of a total number of the plurality of said inversion circuits of the plurality of said uninterruptible power supply devices.

5. The uninterruptible power supply system according to claim 1 , wherein

said control circuit activates one of the plurality of said inversion circuits, a rest of the plurality of said inversion circuits being kept deactivated,

said control circuit determines said total power amount required for said load,

said control circuit compares said total power amount required for said load with a first total rated power amount output by said activated inversion circuit,

when said total power amount is not less than said first total rated power amount, said control circuit activates said rest of the plurality of said inversion circuits being kept deactivated one by one until said total power amount becomes smaller than said first total rated power amount,

when said total power amount is smaller than said first total rated power amount, said control circuit compares said total power amount with a second total rated power amount output, when one of the plurality of said activated inversion circuits is deactivated, by currently activated inversion circuits, and

when said total power amount is smaller than said second total rated power amount, said control circuit deactivates one of the plurality of said currently activated inversion circuits.

6. The uninterruptible power supply system according to claim 1 , wherein when said control circuit deactivates the gate signal applied to the gate electrode of the semiconductor device of the one of the plurality of said inversion circuits that does not contribute to supplying the power amount required for said load, a conversion circuit included in a corresponding uninterruptible power supply device of the deactivated one of the plurality of said inversion circuits is kept activated to shorten a time taken to activate the uninterruptible power supply device including the deactivated one of the plurality of said inversion circuits.

7. The uninterruptible power supply system according to claim 1 , wherein said control circuit receives a feedback value of an inverter load current from each of the plurality of said inversion circuits to calculate the total power output by the plurality of said inversion circuits.