| CPC H02J 9/062 (2013.01) [G01R 31/42 (2013.01)] | 12 Claims |

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1. An uninterruptible power supply system including a plurality of uninterruptible power supply devices connected in parallel to a load, the uninterruptible power supply system comprising
a selection unit that selects, of the plurality of uninterruptible power supply devices, a necessary number of uninterruptible power supply devices to supply power to the load, wherein
each of the uninterruptible power supply devices performs
when this uninterruptible power supply device is selected by the selection unit, an operating action of supplying power to the load,
when this uninterruptible power supply device is not selected by the selection unit, a standby action of standing by without supplying power to the load, and
during the standby action, a diagnostic action of diagnosing whether or not a predetermined part of this uninterruptible power supply device has a failure, and
the selection unit changes uninterruptible power supply devices to be selected, such that the plurality of uninterruptible power supply devices have an equal operating time.
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