Patent ID: 7825541

Claim:
A method of controlling a plurality of parallel-connected UPS units of a UPS system, each of the UPS units being connected on the input side via a choke coil to an AC mains, in disconnectable fashion, and on the output side to a common load bus, and the power supplied by each individual UPS unit being variable, the method comprising the steps of: in the event of a failure of the AC mains: disconnecting at least the UPS units affected by the failure from the AC mains; after the restoration of the AC mains: successively reconnecting the UPS units to the AC mains; and while a first group of the UPS units is connected on the input side to the AC mains and a second group of the UPS units is not connected on the input side to the AC mains: determining a phase angle Δφ between an alternating current of the AC mains and an alternating current on the load bus and adjusting the power supplied by each of the UPS units in the second group as a function of the phase angle Δφ in order to match the powers supplied by the individual UPS units in the second group to one another.