Abstract: An apparatus for uninterruptible power supply (UPS) comprises a rotating electric machine having a generator winding and a plurality of motor windings. The motor windings of the plurality of motor windings are electrically insulated from the generator winding and from one another. The UPS further comprises, for each motor winding, an energy storage for electric energy and an inverter which outputs an alternating current and via which the energy storage is connected to the respective motor winding.

Abstract: In an UPS system, following components are arranged in a machine cabinet: an AC-to-DC converter connected to a DC voltage link on its output side, a DC-to-AC converter connected to the DC voltage link on its input side; a motor/generator electrically connected to the DC voltage link and having a flywheel coupled to its rotor; a bypass to the AC-to-DC converter and the DC-to-AC converter connected in series, a bypass switch being arranged in the bypass; a controller; and a blower which draws air out of the surroundings through air filters, blows the air in the machine cabinet through a heat exchanger, and ejects the air again. The heat exchanger is arranged in a coolant circuit together with a coolant pump, cooling bodies for the power output stages, and coolant channels which include stator channels running through a stator of the motor/generator.

Abstract: A frequency of an AC voltage of an AC grid present at a genset is defined by an UPS. The frequency is altered in one direction away from a desired frequency, if a power demand increases beyond a power supply in the AC grid, and in the other direction, if the power demand falls below the power supply. An alteration of the frequency in the one direction is limited to a maximum value in that missing power is temporarily fed out of an energy storage of the UPS into the AC grid. A shift of the frequency in the one direction is kept until no more power flows out of the energy storage. The genset responds to deviations of the frequency of the AC voltage from the desired frequency in the one and the other direction by an increase and a decrease of supplied genset power, respectively.

Abstract: Parallel-connected UPS units of an online UPS system, which are each 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 whose supplied powers are individually variable, are disconnected from the AC mains in the event of a failure of the AC mains, at least if they are affected by the failure, and are successively reconnected to the AC mains after the restoration of the AC mains. In this case, in order to match the powers supplied by the individual UPS units to one another, while some of the UPS units are connected on the input side to the AC mains and others of the UPS units are not connected on the input side to the AC mains, a phase angle ?? between the AC mains and the load bus is determined, and the power supplied by each of the UPS units which have not yet been reconnected to the AC mains is adjusted as a function of this phase angle ??.