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.