Abstract: An uninterruptible power supply (UPS) system (3) is to be inserted between a alternating current (AC) power supply (4), interruptions of which are to be compensated for, and at least one load (5), which is to be supplied with alternating current (AC) or direct current (DC).

Abstract: In order to provide a system for stabilizing a power supply system comprising a choke, which connects the power supply system to a mains power feed, a converter system connected to the power supply system and having a converter machine with a rotor and at least one three-phase winding, which is in a position to stabilize the voltage in the power supply system to a specific value it is suggested that the converter system comprise a flywheel storage means with a synchronous machine and a flywheel coupled thereto, that the converter system have a static converter system, with which the flywheel storage means can be coupled to the converter machine such that the flywheel storage means can draw power from the converter machine or supply power to it, and that a control be provided which detects the voltage of the power supply system and controls the static converter system such that the converter machine stabilizes the voltage of the power supply system to a predeterminable value by drawing or supplying power.