Abstract: In a method for open-loop and closed-loop control of an electrical drive, which comprises an asynchronous motor (18) which is supplied by a DC-AC invertor (14) with a downstream sine-wave output filter (15) with an AC voltage at a predetermined circular frequency (.omega.), stable operation with a good control response and reliable damping of natural filter oscillations is achieved in that the voltage at the output of the sine-wave output filter (15) is measured, in that the measured filter voltage is assigned a complex filter voltage vector (E) in a complex reference system rotating at the circular frequency (.omega.), and in that the DC-AC invertor (14) is actuated in such a manner that the complex filter voltage vector (E) corresponds to a predetermined required voltage vector (E*).

Abstract: An Uninterruptible Power Supply (UPS) for de-centralized operation in a distributed UPS system is described. The UPS system includes a number of UPS units that do not have communication links between them and therefore operate in a de-centralized manner. Coordinated operation in the UPS system is achieved through a controller associated with each UPS unit. The controller identifies when the operating power signal frequency on the UPS system does not correspond to a nominal operating frequency. In response to this condition, the controller generates a frequency reference signal that is used to control the inverter of the UPS unit. The controller continuously estimates the fractional loading of the distributed system by gauging the system response to disturbances, and sets its own operating point accordingly. The controller also ensures that the system operates at its nominal frequency independent of loading.