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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 ac

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. As a result, the inverter produces a power signal at the target frequency and with a power level equivalent to the power level associated with each of the UPS units of the UPS system. The performance of the overall system is not sensitive to small differences in the nominal frequency settings of the individual UPS units.

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An Uninterruptible Power Supply unit for connection to an Uninterruptible Power Supply system that includes a plurality of similarly controlled Uninterruptible Power Supply units that do not have communication links therebetween, said Uninterruptible Power Supply unit comprising: a power bus node fo

An Uninterruptible Power Supply unit for connection to an Uninterruptible Power Supply system that includes a plurality of similarly controlled Uninterruptible Power Supply units that do not have communication links therebetween, said Uninterruptible Power Supply unit comprising: a power bus node for connection to a power bus that has a plurality of loads and said plurality of Uninterruptible Power Supply units connected thereto, said power bus carrying a power signal with an operating frequency distinct from a nominal power signal frequency; an inverter connected to said power bus node; and a controller to generate a frequency restoration reference signal (wi*) used to produce gate drive signals for said inverter, wherein said controller receives a nominal power signal frequency signal (wo), an actual Dower signal frequency signal(wi), and an actual power level loading signal (Pi) measured locally at said Uninterruptible Power Supply unit, subtracts said actual power signal frequency signal from said nominal power signal frequency signal to produce a delta power signal frequency signal(Dwi), and multiplies said delta power signal frequency signal (Dwi) by the product of a frequency restoration constant (k) and a nominal power rating value (PiR) to yield a first intermediate frequency restoration signal.