Uninterruptible power supply systems provide protection

The uninterruptible power supply (UPS) is a device that maintains a continuous supply of electric power to the connected equipment by supplying power from a separate source when the utility mains are not available. It is normally inserted between the commercial utility mains and the critical loads. When a power failure or abnormality occurs, the UPS will effectively switch from power to its own power source almost instantaneously. This paper describes the most common line problems and the relationship between different existing kinds of UPS. It also presents an overview of the control schemes applied to different distributed UPS configurations. Finally, the applicability of such systems in distributed generation, microgrids and renewable energy systems is outlined.