Uninterruptible power supplies UPS are combinations of rectifiers, inverters, switches and energy storage devices, e.g. batteries, forming a power supply system which ensures a permanent supply of the load in case of a supply voltage breakdown.

Output-Voltage and frequency remain within the static and dynamic limits defined for the load.

The international product standard IEC 62040-3 classifies UPS according to these limits into the classes 1, 2 or 3. UPS can be used for small IT computer networks as well as for computing centers in the field of telecommunications, for Internet nodes, in industrial installations, hospitals and power plants.

UPS systems comprise customised system solutions being combined of rectifiers, inverters and energy storage devices, e.g. batteries. They are used wherever high operating safety and reliability are required for "mission-critical" applications, even under difficult conditions and over long periods. These requirements are established by users in the field of energy supply, industry, telecommunications, chemical and petrochemical industry.