What is Offline UPS, Line Interactive UPS, Online UPS?

Offline UPS

The OFFLINE UPS supplies (or routes) the incoming mains supply directly through to the output usually through a relay contact. Some high frequency noise filtering and surge suppression may be included in this path. The UPS switches on its inverter as soon as mains supply failure is detected or below the normal load and simultaneously switches the output relay to the inverter side to supply battery sourced power to the load. This transition involves a delay on account of the time to reliably detect mains failure and switch over a relay, and the output is broken for this period (usually for 2 to 12msec).

OFF – LINE UPS are usually the least extensive as compared to the other two.

The Block diagram of inverter section of Online ups is shown:

Line Interactive UPS

The true LINE INTERACTIVE design is in fact a combination of OFFLINE & ONLINE, in which the inverter plays a dual role of charging the battery when mains supply is present as well as regulating the output voltage and working as a normal inverter in absence of mains supply, so to the user it appears like an ONLINE System. Line Interactive UPS offers enhanced power protection over the basic Offline designs by providing additional line conditioning.

Online UPS

An ONLINE UPS is the one in which the inverter always supplies power to the protected load and hence the same quality of power is ensured all the time. When mains supply is present, the inverter derives its power from thee mains supplied rectifier and the backup batteries are also kept in charged state. When the mains fail, the source of DC power for the inverter section shifts to the battery without any break whatsoever in the output to the Inverter. It also bears all the vagaries and noise borne out of the mains supply and insulates the secure bus supply from it.

An ONLINE UPS is especially useful for sensitive and critical equipment/devices