The online UPS is also called inverter preferred UPS.
Block Diagram & Working of Online UPS
Fig. 1 shows the block diagram of online UPS.
Fig. 1: Block diagram of the online UPS system.
When the main supply is present, the rectifier/charger provides power to an inverter as well as battery (See Fig. 2 (a)). The battery is charged. The inverter is on and feeds power to the load through UPS static switch.
(a) When mains is present
(b) When mains is absent
Fig. 2 Power flow in online UPS
The UPS static switch is always on and connects load to inverter output. The mains static switch is always off. But when the UPS fails, then load is connected directly to the mains directly through mains static switch. When the mains supply is not available, then battery bank supplies power to an inverter (See Fig. 2 (b)). Thus an inverter is always on and it takes power from rectifier or battery. Fig. 2 shows the power flow when mains is present and mains is absent.
