What is inverter?

An inverter is a device or electronic circuit which converts DC current/Voltage to AC current/voltage.

About UPS

UPS stands for Uninterrupted Power Supply, and inverter is an integral part of a UPS system. It is an equipment which draws energy from AC mains and stores it into a battery by converting AC to DC, and when there is a power outage, it automatically starts supplying stored energy from the battery to the load by converting DC back to AC.

In the presence of NEPA/generator supply, not only does equipment run based on that power, the batteries of the inverter also charge simultaneously and store that power. In the subsequent event of a power outage, the stored power in the inverter battery then comes into play and powers up equipment instead, by converting the stored power from DC to AC for use.

UPS Topologies/Types:

• Standby or Off-line UPS
• Online UPS

The standby or offline UPS/Inverter :

This is the most common type of UPS in use. In day to day language, it is referred to as an inverter. Here, as seen in the figure below, there is an automatic transfer switch that connects the load to utility supply after purifying its quality when power from NEPA/generator (mains) is present. When the mains supply fails (or falls short of the requirement), the transfer switch automatically trips to connect the load to the battery, which then supplies power to the load by converting DC to AC using an inverter circuit.

Standby UPS

On-Line UPS:

On-line UPS, also known as Double Conversion On-Line UPS, is used in higher rating at industries for critical applications, or in lower rating for computers etc. As shown in the diagram below, it is similar to an offline UPS/Inverter, except that the primary power path is the inverter instead of the AC main. In the Double Conversion On-Line design, failure of the input AC does not cause activation of the transfer switch, because the input AC is charging the backup battery source which provides power to the output inverter. Therefore, during an input AC power failure, on-line operation results in no switching time.

Both the battery charger and the inverter convert the entire load power flow in this design. Although this results in reduced efficiency & even the Online technology UPS being higher in cost than their offline counterparts, these UPS have an indispensable requirement in industries where power interruption cannot be tolerated for even a microsecond, eg- in IT sector for powering servers.

On-Line UPS

Can a Standby/Off Line or Line Interactive UPS power up lighting loads along with Computer or Electronics loads?

Technically speaking, yes. A well designed Standby/Off Line or Line Interactive UPS should have the capability to support lighting loads along with Computer or Electronics loads. However, since majority of these type of UPS’s available in the market today are not designed to have the capability to support such mixed loads, most vendors don’t recommend to use mix kind of loads on their UPS systems.