FAQs - On-line UPS
On-line UPS information from single and three phase to monoblock and modular uninterruptible power supplies, battery runtimes, options and accessories.
An on-line double conversion UPS is a Voltage and Frequency Independent (VFI) uninterruptible power supply as defined by BS EN 62040. The inverter in this type of UPS produces a digitally generated sinewave output, supplied from a DC rectifier supply. The DC rectifier/converter supplies DC power to the inverter from the rectified mains power supply or the connected battery set.
The term ‘double-conversion’ online UPS refers to the conversion of mains power supply AC (alternating current) by the rectifier/converter to a DC (direct current) to supply the inverter and charge the battery set. The inverter section to which the load is always connected ‘inverts’ the DC to AC. The AC-DC-AC process is described as ‘double conversion’. There is also a Triple Conversion online UPS mode for some designs covering AC-DC-DC-AC where the DC-DC is a converter.
The inverter section of an double or triple conversion online uninterruptible power supply is designed for continuous running and the powering of the connected load. This features allows the UPS to be connected to battery extension packs for long runtime applications up to seven hours or more. Some smaller online UPS may be restricted to 4hours on battery at full load in order to protect the inverter electronics from heat damage.
In an online UPS system the inverter section constantly powers the load during normal operation with a digitally generated AC (alternating current) sinewave supply and in almost all cases of a higher quality than would be achieved were the load to be connected directly to the mains power supply. The inverter is supplied with a DC (direct current) supply either from the front-end rectifier or battery set. This means that the UPS inverter receives either a supplier via the mains power supply (if present) or the battery set (if the mains power supply fails). The electrical capacitance built-into the inverter covers the almost instantanous transfer between DC power sources to ensure the inverter output is ‘no-break’ and truely uninterruptible.
Online UPS have a built-in automatic bypass. A circuit on the output on the inverter monitors the waveform for any signs of collapse either because of a short-circuit caused by an overload or fault condition. Such an event causes the automatic bypass to transfer the load to the mains power supply or alternative AC power source (such as a generator) to maintain load uptime.