Line-Interactive UPS Systems

Line-interactive uninterruptible power supply (UPS) systems provide both power conditioning and battery backup. This technology is particularly effective in areas where outages are rare, but power fluctuations are common. Line-interactive UPS systems support a wide range of input voltage fluctuations before switching to battery backup.

Line-interactive UPS technology provides power conditioning with a 4-6 millisecond break in power when transferring to battery back-up and protects against the most common power problems experienced in a network. Here the UPS also monitors the voltage level and balances under and over voltages. This technology provides a good choice between reasonable protection and moderate operating costs.

With line-interactive UPS, the inverter becomes part of the output and is always on. The inverter can operate in reverse to charge the battery while AC input is normal and switch to battery power when input fails. Internal components provide filtering and voltage regulation that raises and lowers utility power to the level needed by the connected equipment. In some cases, line-interactive UPS systems rely on the battery to condition power so it may use the battery more frequently than online UPS systems that condition power through the double-conversion process.

When AC input power fails, the unit’s transfer switch opens and the power flows from the battery to the UPS output. With the inverter always on and connected to the output, line-interactive UPS provides additional filtering and yields reduced switching transients when compared to a standby UPS. Line-interactive UPS systems are typically used in rackmount applications below 5000VA.