UPSs that operate in econo-mode (line-interactive topology) are touted as operating at higher efficiency
with commensurate reduced operating costs compared to online (double conversion topology) UPSs.
The truth is that, as with all engineering solutions, there are trade-offs. The table below lists common
adverse power events from power utilities, and compares the two topologies handling of these power events.
The philosophical difference between these two topologies is simply that a line-interactive UPS is always
in bypass mode and relies heavily on sensing and reacting to power events, whereas a double
conversion UPS is always on line and keeps supplying conditioned power regardless of input power
Finally, from a failure mode perspective, there are more ways for things to fail with a line-interactive
unit than with double conversion unit. More sensing means more potential for a sensor failure; more
switching means an increased probability of dropping the load.
When selecting an Uninterruptable Power System, look beyond raw efficiency and balance your power
quality requirements against the performance criteria of these two UPS topologies. Slightly lower
operating costs may come at the expense of power qualityand reliability.