Surge protection for double-conversion UPS

Uninterruptible Power Supplies ensure a continuous and reliable supply to critical loads, and double-conversion is typically the preferred topology. Notwithstanding the superior protection provided by their AC-DC-AC conversion, even double-conversion UPS installations often include external SPD for protecting both the load and the UPS input stage. This is particularly critical during high-efficiency operation (so-called ECO mode), when the load is fed via the bypass path (that is, connecting the AC input to the AC output). In this context, this paper discusses overvoltage attenuation by filtering as complement to surge protection and presents experimental results from a sample installation exposed to high-energy surges.