Uninterruptible power supplies (UPSs) can prevent loads from seeing voltage sags, surges, or other electrical disturbances. UPSs can also power the load with a battery source during complete outages until the generators start. In fact, they can even transfer the load to a secondary stable source using the internal static transfer switch (STS) during abnormal circumstances. Perhaps most importantly, transformerless UPSs are designed to prevent downstream loads from ever seeing an interruption to their power source.
In the late 1990s to early 2000s, large facility data centers were constructed around the United States due to the dotcom era rush. A large number of these facilities purchased transformer-based UPS modules. These modules are now nearing the end of their useful lives. Fortunately, transformerless UPSs are becoming the standard of data center design all across the world. These UPS systems can provide harmonic mitigation and power factor correction with active front-end controls. They can operate with very little output voltage harmonics and a superior step load response. Transformerless UPSs can provide these great characteristics, while providing higher efficiencies over transformer-based topologies.