History of transformer-free UPS technology
First appearing at lower power levels, transformer-free UPS designs have been around two decades or so. A vast majority of designs below 30 kVA are now transformer-free, meaning that the UPS does not contain power line frequency magnetics (transformers or inductors). This transformer-free design trend is moving up in power levels because power line magnetics are both material and labor intensive. On the other hand, the high frequency power processing needed is technology intensive. In general, advances in technology mature sufficiently to support improved value to the customer without sacrificing needed reliability. Once that point is reached, the technology-intensive design becomes the preferred value leader. Technological advances in technology have had a similar impact upon switch mode power supplies as well as personal computers.
Transformer-free UPS: A growing trend
At higher power levels reaching above 30 kVA and now as high as 1100 kVA, the challenge is to switch high currents rapidly at high voltages without high losses or excessive peak voltages. Over the last decade, high power insulated gate bipolar transistors (IGBT) have matured enough to allow conversion frequencies of 10 kHz and above without large sacrifices in efficiency at these higher power levels. In addition, some creative control strategies permit further reduction of switching losses to the point where the new transformer-free technology UPS is competitive with the old technology UPS–even when measured in terms of system efficiency.