Emerson Network Power Outlines Application Considerations for Transformer-free and Transformer-based UPS Design Approaches

The white paper, titled “Comparing Transformer-free to Transformer-based UPS Designs,” takes a close look at the two approaches and reviews the techniques and tradeoffs utilized in the various rectifier, DC energy storage, inverter and static bypass functions of these two designs for various UPS system performance functions.

“While accomplishing similar high-availability performance goals, transformer-based and transformer-free UPS units use somewhat different approaches to meet specific output performance requirements,” said Peter Panfil, vice president of global power, Emerson Network Power. “In choosing between transformer-based and transformer-free UPS solutions, a system designer should determine where transformers are best utilized and whether they should be internal and/or external to the UPS in view of physical and electrical distribution requirements and tradeoffs.”

The Emerson Network Power white paper recommends that for high-power enterprise data centers and other critical applications, a state-of-the-art transformer-based UPS still provides an edge in availability. However, if operational efficiency, expansion flexibility or a limited UPS footprint are of paramount importance, and other appropriate measures are instituted to provide an acceptable level of availability, transformer-free technology may be the optimal choice.

In general, transformer-based UPS systems are highly robust and excel at providing the highest capacities and availability while simplifying external and internal voltage management and fault current control. The latest transformer-free designs offer better efficiency, a smaller footprint and improved flexibility while providing high levels of availability.

Presently, large transformer-free systems are constructed of modular building blocks that deliver high power in a lightweight, compact package. This modular design offers advantages when the timing of future load requirements is uncertain by allowing capacity to be more easily added as needed, either physically or via control settings. On the other hand, a modular design means higher component counts, which may result in lower unit Mean Time Between Failure (MTBF) but an improved Mean Time To Repair (MTTR).