Modern transformerless uninterruptable power supply (UPS) systems

Uninterruptable power supplies (UPS) are widely used to supply critical loads and provide reliable and high quality energy to the load. Until recently, on-line UPS systems with isolation transformer have been widely employed. However, transformerless modern UPS systems have been rapidly replacing the old technology due to their superior performance and size attributes. Transformerless UPS systems have utility friendly input performance and high quality output voltage waveform. Furthermore, smaller size, higher efficiency, and increased reliability are features that spread the transformerless products, rendering the transformer technology obsolete. In this paper, modern transformerless UPS systems with the 6-300kVA range will be discussed and their experimental performance will be illustrated. Input and output power quality performances, energy efficiency performance, and size/weight information will be provided on modern commercial transformerless UPS products.