Modern Transformerless Uninterruptable Power Supply (UPS) Systems brahim Güne 1, Bülent Üstüntepe2, and Ahmet M. Hava3 1,2 ENEL Energy Electronics Company, 34794 Istanbul TURKEY

Department of Electrical and Electronics Engineering, Middle East Technical University, Ankara, TURKEY
hava@metu.edu.tr

Abstract
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.
FULL PAPER
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