This paper introduces a new high-frequency (HF) link on-line Uninterruptible Power Supply (UPS) configuration based on one HF transformer with three windings. The HF link is established using a resonant inverter during normal operation of the UPS and a sinusoidal pulse-width modulation (SPWM) inverter during mains failure. A cycloconverter is used to construct the low-frequency output voltage. Another configuration of the system is also presented such that the system becomes more compact and flexible where the switch-mode operation of the SPWM inverter is avoided by replacing it with a resonant one. In this case, the two inverters are integrated into only one HF resonant inverter and the output is constructed and controlled using a SPWM cycloconverter. The choice of the switching frequency as well as the HF transformer material are investigated. Simulation of the UPS circuit was carried out and verified with experimental results for a 500VA, 20kHz link frequency.
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