The usual way to avoid a computer shutdown during a mains failure is to connect an ac uninterruptible power supply (UPS). Alternatively, in this paper, a simple and high efficiency dc UPS is presented by proposing an isolated bidirectional soft-switching dc-dc converter. The bidirectional dc-dc converter operates under zero-current switching (ZCS) condition by utilizing the leakage inductor of the transformer. ZCS operation is achieved in battery-backup and charging modes, which significantly reduces the power losses in the bidirectional converter. Also, high efficiency is achieved in backup and charging modes because there is only a single dc-dc conversion in each mode. A 1 kW prototype system has been built and tested for a PC power system.
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