A novel ZVS step-up push-pull type isolated LLC series resonant dc-dc converter for UPS systems and its topology variations

High dc gain step-up dc-dc converter continues drawing lots of interests in on-line UPS systems to interface the battery power to unity. Conventional methods, in which using non-isolated converters including cascade converters, can achieve high dc gain but compromise efficiency, while the situation of employing isolated converters is just opposite. To combine the merits of these two type converters and overcome the disadvantages, a novel step-up push-pull type isolated LLC series resonant dc-dc converter was proposed. This converter, besides possessing all advantages of conventional LLC converters, emerges as a higher efficiency can be achieved for the operation is under boost mode, thus the transformer turn-ratio reduces and primary side current decreases. Then the low side gate driving merit of the conventional push-pull converter endows simplification of circuit and ability of cost-effective. Therefore the proposed converter is very suitable for step-up conversion in UPS systems. The detail operation principles and converter´s characteristics were presented, topology variations were shown and the validity and applicability were also verified by a 600 W dual outputs prototype.