Widened-voltage bidirectional isolated multi-level dc-dc converter and method thereof

A bidirectional multi-level DC-DC converter device has a widened-voltage conversion feature and includes a first power converter, a transformer, a second power converter, a third power converter, a first selective switch, a second selective switch and a filter circuit. A first winding at a primary side of the transformer connects with the first power converter while a second winding and a third winding at a secondary side of the transformer connect with the second power converter and the third power converter. The first selective switch connects with a first positive DC output end of the second power converter while the second selective switch connects with a first negative DC output end of the second power converter and a second positive DC output end of the third power converter. The filter circuit connects with an output end the first selective switch, an output end of the second selective switch and a second negative DC output end of the third power converter.