Modified three-phase three-level dc-dc converter -adopting asymmetrical duty cycle control

Three-phase three-level (TPTL) dc/dc converter has the advantages of lower voltage and current stress on switches, which is suitable for high power and high input voltage applications. Adopting a symmetrical control strategy, the ripple frequency of input and output current can be increased significantly, resulting in a reduced filter requirement. However, all the switches are hard-switching, leading to a considerable switching loss. In this paper, an asymmetrical duty cycle control strategy was proposed to the TPTL dc/dc converter. The converter can keep all the advantages compared with the original control strategy, meanwhile, soft-switching can be achieved using the energy stored in output filter inductance and leakage inductances of transformers (or resonant inductances). In this paper, the operation principle with asymmetrical duty cycle control was analyzed, along with the characteristics and soft-switching condition of the converter. Experimental results from a 540~660V input and 48V/20A output are presented to verify the theoretical analysis and the performance of the proposed converter.