Three-phase three-level LC-type parallel resonant DC/DC converter with variable frequency control

For high power applications, a novel three-phase three-level parallel resonant dc/dc converter with variable frequency control strategy was proposed in this paper. The main advantages of this converter are listed as follows. The converter has a simple topology with only six power switches. The voltage stress on power switches is only half of the input voltage, and the three-phase configuration reduces the current stress on power switches effectively. Meanwhile, the output current ripple frequency is six times as the switching frequency, which is much higher compared with single phase converter, resulting in a reduced filter requirement. The parallel resonant tank is introduced to increase the range of soft-switching for switches. In this paper, the operation principle of the converter was analyzed, and the equivalent model and voltage gain characteristics of the converter were obtained according to fundamental harmonic approach. The parameters were designed under the condition that the switching frequency is lower than or equal to the resonant frequency. To validate the feasibility of the proposed converter, a prototype of 440V~590V input and 54V/20A output has been fabricated and tested in the lab, and experimental results were provided to verify the theoretical analysis and the performance of the proposed converter.