Multi-phase multi-level LLC resonant converter with low voltage stress on the primary-side switches

To satisfy the requirement for high voltage and high power applications, a multi-phase multi-level LLC resonant converter with modular structure was proposed in this paper. The voltage stress on the primary switch is only one-nth of the input voltage due to its multi-level structure, the current rating of power devices can be reduced by introducing the proposed multi-phase structure. Using the variable frequency control strategy, the primary switches can operate with zero-voltage-switching (ZVS) and the rectifier diodes can operate with zero-current-switching (ZCS) in a wide input voltage and load range. Take the topology with three modules for example, the operation principle of the converter under variable frequency control method was analyzed, the equivalent model and voltage gain of the converter were derived according to fundamental harmonic analysis. The parameters were designed under the condition that the switching frequency is higher or lower than the resonant frequency. To validate the feasibility of the proposed converter, a prototype with 540V~660V input and 400V/5A output has been built and tested in the lab and the experimental results can be agree with the theoretical analysis.