A novel PFM/PWM hybrid modulated single‐stage FSBB‐LLC AC‐DC converter

Abstract

SummaryBy integrating the four switch buck–boost (FSBB) PFC and full‐bridge LLC resonant converter, a novel single‐stage FSBB‐LLC AC‐DC converter is proposed. Meanwhile, the corresponding PFM/PWM hybrid modulation is put forward. The proposed solution employs a dual‐loop feedback control strategy based on PFM/PWM hybrid modulation to obtain the desired bus voltage and stable output voltage. The bus voltage feedback loop is mainly used to smoothly determine the boost or buck–boost mode of FSBB PFC cell for regulating the bus voltage; the output voltage feedback loop is in charge of stabilizing the output voltage by adjusting the switching frequency or phase shifting angle. Furthermore, an optimal parameter design based on power balance principle is also derived. The experimental results of an 85 ~ 300 V input, 12V/25A output prototype demonstrate that (1) low and narrow bus voltage of 240 ~ 340 V is achieved under the entire input and output condition; (2) the LLC cell operates at DCX mode over the whole load range as the input voltage exceeds 120 V; (3) the output voltage is well regulated even under the no‐load condition; (4) ZVS feature for the shared switches is still maintained; and (5) a peak efficiency of 90.9% and PF values above 0.987 are achieved.