Reducing Common Mode Noise in Phase-Shifted Full-Bridge Converter

The phase-shifted full-bridge (PSFB) converter has been widely used in medium-to-high power applications because of simple topology and ease of achieving soft-switching for power switches. However, with the phase-shifted control, the electric potential variation of the two phase-leg midpoints happens at different times, and the displacement current generated by two midpoints through associated parasitic capacitance (including the parasitic capacitance between two midpoints to ground and the transformer inter-winding capacitance) cannot be cancelled by each other, resulting in a serious common mode (CM) noise. Moreover, the resonant inductor voltage affects the electric potentials of the transformer terminals, which also generates CM noise. To reduce the CM noise in the PSFB converter, this paper proposes a symmetrical resonant inductor together with symmetrical transformer configuration to eliminate the influence of the resonant inductor voltage on the CM noise. Then, a passive cancellation circuit is introduced to cancel the effect of the voltages between the midpoints and the ground on the CM noise. A 1-kW PSFB converter prototype has been fabricated and tested in the lab, and the experimental results are provided to verify the proposed methods.