Modified Bridgeless SEPIC PFC Converter With Reduced Conduction Losses and Simple Structure for Medium-Line-Frequency Applications

Bridgeless power factor correction (PFC) converter has obtained much popularity in medium-line-frequency avionics applications due to its merit of optimized power losses. In this paper, a modified bridgeless PFC converter based on single-ended primary-inductor converter (SEPIC) is demonstrated. The com-plete elimination of all input diodes and the presence of only two conducting semiconductors in power-flowing path result in lower conduction losses as compared to classic SEPIC PFC converters. A common set of energy-storage capacitor and inductor is employ-ed to operate for both positive and negative half-line cycles, leading to higher component utilization as compared to dual-SEPIC PFC converters. Moreover, the voltage stresses on the semiconductors are greatly reduced with the split-capacitor output structure. The proposed converter is designed to operate in discontinuous con-duction mode, and a near-unity power factor can be achieved with no current-loop control. The overall performance of the proposed converter is elaborated in terms of its working principle, control scheme, and characteristic analysis. Finally, a 300-W laboratory prototype with 115-Vrms/400-Hz ac input and 270-V dc output is developed, and the theoretical analysis is authenticated by means of experimental results.