Modified single-switch bridgeless PFC SEPIC structure by eliminating circulating current and power quality improvement

In this study, a modified single-switch bridgeless power factor correction (PFC) single-ended primary-inductor converter (SEPIC) structure is proposed. The major practical drawbacks of the existing structure are the presence of circulating current and high maximum current stress at the input capacitor and line diodes. Therefore, to overcome these problems, the existing structure is restructured by repositioning the line diodes in series with input inductors. Besides, the principle of design parameters optimisation is used based on the balancing energy compensation between input capacitors and output inductor. This structure is designed to operate in discontinuous conduction mode in order to achieve almost a unity power factor. The operation principle and design consideration of the modified structure is introduced in details. The experimental results demonstrate that the total harmonic distortion current is reduced from 56.3 to 4.9% after the optimisation process is performed, and at the same time the dead zones are inherently eliminated. Furthermore, it is shown that the output voltage ripple frequency is always double from the input line frequency of 50 Hz and the output voltage ripple is constantly lower than the maximum input voltage ripple. Thus, the designed parameters of the experimental converter are verified with ∼160 W of the converter output power.