Forward-based AC/DC converter with quasi-active input current shaping technique

This paper presents a forward converter with a quasi-active input current shaping (ICS) scheme. A high frequency pulsating voltage source derived from a cascaded dc/dc forward converter is added to serve as a magnetic switch and drive an inductor for input current shaping. As a result, the input power factor is improved due to the extended conduction angle of the conventional diode rectifier with large output capacitor. It eliminates the use of active switch and control circuit for power factor correction (PFC), which results in improved efficiency and lower cost. To achieve low harmonic content, the input inductor is designed to operate in discontinuous current mode (DCM). The new converter satisfies the input current harmonics regulation IEC61000-3-2 Class D and limits the dc bus capacitor voltage below 450V for universal line applications. In addition the added winding provides a direct power transfer path from the input to the load, which can improve the conversion efficiency. Operating principles, analysis, and simulation/experimental results of the proposed converter are presented.