Power factor preregulator based on modified tapped-inductor buck converter

Power factor preregulators based on buck-type converters with capacitive output filter do not allow a unity power factor due to their inability to draw current from the AC line during those intervals when the input voltage is lower than the output one. This limitation can be overcome by using a modified tapped-inductor buck topology, which can be arranged to operate as a flyback converter when desired. This modification, which requires only an extra line-frequency commutated switch and a diode, allows to extend the input current conduction angle, thus making the converter compliant with harmonic standards like IEC 1000-3-2. A 1 kW converter has been designed, built and tested to validate the theoretical forecasts.