Single Stage High Power Factor Converter Using the Sheppard-Taylor Topology

This paper describes a new usage of the dc/dc converter developed by D.I. Sheppard and B.E. Taylor in 1983, for achieving high power factor and output regulation. This converter may be viewed as a cascade of a modified boost stage and a buck stage, with the two stages sharing the same active switch. Two possible operation regimes are described. In the first regime, the converter's input part, which is a modified boost converter, operates in discontinuous mode, and the output part, which is a buck converter, operates in continuous mode. In this regime, high power factor is naturally achieved and the output voltage is regulated by duty cycle modulation via a simple output feedback. In the second regime, the input part operates in continuous mode and the output part operates in discontinuous mode, with duty cycle modulation maintaining a high power factor and frequency modulation regulating the output. Compared to the usual boost-buck cascade operating in the first regime, the proposed converter has a wider operating range. When operating in the second regime, the modified boost stage has the ability of producing a harmonic free input current, unlike the standard boost PFC whose current always suffers a cusp distortion.