Analysis of single-phase single-stage power-factor-corrected switching converters

Abstract

The distorted input-current waveforms of nonlinear electronic loads cause interference and lead to poor utilization of the utility power system. This is rapidly becoming a serious problem due to the wide proliferation of electronic loads. Input-current shaping or power-factor-correction (PFC) addresses the techniques of reducing the distortion of input-current waveforms drawn from the power line. There are many methods of input-current shaping. This thesis focuses on the analysis and comparison of single-stage cascaded switching power converters which can provide simultaneous power factor correction and tight output-voltage regulation. The study begins with a detailed review of the concept of power factor and the methods of input-current shaping. At the reviewing stage, the automatic PFC is chosen as the subject of the thesis. Topologically there are many ways of realizing automatic PFC. After a detailed comparison between two-switch and single-switch cascaded topologies, the single-switch cascaded version is identified as a suitable candidate for low-power applications. All possible topologies based on pure cascade of the basic second-order converters are derived by using the grafted tree technique. A new buck based topology which is not based on the pure cascade is also derived. Some existing and new rules are used for determining whether a particular cascaded converter is suitable for use as a PFC regulator. Then, the converters which are found suitable are compared against their RMS, peak and average diode, inductor and switch currents. Small-signal dynamical analysis of some well known cascaded converters are also studied in detail. The results from small-signal analysis provide important insights into the dynamics of cascaded PFC converters, which have not been reported in the power electronics literature.