Study On Active Power Factor Correction Based On Step-down Circuit

The active power factor correction technology has become an important research field with the continuous development of society and power electronics technology. The active power factor correction technology based on boost converter has been widely researched. It is a boost converter and its current is continuous in an operating cycle. Based on these characteristics, the active power factor correction technology based on boost converter can obtain a higher power factor. But in some engineering applications we need a lower voltage than the input voltage. The traditional buck converter can’t achieve a high power factor because of its input current is discontinuous. The development of the APFC based on buck converter is limited by this feature. Therefore, there is a high academic value and practical significance in the study of the APFC technology based on buck converter. At present, the research on buck power factor correction technology has achieved a certain development, but there are still some shortcomings.Focus on these existing problems, the principle of buck power factor correction technology is analyzed in this paper. The circuit topology and control method are studied for realizing the decrease of voltage and power factor correction. The Matlab/Simulink model is built in this paper; the simulation results have verified the correctness of the proposed method.The main research contents are as follows:The research background and the research status are analyzed, and the circuit topology, operating principle, and control methods of the Buck APFC circuitare analyzed and studied in detail. The advantages and disadvantages of Buck APFC circuit are given in this paper for the next step research. A new Buck APFC circuit with the single period control method is proposed on the basis of previous studies, and then made simulation verification.In order to simplify the circuit and achieve a good power factor correction, the different power factor correction methods are studied and the advantages and disadvantages of each method are analyzed. The Speic APFC has some special advantages, and then compared with the Buck APFC model by circuit comparing and simulation verification. Meantime, the disadvantage of Sepic APFC is pointed out.In order to overcome the diode loss and reverse recovery problems existed in the basic Sepic APFC circuit, the bridgeless Sepic APFC circuit is proposed. The bridgeless Sepic APFC circuit has the advantages of reducing the number of diode, decreasing the diode loss and improving the system efficiency. To overcome the problem of current reverse recovery in the discontinuous mode, the DCM control method is adopted in this paper.The parameters of main circuit and control circuit are designed, and the chips selection of control circuit and driving circuit are completed in this paper. And then a Sepic APFC model of Matlab/Simulink is built. Finally, the correctness of the proposed method is verified through the simulation.