Research On Boost-Flyback Single Stage PFC Converter

Power technology has advanced considerably in the past decade with the advent of better semiconductor devices,power supply topologies,and control techniques.The development of power electronics makes it possible to produce a power system with high power density,high efficiency,fast dynamic response,high power quality and low cost.Since the conversion of electrical energy from alternating current(AC)to direct current(DC)is a necessary step in most electrical appliances,it is necessary to maintain a high power factor(PF)operation to improve system efficiency.Therefore,power factor correction(PFC)circuit is used in AC-DC converters widely.The active two-stage approach is most commonly used in AC-DC converters.Due to the need for two switches and two sets of control circuits,the active two-stage PFC converter needs more components,large volume and high cost,and control complex.And because it’s energy through the two power processing stages transfer,resulting in the efficiency of the whole converter reduced.This thesis focuses on the research of Boost-Flyback single-stage PFC converter with simple control strategy,low cost,high efficiency and low voltage of bulk capacitor.Boost-Flyback single-stage converter is simple in structure and low cost,but it has the disadvantage of high voltage of bulk capacitor.In traditional Boost-Flyback single-stage PFC circuits,it is inevitable that the bulk capacitor voltage is too high,because this voltage is out of active control.Although it is possible to make the bulk capacitor voltage independent from the load by running Flyback converter under discontinuous conduction mode(DCM),the bulk capacitor voltage must vary widely in order to achieve power balance between input and output in general voltage applications,capacitor with higher withstand voltage is more expensive generally.Some improved topologies or control strategies can eliminate these problems,but at the expense of a lower PF or higher complexity.In this paper,the possibility of using tapped inductor to reduce the voltage of the bulk capacitor of single-stage converter is discussed.By improving the circuit structure and control strategy of traditional Boost-Flyback single-stage PFC converter,a LED driving circuit based on tapped inductor Boost-Flyback single-stage PFC converter with primary side control is proposed.Because the Flyback converter in the critical conduction mode(CRM)can be applied to more power occasions,this approach is realized by running the input converter under the DCM and the output converter under the CRM.Compared with traditional Boost-Flyback single-stage converter,this proposed converter can significantly improve the disadvantage of high voltage of the bulk capacitor.In addition,the current of the LED can be regulated by the primary side regulation strategy without the secondary side current sense circuit and opto-coupler.Hence,the size and cost of the proposed converter can be reduced significantly.Finally,this paper builds the corresponding model of the converter for simulation research with the simulation software.An experimental prototype with 175 Vac-250 Vac input and 60V/ 0.3A output is produced on this basis.The validity of the theoretical analysis above is further verified by the simulation results and experimental results.