Study On Line-Current Distortions Of BCM Flyback PFC Converters With Switching-Frequency Limitation

With the continuous development of science and technology and the continuous progress of society,human development has entered the information age from the industrial age to the intelligent age.The renewal iteration of the times corresponds to the change of production mode and lifestyle.Among them,power electronic technology plays a vital role in promoting the development of science and technology.With the development and innovation of power electronics technology,switching power supply technology is also maturing.At present,switching power supply is widely used in almost all electronic equipment with the characteristics of small size,light weight and high efficiency.It is an indispensable power supply mode in the rapid development of electronic information industry.Power factor is an important index to measure the utilization of electric energy by electric equipment.Each electric equipment should improve this coefficient as much as possible.Lower power factor will increase the reactive power component fed into the power grid and reduce the utilization rate of power grid.When the power supply line capacity is insufficient or the circuit load is large,it will produce the distortion of AC voltage waveform,reduce the power supply quality of the power grid and affect the normal operation of other electrical equipment.In addition,the harmonic pollution caused by a large number of power electronic converter equipment in the power grid will lead to mismeasurement and misoperation of electronic equipment,instruments and protection devices.Harmonic pollution will also cause unnecessary losses of equipment and lines in the power system,reduce the working efficiency and service life of power equipment,and in serious cases,there will be the risk of power grid collapse,which will pose a major threat to the safety of people’s lives and property.The increase of switching frequency can reduce the volume of the converter,but too high switching frequency will reduce the efficiency of the converter and bring the problem of EMI,which makes it necessary to limit the switching frequency in some occasions.This paper takes the critical conduction mode flyback power factor correction converter(BCM flyback PFC)as the research object,and is committed to analyzing the influence of switching frequency limit on the line current distortion of critical conduction mode flyback power factor correction converter(BCM flyback PFC)under different control modes.Through the improvement of the scheme,the input line current waveform is optimized to improve the power factor of BCM flyback PFC converter and reduce the harmonic content of input current.The theoretical expression of input line current under different control modes is derived,and the current curve is drawn by Mathcad software.The Simplis simulation platform is built,and the distortion factors of additional line current in practice are analyzed.Based on voltage mode control and current mode control,two experimental prototypes with rated power of73.5w are made,and the experimental data are recorded and analyzed.The simulation and experimental results demonstrate the correctness of the theoretical analysis.The content of the paper can provide a reference for researchers who do related technical research.