A Constant-on-time Bi-frequency Controller Of CCM Boost PFC Converter

A large number of harmonic currents produces by power electronic equipment are injected into the power grid,distort the voltage waveform of the public power grid,resulting in a decline in power quality.In order to reduce the harmonic pollution of power electronic equipment and ensure the quality and safety of power supply,it is necessary to do the power factor correction(PFC)of AC/DC converter,improve the power factor(PF)of AC/DC converter and reduce the total harmonic distortion(THD).The multi-pulse train(MPT)technology and Bi-frequency(BF)control technology have been proposed in recent years which are used to improve the frequency spectrum characteristics,reduce electromagnetic noise and improve the transient response speed of switched DC-DC converter.Based on MPT control technology and BF control technology,this paper presents a Constant-On-Time Bi-frequency(COT-BF)control method for Continuous Current Mode(CCM)Boost PFC converter.COT-BF control decouples the current control loop from the voltage control loop,improves the transient response speed of the circuit and eliminates the influence of low-frequency output voltage ripple on the current control loop.In addition,COT-BF control uses dual frequency control,which reduces the switching frequency near the peak of input voltage,reduces switching losses and improves system efficiency.For further improvement of the PFC converter's efficiency,this paper presents a piecewise constant on-time bi-frequency(Piecewise COT-BF)control method for CCM Boost PFC converter.Piecewise COT-BF controllers generate multilevel pulses,based on the input voltage at the beginning of each switching cycle,Piecewise COT-BF controllers select one of the multilevel pulses as the control signal.At the same time,it decouples the current loop and the voltage loop eliminates the effect of low-frequency output voltage ripple on the current control loop,and improves the transient response speed of the circuit.In addition,as a pulse frequency modulation control,Piecewise COT-BF control can reduce the switching frequency near the peak of input voltage,reduce switching losses and improve the circuit efficiency.This paper describes the principle and implementation of Piecewise COT-BF controlled and COT-BF controlled CCM Boost PFC converter.The theoretical analysis results are verified with a PSIM simulation and a 300 W experimental prototype.The analyses and experimental results show that Piecewise COT-BF controlled and COT-BF controlled CCM Boost PFC converter has faster response speed,higher circuit efficiency,while maintaining a higher power factor(PF)value and a lower total harmonic distortion(THD).