Research On High Power Factor DCM Single-Stage Boost-Flyback PFC Converter Based On Variable Inductor

Single-stage Boost-Flyback Power Factor Correction(PFC)converter has the following advantages: continuous input current,small output voltage ripple,high theoretical efficiency,simple control and so on.When the converter works in DCM mode,which can achieve switching zero-current turn on and no diode reverse recovery current,and the switching frequency is constant,the converter only needs a single voltage close loop to output a stable voltage,so it has great advantages in low-power applications.However,when the output voltage of the converter is stable,the voltage closed-loop output has a constant duty,Boost can be considered as constant duty cycle control,the input current has large distortion,so the power factor(PF)of the converter is low.To solve this problem,a high power factor control method based on continuous variable inductance(CVI)is proposed in this paper.On the basis of traditional constant duty cycle control,variable inductance is utilized innovatively,let the value of the Boost inductance changes according to a certain law in a half line cycle,so the rise and fall slope of inductance current in the switching cycle is changed,Thus,the peak envelope of inductance current is changed accordingly,which can produce the input current sinusoidally.In theory,the unity power factor in a wide range of input voltage can be realized.In order to achieve the change of inductance value,the variation law and specific expression of inductance in a half line cycle are deduced.The working principle of double Ecore variable inductance is analyzed in detail,and its mathematical model and the relationship between inductance value with bias current are obtained.Based on this,the variable inductance with corresponding variation range is designed.The working characteristics of the converter and the closed-loop control scheme is proposed.Finally,the components are designed and selected reference to the electrical parameters.a50 W experimental prototype was built to verify the performance of the converter under traditional constant duty cycle control and high power factor control.The experimental results verify the effectiveness of the proposed scheme.