Research On Key Technologies Of High-efficiency Bridgeless PFC

AC/DC converters usually need to use power factor correction(PFC)technology to reduce the impact of harmonic currents generated by power electronic equipment on the power grid.The wide application of modern power electronic equipment puts forward higher requirements for the harmonic distortion(THD),power factor(PF)and efficiency of the PFC converter.The evolution of circuit topology,the use and optimization of new devices,and the improvement of various control strategies have promoted the great improvement of indicators such as the power factor and efficiency of the PFC converter.From the perspective of overall circuit design and converter model,this paper studies the key technologies of PFC converter efficiency optimization and current distortion compensation strategy.First,from the perspective of the overall circuit design,the efficiency optimization of the PFC converter is studied from the aspects of topology selection,device selection and corresponding drive optimization.In the choice of topology,the totem pole bridgeless PFC topology achieves higher efficiency,and has the characteristics of simple structure and easy control compared with other topologies.However,the traditional totem pole bridgeless PFC converter is limited by the loss caused by the reverse recovery characteristics of silicon-based devices,and it is difficult to meet higher transmission power requirements.The application of wide-bandgap semiconductor devices such as Si C MOSFET effectively reduces the switching overlap loss,and due to the good thermal conductivity of Si C material,it effectively improves the efficiency and power level of the PFC converter.At the same time,due to the fast switching speed of Si C MOSFET,considering the influence of switching characteristics and loop parasitic inductance,the driving optimization problem is studied to solve the reliability problem of PFC converter caused by the low threshold voltage and high switching speed of Si C MOSFET.Then,aiming at the problem of current distortion in PFC converters under traditional average current control,an optimized control strategy based on feedforward compensation is studied.The current and voltage loops of the PFC converter are analyzed,and the input admittance of the PFC converter is derived based on the closed-loop transfer function of the input voltage and input current,which shows that the input impedance is not pure resistance under the traditional average current control,and,there is a phase difference between the input current and the input voltage.In order to reduce the influence of the phase difference on the PF value,a duty cycle feedforward is introduced into the current loop to compensate.Considering the influence of the interference and delay in the sampling circuit on the control,the phase-locked loop technology is added to reduce the noise of sampling and compensate for the sampling delay.In addition,the traditional voltage loop control strategy has a low update frequency due to the influence of the output voltage ripple,and the output voltage is notched and filtered to increase the voltage loop bandwidth.Through Simulink/Saber cosimulation,the effectiveness of the average current mode optimization control strategy based on feedforward compensation is verified.In order to verify the efficiency of the PFC converter and the effectiveness of the average current mode optimization control strategy based on feedforward compensation,a prototype was made and verified by experiments.Experimental results show that the proposed strategy achieves a higher power factor and improves the overall conversion efficiency of the converter,reaching a peak efficiency of 98.83%.