Research On Control Strategy To Reduce Double-line-frequency Output Current Ripple Of PFC Converter

For a single-stage AC-DC converter with a high power factor,there is an inherent instantaneous power difference between the AC input side and the DC side output side,which produces significant low frequency output ripple at double line frequency.Thereby the performance of the AC-DC converter is seriously reduced.In order to suppress this low-frequency output ripple and maintain high power factor,this paper studies the introduction of Buck/Boost bidirectional converter as a parallel compensation circuit(PCC),which input side is Connected in parallel with the output side of the DCM Flyback PFC converter to compensate the output current ripple at double line frequency of the AC-DC converter.The paper studies the basic principle and main working waveform of a Buck/Boost PCC compensating a DCM Flyback PFC converter in parallel.The time average equivalent circuit of Buck/Boost PCC is established,and the DC steady-state equivalent circuit and AC small signal equivalent circuit are obtained.The circuit is subjected to DC steady-state analysis and AC small-signal analysis;Based on the AC small-signal equivalent circuit,the closed-loop design of Buck/Boost PCC is carried out;An input admittance model of the Buck/Boost PCC is established and the relationship between the input admittance of the Buck/Boost PCC and the low-frequency output current ripple of the AC-DC converter is analyzed;In order to further reduce the low-frequency output current ripple of the AC-DC converter,an input admittance adjustment strategy of the Buck/Boost PCC based on a virtual admittance is proposed.The method of implementing a virtual admittance of the Buck/Boost PCC through an input voltage feedforward control is studied.The effectiveness of the method is verified by simulation.Based on the theoretical analysis,a prototype of a 33.6W AC-DC converter has been built and tested.The experimental results show that the proposed input admittance adjustment strategy of the Buck/Boost PCC can effectively reduce the low-frequency output current ripple of the AC-DC converter and provide a flat drive current for the load...