Research On Single-stage Full-Bridge PFC Bias And Output Voltage Ripple Suppression Strategy

APFC technology plays an important role in suppressing grid-side harmonic pollution and improving energy conversion efficiency,and has become a current research hotspot.The single-stage full-bridge PFC converter combines the advantages of APFC technology and full-bridge DC-DC topology.It has the advantages of fewer switching devices,high power density,no pass-through problems with bridge arm switches,and high efficiency.It is good in medium and high power applications.Application prospects.However,in engineering applications of this converter,there are problems such as transformer bias and large output voltage low-frequency ripple,which greatly affects the performance of the converter.Therefore,it is necessary to conduct an in-depth analysis of the above-mentioned problems and propose corresponding solutions.In the single-stage full-bridge PFC topology,the transformer has a unique magnetic bias problem during high-frequency operation,which affects the safe and reliable operation of the converter.The thesis first briefly analyzes the topological structure of the single-stage full-bridge PFC converter and its control strategy.Then,based on the detailed analysis of the transformer’s working status and the mechanism of the bias generation,a digital bias suppression strategy with positive and negative half-cycle symmetry is proposed.This strategy uses a digital processor to make the positive and negative excitation time of the transformer’s magnetizing inductance equal in each high-frequency switching cycle,and then balances the positive and negative volt-second products of the magnetizing inductance,effectively suppressing the transformer’s demagnetization.This strategy has the advantages of easy implementation,no additional devices,and no influence on the PFC effect.There is an instantaneous power difference between the AC input power and the DC output power of the single-stage full-bridge PFC converter,which causes the inevitable double power frequency voltage ripple to be generated on the PFC output side,and the converter output performance is poor.Analyzed the mechanism of single-stage PFC converter output voltage double frequency ripple generation mechanism,and proposed a method of output voltage ripple suppression based on parallel compensation circuit.The bidirectional Buck-Boost converter was connected in parallel to the PFC output side to absorb AC ripple power,and then Suppress voltage ripple.The principle of ripple absorption of the bidirectional converter is analyzed in detail,and the design method of the absorption capacitor and inductance in the circuit is given.At the same time,a double-frequency current extraction scheme based on a digital band-pass filter is proposed.Although the parallel compensation circuit has a relatively obvious ripple suppression effect,there is still a certain ripple component on the PFC output side.In order to achieve a better ripple suppression effect,an improved suppression strategy for output voltage ripple based on virtual admittance adjustment is proposed.Firstly,a double closed-loop model of the bidirectional Buck-Boost converter is established and its closed-loop input admittance transfer function is obtained.The relationship between the closed-loop input admittance of the bidirectional converter and the PFC output voltage ripple is analyzed.By adding a voltage feedforward link in the bidirectional converter control circuit,and then introducing virtual admittance,the gain of the bidirectional converter’s closed-loop input admittance at twice the power frequency is increased,and a better ripple suppression effect is achieved.Finally,based on theoretical analysis and simulation verification,an experimental platform for a single-stage full-bridge PFC converter and its digital control system was built,and related experiments were carried out to verify the correctness of all the schemes in this paper.