Research On Single Phase Bridgeless PFC Converter With Wide Output Voltage Range

The active Power Factor Correction(PFC)circuit is required for a single-phase AC/DC converter to reduce the harmonics of the grid-side current.However,most PFC circuits are boost output circuits,which cannot be applied to increasing loads that require a wide range of output voltages.This thesis focuses on the study of bridgeless PFC converters with wide output voltage ranges.This research has both theoretical significance and practical value in engineering.In order to understand the working principle of the bidirectional switching bridgeless PFC circuit,the working modes of the circuit are firstly analyzed.On this basis,in order to design the control parameters of the circuit,the small-signal modeling analysis of the circuit is carried out,and the control parameters for the current inner-loop Proportional Resonant(PR)controller and the voltage outer-loop Proportional Integral(PI)controllers are designed according to the transfer function obtained from the modeling.The bidirectional switching bridgeless PFC circuit is simulated by MATLAB/Simulink.Based on this,a 3k W testing prototype is designed and built.The simulation and prototype experiments verify the effectiveness of the dual closed-loop control parameters used in the circuit.Regarding the problem that the bidirectional switching bridgeless PFC circuit cannot realize the buck-boost output,a buck path and a voltage-stabilizing path are added in the circuit to form a bridgeless PFC converter with a wide range of output voltage,which is achieved by switching the boost path and the buck path for buck-boost output.In this thesis,the specific working mode of the circuit is firstly analyzed.Considering that the output voltage of the circuit changes in a wide range,the amplitudes of the boost carrier and the buck carrier should also vary,thus a variable carrier modulation method is proposed.The variable-carrier modulation dynamically adjusts the proportional distribution of the boost carrier and the buck carrier so that it changes with the output voltage amplitude.This method further reduces the Total Harmonic Distortion(THD)value of the grid-side current.Both the buck-boost path and the voltage-stable path of the circuit adopt a dual closed-loop control strategy.The simulation is carried out through MATLAB/Simulink,and a 3k W prototype is built.The simulation and experiment verify the feasibility of the circuit’s buck-boost output function.At the same time,it is verified that the variable carrier modulation method can reduce the THD value of the input current.The single-phase PFC converter has the problem that the double-frequency power fluctuation leads to a too large capacitance of the DC side.Large-capacity capacitors will reduce the power density of the device.In addition,electrolytic capacitors are generally considered when selecting large-capacity capacitors,and the life and stability of electrolytic capacitors will affect the performance of the device.Therefore,the method of double-frequency power decoupling is adopted in this thesis to transfer the doublefrequency pulsating power of the DC side capacitor to the decoupling capacitor,which reduces the capacitance value of the DC side capacitor.A bidirectional buck-boost circuit is used as the decoupling circuit,and a specific double-frequency power decoupling control strategy is designed based on the circuit’s double-frequency power analysis.Finally,the feasibility of the double frequency power decoupling strategy is proved by MATLAB/Simulink simulation and prototype experiments.