Research On Four-phase Interleaved DCM Boost PFC Converter

The proportion of non-linear load in power system load is increasing,such as various rectifiers and frequency converters in household appliances and electric locomotives in railway system,etc.These non-linear loads will lead to grid side current distortion and bring harmonic pollution to power system.Active power factor correction(APFC)can effectively solve the problem of current harmonics,improving the power factor(PF)of the apparatus and reducing the total harmonic distortion(THD)of current.In APFC,the traditional bridge Boost PFC converter has AC input inductor,and the input current will not change abruptly,which can effectively suppress the high frequency harmonics of the input current.This paper introduces the Boost power factor correction topology and its common control methods and expounds the research significance and main content.To analyze the working principle of four-phase interleaved Boost converter,continuous conduction mode(CCM)and discontinuous conduction mode(DCM)time-averaged equivalent circuit model is built and DC steady state analysis is applied.The influence of inductor parameters,including inductance and equivalent series resistance,on the current distribution between phases is demonstrated and the advantages of DCM in four-phase interleaved is revealed.The increase of the input voltage causes the reduction of PF of constant duty cycle controlled Boost PFC converter,and the input current is severely distorted.The principle of four-phase interleaved DCM Boost PFC converter with constant duty cycle control is studied and the factors affecting the input current distortion and PF are analyzed.In order to improve the PF,variable duty cycle control is studied.Compared with the constant duty cycle control,variable duty cycle control can reduce the peak value of inductor current and the ripple of output voltage,but it has poor transient response performance.In order to improve the transient response performance of variable duty cycle control,an improved variable duty cycle control strategy is studied in this paper.The theoretical and simulation results show that the improved variable duty cycle control has unity power factor characteristics and fast transient response performance.The digital control implementation method of improved variable duty cycle control is studied in this paper.In order to design a suitable digital compensator,the control-output transfer function of the improved variable duty cycle controlled four-phase interleaved DCM Boost PFC converter is deduced,the loop compensation is completed in the s domain and the difference equation of the compensator is obtained by discretization.Because of the square root operation is in the improved variable duty cycle control and the square root operation of the digital controller is slowly,a fast algorithm for square root is studied in this paper.Finally,by parameter calculation and component selection,the experimental prototype of 1kW four-phase interleaved DCM Boost PFC converter is designed.The experimental results show that the improved variable duty cycle control realizes the unit power factor and obtains fast input response and load response performance.