Research On Isolated Three-Phase Single Stage SEPIC PFC Converter

In order to suppress power grid harmonics and develop green power electronic technology,people are concerned about the continuous improvement of power factor correction converter topology and the continuous innovation of control methods.However,the three-phase rectifier is usually composed of two stages of circuits in actual use.The front stage implements power factor correction,and the latter implements electrical isolation and output voltage regulation.This method uses many devices,requires many voltage and current sensors to detect the controlled quantity,and the control is complicated,which reduces the reliability of the system.Therefore,based on the single-stage,isolation,simple control and strong reliability,this paper studies two isolated three-phase single-stage SEPIC PFC converters.First,the Direct Three-Phase Systems and the Phase-Modular Systems three-phase rectifier topology classification methods are introduced.And from these two perspectives,the direct bidirectional switch-type three-phase single-stage SEPIC PFC converter and the phase-module three-phase single-stage bridgeless SEPIC PFC converter have been studied.Both work in discontinuous conduction mode.Besides,the working principle and output characteristics are analyzed,the critical discrimination conditions are discussed,and the specific parameter design method is given.And from the aspects of output power and circuit stress,the advantages and disadvantages of two three-phase single-stage SEPIC PFC converters and their applicable occasions are compared and analyzed.Secondly,in view of the problem that the converter has many operating modes in the discontinuous mode,which is not conducive to the establishment of a small signal model by the traditional state space averaging method,taking the phase module three-phase single-stage bridgeless SEPIC PFC converter as an example,the current injection equivalent circuit method is used to model the small signal of the main circuit,and on this basis,the compensator of the voltage control loop is designed.According to the design results,the stability of the system is analyzed and verified in the frequency and time domains.The simulation results show that power factor correction and output voltage adjustment can be achieved by single voltage loop control.The circuit control is simple and the reliability is strong.Rectified power factor is high.Finally,in order to verify the correctness of the theoretical analysis,the system main circuit,overcurrent protection circuit and drive circuit design and device selection were completed.Made the simplest control system based on TMS320F28335 to output PWM pulse.The experimental results show that this converter can achieve the input current to follow the input voltage well by simple control,the power factor is high,and the THD is small.The correctness of the theoretical analysis and the rationality of the parameter design are verified,and the feasibility and superiority of this scheme for three-phase power factor correction under small and medium power is also proved.