Design Of A Novel Two Stage APEF Converter With Soft Switching For Applications Of High Output Voltage

Active power factor correction(APFC)converter is mainly used to solve the problem of the harmonic current injected to the grid which is caused by uncontrolled rectification.In recent research,the main discussion about the traditional Boost PFC converter has been focused on the problem of high THD under the condition of high output voltage when the instantaneous input voltage is around zero.Different control algorithms with powerful digital signal processors are proposed to solve the problem.To step up the output voltage again,a DC-DC converter is designed to connect the PFC converter for applications of high output voltage.Limited by the real duty cycle of the power switches and the dielectric strength of the components in the single DC-DC converter module,it's difficult to realize the high isolated output voltage.This paper makes improvement on the traditional Boost PFC converter by adding an auxiliary resonant circuit to get a resonant operation mode.The new converter is called “Tandem Converter”,which means the resonant circuit is connected after the Boost inductor.When the instantaneous input voltage is low,the PFC converter works in the resonant mode.By keeping the current of the main inductor continues,the THD of the current is reduced.Furthermore,the value of the main inductor can be decreased to reduce the size and cost.The other function of the resonant circuit is to realize the soft-switching of the power MOSFETS,so the switching loss is decreased to reduce the volume of the heat size.All in all,the power density is increased and the power efficiency is ensured.To obtain an isolated high output voltage,in the second stage,an input parallel output series multi-module full-bridge DC-DC converter isdesigned after the PFC stage to step up the output voltage once again.The ring communication structure is applied in the laboratory prototype of modularized DC-DC converter to reduce the cost of the communication.The control system is optimized by using small signal model to analyze the whole control system and the wide control bandwidth is obtained.This paper first analyzes the novel PFC stage in details,and then designs the ring communication structure to apply in the DC-DC conversion system.The influence on the voltage control bandwidth by the communication delay is analyzed in detail to optimize the IPOS control system.The parameters of the converters of the two stages are designed.Finally the converter is tested in a laboratory prototype of which the controller is UCD3138.By MATLAB simulation and experiment results,the feasibility and validity of such an APFC converter design is proved.