Research On A Novel Wide Range Input Quasi-resonant Forward-flyback DC-DC Converter

With the development of technology.Today's society puts higher demands on the performance of power supplies in industrial systems such as aerospace,communications systems,mining and machinery.At present,distributed power systems account for a large proportion of the power supply system.Miniaturization,standardization,and modularization are the development trends of distributed system power supplies.The research content of this paper is a wide-range input quasi-resonant positive flyback DC-DC converter applied to the rear stage of distributed power system.Firstly,this paper derives a wide-range quasi-resonant forward-flyback DC-DC circuit topology based on forward circuits and flyback circuits.The topology forward circuit and the flyback circuit share a primary winding.Power transfer using forward circuits,and the flyback winding connected in series to the primary side of the transformer acts as a magnetic reset and voltage regulator.Designing a resonant network on the secondary side of the forward circuit,resonant inductance is realized by transformer leakage inductance.Implement ZCS of the forward diode to reduce converter losses without additional devices.Secondly,the modal operation of wide-range input quasi-resonant forward-flyback converters in CCM mode,CRM mode and DCM mode is analyzed.Derivate the relationship between its input and output,and further explore its characteristics.Among them,this paper mainly analyzes the wide range input characteristics of the converter and the opening of the bottom of the switch.Based on the analysis,a PWM-COT hybrid control strategy is proposed to secure a fully-resonant operation of the converter,which improves the efficiency and enhances the robustness.Specifically,it is a hybrid control method that specifies a frequency adjustment duty ratio and a constant conduction time adjustment frequency.The simulation model of wide-range input quasi-resonant forward-flyback converter is built by using PLECS simulation software,and the feasibility of the topology is verified theoretically.Finally,according to the characteristics of the converter,this paper designs the transformer and analyzes the voltage stress of the switch.The design scheme of the main circuit and the control circuit is given,and the prototype of the 360V~440VDC input and the 48VDC/300 W output is built.Experimental verification of theoretical analysis.