Research On Control Strategy Of Dual Half Bridge DC-DC Resonant Converter

Renewable energy generation has become an important research point due to the wide application of new clean energy.In the renewable energy generation system,unidirectional DC-DC converter determines the voltage level of output DC bus,which affects the efficiency and stability of the power generation system.Bidirectional DC-DC converter determines the compensation ability of the energy storage system,which affects the bidirectional operation of the power generation system.However,current research on topologies and control strategies of both unidirectional and bidirectional DC-DC converters is difficult to meet requirements such as high-power density,low loss,and high efficiency.To solve this problem,a dual half bridge resonant converter(DHBRC)topology is proposed.According to the requirements of unidirectional and bidirectional operation in the renewable energy generation systems,unidirectional and bidirectional DHBRC are studied,respectively.Inner-phase-shift control strategy is adopted in the unidirectional DHBRC.Dual-phase-shift control strategy is adopted in the bidirectional DHBRC.Both of them can achieve full ranges soft-switching operation.Additionally,Minimum Current Trajectory(MCT)optimization method is used in the bidirectional DHBRC to reduce conduction loss and improve operation efficiency.In this thesis,the development of topology structures,control strategies,and modeling methods of isolated DC-DC converter is introduced and the existing problems in the current research are presented,such as complex topology structures and high loss.For the unidirectional DHBRC,the operation characteristics,steady-state models,and zero voltage switching(ZVS)operating range are analyzed in detail.After that,parameters of the unidirectional DHBRC are designed.The feasibility of the converter is verified through simulation.Then,experimental prototype of the unidirectional DHBRC is built and tested.Experimental results verified the theoretical analysis successfully.For the bidirectional DHBRC,the operation characteristics,steady-state models,ZVS operating range,and MCT optimization method are analyzed in detail.MCT optimization method is adopted to ensure synchronous rectification of secondary side.Since synchronous rectification is realized,backflow power is eliminated completely and current stress on resonant tank is reduced.Finally,parameters of the bidirectional DHBRC are selected and designed.It can be found in the simulation and experimental test that the bidirectional DHBRC achieves soft-switching operation under light load and its efficiency is greatly improved.