Research On Control Of Dual Active Full-bridge Bidirectional DC/DC Converter

With the widespread application and rapid development of distributed power generation,energy storage and electric vehicles,higher requirements for conversion efficiency and power density of the converter are put forward in the context of the continuous popularization of power conversion systems.The high-frequency link power conversion system represented by bi-directional full-bridge DC/DC converter(Dual Active Bridge,DAB)has high conversion efficiency,high power density,low voltage and current stress on power devices,simple structure and is easy to realize soft switch and to integrate,so it has wide application prospects.The control strategy is one of the important research directions of DAB converter.In this paper,a deep research is carried out to provide a theoretical basis for the converter engineering design.The development history,research significance and hot research directions of DAB converter,especially the research status of DAB model and control are reviewed in detail.Through in-depth study of DAB three control strategies: single phase shift(SPS),extended phase shift(EPS)and dual phase shift(DPS).The principles,working modes and power characteristics of these three strategies are analyzed,which lays a base for the later modeling and optimization strategies of the control system.Based on the small signal model,the mechanism of current stress and reflux power is analyzed by studying the double closed-loop control strategy of voltage and current.In order to improve the efficiency,the multi-objective optimization analysis of current stress and reflux power is carried out by using the optimization function of fmincon in MATLAB,and an improved optimization control strategy is proposed.For the typical application of DAB converter,the design goal of main circuit hardware parameters is proposed and completed.Based on the simulation model,the current stress,reflux power and soft switching(ZVS)characteristics of EPS and DSP are analyzed,and the effectiveness of the proposed optimal control strategy is verified.Combing the control requirements,a high-speed digital control system based onDSP + FPGA core control chip architecture is designed,and the overall design scheme and detailed design are completed.In the aspect of hardware design,the design of control core chip,sampling circuit and protection circuit are completed.In the aspect of software design,initialization program,main cycle program,operation control program and fault classification protection mechanism are fulfilled.