Switching Strategy Optimization Of Phase Shift Control For Dual Active Bridge DC-DC Converter

In order to meet the demand of voltage conversion,bidirectional energy transmission and electrical isolation in high voltage ratio and high power applications of electric vehicles,the research of isolated bidirectional DC-DC converter has attracted extensive attention.At present,there are two technical difficulties restricting its further development,namely,low charging efficiency and short battery life.The current stress of the converter determines the loss of the switching device in the process of on and off,which is an important factor affecting the charging efficiency,and the current impact can shorten the battery life.Therefore,reducing the current stress and power loss,improving the capacity and efficiency are the key problems to be solved in the research of isolated bidirectional DC-DC converter.This project focuses on the problem of reducing current stress and switching loss in the research of isolated bidirectional DC-DC converter from two aspects of theoretical research and system design.By studying the working process and mathematical model of isolated bidirectional DC-DC converter with dual active bridge structure,the optimization of control strategy and zero voltage switching is achieved based on the traditional phase-shift control method.The main contents of this project are as follows:（1）The working process of isolated bidirectional DC-DC converter with dual active bridge structure under phase-shift control is analyzed,and the model of its working characteristics is established.Then,the method of achieving zero voltage switching with this structure is studied,and a solution of soft switch based on LC series resonance is designed.（2）By summarizing and analyzing various operation modes of dual active bridge DC-DC converter with dual phase shift control in global conditions,the relationship between transmission power and current stress and phase-shift ratio,voltage conversion ratio is obtained,and their mathematical models are established.Based on this,the Lagrange multiplier method is used to solve the optimal phase-shift ratio combination of current stress in each mode,and the rules of determining the operation mode of the converter by voltage conversion ratio and transmission power are derived,so as to propose a phase-shift control model with global optimization of current stress and a strategy to eliminate the transient DC bias of inductor current.（3）According to the parameter demands of the dual active bridge DC-DC converter in this project,the hardware and software implementation of the converter system is studied by model based design method.（4）Through software simulation,the design scheme of the dual active bridge converter and the optimized phase-shift control strategy are verified,and the experimental platform is built to test dynamic and static performance of the converter in different working conditions.The experimental results show that,compared with the traditional method,the control method used in this project can effectively reduce the inductor current stress and switching loss,improve the conversion efficiency,and eliminate the DC bias on the inductor current in the transient process when the abrupt change of transmission power occurs.Meanwhile,all the specifications of the dual active bridge converter meet the demands.