Research On High Performance Control Technology Of Three-port Isolated Bidirectional DC-DC Converter

Multi-port isolated bidirectional DC-DC converters have attracted more and more research and attention due to their flexible energy management,mutual isolation of ports,low cost,high power density and high efficiency.There are many topologies in multi-port isolated bidirectional DC-DC converters,the most common is multiple active bridges DC-DC converters,which is isolated by multiple H full bridges and common magnetic multi-winding high-frequency isolation.There are two difficulties in applying it to the DC microgrid: 1)The power of each port of the converter is coupled,and the power of the distributed power supply is usually intermittent and random,the power disturbance of the port will cause the power fluctuation of other ports,which affects the normal work of the sensitive load connected to the converter;2)The energy storage device connected to the multi-port isolated bidirectional DC-DC converter will cause the voltage fluctuation of the DC port of the converter,resulting in the voltage ratio of the DC port and the voltage ratio of the high-frequency transformer mismatched,the high-frequency transformer current rises,and the converter efficiency decreases.Therefore,in order to ensure the high efficiency of the multi-port isolated bidirectional DC-DC converter and the high power quality and reliability of the DC microgrid,it is necessary to design a decoupling control strategy and optimize efficiency for the multiport isolated bidirectional DC-DC converter.To this end,this paper takes the Triple Active Bridge(TAB)isolated bidirectional DC-DC converter as the research object,proposes model predictive control to improve the power coupling problem,and for the problem of increased loss,a multiple phase shift modulation strategy is adopted to optimize,and then a model predictive control strategy based on triple phase shift is proposed.The loss is optimized while solving the problem of port power coupling.The specific research content of this paper is as follows:1)Aiming at the problem of power coupling between ports,a model predictive control strategy is proposed.Firstly,the discretized average value model of the TAB converter is established,and then the method of establishing the multi-target predictive model of the TAB converter is studied,the MPC problem is designed and the numerical optimal solution is calculated,and the predictive controller is optimized by combining the parameter sensitivity of the predictive model.Finally,an experimental prototype of the TAB converter was built to verify the proposed control method.2)In order to solve the problem of reduced TAB converter efficiency caused by port voltage fluctuations,an efficiency optimization strategy based on multiple phaseshifting modulation is proposed.First,the Fourier series model and loss model of the TAB converter under multiple phase-shift modulation are established,and then the loss optimization problem is designed and the zero voltage switching(Zero Voltage Switching,ZVS)condition is analyzed.Then numerical optimal solution of the loss optimization problem is solved and control strategy is designed.Finally,MATLAB /Simulink is used for simulation to verify the feasibility of the proposed control strategy.3)In order to simultaneously solve the problem of power coupling between ports and the problem of increased loss,a model predictive control strategy based on triple phase shift is proposed.First,based on the triple phase-shifting modulation that introduces additional phase shift within the bridge at the energy storage port corresponding to the H full bridge,the TAB converter loss optimization problem is established and the numerical optimal solution is obtained.In addition,based on triple phase-shifting modulation,a discrete average model and a prediction model are established,and then the MPC problem is designed and the numerical optimal solution is solved.Combining the solution of loss optimization problem and MPC problem,optimized predictive controller is designed for TAB converter.Finally,MATLAB /Simulink is used to verify the proposed strategy.