Research On Series-Parallel Type Modular DAB Converter

Dual Active Bridge(DAB)converter is widely used in DC microgrid and electric vehicle charging system and etc,due to its advantages of high power density,bidirectional power flow and electrical isolation,which is the main research object of high power bi-directional DC-DC converter.Therefore,this thesis takes the DAB converter and its modular structure as the research object,and deeply investigates its working principle,power transfer characteristics,inductor current working characteristics,and optimizes the power loss.For the multi-module DAB converter composed with the structure of input-series output-parallel(ISOP)method,an optimal control method that also considers power balance is proposed.This thesis first analyzes the operating principle and its operating characteristics under the conventional single phase shift modulation,and points out that the transmission efficiency of DAB converter under the conventional control method is low when the voltage transmission ratio is not matched.To address this situation,this thesis divides the multiple operating modes of DAB converter based on triple-phase-shift control,and an optimization equation with the optimal current RMS value as the target is discussed.According to the proposed optimal control method,the duality of the buck and boost modes is analyzed and the closed-loop control design for the optimal control of the DAB converter triple-phase-shift is carried out,and finally the simulation platform is built for verification.In high power applications,ISOP-DAB system is usually used to achieve high voltage input and high current output,and the modular system will lead to power unbalance of each module due to parameter differences.To solve the above problem,this thesis analyzes the stability of the dual-loop control and chooses to control the input voltage of each module to achieve power balance.The input-output coupling phenomenon is explained by analyzing the mathematical model of the ISOP-DAB system,while the decoupling control under optimal RMS current is proposed.In addition,the advantages of interleaved control and the current ripple cancellation effects under modular structure are explained,and finally the feasibility of this control method is verified by simulation.Finally,a two-module DAB converter prototype is built,which uses a field programmable gate array(FPGA)to implement triple-phase-shift optimal control.Using this platform,the optimal current RMS control of the DAB converter under different voltage transfer ratios is firstly verified,and the efficiency is achieved under different power.Then,the experimental validation of the two-module ISOP-DAB converter is carried out for the control of voltage balance and the inductor current RMS optimization.Furthermore,the corresponding experimental results are given,and the effectiveness of the dual-loop decoupling control under triple-phase-shift optimization proposed in this thesis is verified.