| As the energy source of micro grid energy storage system,multi cell series connected into high-voltage energy storage battery system is generally used to meet the voltage and power requirements of energy storage system.But many battery modules are used in series,SOC,equalization,protection and other control strategies are complex,the calculation error is large,the failure rate is high,any battery module failure will lead to the failure of the whole energy storage battery system.As the core device of micro grid energy storage system,bidirectional DC / DC converter requires more and more cost,power density and efficiency.To design a bidirectional DC / DC converter with low cost,high power density and efficiency,which meets the requirements of energy storage system,has beco me the key research direction of energy storage system enterprises.The main task of this dissertation is to propose an improved energy storage battery scheme by analyzing the shortcomings of the existing high-voltage energy storage battery system and the voltage rise and fall characteristics of the bidirectional DC / DC converter.At the same time,through the theoretical analysis,simulation verification and parameter design of the bidirectional DC / DC converter,a bidirectional DC / DC converter suitable for the energy storage system is developed and obtained in the actual energy storage system application.This dissertation analyzes the structure,working mode and the characteristics of lithium-ion battery in micro grid DC energy storage system,and des igns the energy storage battery and bi-directional DC / DC converter.The equivalent circuit models of Buck / Boost converter and full bridge LLC resonant converter are established.The working principle and the main waveforms of each working mode are analyzed,and the basic characteristics of LLC resonant converter are studied.The simulation circuit model of Buck / Boost + full bridge LLC resonant bidirectional DC / DC converter is established by using Matlab / Simulink software,and the simulation analysis of the system is carried out.The main circuit parameters of Buck / Boost + full bridge LLC resonant bidirectional DC / DC converter are designed,and the loss analysis and efficiency calculation are carried out.According to the conditions of realizin g soft switching when Buck / Boost converter + LLC resonant converter works in different load,the resonant parameters of the resonant cavity are optimized to ensure that the soft switch presents the characteristics of DC transformer at the same time.The efficiency of the converter is obtained by analyzing and calculating the loss of each part in the forward and reverse operation,which provides the theoretical basis for the efficiency verification experiment.Finally,the energy storage battery system is verified by simulation experiments,and the experimental prototype is designed and manufactured.The simulation results show that the system does not need multiple battery modules in series,and the equalization control strategy is simple and has good equ alization effect.The experimental results show that the Buck / Boost + full bridge LLC resonant bidirectional DC / DC converter has good performance and efficiency. |
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