Research On Sorting And Grouping For Second-use Of Retired Battery Modules

Compared with the retired packs and cells,taking the battery module as the object can not only reduce the difficulty of battery pack splitting,but also improve the utilization rate of retired power battery,which has obvious advantages.The dissertation focuses on the retired power battery modules,and conducts research and analysis on the consistent sorting and grouping problems in their second-using,mainly including the following three aspects:(1)A sorting method combining multi-parameter sorting method and dynamic voltage characteristic sorting method was proposed,which comprehensively considered both the internal and external characteristics of the battery,and was a consistent sorting method for retired battery modules.First,considering the battery Rint equivalent circuit and heat accumulation,Coulomb efficiency,capacity attenuation,internal resistance growth and other factors,a cell model and module model of multi-dimensional parameters were constructed,and the relationship between the multiple factors that affect the consistency of the battery module were analyzed.Secondly,based on the principle of curve similarity,the consistency description index between any two dynamic voltage curves was established.Thirdly,a series module simulation model was built in the MATLAB/Simulink,and the variation characteristics of the consistency description index between the voltage curves under the separate action of each consistency influencing factor were analyzed,realizing the organic combination between "multi-factor" and "Voltage curve".Fourthly,experiments were designed to verify the above simulation methods and conclusions.Then,based on the results and conclusions of the simulation,a comprehensive evaluation index of the consistency in the modules and between the modules were proposed,which comprehensively considered the internal and external characteristics of the battery.Finally,a consistent sorting method for retired battery modules was designed,and the correctness and effectiveness of the sorting method were verified through experiments.(2)For the sorted battery modules with good consistency between modules and within modules,considering the change of connection topology,the influence of cell parameters(the cell mentioned in this paragraph was equivalent to the module with good consistency after sorting)on the capacity of large-scale series parallel recombination battery system was studied under the premise of ensuring the safety and reliability of battery system.First of all,different series and parallel combinations of cells were carried out to form large-scale battery systems with different topology.Secondly,based on the cell model constructed in the second chapter,the models of battery systems with different topology were established,and the main parameters affecting the capacity of the battery system were analyzed.Thirdly,the battery system models with different topology were built with MATLAB,and the influence of different cell parameters on the battery system capacity was studied.Fourthly,from a statistical point of view,the principle of the simulation results and conclusions was analyzed.Then,the battery systems with different topology were built in the laboratory,and the correctness and effectiveness of the simulation results and conclusions were verified by orthogonal experiments.Finally,referring to the existing standards,the fault tree of large-scale series parallel battery system was constructed,and the fault tree was qualitatively studied by using the minimum cut set theory,and the fault tree was quantitatively studied by using the analytic hierarchy process(AHP).Combining the two methods,the weak link of the safety of the battery system was determined.(3)For the sorted battery modules with good consistency within the modules but poor consistency between the modules,a flexible grouping study was carried out.First of all,the battery module power unit(BMPU)was constructed,and the flexible grouping scheme was determined based on the series parallel grouping method.Secondly,a comparison was made between series parallel and flexible grouping.Then,a recursive fuzzy control was proposed to achieve power allocation between BMPUs.What is more,for the determined flexible grouping scheme,a differential power control strategy based on feedback linearization backstepping control was proposed,which can respond to the assigned power command reliably and maintain the DC bus voltage stability.Finally,based on the NI real-time simulation platform,real-time simulation experiments were carried out to verify the strategies mentioned above.