Research On SOC Estimation And Active Equalization Of Lithium Battery

In the context of the energy crisis,lithium batteries have become the main power source of electric vehicles.Because the state of charge(SOC)of lithium batteries cannot be measured,it needs to be estimated by corresponding methods,and accurate estimation of SOC is a necessary measure to extend the service life of the battery and help extend the driving range of the car;Lithium battery due to the inherent characteristics of the material,production process,storage process,use process will produce internal resistance,capacity,voltage and SOC inconsistency between the monomer,in addition to improving the production process,storage environment and other conditions,the use of charge and discharge to balance the lithium battery is a feasible method,this method can improve the capacity utilization rate of the battery pack to extend the driving range of electric vehicles.In this paper,a mathematical model of SOC estimation is established for the estimation of the state of charge of lithium batteries,and the SOC estimation is carried out through parameter identification and algorithm,and the experimental verification under working conditions is carried out.For lithium battery equilibrium,the charge-discharge equilibrium research is focused on the analysis of the causes,manifestations and improvement methods of lithium battery inconsistency.The equalization circuit,equilibrium principle and control strategy of "first series and then parallel " and "first series and then string" are designed,and the hierarchical control strategy between battery cells and battery modules is adopted.Use MATLAB/Simulink software to build simulation experimental models for simulation experiments and verification,the specific content:Firstly,the research status of SOC estimation at home and abroad,the research status of active equilibrium technology at home and abroad,and the research status of equilibrium control algorithm at home and abroad are introduced.Secondly,the working principle and SOC definition of lithium battery are summarized,the equivalent model and equivalent circuit model of the battery are analyzed,and the second-order RC equivalent circuit model that is easy to implement in engineering practice is selected to achieve parameter identification by taking Beijing Guoneng PL15181210 power battery as the research object.SOC estimation is achieved using the extended Kalman filter algorithm.Thirdly,an 8-meter pure electric city bus power system is designed,and the experimental model of working conditions is established by combining the model built in Chapter 2 with the vehicle power system,and the influence of the ampere-hour integral method and the extended Kalman filter algorithm on the accuracy of SOC estimation is compared and analyzed under the simulation experiment under the working conditions of Chinese urban buses(CHTC-B).Fourth,the generation,manifestation and improvement methods of lithium battery inconsistency are analyzed,focusing on the equalization circuit design,equilibrium method and equilibrium topology analysis for charge and discharge balance.Fifth,the SOC of the battery is used as the equilibrium variable,the equilibrium threshold is triggered as the equilibrium starting condition,the bottom layer adopts the "difference-average" control strategy,the top module adopts the switch array equalization control strategy to build a simulation model,combined with the 8-meter pure electric city bus power system,and carries out simulation experiments under CHTC-B conditions.Experimental results show that the hierarchical control strategy can improve the rate and efficiency of equalization in the equalization of battery series-parallel modules.Finally,the research shortcomings and the prospects of follow-up work are summarized.