Research On Charging Strategy And Monitoring System Design Of Lithium-ion Battery For Electric Vehicle

With the intensification of the energy crisis and the increasing destruction of the ecological environment,new energy veh icles,especially electric vehicles,have gradually been favored because they use clean energy to cause less environmental pollution.Batteries are the most important component of electric vehicles,but their batteries usually have a long charging time and poor charging safety.As a result,lithium-ion battery charging-related technologies that restrict the development of the electric vehicle industry have received widespread attention.The thesis researches the charging strategy of lithium-ion batteries and designs a battery charging status monitoring system.First,the lithium battery was tested for battery characteristics.At the same time,a second-order RC equivalent circuit model was established and the parameters were identified based on the model.Th en,a multi-objective optimization function for multi-stage constant current charging was constructed,and the particle swarm algorithm was applied to solve the problem,and the optimal charging combination obtained by simulation was compared and verified by experiments.Finally,the SOC estimation algorithm of the battery condition monitoring system was simulated.At the same time,the software and hardware design of the system based on the virtual instrument technology and the designed monitoring system w ere performed.At last,debugging was performed.This article has carried out a series of work on lithium-ion battery chargingrelated technologies,and the results achieved are mainly reflected in:1.Established the battery equivalent circuit modelFirst,an electrochemical workstation was used to build a battery test system for OCV-SOC testing and HPPC experiments on 18650 lithium batteries.Then,a second-order RC equivalent circuit model of the lithium-ion battery was built,and the mathematical expressions of the model states were derived.HPPC charge-discharge experimental data was used to carry out parameter identification using the curve fitting toolbox provided by MATLAB to obtain the battery model parameters under different SOC.2.Found the best charging strategy for lithium batteriesFirstly,based on the second-order RC equivalent circuit model,a lithium battery energy consumption model and a multi-stage constant-current charging simulation model are established.Then,the current value of ea ch stage is an optimization object for multi-stage constant-current charging.The charging time,charging capacity,and charging energy efficiency are selected as optimal objective to construct the objective function,and use particle swarm algorithm to pe rform simulation and optimization to find the optimal charging combination of the multi-stage constant current charging strategy.Finally,compare the simulated charging curve with the actual charging curve to verify the accuracy of the battery model.The comparison between the best charging mode and the traditional constant current and constant voltage charging mode demonstrates the effectiveness of this strategy.3.Designed a lithium battery condition monitoring systemFirst,the hardware design of the s ystem was performed,and data acquisition was performed using the NI Crio 9036 and NI 9215 data acquisition cards.Then,the improved SOC estimation and extended Kalman filter algorithm simulation was performed to ensure that the program can be applied to the monitoring system.Then the software design of the system was carried out.The data acquisition program was written as the lower computer.At the same time,the waveform display,data storage,SOC estimation and other programs were written as the upper computer.Finally,the system was debugged and operated.The results show that the system can not only control the voltage and current.Temperature and other actual measurements can be used for on-line monitoring and data storage.At the same time,the ba ttery SOC can be accurately estimated.