Research On Charging Model And Strategy Of Power Lithium Battery At Low Temperature

In response to the call for carbon peaking and carbon neutrality,the new energy industry has received more and more attention.As one of the representative industries of the new energy industry,new energy vehicles have developed rapidly in recent years.More and more technology companies are deploying in the new energy vehicle market.The performance of new energy vehicles is mainly affected by the power battery system.As an electrochemical battery,power lithium batteries are strongly affected by temperature,the performance degrades significantly in low temperature environments.In order to improve the recognition of new energy vehicles by consumers in colder areas in winter,it is particularly important to solve the problem that the power battery system is difficult to charge in low temperature environment.Firstly,various types of power batteries are introduced.Starting from the internal structure,the working principles of different types of power batteries are analyzed,and the advantages and disadvantages are compared.Based on this,the reasons why lithium-ion batteries have become the mainstream power batteries are explained;By analyzing the structural characteristics and working mechanism of lithium-ion batteries,the reasons for the performance degradation of lithium-ion batteries at low temperatures are explained;in order to study the charging and discharging characteristics of lithium-ion batteries,it is necessary to model them.Compared with the effective current model,an improved method is proposed to pave the way for the low-temperature charging model proposed below;the difference and voltage variation characteristics of the battery cell and battery system charging methods are pointed out,and the theoretical basis for the low-temperature charging strategy proposed below.The lithium iron phosphate battery was selected as the sample to carry out experimental tests under normal and low temperature environments,and the voltage change curve of the lithium-ion charging terminal was obtained.Besides,several equivalent circuit models commonly used at present are simulated in the matlab/simulink software,the obtained simulation curve is compared with the actual terminal voltage curve,and it is found that it does not match the charging curve of the low temperature environment,the lack of the process of the terminal voltage rising to the maximum point will seriously affect the evaluation of the safety of the battery working state.In order to obtain an accurate low temperature model,through the analysis of the principle of the second-order RC equivalent circuit model,an improvement is made on the basis of it,and a new method is proposed.Equivalent circuit model suitable for low temperature environment,and simplified parameter identification was carried out to obtain the parameters of each component in the model.After simulation analysis,it was verified that the terminal voltage curve of this model had the same trend as the actual curve.Finally,since the addition of an auxiliary heating system will increase the production cost of the whole vehicle and the structure of the battery pack will become more complicated,consider using the principle of the battery itself to generate heat during charging for low-temperature charging.The low-temperature equivalent circuit model of lithium battery is simulated by different charging currents,and the current limit that can be charged normally at low temperature is obtained.The charging experiment at a low temperature of-10 °C was carried out,and the results were the same as the model simulation results,which further verified the accuracy of the proposed lowtemperature equivalent current model prediction.The current can be charged with enough power,and there is a good temperature recovery effect during the charging process;the pre-heating process of the lithium battery system is realized by using a coolant tester.Through experimental comparison,it is proved that the proposed low-temperature charging strategy can significantly shorten the user’s Charging waiting time,and more energy saving;further improvement on the basis of constant current charging,using temperature as the switching basis,switching high current for charging when the battery system temperature reaches the set value,experiments show that the proposed improved low-temperature charging The strategy has a good charging effect.The charging capacity is 93% of the constant current charging,but the charging time is only 77% of the constant current charging,and the battery system temperature at the end of charging is closer to the normal temperature,so that the power lithium battery system can play a role.Better performance,the overall charging effect has been significantly improved.