Research On Charging Method Of Power Lithium Battery Based On Electrothermal Coupling Model

In recent years,with the rapid development of new energy vehicle industry,power lithium batteries have been widely used in the core components of electric vehicles due to their excellent performance.However,the development of electric vehicles is hindered by the long charging time and rising temperature of power lithium-ion batteries.Temperature is an important factor affecting the performance and safety of lithium-ion battery.In serious cases,it will cause thermal runaway of the battery.Research on charging methods considering temperature can improve the performance and safety of lithium-ion battery.Therefore,a multi-stage constant current optimization charging method based on the electrothermal coupling model is proposed in this paper.The method can shorten the charging time within the allowable range of charging temperature rise and ensure the safety and reliability of battery charging.The main research work and contents are as follows:1)Based on the working principle of lithium-ion battery,the characteristics of lithium-ion battery(including open-circuit voltage,internal resistance and capacity characteristics)at room temperature and different temperatures were studied and analyzed by using the static method and HPPC(mixed pulse power characteristics)test method.2)The advantages and disadvantages of four equivalent circuit models of lithium battery were analyzed.Thevenin equivalent model was selected to establish the electric model,and the least square method was used to identify the parameters su ch as ohmic internal resistance,polarization capacitance and polarization resistance.According to the heat generation equation in the charging process,a thermal model was established,and the temperature entropy coefficient was identified by the remaining Charge(SOC)under variable temperature,thus improving the accuracy of the thermal model.Finally,the coupling of the electrothermal model was realized,and the experimental results were verified by constant discharge,different SOC and different charging ratio.The results show that the model has high accuracy and small error in estimating the battery temperature.3)Based on the established electrothermal coupling model and the characteristics of lithium-ion battery,a multi-stage constant current optimization charging method was proposed to optimize the charging time under the constraint of charging temperature rise.The construction of objective function and the design of constraint conditions are given in detail,and the genetic algorithm is used to solve the objective function.In order to charge more power,the upper SOC boundary of the charging curve was optimized,and the order number of the multi-order constant current optimization charging method was determined,and the optimal charging current curve was obtained.4)In order to verify the effectiveness of the proposed optimization of charging methods,respectively from the different working conditions and the traditional multistage constant current charging method through experiment contrast,the results show that the proposed optimization charging method can shorten the charging time of at the same time,reduce the charge temperature,reduce the maximum polarization voltage,improve the acceptable charging current,and is suitable for the old and new batteries,It indirectly prolongs the service life of the battery and has good practical significance.