Research On Modeling And Optimized Charging Strategy Of Li-Ion Battery

With the continuous improvement of power batteries,new energy vehicles and related technologies are becoming more and more mature.Due to the change of people’s concept of life and the constantly innovating technological level,new energy vehicles that use Li-ion batteries as energy sources are likely to replace fuel vehicles as the main transportation tool in the future.Li-ion batteries have become one of the main energy sources of new energy vehicles due to their high specific energy and long cycle life.However,Li-ion batteries still have shortcomings such as long charging time and poor thermal stability.In addition to improving the chemical structure of the battery itself,optimizing the charging strategy is still an important way to improve the charging performance.This paper proposes an adaptive current charging strategy based on a detailed analysis of the multi-stage constant current charging strategy.And an accurate battery model was established to simulate the charging process and calculate the charging loss.(1)This paper proposes an improved Li-ion battery equivalent circuit model parameter fitting strategy,and improves the traditional equivalent circuit model.The traditional parameter fitting method is nonlinear least squares.The fitting effect of this method is not ideal.The fitting result is unstable and the error cannot be minimized according to the characteristics of the data.In this paper,genetic algorithm is used and a reasonable objective function is designed to optimize the fitting process.An additional resistance is used to represent the most rapidly changing part of the polarization effect.The results show that the proposed fitting method and the improved model have higher fitting accuracy than traditional fitting methods and models.(2)This paper analyzes the multi-stage constant current(MSCC)charging strategy based on SOC staged.The NSGA-III is used to optimize the current in each stage of the MSCC charging strategy.The objective function is charging loss and charging time.Find the best charging combination by taking the equidistant points on the optimal front for charging experiment and comparing with the gradient current CC-CV method.The results show that compared with the CC-CV method the proposed charging pattern can reduce the temperature rise and loss under the same charging capacity.(3)Retain the advantages of the MSCC charging strategy,and strive to make the charging strategy simplest according to the characteristics of the internal resistance of the battery.This paper proposes an adaptive current charging strategy on the basis of researching the MSCC charging strategy.Firstly,the CC-CC-CV charging mode is analyzed.On this basis,the current is self-adapted by increasing the number of segments in the first constant current stage of CC-CC-CV.Comparative experiments show that this adaptive current charging strategy can significantly reduce ohmic losses,and this advantage becomes more and more obvious as the average charging current increases.