| Global auto industry has successively introduced plans to ban or sell fuel vehicles.The popularity of new energy vehicles represented by electric vehicles is imperative.The energy required for the operation of electric vehicles is provided by the power battery pack to ensure safe and efficient operation of the battery pack,which has become an important goal of electric vehicle research.At present,the battery management system(BMS)research mainly includes: analyzing the relevant characteristics of the power battery to establish an equivalent model,estimating the battery state of health(SOH)and the state of charge of the battery,(SOC)for high-precision estimation and other aspects.Among them,the power battery SOC estimation is one of the key issues in the research.Accurate estimation of the SOC is not only important for the use of the battery itself,but also the important basis for the cruising range of electric vehicles.In this paper,the following work is carried out on the estimation of the SOC of the power battery.(1)Lithium-ion battery is selected as the research object,and the working principles and basic characteristics of lithium-ion battery are analyzed in detail.Considering the accuracy of the battery equivalent model and the real-time problem of computational complexity when participating in SOC estimation,the Thevenin equivalent circuit model is used as the mathematical model of the variable structure filtering algorithm.The parameters in Thevenin equivalent circuit model were identified by Hybrid Pulse Power Characteristic experimental method,and the accuracy of the model was verified by constant current discharge.The results show that the equivalent circuit model used in this paper has higher precision.(2)In the SOC estimation process,the Amphere-hour integral method highly depends on the initial value,and the error accumulation cannot be self-corrected during the operation,resulting in an increase in the estimation error.In the Variable Structure Filter(VSF)operation,due to the sliding mode convergence characteristics,it can quickly converge to the SOC true value,and does not depend on the initial value.It can quickly converge to the vicinity of the true value of the SOC,and does not depend on the initial value,but there will be chattering around the true value.In order to reduce the problem of variable structure filtering chattering,the variable structure filter gain coefficient is adjusted in stages to improve the accuracy of variable structure filtering SOC estimation.In this paper,the method of ampere-variable structure filtering cyclic operation is proposed to estimate the SOC,and the running time of the ampere-hour integral is set.The variable structure filtering is used periodically to correct the integral error of the ampere-hour integral.The experiment of ternary lithium battery is carried out by the federal urban driving schedule(FUDS).The SOC estimation results show that the accuracy of the algorithm of the Amphere-hour-variable structure filtering cycle is higher than that of the single ampere-time integration algorithm.(3)The experimental platform for SOC estimation of lithium-ion battery in Amphere-variable structure cyclic operation is built,and related software programs and hardware circuits are designed.The test is carried out for the established experimental platform.The results show that the platform can meet the relevant data acquisition accuracy and verify that the proposed SOC estimation method has higher precision.In view of the advantage of the Amphere-hour variable structure cyclic operation algorithm in estimating the SOC of lithium-ion battery,the algorithm can meet the requirements of electric vehicle estimation accuracy of battery SOC,and has great application value. |
