Design And Implementation Of SOC Estimation And Active Equalization For Lithium-Ion Battery

With the development of economy and society, the demands of cars become more and more big. However, the non-renewable fossil energy that cars use is limited, and the gas that cars exhaust have seriously polluted the environment. Therefore, the governments around the world pay more and more attention to the development of electric cars that use clean energy. The three key technologies of electric cars is battery, motor and electric control. The monomer battery can t meet the large voltage and high-power demand of electric cars. So, dozens or even hundreds monomer battery are in series to provide energy for electric cars and then the battery management system has become one of the key parts of electric cars. This paper studies the SOC estimation and active equalization of lithium-ion battery series. Besides, a battery management system for 64 V, 20 AH lithium-ion battery series has been designed in this paper.Firstlyxit has analyzed the characteristics of the lithium-ion battery in the process of charging and discharging, and then analyzed several equivalent circuit model. Besides, the model of lithium-ion battery for SOC estimation has been chosen and the parameters of the model have been acquired through the pulse discharge method and recursive least squares method. Secondly, the SOC estimation algorithm of lithium-ion battery have been researched and both AH algorithm and Extended Karlman Filter algorithm have been used to estimate the SOC of lithium-ion battery, after that, the Matlab simulation experiment of SOC estimation algorithm have been complete under UDDS conditions. Thirdly, the non-uniformity characteristics of lithium-ion batteries in series and its damage have been analyzed, after that, several active equalization circuit have been analyzed and simple inductance active equalization circuit has been designed. Fourthly, a battery management system for 64 V, 20 AH lithium-ion battery series was designed. The system includes data acquisition module and master control module.Finally, the experiments of voltage, current, temperature and other data acquisition have been done in this paper, and the data of the experiment was analyzed. The SOC estimation algorithm proposed in this paper has been verified, and the inductance active equalization circuit has been verified too. As to the experimental results, the error of lithium-ion battery SOC estimation is less than 7% by using the SOC estimation algorithm proposed in this paper. The dispersion degree of the battery voltage is less than 2% after using the simple inductance active equalization circuit. So, the SOC estimation method and the battery active equalization method proposed in this paper have some practical value.