Research On SOC Estimation And Applications For Li-ion Battery Pack

Currently, confronted with more and more serious social energy and environment problem, energy conservation and renewable energy developments is becoming the new trends of international industrial development. Li-ion batteries are widely applied in the fields of new energy due to the advantages of low-pollution, high energy density and long cycle life. The accurate estimation of State of Charge, referred to as SOC, plays a significant role in application of Li-ion batteries and becomes the key technology of improving the batteries’ efficiency. To solve the existing problems, the dissertation studies the SOC estimating methods for Li-ion batteries. Based on the correlative theories, we propose some improved methods and apply them in practice. The study contains the following aspects:(1) Survey of Li-ion batteries and research on SOC estimation. Firstly, we analyze the working principle, basic performance, charging and discharging characteristics, and the definition of SOC. Then, after studying the characteristics of Li-ion batteries and the existing problems in the traditional method of open circuit voltage, an improved open circuit voltage model is established according the relations among SOC, open circuit voltage and standing time obtained in the experiments. According to the experiment data, the effects of discharge rates, temperature and cycles on SOC is studied and an improved ampere-hour integral method is modeled.(2) A battery pack SOC estimation model based on Structural Logic Tree is proposed. To overcome the limitations of current battery pack SOC definition, it takes the battery pack structure and the individual variation of each cell into consideration. Based on the concept of the battery pack SOC which is redefined in this paper and the arithmetic rule of Structural Logic Tree, a new quick estimation model of battery pack SOC is realized.(3) Online SOC estimation for the Man-portable Modularization Photovoltaic Power System. To verify the effectiveness of the SOC estimation model proposed in this paper, we apply the model on the Man-portable Modularization Photovoltaic Power System. Experiment shows that the model is quick and effective.