The modeling and simulation on electrothermal characteristics of electric vehicle lithium-ion battery

The rising trend in global average temperatures has become difficult to ignore. Therefore, many countries around the world have proposed various plans to deal with the unrestrained use of fossil fuels and formulated roadmaps to wean themselves off fossil energy. In the field of automotive production design, many companies have begun to focus on the use of renewable energy. Therefore, the presence of electric vehicles in the market has gradually increased in recent years. Usually, the energy of electric vehicles comes from the chemical energy in the battery, so the battery management system (BMS) effectively evaluates and monitors the battery, which is the key to ensuring the safe and smooth running of electric vehicles. However, the car will face various complex conditions on the actual road, and the parameters of the battery such as voltage, soc, current and so on show nonlinear changes. Therefore, it is urgent to establish a mathematical model in BMS to reflect the dynamic characteristics of batteries under complex conditions accurately. This thesis uses the experimental data of an 18650 ternary Li-ion battery to build an electrothermal coupling model, whose parameters can be updated according to the soc, current, and temperature, so as to accurately reflect the voltage and temperature variation of the battery, and improve the ability of BMS to evaluate and predict the state of the battery. The main contents are as follows: Firstly, the working principle of the battery is analyzed, and the second-order RC equivalent circuit model is selected as the basis of the electrical characteristic model. Using the experimental data in the HPPC test, the model's parameters are identified based on the least squares algorithm. After building the model in Matlab Simulink, error verification was performed to confirm the accuracy of the electrical characteristic model. Then, the experimental data of lithium batteries, which are the same type and have similar specifications, are used to verify the migration of the model parameters, and prove that the model parameters have good adaptability. The Bernadi heat generation model and lumped parameter model based on the equivalence principle are used as the basis of the battery thermal model. Finally, the two models are fused into an electrothermal coupling model, and the model architecture is established on Matlab. In the end, a simple longitudinal motion model of the vehicle is established according to the kinematics principle of the vehicle, and the current curve of the automotive lithium battery pack under specific driving conditions (NEDC, WLTC, etc.) is obtained. Using this as the current command input of the electrothermal coupling model, the terminal voltage, soc, temperature, and other data for a single lithium battery are collected to study the electrothermal characteristics of the lithium battery. This study will help us to build a more powerful BMS system in the future.