The Estimating Of Lithium-ion Battery Model And SOH Of Electric Vehicle

As the main power of new energy vehicle, the performance of batteries affectsthe performance of new energy vehicle directly. The research for battery has high priorityfor automobile companies all over the world. The performance of a battery includes theState of Charge and the state of health which are short for SOC and SOH. It can improve theperformance of a battery and reduce the battery maintenance cost through monitoringSOC and SOH real-time.We use the12Ah lithium-ion battery as the research object in the paper. The main workcan be divided into5parts.First we expound the significance of power battery and introduce different kinds ofbattery models which are used to simulated battery performance. Analyzing the currentstatus of battery SOH estimation and expounds the definition of SOH in different angles.This paper explains the working principle of lithium-ion battery and explains thecharacteristics of lithium-ion battery through experimental investigation. Then calibrate therelationship between the SOC and the open circuit voltage, the SOC and internal resistancefor12Ah lithium-ion battery. Then do research about the electrical characteristics of thebattery. Identify the characteristics of the battery capacity, charge-discharge efficiencycharacteristics. Then calculate the charge-discharge efficiency characteristics. Analyze thepolarization phenomenon of a battery and explain the reason about battery capacity fadingaccording to the principle of chemical reaction.Establish the basic battery model based on the electrochemical reaction, and then weestablish the Randle equivalent circuit model through mathematical derivation. Themotion of electrons inside the battery includes the diffusion phenomenon and migrationphenomenon. Modeling the two electronic sports phenomenon of the battery and establishingan equivalent circuit model with2RC cells. Build the equivalent circuit model under theenvironment of Simulink and identify the parameters of the battery model. Then compare theoutput between the model in Simulink and real datesAccording to the equivalent circuit model of previous build, we do the cyclelife experiment. Then study the life characteristics of the battery. According to theexperimental data of battery life changes we get the changing law of a battery. After repeatedstudy about the performance of the battery we explore the changing law about the capacityof the battery, the discharge efficiency, the energy efficiency, the battery resistance. Themathematical model between SOH and cycle life is established and use this model to predictthe SOH of a battery.We use the voltage curve fitting to estimate battery SOH in order to improvethe accuracy and applicability of battery SOH estimation. First normalize the charging curveof lithium-ion battery at different discharge rate and different SOH. Then compare thecharging voltage error after normalization. Validate the estimation algorithm of12Ahlithium-ion battery based on the experimental data. Verify the accuracy of voltagecurve estimation and analyze the estimation results.