Study On Temperature Field Of Lithium-ion Battery Package In Electric Vehicle And It's Dissipation Structural Optimization

With the advantages of high voltage, high energy, high specific power, excellent cycle ability, low self discharging, environment friendly and so on, lithium-ion batteries have become the predominant batteries in EV and HEV. Lithium-ion batteries-powered EV has already become the international competitive hotspot. The international mainstream motor companies will strive to promote the lithium-ion batteries-powered EV in the following several years. Lithium-ion batteries, many experts believe, have huge tactic significance as petroleum nowadays. However, there are some problems existed, especially the heat that produced in charging and discharging of lithium-ion batteries, which will bring about internal temperature rise in lithium-ion batteries pack, inhomogeneous temperature among cells, instability, even impairment of the safety and service life of batteries. Therefore, constructing theoretic models for the temperature field analysis of batteries, using numerical simulation technique to analyze temperature distribution of batteries under the given conditions, optimizing heat radiation structure and predicting heat radiation performance are of important realistic significance to improve service performance of the batteries. At present, batteries in EV and HEV generally have cooling structure with the aid of the suction of fans. One disadvantage of this cooling structure is that the fans will consume batteries capacity, which will reduce the useful power of batteries. If we use natural cooling, when the vehicle is running, the air which has relative motion with the vehicle can cool the lithium-ion batteries. Using the computational fluid dynamics (CFD) software, the model was build and applied to simulate numerically flow field and temperature field of the Lithium-ion battery packs under natural air cooling situation. An optimal scheme, which can improve the conformity of flow field and temperature field, was proposed based on natural cooling and no consuming batteries capacity.The main works in this thesis include:â‘ According to the conservation of mass, momentum and energy of heat transfer theory, the unsteady state three-dimensional transient thermal model of lithium-ion battery pack was established, and both heat generating principle and heat transfer characteristics of lithium-ion battery were analyzed.â‘¡ADVISOR, the electric vehicle simulation software was used to establish the simulation model, which includes the major components of pure electric vehicle and the vehicle. Using this model, we can simulate its dynamics and continuous driving mileage. Furthermore, the current variation tendency of battery pack under all working conditions can be obtained.â‘¢Using the method of computational fluid dynamics (CFD), the flow field and temperature field of lithium-ion battery pack's original program flow were numerical simulation analyzed. An optimal scheme of dissip ation structure was proposed and its simulation results of thermal performance were obtained.â‘£To confirm accuracy of simulation analysis, a temperature measurement experiment of the battery packs of Electric Vehicle (EV) during charging and discharging periods was carried out under the uniform condition to confirm the accuracy of simulation analysis. The experimental data consist well with the simulation result, which indicates the rationality of the model of the temperature field.