并联电池模块的热电特性实验研究

发布时间：2019-05-27 08:32

【摘要】：由于其高效率与低排放,使用锂离子电池作为动力源的电动汽车有望取代以化石燃料作为能源的内燃机汽车。电动汽车的普及将有效解决全球变暖和空气污染等重大社会问题。作为电动汽车的核心部件,锂离子电池的一个关键问题就是老化及其伴随的功率、能量密度降低。已有研究表明,温度、电荷状态(SOC)、充放电倍率是影响锂离子电池老化进程的主要因素。在电动汽车中,锂离子电池以成组方式使用。由于电池之间存在着不一致性,且各个电池所处的位置不一样,因此造成了不同电池承受不同的载荷与热环境,势必使得不同电池的老化存在不一致性。本论文研究了电池不一致性以及热效应对电流分布不均匀特性的影响,通过设计一个两枚电池并联的实验模组来探究在不同的工况(充放电倍率、温度等)下电流分布的变化。首先,本实验优先探究了电池内阻对并联电池组电流分布的影响的重要性。并提出并比较了五种不同的方法。其次,不同负载、温度等工况也会对电池组产生不同的影响,实验亦探究了在不同的热边界条件和内阻下并联电池组的电流分布的差异。在此研究中,对于并联电池组,通过考察单体电池的内阻、初始开路电压和热边界条件的差异来探究这些因素对电池组电流分布的影响。首先,研究测定了单体电池的内阻。由于内阻对并联电池组的电流分布有着重要作用,本研究应用并比较五种不同的内阻测量方法。第二,研究改变了电池组的加载电流和环境温度等工况,分别考察单体电池内阻、达到SOC平衡所需时间和热边界条件对电池组的影响。研究发现并联电池组的电流分布受三个主要因素影响:(1)并联电路中每个支路的电阻差异,其中包括单体电池的内阻和接触电阻;(2)单体电池的开路电压(OCV)差异,取决于其SOC和温度和(3)由于在电池组中的位置不同,单体电池本身的温度差异。为了尽量减少并联电池组的电流分布和SOC差异,我们考察了以下因素的影响:1)连接导线电阻:用具有相同的长度的银导线取代铜导线,电池组充放电过程的SOC和电流分布的差异减小;2)单体电池之间的初始开路电压差异:每次充放电循环结束后,静置时长增加致13小时,下一次充放电循环中的电流和SOC的分布差异减小;3)通过改善电池组的热环境的一致性,可以消除该电池组各部分由于包裹条件不同而导致的巨大的电流分布差异。我们期待,在此处获得的结论也能够适用于有更多电池的模组中。
[Abstract]:Because of its high efficiency and low emission, the electric vehicle with lithium ion battery as the power source is expected to replace the internal combustion engine vehicle with fossil fuel as energy source. The popularity of electric vehicles will effectively solve major social problems such as global warming and air pollution. As the core component of electric vehicle, one of the key problems of lithium-ion battery is aging and its accompanying power and energy density reduction. It has been shown that temperature and charge state (SOC), charge and discharge rate are the main factors affecting the aging process of lithium ion batteries. In electric vehicles, lithium-ion batteries are used in groups. Because of the inconsistency between batteries and the different positions of each battery, different batteries bear different loads and thermal environment, which is bound to make the aging of different batteries inconsistent. In this paper, the effects of battery inconsistency and thermal effect on the uneven current distribution are studied. A parallel experimental module of two batteries is designed to explore the changes of current distribution under different operating conditions (charge-discharge rate, temperature, etc.). First of all, the importance of the influence of battery internal resistance on the current distribution of parallel batteries is investigated. Five different methods are proposed and compared. Secondly, different load, temperature and other working conditions will also have different effects on the battery pack, and the experimental results also explore the difference of current distribution of parallel battery pack under different thermal boundary conditions and internal resistance. In this study, the effects of these factors on the current distribution of parallel batteries were investigated by investigating the internal resistance of single cell, the difference of initial open circuit voltage and thermal boundary conditions. Firstly, the internal resistance of the single cell was studied and measured. Because the internal resistance plays an important role in the current distribution of parallel batteries, five different internal resistance measurement methods are applied and compared in this study. Secondly, the loading current and ambient temperature of the battery pack are changed, and the internal resistance of the single cell is investigated, and the effects of the time needed to achieve SOC equilibrium and the thermal boundary conditions on the battery pack are investigated. It is found that the current distribution of parallel battery pack is affected by three main factors: (1) the resistance difference of each branch in parallel circuit, including the internal resistance and contact resistance of single cell; (2) the difference of open circuit voltage (OCV) of single cell depends on its SOC and temperature and (3) the temperature difference of single cell itself due to the different position in the battery pack. In order to minimize the current distribution and SOC difference of parallel battery pack, we investigated the following factors: 1) connecting conductor resistance: replacing copper wire with silver wire of the same length, The difference between SOC and current distribution in the charge and discharge process of battery pack is reduced. 2) the difference of initial open-circuit voltage between single cell: after each charge-discharge cycle, the static time increases for 13 hours, and the difference between current and SOC distribution in the next charge-discharge cycle decreases; 3) by improving the consistency of the thermal environment of the battery pack, the huge difference of current distribution caused by the different encapsulation conditions of the battery pack can be eliminated. We expect that the conclusions here will also apply to modules with more batteries.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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