应用于高寒地区的电动汽车电池管理关键技术研究

发布时间：2018-09-14 12:43

【摘要】：电动汽车动力电池系统是电动汽车的能量来源,是电动汽车的核心部件,电池内部复杂的电化学反应容易受到温度的影响,而高纬度寒冷地区冬季气温低、冬夏温差大,为电动汽车电池管理带来了新的挑战。因此,对电池系统合理而有效的管理是提升电池使用效率、延长电池使用寿命、保障电池组使用安全,优化系统能量管理策略的基础。但是由于电池温度特性原因,在高温环境下电池加速老化,形成不可恢复的容量损失。而在低温环境下,电化学反应速率降低、内阻增大、参与反应的锂离子数量减少,造成电池组容量和功率特性的衰减,充电时甚至可能出现锂枝晶刺穿隔膜形成内部短路,威胁使用安全。同时,长期循环使用后电池自身特性不一致造成的电量不均衡不仅影响电池组容量和功率特性,还会引发电池生热、温度以及库伦效率的不一致,使电池组性能进一步恶化。上述问题极大地制约了电池系统性能发挥,增大了电池系统使用风险和使用成本。针对以上问题,本文旨在解决电动汽车电池系统由于外界环境温度和电池自身特性不一致引发的电池组性能衰减问题,以及由于电池SOC不一致引发的生热及温度不一致问题。为了实现这一目的,本文分别从理论和实际角度出发对温度引起的电池性能衰减机理进行分析,针对电动汽车电池系统低温运行特点制定串联电池组低温热管理策略,在低温预热模式下采用基于变功率调节的低温预热控制方法提升电池性能,预热起动后进入运行监控模式估计电池内部温度和峰值功率状态。针对电池特性不一致引起的电池组性能衰减及生热和温度不均问题开展仿真研究,对多种常见特性不一致带来的容量和功率衰减机理进行分析。针对影响电池组性能最为严重的SOC不均衡问题,设计串联电池组均衡系统并开发优化均衡控制策略以改善电池组电量一致性,缓解SOC不均衡对电池组性能及热稳定性的影响。具体研究内容如下:针对电动汽车电池组性能衰减机理问题,从理论上分析环境温度和电池特性参数一致性对串联锂离子电池组性能影响机理,通过实验验证环境温度对电池内阻、开路电压、放电容量、峰值功率的影响,为电池低温热管理系统及控制方法设计提供依据。建立电池特性参数一致性分析模型,分析内阻、开路电压和电量不一致对电池端电压、电池组容量和峰值功率带来的影响,定义电池组容量和功率衰减率对不同类型不一致造成的电池组性能衰减进行评价。此外,还对电池电量不一致带来的电池组温度和老化差异进行分析。针对电池系统运行过程中电池内部温度和峰值功率无法实际测量的问题。利用电池等效电路模型,根据实时采集的电池电压和电流数据,结合扩展卡尔曼滤波在线估计模型参数,并根据电池电压和电流限制条件估计运行过程中的峰值充放电功率;建立电池内部温度估计模型,分析熵变生热和过电势生热对电池总体生热的影响,并在恒流充放电过程中对两种生热带来的影响进行分析,提出基于自生热的电池内部温度估计方法,利用实时采集的电池表面和环境温度估计电池内部温度。针对串联电池组低温热管理控制策略问题,通过对低温运行状态的分析将低温运行分为低温预热起动和起动后的运行监控两种模式。通过分析电池低温预热模型,给出了预热目标温度确定方法,提出了基于比例因子自校正的变功率低温预热模糊控制方法,根据电池表面最大温差和电池平均温度调节预热功率,提高电池性能的同时节省预热能耗。在起动后运行过程中监控电池峰值功率和内部温度变化,利用峰值功率估计方法实现变温度状态下的电池功率能力估计,根据电池表面和环境温度结合内部温度估计方法实现电池内部温度的准确估计。最后,针对串联电池组电池电量不均衡引发的电池组性能衰减和生热及温度不一致问题,提出一种基于双向全桥的串联电池组主动均衡结构,实现串联电池组模块与模块内任意单体与之间的双向电量主动均衡。在此基础上提出了均衡时间和电量一致性优化均衡控制策略,该策略根据电池初始SOC不均衡状态进行全局寻优,提前预知所需均衡步骤、时间以及均衡后电量分布,寻求最短时间内达到电量一致的最优途径,避免往复均衡带来的能量浪费。
[Abstract]:Electric vehicle power battery system is the energy source of electric vehicle and the core component of electric vehicle. The complex electrochemical reactions inside the battery are easily affected by temperature. The low temperature in winter and large temperature difference in winter and summer in high latitude and cold regions bring new challenges to the battery management of electric vehicle. Management is the basis of improving battery efficiency, prolonging battery life, ensuring battery safety, and optimizing system energy management strategies. However, due to the temperature characteristics of the battery, the battery accelerates aging at high temperatures, resulting in irreversible capacity loss. The large number of lithium ions involved in the reaction decreases, resulting in the decrease of the capacity and power characteristics of the battery pack. Lithium dendrite piercing through the diaphragm may even occur during charging, resulting in internal short circuit and threatening the safety of use. At the same time, the imbalance of power caused by the inconsistent characteristics of the battery itself after long-term recycling not only affects the capacity and power characteristics of the battery pack, but also affects the battery pack These problems greatly restrict the performance of the battery system and increase the risk and cost of the battery system. In view of the above problems, this paper aims to solve the problem of the battery system of electric vehicles due to the external environment temperature and the battery itself. In order to achieve this goal, the mechanism of battery performance attenuation caused by temperature is analyzed theoretically and practically, and the low-temperature operation characteristics of battery system in electric vehicles are formulated. The low temperature thermal management strategy of series battery pack is to adopt the low temperature preheating control method based on variable power regulation in the low temperature preheating mode to improve the performance of the battery. In order to solve the problem of SOC unbalance which affects the performance of batteries most seriously, a series battery equalization system is designed and an optimal equalization control strategy is developed to improve the power consistency of batteries and alleviate the unbalance of SOC on batteries. Specific research contents are as follows: Aiming at the performance attenuation mechanism of EV battery pack, the influence mechanism of environmental temperature and battery characteristic parameter consistency on the performance of series Li-ion battery pack is analyzed theoretically, and the effect of ambient temperature on battery internal resistance, open circuit voltage, discharge capacity and peak power is verified by experiments. The influence of internal resistance, open circuit voltage and inconsistency of power on battery terminal voltage, battery pack capacity and peak power is analyzed, and the influence of battery pack capacity and power attenuation rate on different types of inconsistency is defined. The performance attenuation of battery packs is evaluated. In addition, the differences of temperature and aging caused by the inconsistency of battery capacity are analyzed. Extended Kalman filter is used to estimate the model parameters on-line, and the peak charge and discharge power is estimated according to the battery voltage and current constraints. The model for estimating the internal temperature of the battery is established, and the influence of entropy and overpotential on the overall heat generation of the battery is analyzed. Based on the analysis of the influence, a method for estimating the internal temperature of the battery based on autogenous heat is proposed, and the internal temperature of the battery is estimated by the surface and ambient temperature of the battery collected in real time. By analyzing the low temperature preheating model of batteries, the method to determine the preheating target temperature is given. A fuzzy control method of variable power low temperature preheating based on proportional factor self-tuning is proposed. The preheating power is adjusted according to the maximum temperature difference on the surface of the batteries and the average temperature of the batteries. The peak power and internal temperature of the battery are monitored during the operation of the battery after moving. The power capacity of the battery under the condition of variable temperature is estimated by the peak power estimation method. The internal temperature of the battery is estimated accurately according to the surface and environmental temperature of the battery and the internal temperature estimation method. Battery performance attenuation, heat generation and temperature inconsistency caused by weighing are discussed. An active equalization structure of series battery pack based on bidirectional full bridge is proposed to realize bidirectional active equalization between series battery pack module and any unit in the module. Simply, according to the initial SOC imbalance state of the battery, the strategy searches for the global optimization, predicts the required equalization steps, time and power distribution after equalization in advance, seeks the optimal way to achieve the same power in the shortest time, and avoids the energy waste caused by reciprocating equalization.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：U469.72

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