【作者】 李涛；

【导师】 马正伟；

【作者基本信息】 深圳大学 ， 交通运输工程（专业学位）， 2022， 硕士

【摘要】 全球能源危机和环境污染问题愈演愈烈,使得电动汽车变成各国汽车发展的主流。动力电池作为电动汽车的动力源,其性能好坏直接关系到电动汽车性能的发挥。锂离子电池因能量密度高、再生循环能力强以及无记忆效应等优势,成为电动汽车动力电池的首选。但是锂离子电池也存在缺点,尤其在低温环境下,锂离子电池的容量和放电能力大打折扣,严重影响电动汽车的动力性能;在低温时充电,通常达不到额定容量,且大倍率充电容易生成金属锂,导致电池健康状态、循环寿命和安全可靠性均下降,这些不利因素对电动汽车寒冷地区的推广造成了巨大的障碍,因此,在低温环境下对电池加热就显得很有必要。本论文针对低温无车载其他热源的问题,对加热功率和电池续航的最优控制问题进行了深入研究,结合内、外加热的优点,提出一种基于模糊控制的动力电池低温加热策略,在放电时,利用低温内阻增加的同时使用加热膜对电池内外部加热来提升电池温度,并设计加热系统,实现锂离子电池在不同温度、放电电流和不同初始SOE的最佳加热功率控制。论文主要研究工作包括:(1)综述了锂离子电池的温度特性、低温加热的基本方法和国内外研究现状,对当前已应用和正在研究的电池低温加热技术存在的问题进行了分析,并提出了论文的研究内容。(2)通过锂离子电池的反应机理分析了电池失效和老化现象,并在此基础上总结对比低温加热常用的电路模型,并确定采用的等效电路模型;通过搭建电池实验平台,开展不同环境温度下磷酸铁锂电池的性能测试。基于电池性能测试数据和Thevenin等效电路模型,利用最小二乘法对模型进行参数辨识,从微观角度分析了温度对电池性能的影响,以及温度影响电池性能的原因。(3)在电池产热和传热的基础上,构建电池温升模型。通过实验获取等效热转移系数,并在不同条件下进行加热实验,通过仿真和实验对比,验证了电池温升模型的有效性。(4)基于模糊控制理论,设计三个不同低温等级的模糊控制器,依据各状态低温加热实验结果制定模糊控制规则,确定电池在各种状态下的最佳加热功率,并将各状态下的最佳功率表格化,利用查表方式由输入直接输出最佳加热功率,从而实现对低温电池的加热。(5)设计了电池低温加热系统,主要包括控制系统和电池系统两个部分。控制系统由Speedgoat目标实时机和DC/DC转换器构成,电池系统由1个两并四串的模组和加热膜构成;利用电池加热系统,在环境温度为-20℃时,分别在电池模组SOE为100%和50%,利用2个工况对策略进行验证,实验结果表明,用较小的功率让电池温度上升到正常的工作范围,隐藏的部分容量得到了恢复,也增加了电池续航里程。更多还原

【Abstract】 The global energy crisis and environmental pollution have become increasingly serious,making electric vehicles the mainstream of automobile development in various countries.As the power source of electric vehicles,the performance of power battery is directly related to the performance of electric vehicles.Lithium-ion battery has become the first choice for vehicle-level power batteries due to its high energy density,strong regenerative cycle ability and no memory effect.However,lithium-ion batteries also have shortcomings,especially in the low temperature environment,the capacity and discharge capacity of lithium-ion batteries are greatly reduced,which seriously affects the dynamic performance and endurance of electric vehicles.When charging at low temperature,it usually cannot reach the rated capacity,and large rate charging is easy to generate lithium metal,which reduces the concentration of Li~+,resulting in the decline of battery health,cycle life and safety and reliability.These unfavorable factors have caused great obstacles to the promotion of electric vehicles in cold regions of China.Therefore,it is necessary to heat the battery at low temperature.In this paper,aiming at the problem that there are no other heat sources on the vehicle at low temperature,the optimal control problems of heating power and battery life are studied in depth.Combined with the advantages of internal and external heating,a low-temperature heating strategy of power battery based on fuzzy control is proposed.When discharging,the internal and external heating of the battery is used to increase the battery temperature by using the heating film while the low-temperature internal resistance is increased.The heating system is designed to realize the optimal heating power control of lithium-ion battery at different temperatures,discharge currents and different initial SOE.The main research work includes:(1)The temperature characteristics of lithium-ion batteries,the basic methods of low-temperature heating and the research status at home and abroad are reviewed.The problems existing in the current applied and under-studied low-temperature heating technologies of batteries are analyzed,and the research contents of this paper are proposed.(2)The failure and aging phenomenon of lithium-ion battery were analyzed by the reaction mechanism of lithium-ion battery.On this basis,the common circuit models of low temperature heating were summarized and compared,and the equivalent circuit model was determined.The performance test of lithium iron phosphate battery under different ambient temperature was carried out by building a battery experimental platform.Based on the battery performance test data and Thevenin equivalent circuit model,the least square method is used to identify the parameters of the model.The influence of temperature on the battery performance is analyzed from the microscopic point of view,and the reason why temperature affects the battery performance is analyzed.(3)Based on the internal heat generation and heat transfer mechanism of the battery,the temperature rise model of the battery is constructed.The heat transfer coefficient and other parameters were obtained through the cooling experiment,and the heating experiment was carried out on the battery under different conditions.The validity of the battery temperature rise model was verified by comparing the model simulation and experimental data.(4)Based on fuzzy control theory,three fuzzy controllers with different low temperature levels are designed.According to the experimental results of low temperature heating in various states,the fuzzy control rules are formulated to determine the optimal heating power of the battery in various states.The optimal power in various states is tabulated,and the optimal heating power is output directly from the input by lookup table,so as to realize the heating of low temperature batteries.(5)The battery low temperature heating system is designed,including control system and battery system.The control system consists of Speedgoat target timing and DC/DC converter.The battery system consists of a two-parallel and four-string module and a heating film.Using the battery heating system,when the ambient temperature is-20°C,the SOE of the battery module is 100%and 50%,respectively.The strategy is verified under two conditions.The experimental results show that the battery temperature is raised to the normal working range with a small power,and the hidden part of the capacity is restored,and the battery mileage is also increased.更多还原