锂离子动力电池分段智能充电策略研究

发布时间：2018-01-20 10:40

本文关键词： 锂离子电池脉冲充电分段充电遗传算法田口方法　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：为应对环境和能源危机,新能源电动汽车取代传统燃油汽车的趋势不可避免。在政策和市场的驱动下,我国电动汽车近年来呈爆发式增长的趋势。动力电池作为电动汽车的动力源泉,直接影响电动汽车的性能和寿命。其中锂离子动力电池以其比能量高、自放电率低、循环寿命长等特点脱颖而出,成为电动汽车动力电池的首选目标。然而,锂离子动力电池的容量、充电速度和寿命仍是制约电动汽车发展的关键因素,相关技术水平亟待提高。本文通过实验对比分析几种常用充电策略对电池的影响,结合电池的内阻特性,最终把针对恒流阶段的分段充电策略作为研究对象;基于遗传算法的分段智能充电策略能根据电池内阻的变化调整充电电流,在不降低充电速度的同时提高充电效率;根据无析锂快速充电原理改进的分段充电能够降低充电过程中出现析锂的可能性。具体的工作内容主要包括以下几个方面:1、分析现有的锂离子充电技术,对恒流恒压充电、多段恒流充电和脉冲充电进行实验研究。理论分析和实验结果表明:电池端电压达到截止电压后恒压充电是最快的充电方法,针对恒压阶段的多段恒流充电只能缩短充电时间,不能提高充电速度;脉冲充电与电流平均值相同的恒流充电相比,不能提高充电速度但会使电池提前达到截止电压,缩短充电时间,减少充入电量,并导致电池温度升高;"最小阻抗频率"是对充电电流中交流成分的优化,而交流成分本身对充电无益。2、建立锂电池的二阶RC等效电路模型,并在其基础上构建能耗模型,通过HPPC实验辨识模型参数,并在Matlab中验证了模型的有效性。考虑到电池内阻随SOC变化,本文将电池的内阻能耗作为目标函数,在能耗模型的基础上采用遗传算法对分段充电进行优化。仿真结果表明电池内阻变化越大、充电分段越精细,分段充电对能耗的优化效果越好。对于三元电池,在每5%一个阶段的情况下,能够降低2.2%的能耗。最后充电实验的结果验证了分段充电的有效性。3、内部析锂是影响电池寿命的重要因素,理论上将电池负极表面的锂离子浓度维持在饱和浓度能够实现锂离子电池的无析锂快速充电。本文参照该理论改进分段充电的分段方法,结合所用的电池,在0-40%SOC的阶段采用最大电流2C充电使锂离子浓度迅速趋于饱和,之后每10%一个阶段,充电电流不断下降以维持饱和浓度,直到80%SOC。采用田口方法设计实验,以充电时间、功耗和电池温度的加权和为价值函数,分析实验数据得到了后四个阶段的最优电流值。最后设计实验进行验证。
[Abstract]:In order to cope with the environmental and energy crisis, the trend of replacing traditional fuel vehicles with new energy electric vehicles is inevitable, driven by policies and markets. As the power source of electric vehicles, power battery has a direct impact on the performance and life of electric vehicles in recent years, among which the lithium ion battery has a high specific energy. The characteristics of low self-discharge rate and long cycle life stand out and become the preferred target of electric vehicle power battery. However, the capacity of lithium ion battery. Charging speed and life are still the key factors restricting the development of electric vehicles, and the related technical level needs to be improved. This paper analyzes the influence of several common charging strategies on the battery through experiments, combining with the characteristics of battery internal resistance. Finally, the piecewise charging strategy for the constant current stage is taken as the research object. The intelligent charging strategy based on genetic algorithm can adjust the charging current according to the change of battery internal resistance and improve the charging efficiency while not reducing the charging speed. According to the principle of rapid charging without lithium evolution, the piecewise charging can reduce the possibility of lithium evolution during the charging process. The specific work includes the following aspects: 1, analyzes the existing lithium ion charging technology. The theoretical analysis and experimental results show that constant voltage charging is the fastest charging method when the terminal voltage of the battery reaches the cut-off voltage. Multi-stage constant current charging at constant voltage stage can only shorten the charging time and can not improve the charging speed. Compared with the constant current charging with the same average current, pulse charging can not improve the charging speed, but will make the battery reach the cut-off voltage ahead of time, shorten the charging time, reduce the charge charge, and lead to the increase of battery temperature. The "minimum impedance frequency" is the optimization of the AC component in the charging current, and the AC component itself is not beneficial to charging. The second-order RC equivalent circuit model of the lithium battery is established, and the energy consumption model is constructed on the basis of the model. The model parameters are identified by HPPC experiment, and the validity of the model is verified in Matlab. Considering the change of battery internal resistance with SOC, the energy consumption of battery internal resistance is taken as the objective function in this paper. On the basis of the energy consumption model, genetic algorithm is used to optimize the battery charging. The simulation results show that the larger the battery resistance change, the more fine the charging section, the better the energy consumption optimization effect. For the ternary battery. At every 5% stages, the energy consumption of 2.2% can be reduced. Finally, the results of the charging experiment verify the effectiveness of subsection charging. The internal lithium evolution is an important factor affecting the battery life. In theory, the lithium ion concentration on the anode surface of the battery can be kept at saturation concentration to realize the rapid charging of lithium free lithium ion battery. According to this theory, the piecewise charging method is improved, and the battery used is combined. In the 0-40SOC stage, the maximum current 2C charge makes the lithium ion concentration rapidly saturated, and then every 10% stage, the charge current decreases continuously to maintain the saturation concentration. The experiment was designed by using the Taguchi method, and the value function was the weighted sum of charging time, power consumption and battery temperature. The optimal current value of the last four stages is obtained by analyzing the experimental data. Finally, the experiment is designed to verify it.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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