计及电池老化抑制的电动汽车引导型制动能量回馈机理与控制研究

The electric vehicle (EV) braking energy recovery system is capable of effective reduction of energy losses and improvement of EV driving distance. However, nonlinear and irregular shocking current of the power battery will occur in the conventional braking energy recovery charging mode when the requirements for braking performance and energy recovery ratio are relatively high. This may lead to more deposition of lithium ions and growth of the SEI layer, so the battery ageing is getting faster. Based on this problem, with eyes on the entire driving process, this study is aimed at connecting the regenerative braking and electric driving processes which together influence battery ageing. The mechanism and quantization rule with respect to influence of driving process on battery ageing based on anode lithium ion concentration distribution characteristics, can be explored from the angle of connection of multiple domains including mechanics, electromagnetics and electrochemistry, by establishing and validating the multi-scaled mathematical expression from driving process- motor and battery operation variables- anode lithium ion concentration- ageing characterization parameters (e.g., lithium ion deposition thickness, SEI thickness, etc.). Then a guiding braking energy recovery control strategy is proposed involving requirement consideration of energy recovery ratio and dynamic performance, and battery ageing could be suppressed via guidance design of an optimal charging curve according to the anode lithium ion concentration modification function of the strategy. This study integrates with multiple subjects of electric energy storage, electric machinery and power electronics, and provides a new resolution for regenerative braking research. The battery lifetime extension is expected, resulting in positive promotion for development of the EV industry.

电动汽车制动能量回馈系统可有效降低能量损耗、提高电动汽车续驶里程，但制动性能和能量利用率要求较高时，动力电池在制动能量回馈传统充电模式下会产生非线性不规则冲击电流，导致负极锂离子沉积和SEI膜增长过快，加速电池老化。针对此问题，本项目放眼于整个行驶过程，不割裂回馈制动与行驶驱动影响电池老化的关联性，通过创建行驶过程-电机电池运行变量-电池负极锂离子浓度-老化表征参数（锂离子沉积、SEI膜厚度等）的多尺度数学描述，进而从连接动力、电磁、电化学多域整体的角度揭示基于负极锂离子浓度分布特性的行驶过程影响电池老化的机理与量化规律；相应提出引导型制动能量回馈控制策略（考虑能量利用率与动力性要求），通过基于负极锂离子浓度调理机制的优化充电曲线引导型设计来抑制电池老化。本研究融合电能存储、电机、电力电子等学科，为制动能量回馈研究提供了新思路，并有望延长动力电池寿命，对电动汽车产业发展产生积极的促进作用。

电动汽车制动能量回馈系统一方面可有效地降低能量损耗，提高电动汽车续驶里程，但另一方面其未充分考虑电池内部电化学和材料学机理的充电模式产生的非线性不规则冲击电流会导致动力电池老化的加速，反而造成电动汽车整体成本的上升。目前研究尚未从电池锂离子浓度分布变化的角度研究电动汽车行驶过程（包含再生制动过程）影响动力电池老化的根本机理和量化规律。此外，绝大多数电动汽车研究者也仅仅由行驶工况研究到动力电池特性的外部表征，即电池充放电电流这一层面。然而，充放电电流的强度、频率等对电池的寿命有着深远的影响，然而二者之间的关联性及影响机制尚不明晰。直接以外部表征的充放电电流作为输入参数来估算电池老化的电池模型，其精确度并不能够满足电动汽车未来发展需求。针对上述问题，本项目通过负极（包括石墨和相邻电解液界面）锂离子浓度分布的变化特性将电池外部表征和内部老化效应两者联系起来。着眼于整个行驶过程中的电池老化效应，结合宏观（车辆行驶工况与再生制动各关键组件）到微观（电池内部电化学反应和材料变化）的多尺度研究方法，通过协调式引导型制动能量回馈电池电流曲线的引导设计来产生有利于电池健康的锂离子浓度分布状态，从而有效减缓电动汽车动力电池的整体老化进程。因此，基于电化学老化模型，建立锂离子电池负极锂离子浓度与电池工作电流之间的关系式，获得电池老化表征参数与负极锂离子浓度的数学关系。最终通过考虑电池老化机理，限制充电条件、兼顾电池负极锂离子浓度分布状态以及老化参数的变化规律等因素，提出基于模型预测控制的优化脉冲充电方法，在实现快速充电的同时实现电池寿命的提升。实验和仿真效果表明，满充充电时间在与2C充电倍率相当的情况下，500次循环充放电循环后，显著提升电池使用寿命10%以上。