高压大容量磷酸铁锂电池组的主动均衡系统研究

In order to satisfy the requirements of electric vehicle (EV) on driving distance, speed, and grade ability, the voltage, energy, and power levels of the battery in the EV are increased continuously, requiring vast amounts of single battery cells connected in series or in parallel. Due to the inconsistency among the single battery cell, the cycle life of the battery pack connected in series is reduced greatly. For the LiFePO4 battery, its voltage is changed quickly when the capacity is close to full or empty, so the problem resulted by the inconsistency is more serious. In order to solve this problem effectively, active equalization system for high-voltage and large-capacity LiFePO4 battery pack is researched in this project, whose topics are to propose high-performance equalization method and structure. For the equalization method, its main research contents are the interaction mechanism and optimal combination among the different balanced approaches. And for the equalization structure, the modularized multi-stage equalization structure (MMES) and its optimal design, coordinated control scheme, energy management strategy, stability analysis and control are the researched key points. Finally, a platform based on MMES will be fabricated, and then the proposed equalization method, structure, and corresponding analysis, strategy can be verified. The research results of this project will promote the further mature application of the battery pack, and provide theoretical and technical basis for the large-scale development of the EV.

为了满足行驶里程、速度以及爬坡能力的要求，车载电池的电压、能量、功率等级越来越高，需要大量的单体电池串、并联成组使用。电池串联成组使用后，由于单体电池间的不一致性，其循环寿命大大降低，制约电动汽车的大规模发展和应用。对于磷酸铁锂电池，其电压在容量充放电末期会快速变化，不一致性问题更加严重。为了有效解决一致性的问题，本课题针对高压大容量磷酸铁锂电池组开展高性能均衡方式和均衡结构的研究。均衡方式方面重点开展各种均衡方式相互作用机理以及优化组合方式研究；均衡结构方面，重点开展模块化多级均衡结构及其优化设计方法、协调控制策略、能量优化管理策略、稳定性分析和控制策略的研究。最后，通过搭建模块化多级均衡系统平台对提出的均衡方式、均衡结构以及相关分析和控制策略进行实验验证。课题研究成果将推动我国电池成组技术的进一步成熟应用，同时也为电动汽车的大规模发展提供理论和技术支撑。

锂离子电池以其比能量高、热稳定性较好、自放电率低、动态响应快、无记忆效应和寿命较长等优点，广泛作为动力电源使用。为满足大功率动力电源的功率要求，需要将数百个电池单体串联使用。但由于制作工艺限制，各单体参数不一致，这种差异会随着电池充放电过程而放大，影响整体的有效容量和寿命。本项目采用大电流主动双向均衡电路、高精度SOC预测算法、支持大串联数量全范围任意能量转移的快速均衡策略等关键技术，研制出模块化的大容量锂电池均衡管理系统，满足高压、大容量锂电池组对能量管理的需求，解决了大容量动力电池组由于电池差异性问题，导致电池性能和寿命衰减较快、不满足实用需求的突出问题。本项目开展的主要研究内容包括：大电流双向均衡拓扑仿真建模、效率优化及电磁兼容性研究；均衡速度快、转换效率高的模块化主动均衡电路架构和控制策略研究；基于高精度数据采集和电池模型辨识的电池容量、内阻、剩余容量估计算法研究。本项目研究成果的关键技术指标为：DC510V～714V，130Ah锂电池组的主动均衡管理；均衡模块能实现双向充放电，稳态均衡电流6A，转换效率大于85%；控制电池组的不一致性，提升10%的可用容量，使电池组满足8年的全生命周期质保要求。本项目的重要科学意义在于通过模块化锂电池均衡管理系统进行能量在线转移，可以有效削弱电池本体差异性、热管理、电化学衰退等客观因数导致高压电池组整体可用容量的损失，延长电池组使用寿命，改善单体电池一致性，降低锂电池组全寿命周期的成本。