串联储能电源高效均衡系统结构及控制策略研究

Differences in chemical characteristics, operating temperature or different internal resistance can cause differences in cell remaining capacity, leading to overcharging or overdischarging of respectively most charged and most discharged cells, decreasing the total stack storage capacity, shortening the battery lifetime and, eventually, permanently damaging the cells. Cell voltage equalizers are usually used for series-connected energy storage cells to eliminate cell voltage imbalance that may cause premature deterioration and reduce the available energy of the cells.Conventional cell voltage equalizers cannot meet requirements of large capacity energy storage system for low transfer efficiency, circuit complexity increaseing proportionally with the number of series-connected energy storage cells..Cell equalization system during bidirectional operations are investigated based on the experimentally established State Of Charge (SOC) estimators in order to select the target cell for charge distribution. The directed graph and weighted matrix representation of each equalization structure are defined to deduce a realistic direct graph model and then establish a real equalization structure.A hierarchical structure of the equalization is proposed based on tree diagram and optimal spanning tree, using certain direct equalization structures as basic module. A multi-layer tree structure equalization system topology was build after investigating optimization combinations of various equalization topologies. For some complicated unbalanced applications, a optimal control strategy, created with optimization algorithms, for a novel cell equalizer configuration, with the potential to fulfil expectations of the following: 1) high efficiency; 2) high speed; and 3) simple structure. Issues, such as the limitations on maximum and minimum cell voltage, noise, and quantization errors, are explored. In this application, equalization circuit, equalization system topology and unbalance status control strategy are researched to solve the problems such as long energy path, slow equalization speed and low equalization efficiency existing in long series connected cell strings.

能量均衡技术是防止串联储能系统过充和过放，避免储能系统有效容量和安全性降低，提高循环使用寿命的有效方法。在前期科研实践基础上，拟从建立储能单体物理端行为特性模型入手，归纳充放电参数对电源特性的影响，完善储能单体在充放电过程中各外部参数对SOC表征力的分析，奠定建立基于单体SOC的高效均衡方法的研究基础；建立均衡过程能量流的传递模型，提出均衡系统结构的有向图描述方法，用以分析能够实现的串联单体间能量直接交互传递的均衡电路拓扑；基于多种均衡拓扑的结构特征和同构性分析，进行多种均衡拓扑的优化组合方法研究，构建多层均衡系统；建立复杂失衡条件下储能系统的能量传递模型及其均衡代价函数，设计均衡路径寻优算法实现均衡策略的优化设计。为实现兼有均衡效率高、均衡速度快、线路结构简单的均衡系统结构及其均衡策略研究提供分析和设计的理论依据，促进动力型串联储能均衡技术进步和工业化应用。

动力锂离子电池作为储能设备应用于人造卫星、电动汽车和不间断电源等领域时，为了满足电压等级的要求，通常需要几十节甚至上百节串联使用。在串联电池组的使用过程中，由于各单体电池参数的不一致性，使单体之间电压出现不平衡，进而导致电池组的有效使用容量降低，循环寿命减少。因此，为了提高串联电池组的工作性能，开展锂离子电池均衡技术的研究是十分必要的。本项目将图论中的有向图和赋权矩阵引入到均衡拓扑结构的分析中，分别建立了典型结构的有向图及赋权矩阵描述，重点研究了均衡结构本身对能量传递路径的影响，在此基础上，归纳总结出理想均衡拓扑的有向图描述，明确了理想均衡拓扑中任意两个单体间都应有能量的直接流通路径，分析了理想均衡拓扑的可实现性，为寻求新型拓扑结构提供了理论指导。在对现有拓扑结构分析的基础上，构建了几种基于不同均衡器的多层均衡系统，通过理论分析和实验分析，研究均衡系统的性能最优组合方法。提出了一种基于多输出绕组变压器的均衡拓扑，该拓扑可以在两步内实现任意单体间能量的直接传递。均衡器根据电池组的不同失衡情况工作于三种模式，即反激模式、无输出电感正激模式和反激-反激模式，力求在不同失衡条件下均能实现快速、有效的均衡；对主电路的电磁元件和双向开关等进行了设计；分析了变压器漏感等参数对均衡器效率的影响，为进一步提高均衡器的效率提供理论依据。此外，建立了复杂失衡条件下储能系统的均衡策略优化控制模型，建立了能量传递模型及其均衡代价函数，设计均衡路径寻优算法实现均衡策略的优化设计。为实现兼有均衡效率高、均衡速度快、线路结构简单的均衡系统结构及其均衡策略研究提供分析和设计的理论依据，促进动力型串联储能均衡技术进步和工业化应用。