适合电池梯次利用和混用的模块化多电平电池储能系统关键技术研究

The MMC-BESS is characterized by modular structure, excellent voltage quality and easy achieveing high voltage. It is unnecessary for BESS to achieve high rating by series connection and/or parallel connection, which could degrade the lifetime and capacity of battery becasue of cask effect. Modular structure makes MMC-BESS insensitive to battery consistency, and makes secondary used batteries and different batteries in one BESS possible..Following issues caused by secondary used batteries and different batteries will be resolved in this project..1) DC current could be injected into AC grid by transformerless MMC-BESS, and it may be worse due to secondary used batteries and different batteries;.2) There were circulating current with DC, grid frequency and switch frequency between MMC-BESS's in parallel, which will degrade MMC-BESS output power;.3) Greater balancing capabilty was required to maximize battery capacity utilization..Three topics studied in this project will be helpful to secondary used batteries and different batteries running in one MMC-BESS..1) The mechanism causing DC component in MMC-BESS with secondary used batteries and different batteries will be analyzed, then the DC current suppressing mothod will be proposed and verified by simulation and experiement;.2) The mechanism causing circulating current in MMC-BESS with secondary used batteries and different batteries will be analyzed, then the circulating current control strategy will be proposed and verified by simulation and experiement;.3) Balancing control strategies by transfering energy through DC terminal, DC bus and/or AC grid will be studied, and the balancing capability analysis of MMC-BESS which is guide for MMC-BESS design will be carried out.

模块化多电平结构具有高度模块化的特点、优良的输出特性和简单的电压扩展方式。该结构以模块的形式隔离了电池特性的差异，在极大降低了电池直接串并联规模的同时，使得在各子模块中采用不同梯次的电池和不同类型的电池成为可能。.电池的梯次利用和混用导致一些新的问题需要解决：.1）MMC无变压器并网可能在电网中产生直流分量，梯次利用的电池导致模块电压不同会使得这个问题更加严重；.2）并联运行的MMC-BESS之间可能产生直流、工频和高频环流；.3）电池梯次和混用的MMC-BESS需要更强的均衡功能，以最大化利用电池容量。.本申请将通过对如下三个内容的研究来实现和促进储能电池的梯次利用和混用。.1）适合电池梯次利用和混用的MMC-BESS交流侧直流分量的产生机理与控制策略；.2）适合电池梯次利用和混用的MMC-BESS并联环流机理和环流抑制技术；.3）MMC-BESS的均衡控制策略和均衡能力边界的研究。

模块化多电平电池储能系统（MMC-BESS）具有交流和直流两个对外端口，可以起到交直流互联、能量缓冲和稳定电网的作用。在微电网、海上风电等领域具有广泛的应用前景。.模块化多电平结构具有高度模块化的特点、优良的输出特性和简单的电压扩展方式。MMC-BESS以模块的形式隔离了电池特性的差异，在极大降低了电池直接串并联规模的同时，使得在各子模块中采用梯次电池和不同类型的电池成为可能。本项目通过对如下三个内容的研究来促进和实现储能电池的梯次利用和混用。.1）适合电池梯次利用和混用的MMC-BESS交流侧直流分量的产生机理与控制策略；.理论分析了电池电压不一致，驱动信号不匹配，开关特性不一致，SOC均衡策略对MMC-BESS交流侧电流直流分量的影响。推导了在电流控制环前向通道和反馈通道引入直流干扰对系统网侧输出电流产生的影响，仿真验证了直流电流分量抑制策略的可行性。.2）适合电池梯次利用和混用的MMC-BESS并联环流机理和环流抑制技术；.分析了子模块端口电压波动、子模块电池电压不一致性、开关信号不一致性和开关器件参数不一致性等对MMC-BESS环流的影响，提出了适合MMC-BESS的环流控制策略，搭建了6（桥臂）*8（子模块）的MMC-BESS实验平台，并在实验平台上对环流控制策略进行了验证。.3）MMC-BESS的均衡控制策略和均衡能力边界的研究。.针对MMC-BESS的并网运行工况论证了其在线均衡的基本原理，分析了电池梯次利用中多方面的差异因素对均衡控制的影响，提出了适合电池梯次利用的MMC-BESS在线均衡策略，分相间、桥臂间、子模块间三级将均衡策略细化到具体的电压电流控制方法，通过仿真和实验样机验证了在线均衡策略的有效性。.分析了MMC-BESS离线均衡的需求和等效电路，建立了离线运行的数学模型，提出了一种基于纯直流控制、支持电池梯次利用的MMC-BESS离线均衡控制策略，并通过Matlab/Simulink仿真和MMC-BESS实验样机验证了离线均衡策略的有效性。