基于超级电容储能的模块化多电平变换器变频运行与能量管理机制研究

During variable-frequency operation the trend of fluctuations of submodule capacitor voltages in modular multilevel converters (MMC) is time-varying and nolinear. It is the main bottleneck for popularization and application of the MMC technology in the field of medium voltage drive. In this project special focus is given on a new type of distributed and embedded supercapacitor energy storage modules integration based MMC system and its control. Applicants propose that it can make up the bridge arm energy gaps by releasing and recycling energy from external supercapacitor energy storage power units in variable-frequency operation mode, making the submodule capacitor voltages controlled within a reasonable range, to realize stable operation of the MMC in the whole frequency domain. While fully excavating the integration structure for improving the performance of system, the project will also engage in the scientific research of the variable-frequency operation of supercapacitor energy storage based MMC in the field of mathematical laws for changing of internal state, the state of charge (SOC) balancing for supercapacitor, and building an optimal energy management mechanism. Through the above work, it is able to solve the common foundation issues of power flow control for the distributed and embedded supercapacitor energy storage system. The conclusions can provide policy basis and scientific guidance for energy-saving and stable operation of the MMC-fed medium voltage drive systems.

模块化多电平变换器变频运行时子模块电容电压波动趋势的时变性和非线性是制约该技术在中压传动领域推广应用的主要瓶颈。本项目探索研究一种新型的基于分散嵌入式超级电容储能模块接入的模块化多电平变换器系统及其控制，拟通过外部接入的超级电容储能功率单元的能量释放和回收的方式弥补变频运行时的桥臂能量缺额，使子模块电容电压能够被控制在合理的范围，实现全频域稳定运行。在充分挖掘该集成结构提高系统性能的同时，本项目还将对变频运行的超级电容储能型模块化多电平变换器内部状态变化数学规律及超级电容储能单元荷电状态均衡进行科学研究，构建能量优化管理机制。通过开展上述工作，能够解决分散嵌入式的超级电容储能系统功率流控制的共性基础问题，为模块化多电平变换器供电的中压传动系统节能稳定运行提供理论依据和科学指导。

本项目针对模块化多电平变换器在中压传动应用存在的电容电压波动瓶颈问题提出一种新的集成超级电容储能单元的拓扑结构；以降低子模块电容电压纹波为目标，研究适合这种拓扑的调制策略、控制方法、变换器子模块配置方法；研究了超级电容储能单元与多电平DC-AC接口部分的能量交互过程，以及超级电容储能单元单元间的SOC均衡控制策略；总结储能型模块化多电平变换器内部状态变化的数学规律，探索建立适合低频和变频运行的控制理论和方法。本项目对于MMC电路拓扑在中压大功率交流电机调速和轨道交通牵引传动领域的应用具有重要的理论价值和现实指导意义。