一种改进的模块化多电平换流器电压平衡方法

摘要

基于排序的子模块电容电压均压方法是目前应用于大容量模块化多电平换流器(Modular Multilevel Converter,MMC)型高压直流输电系统的主流均压方式,存在排序运算量大、开关频率高等缺陷,带来较大的硬件投入,降低MMC运行可靠性.针对上述问题,引入时间复杂度更低的基数排序,结合MMC运行特点,去除冗余关键字,降低时间复杂度,在此基础上,根据控制器所需投入子模块数m,优化子模块全排序为寻求m个子模块,去除冗余运算,同时提出重排序判据,使MMC控制器选择性地排序,减少排序频度,增大原有触发脉冲维持时间,降低开关频率.最后,在MATLAB/SIMULINK搭建21电平MMC模型,仿真结果表明,改进基数MMC均压算法能在较好维持电容电压平衡的同时,大幅减少运算量,降低开关频率,验证了改进均压方法的可行性与有效性.%The Sort-based sub-module capacitor voltage method is the mainstream method used in superpower MMC-based on high voltage direct current (HVDC) transmission system, which has some deficiencies such as large amount of sorting-computation and high switching frequency.The existing deficiencies bring greater hardware investment while decrease the MMC reliability.To solve the issue above, an improved algorithm based on the lower time complexity radix sort is proposed.First, by analyzing the characteristics of MMC operation, redundant keywords are removed to reduce the time complexity, and on this basis, the full sort of the sub-module is optimized so as to search the SMs which meet demands of reducing the redundant operation;then the strategy of re-ranking is put forward to make the MMC controller sort selectively to reduce ordering operations and increase the original trigger pulse duration and reduce the switching frequency.Finally, simulation was carried out based on a 21-level MMC-HVDC system in MATLAB/SIMULINK.The efficiency and correctness of the improved sorting method in reducing switching loss sort frequency and calculation amount are proved.