基于线性最优的MMC子模块电容电压均衡控制策略

摘要

为进一步优化模块化多电平换流器(MMC)子模块控制策略,尤其是能够兼顾子模块电容电压波动、桥臂环流二次谐波含量、子模块绝缘栅双极型晶体管(IGBT)投切次数和算法计算量四方面的性能,提出一种基于线性最优解的MMC子模块电容电压均衡控制策略.首先,阐述了子模块电容电压波动和子模块IGBT投切次数之间的相悖性,通过理论分析证明子模块电容电压波动与桥臂环流二次谐波含量之间也存在非线性关系,需寻找适当算法使其三者同时达到最优情况.然后,针对此目标,对传统算法进行优化,增加附加调节子模块功能,并结合子模块电容电压均衡控制策略,详细阐述了所述算法的控制流程及其优越性.最后,通过动模试验对传统控制策略、子模块电容电压均衡控制策略、所提控制策略及其他采用不同数量的附加调节子模块的控制策略进行对比.试验数据表明,所提策略可以在子模块电压波动、桥臂环流中的二次谐波含量和子模块IGBT投切次数三方面达到线性最优.%To further optimize the modular multilevel converter (MMC) sub-module control strategy,especially the added ability to balance the performance of sub-module capacitor voltage fluctuations,the second harmonic of bridge arm circulating current,sub-module insulated gate bipolar transistor (IGBT) switching frequency and algorithmic computation,a kind of strategy based on the linear optimal solution is promoted to control the multilevel converter sub-module capacitor voltage balance.First,the inconsistency between sub-module capacitor voltage fluctuations and IGBT switching frequency in the submodule is described.The analysis has also proved the existence of a nonlinear relationship between sub module capacitor voltage fluctuation and second harmonic of the bridge arm circulating current and the necessity of finding an appropriate algorithm for them to be in an optimal situation at the same time.Then,for this goal,combined with a control algorithm proposed in literature,a strategy using an additional sub-module regulator is proposed to optimize the conventional algorithm and the control flow algorithm and its advantages are given.Finally,the conventional control strategy,the strategy proposed in literature,the proposed strategy and another control strategy which uses different quantities of additional sub-module regulator are compared by a dynamic simulation test.Experiment data indicate that the proposed strategy can achieve linearly best between sub-module voltage fluctuations,second harmonic of bridge arm circulating current and sub-module IGBT switching frequency.