电网不平衡下基于MMC的分数阶积分滑模控制策略研究

Fractional‑order integral sliding mode control strategy based on MMC under unbalanced grid conditions

为增强模块化多电平换流器(modular multilevel converter,MMC)在电网不平衡条件下的系统性能,该文提出一种分数阶积分滑模控制(fractional order integral sliding mode control,FO‐I‐SMC)策略。首先,分析MMC的拓扑结构,并推导出正、负序电压与输出电流的基频外特性方程和正负零序环流的二倍频内特性方程。其次,结合控制目标和MMC的数学模型,设计出应用于电网电压不平衡的分数阶滑模控制器。该控制器旨在降低交流侧输出电流与直流侧环流谐波含量。最后,在MATLAB/Simulink仿真平台建立相应模型,验证该算法的有效性。研究结果证明:采用FO‐I‐SMC控制策略的MMC的系统性能要明显优于采用比例积分(proportional integral,PI)控制策略和积分滑模控制(integral sliding mode control,ISMC)策略的。

To enhance the system performance of the modular multilevel converter(MMC)under unbalanced grid conditions,this paper proposes a fractional order integral sliding mode control(FO-I-SMC)strategy.Firstly,the topology of the MMC is analyzed,and the fundamental frequency external characteristic equations of positive-and negative-sequence voltages and output currents,as well as the double frequency internal characteristic equations of positive-,negative-,and zero-sequence circulating currents,are derived.Secondly,combining the control objectives with the mathematical model of the MMC,a fractional order sliding mode controller is designed for application in unbalanced grid voltages.This controller aims to reduce the harmonic content in the AC-side output current and the DCside circulating current.Finally,a corresponding model is established on the Matlab/Simulink simulation platform to verify the effectiveness of the proposed algorithm.The research results demonstrate that the system performance of the MMC using the FO-I-SMC strategy is significantly better than that using the proportional integral(PI)control strategy and the integral sliding mode control(ISMC)strategy.