Recent applications of modular multilevel converter (MMC) have posed various problems such as ac/dc grid faults, asymmetric operation conditions, ac grid voltage excessive harmonics, and ac circulating currents, which deteriorate the system's performance and also threaten the safe operation. In this article, an improved comprehensive control architecture of MMC is proposed to maintain a stable voltage control, eliminate harmonics in ac-side and circulating currents, and dc-bus voltage ripple under ac/dc grid faults and harmonic operation conditions. The proposed comprehensive control consists of improved hierarchical voltage control and repetitive controller-based arm current control. The improved hierarchical voltage control, including a novel negative-sequence current injection and dc-circulating current injection-based leg-averaging control and their seamlessly switching handling, enables the MMC to operate under various operating conditions, thereby producing the arm current reference for inner-loop control. The proposed repetitive controller-based arm current control can recognize the control of multifrequency components of arm current without separating positive-, negative- and zero-sequence current components of ac-side currents and circulating currents. Finally, the simulation and experimental studies of the three-phase MMC were carried out in detail, and the findings demonstrate the efficiency and merits of the proposed control method.

中文翻译：

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交流/直流电网故障和谐波运行条件下模块化多电平转换器的改进综合控制

模块化多电平转换器（MMC）的最新应用带来了各种问题，例如ac / dc电网故障，不对称运行条件，ac电网电压过高的谐波和ac循环电流，这些都会使系统性能下降，并威胁安全运行。在本文中，提出了一种改进的MMC综合控制架构，以维持稳定的电压控制，消除交流侧和循环电流中的谐波以及交流/直流电网故障和谐波运行条件下的直流总线电压纹波。拟议的综合控制包括改进的分级电压控制和基于重复控制器的臂电流控制。改进的分级电压控制，包括新颖的负序电流注入和基于dc循环电流注入的均线控制以及它们的无缝切换处理功能，MMC可以在各种工作条件下运行，从而产生用于内环控制的臂电流参考。所提出的基于重复控制器的臂电流控制可以识别臂电流的多频分量控制，而无需分离交流侧电流和循环电流的正序，负序和零序电流分量。最后，对三相MMC进行了详细的仿真和实验研究，结果表明了该控制方法的有效性和优点。从而产生用于内环控制的臂电流参考。所提出的基于重复控制器的臂电流控制可以在不分离交流侧电流和循环电流的正序，负序和零序电流分量的情况下识别臂电流的多频分量的控制。最后，对三相MMC进行了详细的仿真和实验研究，结果表明了该控制方法的有效性和优点。从而产生用于内环控制的臂电流参考。所提出的基于重复控制器的臂电流控制可以在不分离交流侧电流和循环电流的正序，负序和零序电流分量的情况下识别臂电流的多频分量的控制。最后，对三相MMC进行了详细的仿真和实验研究，结果表明了该控制方法的有效性和优点。