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Keywords

modular multilevel converter, submodule fault, fault-tolerant control, fundamental frequency control, sliding mode control

Abstract

To address the problems of asymmetric arm operation and fundamental and second-harmonic circulating currents caused by submodule faults in a modular multilevel converter (MMC) under hot standby in a flexible direct current system, a fault-tolerant control strategy coordinated by an improved PIR circulating current control and an inner-loop current sliding mode control is proposed. By introducing a three-parameter notch filter to precisely separate the circulating current components, the improved PIR control achieves the coordinated suppression of fundamental and second-harmonic harmonics. Simultaneously, the traditional PI inner-loop control is replaced by the sliding mode control to significantly improve the dynamic response speed and robustness of the system. Simulations based on Matlab/Simulink and RT-LAB hardware-in-the-loop experiments show that the proposed strategy can effectively suppress the circulating current harmonic components, rapidly stabilize the capacitor voltage and direct current, and reduce the grid-side alternating current fluctuation. Furthermore, it achieves stable system recovery with superior regulation performance after a submodule fault, verifying its multi-frequency harmonic suppression capability and dynamic control advantages.

DOI

10.19781/j.issn.1673-9140.2026.03.025

First Page

269

Last Page

279

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