MMC Fault-Tolerant Control via Multiple-SOGIs Based Circulating Current Suppression

One of the main fault types for modular multilevel converters is sub-module failures due to their impact on system reliability and operational availability. A fault-tolerant control method is hereby proposed in the presence of circulating current suppression using multiple second-order generalized integrators. The multiple second-order generalized integrators can extract dominant fault harmonic components separately, which are utilized for circulating current suppression control under faulty conditions. A comparative study is carried out using a medium voltage modular multilevel converter model created in MATLAB/Simulink, with classical proportional integrator-based and parallel proportional resonance-based methods. Results show that the fault-tolerant method using multiple second-order generalized integrators can achieve better fault harmonic suppression than the classical PI-based one. With respect to the similar parallel proportional resonance-based method, the proposed method can be an alternative solution but requires less parameter tuning efforts, and specific harmonic orders can be flexibly extracted.