Multi-Point Open Circuit Faults Diagnosis Strategy of Modular Multilevel Converter Under Low Modulation Index
Lianqiang Wang, Li Zhang, Yongsheng Xiong, Zhuang Kang
Abstract
Modular multilevel converter (MMC) is one of the most attractive topologies in medium-voltage motor drives. Unfortunately, the open-circuit (OC) faults of the submodule (SM) switching devices affect seriously the MMC's reliable operation. Under the condition of a low modulation index, OC faults have a more severe impact, and the fault characteristics change fundamentally, bringing great challenges to the fault diagnosis strategy. Therefore, this article proposes a multipoint SM OC fault diagnosis strategy under a low modulation index, which consists of fault detection (FD) and fault location (FL). In more detail, FD improves the existing sliding-mode observer and realizes a rapid detection of the faulty arm and fault type. As for FL, it achieves the recovery of arm current and the differentiation of the SM capacitor-voltage data. Moreover, the OC fault diagnosis of SM can be achieved quickly and accurately through the strategy proposed in this article while using a low modulation index. In addition, this proposed strategy has fault tolerance and can reach the stability degree of MMC in a short time. Finally, the multipoint and the multitype fault diagnosis are carried out through simulation and experiment to verify the effectiveness of the proposed strategy.