The four-wire T-type three-level rectifier (four-wire 3LT2R) has a wide range of applications because of its excellent performance. However, the open-circuit fault of transistors can lead to power loss, current harmonics, and even system crashes. A novel open-circuit fault diagnosis method for four-wire 3LT2R based on the three-phase currents and modulation voltages is proposed in this article, considering power factor regulation. At first, the relationship between the power factor and the working interval of the transistor is deeply analyzed. Then, the diagnostic method is designed based on the analysis. The “zero current” in each phase current is used to detect the faults with the different features related to the size of working intervals. After the fault is detected, the fault transistor is located according to the polarities of the currents and the modulated voltages. No additional sensors are needed. Experiments are carried out, and the results show its high effectiveness, robustness, and applicability for different power factors.

中文翻译：

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四线制T型三电平整流器的一种开路故障诊断方法

四线制T型三电平整流器（四线制3LT2R）因其优良的性能而得到广泛的应用。然而，晶体管的开路故障会导致功率损耗、电流谐波甚至系统崩溃。本文提出了一种新的基于三相电流和调制电压的四线制 3LT2R 开路故障诊断方法，同时考虑功率因数调节。首先深入分析了功率因数与晶体管工作区间的关系。然后，在分析的基础上设计诊断方法。各相电流中的“零电流”用于检测具有与工作间隔大小相关的不同特征的故障。检测到故障后，根据电流和调制电压的极性定位故障晶体管。不需要额外的传感器。进行了实验，结果表明其高效性、鲁棒性和对不同功率因数的适用性。