In recent years, T-type three-level inverter (TLI) has attracted attentions due to its advantages, such as simple structure and higher efficiency. Neutral point voltage (NPV) is very critical for its normal operation, and the necessary conditions of maintaining NPV balance respectively in a switching cycle and in a fundamental cycle are simply reviewed in this paper. With the increment of power switches, the reliability of T-type TLI becomes particularly important. When switch faults occur, fault-tolerant control strategies are usually adopted. However, in existing literatures, it is unknown whether the NPV balance can be still maintained under different fault types. Therefore, the application range of a fault-tolerant control is also unknown. In this paper, based on the necessary conditions of maintaining NPV balance, the application ranges of two representative fault-tolerant control strategies are revealed under different open-circuit (OC) fault types in inner switch. It found that the application ranges are closely related to the modulation index, load power factor (PF) and OC fault type. Finally, the correctness of the theoretical analysis is verified by the experimental results.

中文翻译：

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T型三电平逆变器在内部开关单相/多相开路故障下容错控制的应用范围

近年来，T型三电平逆变器（TLI）以其结构简单、效率高等优点备受关注。中性点电压（NPV）对其正常运行非常关键，本文简单综述了在开关周期和基波周期中分别保持NPV平衡的必要条件。随着功率开关的增加，T型TLI的可靠性变得尤为重要。当发生开关故障时，通常采用容错控制策略。然而，在现有文献中，在不同的故障类型下是否仍能保持 NPV 平衡尚不清楚。因此，容错控制的应用范围也是未知的。在本文中，基于保持 NPV 平衡的必要条件，揭示了两种具有代表性的容错控制策略在内部开关不同开路（OC）故障类型下的应用范围。结果发现，应用范围与调制指数、负载功率因数（PF）和OC故障类型密切相关。最后通过实验结果验证了理论分析的正确性。