Application Ranges of Fault-Tolerant Control for T-Type Three-Level Inverter Under Single/Multi-phase Open-Circuit Faults of Inner Switches

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.