This paper proposes a voltage difference residual-based fault diagnosis approach for three-level converters in electric traction systems. Compared to the existing open-circuit fault diagnosis approaches, the proposed approach can, not only detect and identify the faulty devices among the transistors and clamp diodes in both of rectifier and inverter, but also hierarchically diagnose the leg-level and device-level faults. Furthermore, no additional sensors are required and all of specified parameters can be directly identified. Specifically, the current related term in the DC-link voltage difference equations are analyzed and modeled under the normal case and open-circuit fault cases in the transistors and clamp diodes, respectively. Subsequently, the estimation models of the DC-link voltage difference are developed, and then, the residuals and their evaluation functions between estimation and actual are generated. Further, by analyzing the residual evaluation functions for various cases and building the current similarity functions, the hierarchical diagnosis algorithms are proposed to identify the leg-level and device-level faults. Finally, hardware-in-the-loop experiments are performed. The results show the effectiveness and robustness of the proposed approach.

This paper proposes a voltage-based hierarchical diagnosis approach for insulated gate bipolar transistors (IGBTs) open-circuit fault of two-level AC-DC-AC traction converters. The proposed approach can diagnose the open-circuit fault in the single-phase rectifier as well as in the three-phase inverter without extra sensors. Moreover, no mandatory control signal injection is required, which ensures safe operation. In addition, the different levels of diagnostic results are flexibly determined by the presented hierarchical diagnosis architecture, which depends on the market requirements of wide use of IGBT modules. To be specific, firstly, a mixed-logic-dynamic estimation model of DC-link voltage is established. Secondly, the diagnosis characteristic function (DCF) is constructed by way of a residual characteristic analysis under normal and various open-circuit fault cases. Thirdly, the vector angular similarity function (VASF) is calculated for leg-level diagnosis and the control signals switching matching method is used to locate the fault in the device-level. Finally, the experimental results show the effectiveness of the proposed approach.