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This paper presents a fault diagnosis method in the two-level three-phase voltage source converter (VSC) systems based on the average phase voltage (APV) model without additional sensors or hardware circuits, which can diagnose and locate multiple open-circuit (OC) faults correctly and quickly. First, based on the idea of average phase voltage within one switching period and the changing rules of basic voltage vector after OC faults, the APV model consisting of grid side APV (GAPV) model, pre-fault converter side APV (CAPV) model, and post-fault CAPV model is proposed. The APV model can be used to estimate the phase voltage under different OC faults. And then, the residual feature between GAPV and CAPV is analyzed under different single or multiple OC faults. With the help of the proposed APV model, both single and multiple OC faults can be diagnosed by deviation polarity, which avoids the complex deviation polarity sequences judgment. Meanwhile, the fault diagnosis method has the ability of correctness verification, which can strengthen the robustness and prevent false alarms. Finally, the effectiveness of the proposed model and method is validated with experiments, the multiple OC faults can be located within 2.5 ms.

This paper presents an open‐switch fault detection, and identification method for a neutral‐point clamped rectifier system. A new calculation method for phase‐to‐phase pole voltage deviations is proposed for reducing calculation errors. In this way, the more accurate diagnosis can be achieved. Both single‐switch faults, and multiple‐switch faults can be identified effectively by using fewer diagnostic variables, which makes the diagnostic method simpler, and more reliable. And all the variables can be simply calculated by signals which are available to the control system of the rectifier, avoiding the use of additional hardware. Moreover, different voltage thresholds are designed for different faulty feature sections to further reduce the diagnostic time. Additionally, a diagnostic result checking method is proposed to avoid the misdiagnosis when considering the effect of outer‐switch faults. Finally, experiments are carried out, and the results show the robustness, and effectiveness of the proposed method.

The open-switch fault of voltage source converters (VSC) may change the switching state and distort the current, which is the basis for model-based fault diagnosis methods. Based on the analysis of the switching state, this letter presents a post-fault current model to estimate the current of each phase after one open-switch fault occurs. Combined with the current model-based method, the proposed post-fault model can be used not only to check the accuracy of the diagnosis result but also to detect multiple open-switch faults. The current, voltage, and driving signals used in this model are all from the VSC control system, therefore, this model can be easily implemented without additional sensors or hardware. Finally, the effectiveness of the proposed model is verified by the experimental results.

The open-switch fault of three-phase voltage source rectifiers (VSR) may lead to ac current distortion. In the past decade, some current-based fault diagnosis methods have been proposed, which directly used the phenomenon of current distortion but lacked a detailed analysis of the cause of it. In this paper, the current distortion of VSR with unity power factor operation is analyzed from two aspects: the effect of the three-phase switching state on the ac current and the response of the VSR control system after the fault. Besides, the impact of the VSR system and control parameters on the current distortion is also discussed. The analysis verifies the feasibility of the distortion current for fault diagnosis, providing a theoretical basis for current-based fault diagnosis methods of VSRs. To substantiate the analysis of the distorted current, we designed a simplified fault diagnosis method, which determined the faulty phase by the difference of the normalized three-phase distorted current, and located the faulty switch by the grid voltage angle. The experiments are conducted to verify the analysis of current distortion and the reliability of the proposed fault diagnosis method.