Mingyun Chen

This article proposes an open-circuit (OC) fault diagnosis method in three-level neutral-point-clamped (NPC) rectifiers. In this method, OC faults are detected based on the deviation between actual and expected reference voltages, which are obtained without complex calculation, precise modeling, and extra hardware. More importantly, this method innovatively incorporates fault-tolerant control into the diagnosis process to locate the faulty switch more accurately and quickly. Fault-tolerant control is triggered before confirming the faulty switch. It can completely or partly eliminate reference voltage distortion caused by any outer-switch faults. Making use of this feature, outer- and inner-switch faults can be differentiated by checking whether reference voltages return to normal. Unlike other invasive methods that amplify fault characteristics, this method does not aggravate fault consequences. Using fault-tolerant control to replace the invasive location step of other methods can make a timely intervention of OC faults and save computing resources used for fault diagnosis and tolerance. Also, this method considers different operating states of NPC rectifiers, including modulation index and power factor variation. Moreover, this method can be easily extended to multiple-switch and clamping diode fault diagnosis. Experiments are carried out to confirm the effectiveness of the proposed fault diagnosis method.

This article proposes a new open-circuit (OC) fault diagnosis method for power switches in three-level neutral-point-clamped (NPC) rectifiers. This method is based on fault assumption by introducing a new voltage deviation for diagnosis, which is the difference between the switching-state-based voltage and the fault-assumed-based voltage, where the fault-assumed-based voltage is the estimated pole voltage when all inner switches are assumed to be in the OC state. After average and sum operations, diagnostic variables are developed from three-phase voltage deviations without extra hardware and precise modeling. Since the fault characteristics of each switch reflected by diagnostic variables are not changed by other concurrent OC faults, multiple-switch faults can be diagnosed in the same way as single-switch faults. As a result, the proposed method can detect both single-switch and multiple-switch faults without complex diagnostic rules and procedures. Besides, adaptive thresholds are designed by considering voltage imbalance, current amplitude, and power factor. Owing to the self-adjusting characteristics of thresholds, the proposed method provides reliable diagnostic results in various operating states of NPC rectifiers and has good robustness against transient changes. Experiments are performed to confirm its effectiveness and robustness.

This article proposes an open-circuit fault diagnosis method in power semiconductors of three-level neutral-point-clamped (3L-NPC) rectifiers by using a fault injection strategy. To enhance the anti-interference ability of the diagnosis method, an improvement is made in the traditional calculation method of phase-to-phase pole voltage residuals by selectively adopting the quantifying operation according to the current level. Then, the normalized and quantified residuals are obtained as the diagnosis variables. All signals for calculations are derived from the controller and pre-existing sensors, avoiding the requirement of extra hardware. To improve the diagnosis accuracy and speed, a fault injection strategy is designed. A preidentification method provides guidance for choosing the type of fault to inject. On this basis, the fault injection is implemented by revising the switching signals sent from the modulation module for a short time. In this way, inner-switch faults and outer-switch faults are easier to be differentiated, and the misdiagnosis of simultaneous multiple-switch faults is avoided. Therefore, the proposed diagnosis method is accessible to detect single-switch faults as well as multiple-switch faults in 3L-NPC rectifiers more accurately and fast. The experiments are carried out to confirm the effectiveness and the robustness of the proposed fault diagnosis method.

This article 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 APV 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, prefault converter-side APV (CAPV) model, and postfault 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.