A Diagnosis Method for Power Switch and Current Sensor Faults in Grid-Connected Three-Level Neutral-Point Clamped Inverters Based on Adaptive Sliding Mode Observer
Xu Shuiqing1, Xu Xiaofan1, He Yigang2, Chai Yi3
1. College of Electrical Engineering and Automation Hefei University of Technology Hefei 230009 China; 2. School of Electrical Engineering and Automation Wuhan University Wuhan 430072 China; 3. State Key Laboratory of Power Transmission Equipment Technology Chongqing University Chongqing 400044 China
Abstract：The grid-connected three-level neutral-point clamped (3L-NPC) inverter is widely used in grid-connected systems for new energy generation due to its advantages such as low output voltage and current harmonics. However, an open-circuit fault in power switch or a fault in the current sensor within the inverter can lead to a decrease in system performance and may even trigger significant safety incidents within the power grid. Nowadays, most of the fault diagnosis methods for 3L-NPC inverters focus on single-fault diagnosis. Therefore, this paper presents a simultaneous fault diagnosis method for both the power switch open-circuit fault and current sensor fault in 3L-NPC inverter based on an adaptive sliding mode observer. Firstly, an adaptive sliding mode observer with fast convergence speed and significant chattering suppression is designed to accurately estimate the three-phase current value in normal state. Then, fault diagnosis variables are designed using estimated and actual currents.In the absence of a fault in the inverter, the fault detection variable dx stays within the adaptive threshold range. However, in the event of a fault, the detection variable dx rapidly surpasses the adaptive threshold. The faulty phase can be determined based on the absolutemaximum values of the fault detection variables ra, rb and rc. Additionally, if the sum of the three-phase currents falls within the adaptive threshold range, it signifies a power switch open-circuit fault on the faulty phase. Conversely, it indicates a sensor fault has occurred on the faulty phase. On the basis of completing the fault detection, we further carry out fault identification. In the event of a power switch open-circuit fault in the inverter, the specific location of the faulty power switch can be determined using the fault localization variable wx. In cases of a current sensor fault within the inverter, a rapid identification of the type of current sensor fault can be achieved by combining the fault localization variable wx with the fault identification variable Bx. Through the establishment of a hardware-in-the-loop experimental platform, we have successfully validated the effectiveness of the fault diagnostic algorithm presented in this paper. The diagnostic algorithm demonstrates a remarkable trait of not producing false alarms even under conditions involving DC-side voltage fluctuations, grid voltage fluctuations, and inductive parameter imbalances, showcasing its robustness. In conclusion, after conducting experimental verification and analysis, it can be affirmed that the fault diagnosis method devised in this paper possesses the following advantages: (1) The simultaneous diagnosis method of power switch open-circuit faults and current sensor faults of 3L-NPC inverter is proposed, which not only prevents false fault reports arising from the mutual influence of these two fault types in a single diagnosis but also facilitates prompt implementation of follow-up maintenance measures after detecting the faults. (2) Through the design of an innovative adaptive convergence law, we have constructed an adaptive sliding mode observer with rapid convergence and substantial jitter suppression. This enhancement results in more precise current observations, thereby ensuring the effectiveness of the fault diagnosis method. (3) A novel fault detection and identification method is introduced. Through the utilization of only actual and estimated current values, without the need for intricate data processing or additional hardware configurations, fault detection and diagnostic variables have been designed, enabling rapid and accurate fault diagnosis.
许水清, 许晓凡, 何怡刚, 柴毅. 基于自适应滑模观测器的中点钳位型三电平并网逆变器开关管和电流传感器故障诊断[J]. 电工技术学报, 2024, 39(13): 4066-4078.
Xu Shuiqing, Xu Xiaofan, He Yigang, Chai Yi. A Diagnosis Method for Power Switch and Current Sensor Faults in Grid-Connected Three-Level Neutral-Point Clamped Inverters Based on Adaptive Sliding Mode Observer. Transactions of China Electrotechnical Society, 2024, 39(13): 4066-4078.
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2024, Vol. 39 
