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Fault Diagnosis of Rotating Rectifier in Nuclear Multi-Phase Brushless Excitation System Based on Convolutional Neural Network |
Liang Zhengqiu1, Hao Liangliang1, Zhou Yanzhen2, Duan Xianwen3, Wang Guang4 |
1. School of Electrical Engineering Beijing Jiaotong University Beijing 100044 China; 2. Department of Electrical Engineering Tsinghua University Beijing 100084 China; 3. China Nuclear Power Operations Co. Ltd Shenzhen 518172 China; 4. Nanjing NR Electric Co. Ltd Nanjing 211102 China |
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Abstract The multi-phase brushless excitation system is widely used in large-capacity nuclear power plants. The safe and stable operation of nuclear power plants depends on accurately diagnosing rotating rectifier faults. However, the existing methods cannot accurately distinguish all types of faults, which makes it challenging to meet the demands in practice. Recently, as a representative artificial intelligence method, deep learning has provided new ideas for solving this problem. Therefore, this paper develops a fault diagnosis scheme for the rotating rectifier based on a convolutional neural network. First, taking an 11-phase brushless excitation system as an example, the excitation current characteristics after the rotating rectifier fault are analyzed. The results show that the excitation current waveforms contain amplitude and phase information of all fault harmonics, which can be varied under different fault modes and used for fault diagnosis of the rotating rectifier. Then, a one-dimensional dilated convolutional neural network (1D-DCNN) model is introduced to realize fault diagnosis. The 1D-DCNN establishes a mapping relationship from the input (excitation current waveforms) to the output (fault mode). Meanwhile, the difference between the largest and second-largest probability of the output is defined as the confidence based on the conditional probability of samples belonging to different fault modes given by the model, which is used to measure the reliability of the diagnosis results. The process of fault diagnosis based on the 1D-DCNN model includes three stages. At stage 1, raw data at several voltage levels are acquired to ensure the model has applicability and generalizability under different voltage levels. Then, the data are preprocessed regarding sliding window segmentation, filtering, and mean normalization. At stage 2, the 1D-DCNN model is trained to diagnose rotating rectifier faults online. At stage 3, the Score-CAM method is introduced to clarify the interpretability of the 1D-DCNN model. Finally, the prototype experiment verifies the effectiveness of the proposed 1D-DCNN model. Diode open-circuit faults in an 11-phase brushless excitation system are mainly studied, which includes eight fault types. The processed samples are divided into training, verification, and test sets. The verification set is utilized to determine the hyperparameters of the model. The variable control method is used to optimize the hyperparameters of each layer sequentially. Next, the Score-CAM method provides interpretability for the 1D-DCNN model and explains the hyperparameter influence on fault diagnosis performance. The diagnostic accuracy and confidence of different models are compared by the original test set and the test sets with noise. The 1D-DCNN model shows better anti-noise ability, which indicates that selecting the appropriate confidence threshold improves the classification accuracy of the model. In conclusion, the feasibility of fault diagnosis of rotating rectifiers based on a convolutional neural network is verified, providing a new data-driven idea for the fault diagnosis of rotating rectifiers.
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Received: 08 August 2022
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