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基于阳极电流波动信号的铝电解槽槽况诊断方法研究
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摘要
铝电解槽的稳定性研究是铝电解生产中的热点课题,从铝电解槽可在线采集量入手诊断其运行状况,进行相应的操作是提高其稳定性的重要措施。阳极电流是铝电解槽中一个能够在线采集的重要参数,其信号中包含大量的与电解槽运行状况相关的信息。可从阳极电流信号中提取槽况特征,建立相应的槽况诊断模型。
     以160kA系列预焙铝电解槽为研究对象,采集了正常槽和典型故障槽的阳极电流信号,利用“频谱—小波包—神经网络”相结合的方法对信号进行分析处理,得到以下结论:
     (1)利用频谱分析方法,研究不同槽况下阳极电流信号的频谱特点。采用Yule-Walker方法的功率谱估计提取出不同槽况阳极电流的频谱特征,较好区分了正常槽、冷槽及极破损槽,并得到正常槽、冷槽及极破损槽功率谱曲线主谱峰的频率范围,分别为:0.003~0.018Hz、0.023~0.027 Hz、0.027~0.031 Hz。将功率谱分析结果与HHT的边际谱分析结果进行对比,结果表明功率谱分析结果具有较好的可靠性。
     (2)根据功率谱分析结果,提出了阳极电流信号的小波包能量特征概念。对阳极电流信号进行小波除噪,对除噪后的阳极电流信号进行小波包4层分解和5层分解,并提取其能量特征向量。根据小波包4层分解和5层分解的结果,优化分析,选择合适的小波包重构系数,提取了不同槽况下的能量特征向量,并做归一化处理,使不同槽况下能量特征向量的差距明显,较好的区分了不同槽况下的阳极电流信号的特征,为槽况的诊断提供依据。
     (3)根据阳极电流信号小波包能量特征向量,建立了基于BP神经网络的故障诊断模型,并对其验证。仿真与验证结果表明:此网络辨别的模式简单,识别的准确率高,有利于在线监测和实时识别。
Stability is one of the spotlights in aluminum electrolysis process research. Diagnosing the working conditions of an aluminum reduction cell from its online parameters in order to take proper measures is an important strategy to enhance its stability. Anode current is one of the important parameters that can be collected online, whose signals contain a lot of information concerning the performance of an aluminum reduction cell. Diagnosis method is established by extracting characteristics from anode current signals.
     As the object of 160kA pre-baked anode cells, anode current signals were collected under either normal cells or typical problem cells. These signals were analyzed by the method of "spectrum-wavelet packet-neural network" with results are as follows:
     (1) Spectral characteristics of anode current signals in different cell states were investigated by spectral analysis method. Power spectrum estimation based on the Yule-Walker method was put forward to extract the spectral characteristics of anode current signals in different cell states, by which normal, cold and cathode fail cell would be distinguished by recognizing their frequency ranges of main peak as 0.003-0.018Hz,0.023-0.027Hz, and 0.027-0.031Hz respectively. The results of power spectrum estimation analysis have been compared with the results of HHT (Hilbert-Huang Transform) marginal spectrum analysis, which shows it is reliable for power spectrum estimation to analyze the anode current signals.
     (2) According to the results of power spectrum analysis, the concept of wavelet packets energy characteristics for anode current signal was introduced. Wavelet packets decomposition was performed at level 4 and 5 for anode current signals de-noised with wavelet, and related decomposition energy characteristics vectors were extracted. The results of wavelet packets decomposition was optimized, the appropriate wavelet packets reconstruction was selected, and the energy characteristics vectors of anode current signals were extracted in different cell states. Energy characteristics vectors that were normalized have obvious difference, which make a better distinction between the different cell states, provide the evidence for the diagnosis of cell states.
     (3) According to the wavelet packet energy characteristics vectors extracted from anode current signals, diagnosis model based on BP neural network was established and verified. Simulation results show that the model of network identification is simple in construction, high accuracy in recognition, and convenient to realize on-line monitoring and real-time identification.
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