# Weak Fault Feature Extraction and Enhancement of Wind Turbine Bearing Based on OCYCBD and SVDD
## 6 Engineering Case Verification
### Engineering Signal Analysis and Result Comparison  
The proposed method is then applied to this engineering signal. Figure 17a is the calculated fast spectral coherence, and the search center of cyclic frequency is confirmed as \(a^{M}\) = 80.47 Hz. Then the cyclic frequency is optimized within the scope of [78 Hz,83 Hz] and the search step size is 0.05 Hz. Figure 17b shows the calculated MFWEE values corresponding to different cyclic frequencies, and the optimal cyclic frequency \(a^{o}\) = 79.4 Hz is selected based on the MFWEE minimum value. Within the scope of [20,200], the optimal filter length parameter is further searched with step size of 1. Figure 17c display s the calculated FWEE indicators corresponding to different filter lengths, and we can determinate the optimal filter length \(L^{o}\) = 157 according to the FWEE minimum value. Then the  
Figure 16: The collected engineering signal: (**a**) The waveform of engineering signal; (**b**) The frequency spectrum of engineering signal; (**c**) The envelope spectrum of engineering signal. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number of Balls** & **Diameter of Balls (mm)** & **Pitch Diameter (mm)** & **Contact Angle (\({}^{\circ}\))** \\ \hline
8 & 41.275 & 190 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Structure parameters of SKF6324 bearing. optimal influencing parameters are substituted into CYCBD to perform deconvolution operation on the engineering signal, and the obtained result is displayed in Figure 17d. The periodic impact components in the waveform are very rich, and the kurtosis index of this deconvolution signal is 8.74, which means the SNR of engineering signal has been improved drastically. Then the instantaneous energy signal of deconvolution signal is further calculated by FWEO operation. And SVDD is executed to reduce the noise interference and enhance the fault signature. During the process of signal denoising, the fitting error values corresponding to different singular value orders are obtained. From Figure 17e, we can find that the order 9 accords with the requirement of effective singular value order determination principle, then the former 9 singular values excepted for the first one are adopted to acquire the purified instantaneous energy signal. The corresponding enhanced energy spectrum of deconvolution signal is calculated and displayed in Figure 17f. And the peak spectral lines \(fo\)-\(3 fo\) corresponding to outer ring fault are noticeably presented in this figure. Thus, it is highly doubt there is local defect on the outer ring of generator front bearing, and the boarding check results verify this diagnosis conclusion. Thus, the effectiveness of presented method in achieving accurate weak fault detection for wind turbine bearing is demonstrated through this engineering case. The comparison methods of SK, MED, and MCKD are also applied to this collected engineering signal. The kurtogram is depicted in Figure 18a, and the band-pass filter is constructed in terms of the kurtogram information to process the engineering signal. Figure 18b displays  
Figure 17: Analysis results of engineering signal by proposed method: (**a**) The fast spectral coherence; (**b**) The MFWFE values corresponding to different cyclic frequencies; (**c**) The FWEE indicators corresponding to different filter lengths; (**d**) The waveform of deconvolution signal obtained by OCYCBD; (**e**) The fitting error values corresponding to different singular value orders; (**f**) The enhanced energy spectrum of deconvolution signal. effectively reflect the richness of periodic impact component, is proposed to evaluate the quality of deconvolution signal during parameter optimization process. 2. The OCYCBD method fusing the fast spectral coherence with the equal step size search strategy is put forward to overcome the drawback of CYCBD, by which the optimal deconvolution result can be achieved automatically. 3.