Application of adaptive local iterative filtering and approximate entropy to vibration signal denoising of hydropower unit

In actual field testing environments of hydropower unit, unit vibration signals are often contaminated with noise. In order to obtain the real vibration signal, a vibration signal de-noising method of hydropower unit based on adaptive local iterative filtering (ALIF) and approximate entropy is presented. For the proposed method, the ALIF method is used to decompose vibration signal into several stable components. The approximate entropy of each component is calculated. According to a preset threshold value of approximate entropy, the eligible components are retained to achieve the noise cancellation of hydropower unit's vibration signals. The ALIF-based method and the wavelet denoising method is compared by simulation signal and real signal. The root mean square error (RMSE), partial correlation index and signal to noise ratio (SNR) are used to evaluate the noise reduction ability of two methods. The results show that compared to the classical wavelet denoising method, the noise canceling ability of this proposed method has improved in some extent. It can more effectively suppress the noise of hydropower unit's vibration signals. The denoised vibration signals are used to synthesize the shaft orbits of hydropower unit. This can effectively identify the rotor shaft orbit graphics and the operation state of hydropower unit.