Research On Identification Method Of Bearing Current Damage In Wind Turbine Based On Bispectrum Analysis

Bearing is the key components of the wind turbine,because pulse width modulation is used in inverter of the wind turbine,a common mode voltage is formed at the neutral point of the stator winding of the motor,the shaft voltage is induced on the shaft and the shaft current is generated,and the shaft current can damage the wind turbine bearing that will shorten the bearing life,and it can seriously affect the safe operation of wind turbines.Therefore,it is of great significance to research the method about the shaft current damage identification of wind turbine bearing,The main research work are as follows:(1)A simulation test bed about wind turbine shaft current damage is established,and the fault vibration signal of the shaft current damage bearing is collected,the characteristics of time domain and frequency domain signal both bearing common fault and shaft current damage fault are analyzed,it can be seen from envelope spectrum,the characteristic frequency of the pitting and shaft current damage on outer ring are presented as the fault characteristic frequency of the outer ring and its harmonic frequency,fault characteristic frequency amplitude of shaft current damage is greater,higher harmonic frequencies are relatively weak.(2)A method of bearing current damage identification based on the maximum concentrated carrier frequency is proposed by Modulation Signal Bispectrum(MSB)theory.By modulating bispectrum analysis,the bearing vibration signal construct a bispectrum which is composed of signal frequency and carrier frequency,for the same outer ring fault,that is pitting fault and shaft current damage fault,from the perspective of the maximum carrier frequency,the maximum carrier frequency of the pitting fault is concentrated around 2600 Hz,and the maximum carrier frequency of the shaft current damage is concentrated near 2400 Hz.(3)A diagonal slice analysis method based on frequency shift modulation bispectrum is proposed by improving the algorithm of MSB.First,demodulating bearing vibration signal is analysed through the modulation signal bispectrum,the maximum carrier frequency of the fault signal is obtained,and then shift whole modulation bispectrum to the origin of coordinates which distance is the maximum carrier frequency,the frequency shift modulation bispectrum is obtained,finally,the diagonal slice spectrum of the modulated bispectrum can be obtained through diagonal slice,the fault characteristic frequency of the bearing is extracted.This method can effectively reduce the influence of fault harmonics frequency and frequency aliasing,the characteristic frequency of each fault is extracted from the multi-fault composite bearing vibration signal,and the bearing fault location and fault type is distinguished by combining with the bispectrum maximum carrier frequency.(4)A fault diagnosis method is proposed combined the bispectrum with locality preserving projection.Firstly,the envelope of vibration signal and the bispectrum calculation are carried out by the Hilbert transform,and then the signal bispectrum is projected to the intrinsic dimension space in the case of ensuring local structure of bispectrum is constant,the fault characteristics of the bearing is obtained and recognize fault pattern.The experimental results show that the method can effectively identify the bearing shaft current damage,and the recognition accuracy of classification of bearing fault included shaft current damage is more than 96.25%.