Research On Detection Method Of Air-Gap Eccentricity Fault For Inverter-Fed Induction Motor

Induction motors are widely used in various fields because of their simple structure,reliable operation and low cost.However,the occurrence of motor faults is inevitable due to factors such as harsh working environment and variable operating conditions.Among them,the air-gap eccentricity fault is one of the most common faults of the motor,which is caused by the uneven air gap between the stator and the rotor of the motor.Currently,extensive research has been conducted on air-gap eccentricity of linefed induction motors.However,with the development of AC speed regulation technology and the advancement of energy conservation and emission reduction,more and more motors are driven by inverters.The previous detection method of air-gap eccentricity fault of line-fed motor may no longer be applicable.Based on this,this thesis conducts an in-depth study on the detection method of air-gap eccentricity fault of inverter-fed induction motor.The main research contents are as follows:(1)A fault detection method based on instantaneous power ripple track is proposed for the detection of air-gap eccentricity fault in induction motor under constant frequency and time-varying load.The method first uses a low-pass filter to filter out the high-frequency harmonic components introduced by the inverter in the stator voltage and current signals,and calculates the instantaneous values of the active and reactive power of the motor by means of the instantaneous power definition.Then,a band-pass filter is used to eliminate the effect of other harmonic components of the instantaneous power,retaining only the ripple component generated by the air-gap eccentricity fault.Finally,the characteristics of the instantaneous power ripple track of the motor are used to determine whether the motor has an air-gap eccentricity fault.In addition,a fault indicator is given to assess the severity of the air-gap eccentricity fault based on the magnitude of the ripple track.The effectiveness and superiority of the proposed method were verified by experiments.(2)A fault detection method based on frequency adaptive FRFT filtering is proposed for the detection of air-gap eccentricity fault in induction motor under dynamic variable frequency speed regulation.Firstly,the instantaneous frequency curve of the fundamental component is extracted using the short-time Fourier transform.Then,according to the change rate of the frequency curve,the original current signal is adaptively segmented into linear frequency modulation signals with different modulation frequencies,and the operating mode of the motor is determined.Finally,FRFT is used to filter out the fundamental frequency components in order to highlight the fault characteristics and thus achieve fault detection.In addition,a fault index is given to evaluate the severity of the air-gap eccentricity fault based on the magnitude of the time-frequency energy of the air-gap eccentricity component.Simulation and experimental results show that the proposed method can accurately detect air-gap eccentricity faults,and has the advantages of clear fault characteristics and high reliability.(3)In order to ensure the practical application of the proposed method to industrial sites,this thesis establishes an online detection system for air-gap eccentricity faults in induction motors based on Lab VIEW.The design and implementation of the hardware and software parts of the system are described in detail,and system tests are conducted to verify the feasibility and effectiveness of the system.64 figures,7 table and 85 references are included in this thesis.