The Application Of Generalized Demodulation Method In Fault Diagnosis Of A Asynchronous Motor Variable-frequency System

With the modern technology progressing and electrification improving, theVariable-Frequency system on the basis of inverter and induction motor has beenwidely applied in various industries, owing to its high energy efficiency, superiorperformance of speed control and excellent reliability. However, due to the fragility ofpower electronic devices and complexity of the motor load, the Variable-Frequencysystem is prone to malfunction and may lead to serious safety accidents. Thus, faultdiagnosis and online monitoring technology in the Variable-Frequency system has beena hot topic in academia. By monitoring and analysis of the Variable-Frequency system,faults can be found timely and effectively and making it possible for preventing furtherdeterioration. And it also makes it convenient for troubleshooting and reducing losses.When faults occur in the control system, the fault signal often contains a largenumber of nonlinear, time-varying component, the traditional signal processingmethods, such as Fourier transform could not efficiently extract the fault feature. As atime-frequency analysis method, generalized demodulation time-frequency analysismethod has an excellent processing result for multi-component non-stationary signals.Considering the superiority of this method, it will be applied to fault diagnosis of theVariable-Frequency system in this thesis.The thesis summarized characteristics of the squirrel cage induction motor andinverter’s common faults and diagnostic methods of them. Based on the summarization,the generalized demodulation analysis method is introduced to extract thecharacteristics of the IGBT inverter circuit fault, broken of motor rotor bars and air-gapeccentricity. By establishing fault simulation models in MATLAB, the stator currentsignal of normal and fault conditions were demodulated to extract the faultcharacteristic frequency. And by comparing the spectrum of normal operation and faultprocesses, it could be seen that the generalized frequency demodulation analysismethod can effectively determine the faults of broken rotor bars and air gap eccentricity. Finally, Park vector method was applied to the fault diagnosis, in whichthe IGBT’s open circuit fault occurs in the frequency control system during the courseof the dynamic speed control. The features of the Park vector maps were obtained withdifferent parts of IGBT fault. At last, simulation and experimental results give theproof of the effectiveness of the method.