| Induction motors are widely used in industrial applications for their ruggedness, efficiency and reliability. However, many kinds of failures could appear during the lifetime of induction motors due to stressed operating duty and/or atrocious operating circumtances. And bearing fault accounts for approximately30%, even up to40%, of induction motor failures. Thus, it is of great significance to detect bearing fault at an early stage for the reduction of maintaince costs and downtime. Recently, the use of Variable Frequency Speed Regulation (VFSR) induction motors, not suppled by AC grid but converter-fed, has been spreading for its high efficiency and good performance of speed adjustment, as would be a new challendge/trouble for the detection of bearing fault due to the complex switching operation and control of the converters. This thesis just addresses itself to the challendge/trouble.The bearing fault feature based on current signal was thoroughly analyzed in this thesis. Firstly, according to the conventional theory on bearing fault feature, the influences that the converter exterted on the spectra of stator current (converter output current), power supply current (converter output current), rectifier output current, inverter input current, as well as smoothing capacitor current, were revealed clearly. And the characteristic frequencies of the feature components in those currents, associated with bearing fault, were extracted. Secondly, the MATLAB/SIMULINK simulation models of V/F Control VFSR, Vector Control VFSR and Direct Torque Control VFSR induction motor, healthy or faulty with bearing fault, were established respectively, and the corresponding simulation has been completed. Finally, subdivision FFT was used to analyze the simulation results for validating the feature of bearing fault in VFSR induction motors.The main contribution of this thesis lies on providing some basis for the detection of bearing fault in VFSR induction motors. |
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