Application Of Hilbert-huang Transform Method In Fault Diagnosis For Variable Frequency Speed Control Induction Machine System

Motor is the power equipment most widely used in all kinds of industries. With the development of modern science and technology, and the improvement of automation degree, asynchronous motors plays a more and more important role in modern industrial plants. When it works out of order or off-the line, not only the motor itself is destroyed but also the whole system would be in danger, and even the personal safety would be in danger and then the enormous economic losses would be caused. All these show that the condition monitoring and fault diagnosis is imperative and necessary. Under such a background, the techonology of the fault monitoring and diagnosis is hot and development. Through Motor status by monitoring and analysis of timely and effective manner on the motor maintenance, troubleshooting, in order to achieve the motor predictive maintenance, without affecting production.With the development of the variable frequency drives and its widely application in industry, the reliability of the variable-speed drive system has been considered much more than ever. A great deal of research effort has been and being spent on the fault detection and diagnosis of the drive system. For the variable-frequency adjustable-speed induction motor system, the original diagnostic method has difficulty in adapting the system for the change of power frequency in the variable-speed process. The operation mode needs to be determined at first, and then different diagnostic methods are used in different modes. In the fault diagnosis process, the fault related characteristic components are often submerged by the strong power supply because the fault characteristic components of the signal is weak. So it needs to convert the frequency signal of power line into the constant in new time-frequency domain.This paper describes the work principle of the frequency conversion speed regulation asynchronous electric motor and detailedly analyses the the characteristics of the mechanism for the rotor eccentricity and broken rotor bars of the three-phase squirrel cage induction motor. Also the Hilbert-Huang Transform method and its two important concepts are described, and the HHT method is applied to judge the operation mode of the motor. This method can quickly extract the rule of the power frequency to the time and it is able to distinguish the operation mode of the motor effectively. Then it provides the basis for the fault diagnosis to the variable-frequency adjustable-speed induction motor. In order to overcome the influence on the fault characteristics from power line broadband frequency component, the frequency signal of power line is converted to constant-frequency signal, so Generalized Fourier transform is brought in. Identification of the operation mode by HHT (Hilbert-Huang Transform) method can provide the required transfer function for Generalized Fourier transform to convert into the constant frequency signal for highlighting the fault features purpose. At last, the article conducts the simulation of operation mode based on HHT in terms of line frequency modulation and the situations including the normal state, broken rotor bars, the rotor eccentricity rotor and both the broken rotor bars and the rotor eccentricity rotor. The results of the experiment showed that this method got better effect.