Studies On Induction Motor Starting Character Indirect Measurement Based On Wavelet Theory

With the development of modern science and technonlogy ,electric machines play a more and more important role in modern industrial plant. In the domain of motor test, the characteristics of motor starting speed is of the important one. A creative ideas of applications of wavelet theory in the motor testing field is discussed in this paper.The traditional signal analysis methods,such as Fourier transform ,is not so efficient and useful for the starting signal of the motor testing field.A fast n characteristic testing system without speed sensor is successfully developed,based on orthogonal wavelet packet transform and wavelet ridge.Traditional analysis method of signal is not efficient to nonstationary signal ,such as motor starting current signal .however wavelet analysis has the excellent time-frequency local performance ,it can detect the different frequency component of signal by its adjustable time-frequency window. In view of the superiority of wavelet transform to nonstartionary signal,this paper focuses on how to apply the starting testing signal.This dissertation contains the following parts:1). Analyze speed character in stator slot harmonic current and rotor current in the induction motor and propose the relation in slot harmonic frequency and speed. On the basis of this .propose the nondirect measurement principle of the induction motor.Establish the simulation model of the induction motor with Matlab\Simulink and research the starting performance of the induction motor .2). More systematic summary explain wavelet basic theories , put in order Fourier transform , short-time Fourier transform ,the wavelet transform (Continuous Wavelet Transfrom and Discrete Wavelet Transform) and Multiresolution Analysis Their inner link and difference is explained.Expound limitation of the FT(pure frequency domain analysis) and the wavelet is super in the nonstationary signal and reason of dealing with the respect..3) It is induction motor in field of testing for particularity where signal deal with,it explain emphatically wavelet theory not light go making an uproar, filtering, reconstructing and time-frequency analysis. We prppose a new thresholding denoisingalgorithm based on the wavelet energy cell and apply it to start stator and rotor current signal.We filters and reconstructs stator current signal and require low-frequency and high-frequency component.Propose two time-frequency analysis algorithms -orthogonal wavelet packet transform and wavelet ridge and give their program processes.we apply them to the frequency extraction of the stator slot harmonic and rotor current signal.We successful get start character of the induction motor.Test result demonstrates:the method realizes the starting performance nondirect measurement of the induction motor.By comparision,the nondirect measurement removes the speed and torque sensor and measurement result is perfectly accurate.4) Design current data acquisition system of the induction motor and require start stator and rotor current data. The system is composed of the induction motor, current sensor, RVO data acquisition card and PC. Test includes the choice of test instrument test design and connection and data pre-process.5) apply wavelet analysis to start stator current signal: denoising filtering and reconstructing and time-frequency analysis.We extracting the frequency of slot harmonic in stator current. The 5th chapter systematic pluses and minuses of the two analysis, the scope of application and existing problem, the frequency-time relation of the current signal of the rotor is extracted with wavelet theory at the same time.The result that the stator current and rotor current test are compared.Test result demonstrates:rotor current method is simple and feasible but its accuracy is not satisfactory. By comparision, stator current method is more difficult than rotor current.