Research On Fault Diagnosis And Fault Tolerant Control Of Three Phase Inverter

In recent years more and more attention is paid to energy issues, while implementation offrequency control of the motor is a good way to save energy. With the development of powerelectronics technology and the upgrading of the power electronic devices, variable frequencysystem has been widely used in various fields. It is very important to make sure of the variablefrequency system run safety. In the system, the reliability of the inverter has not been effectivelysolved. It is a prerequisite to ensure the normal operation of the motor system that how toquickly and accurately determine the type and the location of the inverter failures and areasonable circuit redundancy design. Therefore it is necessary to study the fault of the inverter.This paper first analyzes the mathematical model and the operating principle of thepermanent magnet synchronous motor in the three-phase stationary frame and the dq axis. Themain study is the structure of permanent magnet synchronous variable frequency system and itspulse width modulation mode.The possible failures of the inverter and the causes of these failures are analyzed in thisthesis. In the environment of matlab simulink, S function is used to written the normal invertercondition simulink module and fault state simulink module when the switching device is open orshort-circuit. The simulation of the inverter-fed permanent magnet synchronous motor isachieved. The output characteristics of the inverter-fed permanent magnet synchronous motorspeed control system are obtained.In this paper, using the advantage of wavelet analysis, signals obtained from the simulinkanalysis of the inverter are analyzed and processed by selecting the db5wavelet basis of thedaubechies wavelet. The seventh layer of the detail signal obtained from the wavelet analysis isused to conducted envelope and spectral analysis. The type of failure is determined by the peakand different harmonic of the spectral analysis. And also the inverter fault is diagnosed.After the fault detection, in order to reconstruction of the inverter, the fourth bridge arm isadded to the original three-phase inverter. The fault bridge arm is removed by the fault isolationcircuit. Use of the two-way switch characteristics of triac, the fourth bridge is switched to thecircuit. So the reconstruction of the inverter is accomplished, the operation of the system isnormal again.