Study On Fault Monitoring Method Of Inter-turn Short-circuit And Demagnetization Of Permanent Magnet Wind Generator

In recent years,wind energy plays a more and more important role in power system because of its large reserves,high technical maturity and easy exploitation.Direct drive permanent magnet synchronous wind turbine has outstanding advantages such as high efficiency,low noise and high power density.It has gradually become the mainstream choice of wind turbines with capacity of 5MW and above.However,owing to the impact of harsh environment,various faults of permanent magnet synchronous motor（PMSM）occur frequently in the operation process.These faults can affect the reliability,economy and safety of wind turbine.This paper studies the two faults of inter-turn short-circuit and demagnetization of PMSM,and designs the fault diagnosis methods.The methods can judge whether the fault occurs in the early stage of the fault,so as to improve the reliability of the unit.Based on the mathematical model of permanent magnet synchronous motor under normal conditions,the influence of two faults on electromagnetic parameters is analyzed in this paper.And deduces the mathematical model under inter-turn short-circuit and demagnetization fault,which provides the foundation for the construction of the model.This paper studies the characteristics and diagnosis technology of inter-turn shortcircuit fault of PMSM with star connection and triangular connection.And compares the changes of motor related output before and after the fault.The change of zero sequence component during inter-turn short-circuit urn to turn short circuit is analyzed.For the inter-turn short-circuit fault of star connected PMSM,a method based on zero sequence voltage is proposed to eliminate the interference of other factors on fault diagnosis.And the fundamental wave is extracted by FFT technology to detect the fault.For triangular connected PMSM,this paper completes the fault diagnosis by detecting the zero sequence current component.In addition,the fault indication is defined to remove the influence of speed on the zero sequence component of fault.For the identification of fault phase,the method of initial phase angle of zero sequence component can effectively realize the identification of fault phase.Pointing at the two fault forms of uniform demagnetization and local demagnetization of permanent magnet,the fault diagnosis methods are given respectively.For uniform demagnetization fault,by analyzing multiple fault characteristics before and after motor demagnetization fault,a uniform demagnetization fault diagnosis method based on flux identification is proposed.This method can quickly and effectively identify the flux linkage and back EMF of PMSM;The local demagnetization fault is directed against,through the research of theory and simulation,the method of local demagnetization fault diagnosis with flux linkage and back EMF as fault characteristics is further proved.Therefore,for the two demagnetization methods,the demagnetization fault diagnosis can be realized by detecting the back EMF and flux linkage amplitude.Meanwhile their amplitude can also be used as the basis for evaluating the demagnetization degree.The fault diagnosis methods proposed in this paper can realize two kinds of fault diagnosisfurther,heighten the reliability of wind turbine and cut down the running cost of wind turbine.The methods provide an important technical basis for promoting the development of wind power industry.