Analysis On Stator Winding Electromagnetic Force Of Doubly Fed Induction Generators Under Air-gap Eccentricity Fault

Double-fed induction generator(DFIG)is one of the most widely used wind generators at present,and its safe and stable operation is of great significance to promote the development of wind power industry.Air gap eccentricity is one of the common mechanical faults of wind generators,and the wear problem caused by winding vibration is a common problem faced by domestic wind generators at present.It is of great significance to study the electromagnetic force(EMF)of the stator winding under the air gap eccentricity fault of the wind generators,which is important to explore the damage mechanism of the winding insulation wear and ensure the safe and reliable operation of the wind generators.This paper takes the YR180 LA type(11k W,two-pole)DFIG simulation unit as the analysis object.And the method of combining theoretical derivation and simulation calculation is used to study the electromagnetic force characteristics of generator stator windings under normal,static eccentricity,dynamic eccentricity and composite eccentricity conditions.Firstly,the expressions of air-gap magnetic flux density(MFD)and stator winding EMF under normal and eccentric faults are obtained through theoretical derivation.Then,the finite element simulation is used to verify,and the simulation calculation is consistent with the theoretical results.The results of this study show that:(1)Under normal conditions,the air gap MFD of the generator is symmetrically distributed along the circumferential direction.The time-domain waveform of MFD approximates a cosine curve,and the component in its amplitude spectrum is the fundamental wave.The time-domain waveform of the EMF of the stator winding is also similar to the cosine curve,and the amplitude spectrum contains DC components and even frequency multiplications.(2)Under the static eccentricity fault of the air gap,the air gap MFD is unevenly distributed along the circumferential direction,and the change of its amplitude at different positions is inversely proportional to the change of the air gap length at the corresponding positions.The magnitudes of the EMF amplitude of the stator windings also change,and the change of the magnitudes is also inversely proportional to the change of the air gap length at the corresponding position of the windings.(3)Under the dynamic eccentricity fault of the air gap,the frequency components related to the slip are newly added to the amplitude spectrum of the air gap MFD.The frequency doubling components related to the slip are also added to the frequency spectrum of the EMF of the stator windings after the fault.(4)Under the composite eccentricity fault,the characteristics of the air gap MFD and the stator winding EMF under the two single faults are all exhibited,and no other obvious characteristic information is found.The results of this paper provide supplements and references for the detection and diagnosis of DFIG air-gap eccentricity faults,and also provide a theoretical reference for exploring the insulation wear laws of stator windings under air-gap eccentricity faults.