Effects Of Inter-turn Short-circuit Fault On Demagnetization Of Permanent Magnet Synchronous Machines

The maximum potential safety hazards of permanent magnet synchronous machines(PMSM)are magnetic field fluctuations and permanent magnet(PM)demagnetization problems,which have severely restricted further promotion and application of the PMSM.Thus,the demagnetization of the PMSM has always been an important research focus.Over the last few decades,for the study conducted by researchers on loss of field due to inter-turn short-circuit fault of permanent magnet synchronous motor,the inter-turn short-circuit fault model is established by short-circuiting a certain proportion of the normal winding.There is some difference between this and the actual inter-turn short-circuit fault of motor.Field practice shows that,when a turn-to-turn failure occurs,it is most likely to appear in the end-windings of the first turn of the phase belt(FTPB).Therefore in this paper,the FTPB that is short-circuited fault of the PMSM under different loads and speeds are studied,which has an important academic significance and engineering value.The main contributions are the following:Aiming at short-circuit fault characteristic parameters of the first turn of the phase belt,short-circuit fault model of the FTPB of the PMSM is established using the finite element method.The electromagnetic torque and three-phase currents of short-circuit fault of the FTPB of the PM motor are extracted.Ripples of the electromagnetic torque is calculated.The harmonic contents of the waveform of electromagnetic torque and three-phase currents are analyzed using the Fast Fourier Transform(FFT)method.The law for each characteristic parameter to change with the motor load and speed is researched.The conclusions can be used as the basis for online diagnosis of short-circuit fault of the FTPB of the PMSM.The characteristics and rules of the occurrence of short-circuit fault of the FTPB,three-phase currents of short-circuit coil,demagnetization magnetic field,distribution of the demagnetization area and magnetic flux density distributions of the PMSM under different loads and speeds are researched,aiming at the influences of short-circuit fault of the FTPB of the PMSM on loss of field of the rotor PM.In addition,the occurrence of irreversible demagnetization fault on the rotor PM is verified by observing the varying trajectories of the flux densities of the referencepoints on the rotor PM located at different points.The conclusions can provide technical reference for design of permanent magnet synchronous motor.The thesis establishes the PMSM fault model using the finite element method,which can used to investigate the characteristics of the demagnetization PMSM without the fault of the FTPB that is short-circuited.Both the three-phase currents and the electromagnetic torque before and after the short circuit fault,ripples of the electromagnetic torque,and the harmonic contents of the waveform using the Fast Fourier Transform(FFT)are studied by investigating the demagnetization PMSM running under different loads and speeds.The results can be used to judge whether irreversible demagnetization occurs on the PM,which makes a contribution to the theoretical basis for the on line diagnosis of the PMSM,after when the motor of the FTPB is short-circuited.