Analysis And Suppression Of Electromagnetic Noise,Current Harmonics And Excess Loss Of 3-Phase Induction Machines

Among electric machines,induction machines are mostly used for various applications,thus,noise,current pollution to the grid and losses of the induction machines have received a great attention.This dissertation mainly focuses on the study of performance improvement of the induction machines in these three aspects.The magnetic field harmonics are the major sources of the electromagnetic vibration and noise,stator current harmonics,parasitic torques and stray losses of the induction machines.Therefore,in this dissertation,the magnetic field harmonics of the three-phase induction machine with squirrel-cage rotor are firstly derived and analyzed in detail,with some major components of the magnetic field harmonics being summarized.And the machanism of the electromagnetic vibration and noise of induction machines is also analyzed.Based on the analysis of the magnetic field harmonics,a new rotor or stator structure using auxiliary slots is proposed to reduce the electromagnetic vibration and noise,which are caused by the stator and rotor slot permeance harmonics.A 2-pole 5.5 kW three-phase induction motor is selected as a sample motor in order to validate the effectiveness of the proposed structures,with help of finite element analysis(FEA)and experiments.The experiment results show that the induction motor with the proposed rotor structure has about 5 dB(A)reduction of the overall sound pressure level compared with the original one.Then,the stator line current harmonics of induction machines are analyzed.Usually,closed-slot rotors can be used in induction machines to reduce the stator line current harmonics efficiently.However,it is found that some induction machines with closed-slot rotors may suffer from local saturation in the rotor slot bridges,and thus,exhibit significant low-order time harmonics in the stator currents,which is a pollution to the grid.Such phenomenon is revealed with theoretical analysis,and validated with both FEA and experiments.Then suggestions are given to eliminate the studied stator current harmonics.Finally,excess losses of induction machines are studied,and espically that is caused by the interlocking dowels in the stator core.Influences of the number,location and size of the interlocking dowels in the stator core are studied,respectively.Results show that the selection of some special numbers of the interlocking dowels in the stator core can reduce the losses in the dowels and then improve the motor efficiency.Meanwhile,influence rules of the location and size of the interlocking dowels are also obtained,in order to have a reasonable choice to design the interlocking dowels.