Analysis And Verification Of Electromagnetic Vibration Characteristics Of Small Induction Motor

With the requirement of reducing vibration and noise of electromechanical equipment increases,the control of vibration and noise of motor become the hot topic around the world.For a complex electromechanical coupling system,the vibration and noise of motor is coupled with multi-physical field.In order to accurately predictthe vibration and noise to design a low-noise motor,the relationship among the different physical fields should be investigated.In this paper,a 7.5kW three-phase induction motor isstudied.The coupling of the bearing system and electromagnetic force for such motor are analyzed.The method is verified through the designed test bench.The main contents are as follows:First of all,the dynamical model of the motor is established through finite element method,and the accuracy of model is verified by modal test.Thenthe electromagnetic forceis calculatedanalytically and numerically.For the analytic method,the electromagnetic force can be approximated by multiplication of the magnetic potential and the magnetic conductance.Considering the slot effects of the stator and rotor,the electromagnetic excitation characteristics of uniform air gap,rotor eccentricity and fluctuation of rotor speed are analyzed.Meanwhile,such electromagnetic excitationsfor the aforementioned working conditions are calculated using FEM.It is found that the main electromagnetic forces of the motor are caused by the main flux density and the harmonic flux density.It is also found that the harmonic magnetomotive force induced by the harmonics of the power supply,the asymmetric electromagnetic field caused by the eccentricity of the rotor,and the modulation of the electromagnetic field by fluctuation of rotor speed will deteriorate the electromagnetic forces.Then the coupling model of the unbalanced magnetic pull and the unbalanced centrifugal force for the electric motor is established.The whirling vibration response of the shafting system due to such coupling effect is computed.The results show that the coupling effect between rotor system and electromagnetic excitation is strong.Finally,the vibration response of the motor excited by the electromagnetic force is obtained using the methodology of Newmark,and the orbit of the rotor as well as the contour of the electromagnetic force is calculated.A special test rig for asynchronous motorwith the end cap separated from the stator is designed.Through the test,the responses of the stator with different eccentricity and unbalance mass of rotorhave been obtained.The test results are compared with the computational results,which can validate the correctness of the analysis.