Analysis Of Electromagnetic Vibration Noise Radiated By Variable-frequency Motor

The noise radiated by motor is attracting more and more attention because of the popularization of variable-frequency motors.Electromagnetic vibration noise,which is caused by the vibration of stators,plays the main role in the noise of motors and the activation is the electromagnetic force distributed in the air gap.A large amounts of research has been developed to solve the problem.However,only few of them focus on the electromagnetic vibration noise of variable-frequency motor.To this end,a mathematical model of inverter was built to analysis the frequency component of the output current based on SPWM.Then,the electromagnetic force was calculated according to the Maxwell tensor principle.An analytic method was proposed to analyze the vibration characteristic of stators in which the deformation of the teeth was considered and this model was solved by generalized vibrational principle based on the energy theory of structural mechanics.A statistical energy method was developed to solve the noise problem in high frequency.The power flow equations were built and the statistical parameters were obtained.Finally,an electromagnetic-mechanic-acoustic coupled simulation model was built to analyze the vibration and noise of a variable-frequency motor and the vibration experiment was conducted to analysis the vibration characteristics of the motor under variable-frequency excitation.Some conclusion was made.The main frequency components of output current in inverters are fundamental frequency and the frequency distributed around the switching frequency,and other components like the frequency of electronic devices can be ignored.The electromagnetic force only contains one kind of frequency which is the even multiple of the current frequency in coils and the spatial frequency is the multiplication of the number of poles.The proposed analytic method can solve the characteristic frequency in lower orders with a high precision,and the error compared with the simulation is no more than 4%.In high frequency,the developed statistical energy model can calculate the noise of stators with an error of 2d B compared with the result of simulation.According to the experiment results,frequencies of the vibration signal produced by the variable-frequency motor mainly contain the rotor frequency and the harmonics of the double current frequency,and the high frequencies band is concentrated on the switch frequency of the converter.All the experiment results verify and are consensus with the theoretical analysis in this paper.