Study On Electromagnetic Noise Reduction Of A Motor

The subway is an important part of the urban public transportation system,which greatly alleviates the problem of urban traffic congestion,but reducing vehicle noise and improving ride comfort is an urgent problem to be solved.Generally,the running speed of subway vehicles does not exceed 120km/h.Therefore,it is recognized that wheel and rail noise is the main noise source.However,the actual operation found that the noise of the traction motor sounds more obvious and harsh to the human ear.The preliminary analysis found that the noise is mid-frequency tonal noise,and the difference between the mid and low-frequency bands covered by wheel and rail noise is very large,which brings a great deal to people.Annoyance has become the main noise source of subway vehicles and needs to be solved urgently.Traction motors of subway vehicles mostly use squirrel cage three-phase induction motors.Therefore,this paper takes a squirrel cage three-phase induction motor as an example to analyze its electromagnetic noise characteristics and noise reduction measures,and provide a theoretical basis for reducing the electromagnetic noise of traction motors.First,according to Maxwell theory,the main order and frequency of the radial electromagnetic force wave of the motor are calculated,and the finite element analysis software is used to calculate the air gap magnetic flux density and the radial electromagnetic force wave distribution of the motor,and the two methods are used.The order and frequency of the obtained radial electromagnetic force wave were compared and analyzed.Secondly,the structure mode of the motor stator,stator and winding(stator assembly),stator and case,and the whole machine(excluding the rotor system)was calculated and analyzed.Third,analyze the vibration and radiation noise of the motor(excluding the rotor system)under the action of the radial electromagnetic force wave.Finally,in order to reduce the amplitude of the low-order radial electromagnetic force wave,the stator and rotor slot matching,the degree of the rotor skew and the length of the air gap between the stator and rotor are optimized.The research shows that due to the opening of the motor,there is a sudden change in the air gap magnetic flux density and the radial electromagnetic force distribution.The theoretical and simulation results are consistent.The simulation calculation obtains the order,frequency and force of the low-order electromagnetic force.The simulation value of order and frequency is consistent with the theoretical value.After calculating the structural modal,it is found that the vibration shape of each part of the motor presents elliptical,triangular,quadrilateral and pentagonal changes successively,and the motor base and front and rear covers affect the natural frequency of the structural modal larger.After calculating the vibration response caused by the radial electromagnetic force,it is found that resonance is prone to occur at 900 Hz and 2200 Hz,and the sound pressure level of the electromagnetic noise generated at these two frequencies has a peak.After optimizing the structural parameters of the motor,the model with a slot fit of 60/56,a rotor skew degree of 10° and an air gap length of 1.5mm has the lowest radial electromagnetic wave amplitude,so it is selected as the optimized one model.