Research On Electromagnetic Noise Of Motors Based On Sound Quality

Under the guidance and support of the national policies,the scale of the new energy automobile industry has grown rapidly.Pure electric vehicles use motors to replace engines of traditional fuel vehicles.The sound pressure level in the car has been greatly reduced.However,consumers’ complaints about noise have not been decreased.This puts forward higher requirements for the design of electric vehicles NVH performance.For the evaluation index of noise in the electric vehicle,not only sound pressure level,but also noise quality characteristics that reflect the subjective feelings of passengers need to be considered.In this context,this article aims to choose sound quality as the goal of electromagnetic noise optimization.By establishing the sound quality prediction model and electromagnetic noise multi-physics simulation model,the influence of motor structure parameters on noise and sound quality is studied,which providing a new design idea for motor noise control of electric vehicles.The main research contents of this paper are as follows:First of all,the structure and operating principle of permanent magnet synchronous motors in vehicles are introduced and causes of motor noise are explained.The theories of PMSM air gap magnetic field are analyzed to deduce the formula of radial electromagnetic force and characteristic frequency of the radial electromagnetic force is summarized.A two-dimensional electromagnetic field simulation model of a PMSM is built based on Maxwell to solve the air gap magnetic density and radial electromagnetic force wave.By comparing frequency spectrum obtained by the Fast Fourier Transform with characteristic frequency,the accuracy of the theoretical analysis results is verified.Secondly,the test system and methods of motors are introduced.The steady-state and accelerated noise of different speeds and torques are tested.By using ANSYS Workbench to complete modal analysis of the stator assembly and stator assembly with casing models,the modal frequencies and modes of each order are determined.Using methods such as spectrum analysis,waterfall graph analysis and order analysis to analyze the test data with modal frequency and characteristic frequency of the radial electromagnetic force.Then,jury tests of noise in sample library are organized and objective evaluation indicators are computed.A GA-BP model taking objective sound quality evaluation indicators as input and irritability as output is established.Based on the sensitivity coefficient index,the impact of noise in each critical frequency band on the overall sound quality objectively is quantified and noise source corresponding to the sensitive frequency band determine is determined,which provides guidance for the next step of structural parameter optimization.Finally,a PMSM electromagnetic noise simulation model based on magnetic-structure-acoustics fields is completed to calculate the vibration and noise level of motors.By comparing test data with simulation results,the accuracy of the simulation model is verified.Subsequently,the rotor skewing is used as the optimization scheme.The influence of the rotor skewing angle on the radial electromagnetic force wave are analyzed.What’s more,the effects of linear,V and Z type of skewing schemes on the motor output electromagnetic noise,torque and sound quality are compared.