Sound Quality Evaluation Of Electromagnetic Noise Of Interior Permanent Magnet Synchronous Motors

Pure electric vehicles are too quiet and lack of powerful sense at low speeds,while the high-frequency electromagnetic noise of interior permanent magnet synchronous motors(IPMSMs)is likely to make people feel annoyed at high speeds.Consumers’ requirements for NVH performance of pure electric vehicles no longer stay at the low noise level,but put forward higher requirements for sound quality.The electromagnetic noise of IPMSMs has the characteristics of high frequency and time variation.Thus,sound quality evaluation of electromagnetic noise is getting more and more attention.This article aims at sound quality evaluation and prediction of electromagnetic noise of IPMSMs,which provides theoretical basis and engineering guidance for improving the sound quality performance of IPMSMs and pure electric vehicles.(1)Analysis of air-gap magnetic field and electromagnetic force wave characteristics of the IPMSM.The analytical models of no-load radial and tangential air-gap magnetic fields are established based on magnetic equivalent circuit method and boundary conditions of macroscopic equations.The analytical models of the synthetic air-gap magnetic field and electromagnetic force wave are obtained by superimposing the no-load magnetic field and armature reaction magnetic field.The three-dimensional geometrical model and the electromagnetic finite element model of the IPMSM are established.The air-gap magnetic field and electromagnetic force wave are calculated by the electromagnetic finite element simulation,and their amplitude-frequency characteristics are analyzed.The spatial orders of air-gap magnetic field are np±i Qs,and the frequency of air-gap magnetic field are μfc and fs±kfc,where p is the pole number of the motor,Qs is the number of stator slots,fc is the fundamental current frequency,fs is the switching frequency of inverter,n=1,3,5,…,i=0,1,2,3,…,μ=1,3,5,…,k=0,1,2,3,….The spatial orders of electromagnetic force wave are 2np,and the frequency of electromagnetic force wave are 2μfc and fs±kfc.(2)Simulation calculation and experimental verification of electromagnetic noise of the IPMSM.The multi-physical coupling simulation model of electromagnetic noise of the IPMSM is established and the experimental verification is carried out.The simulation results and experimental results of the electromagnetic noise are compared.The frequency spectrum of simulated electromagnetic noise is used to synthesize virtual electromagnetic noise audio.The results show that the simulation results of electromagnetic noise under steady state and accelerated conditions have the same frequency characteristics,and the main frequencies are 2μfc and fs±kfc.The experimental results of electromagnetic noise also have similar frequency characteristics.There is a certain error in the amplitude of the time domain waveform between the simulated electromagnetic noise and the measured electromagnetic noise.The difference between the virtual electromagnetic noise and the experimental electromagnetic noise is mainly caused by th e difference of the low frequency components.(3)Sound quality evaluation of virtual electromagnetic noise samples and experimental electromagnetic noise samples.The objective psychoacoustic parameters of the virtual electromagnetic noise samples and experimental electromagnetic noise samples are calculated respectively,and the subjective evaluation experiment is carried out.The subjective and objective evaluation results of the virtual electromagnetic noise samples and experimental electromagnetic noise samples are compared and analyzed.In addition,the correlation between subjective and objective evaluation results of virtual electromagnetic noise samples is also calculated.The results show that the A-weighted sound pressure level,loudness and sharpness of noise samples increase first and decrease then with the increase of rotational speed,and reach the maximum value near 7100 rpm.The calculated results of roughness,fluctuation strength,tonality and articulation index are quite different,and there is no obvious consistent trend with the increase of rotational speed.The subjective feeling of the evaluation subjects shows an obvious trend with the change of rotational speed.The lower the rotational speed is,the subjective feelings of the evaluation subjects tend to be ‘comfortable’ and ‘weak’.The higher the rotational speed is,the subjective feelings of the evaluation subjects tend to be‘annoying’ and ‘powerful’.The subjective evaluation values of‘annoying-comfortable’ and ‘weak-powerful’ of the virtual electromagnetic noise samples are mainly related to the A-weighted sound pressure level,loudness and sharpness.(4)Sound quality prediction model of electromagnetic noise of the IPMSM.The subjective and objective evaluation results of virtual electromagnetic noise samples are used to establish sound quality prediction models based on BP neural network,generalized regression neural network(GRNN)and support vector machine(SVM),respectively.The subjective evaluation values of the virtual electromagnetic noise and the experimental electromagnetic noise are used to establish the sound quality prediction model based on linear regression.The results show that the sound quality prediction model based on support vector machine(SVM)has smaller error and higher stability.There is a certain linear relationship of the subjective evaluation values between the virtual electromagnetic noise samples and experimental electromagnetic noise samples.The sound quality prediction model based on the linear regression has a high precision.