Browse Publications Technical Papers 2019-01-1492

Test and Analysis of Electromagnetic Noise of an Electric Motor in a Pure Electric Car 2019-01-1492

Compared with the low-frequency ignition order of mechanical and combustion noise of an internal combustion engine, the noise of electric drive assembly of electric vehicles is mainly the high-frequency whining noise generated by electromagnetic forces of motors and gear meshing of reducers, as well as the high-frequency umbrella-shape noise generated by DC/AC pulse width modulation. Although the radiated sound power of these high frequency noise is far less than that of an internal combustion engine, the high frequency noise of the motor and the reducer is subjectively quite annoying. This paper studies the characteristics of electromagnetic noise of a permanent magnet synchronous motor in an electric car. By testing and analyzing of noise sources of an electric motor in the car and on a test rig, the spatial order characteristics and amplitude-frequency characteristics of the electromagnetic forces are revealed. The noise orders are multiples of the number of motor poles. The most critical order is 48th order, and its spatial order is 0th order. The peak of this 48th order is due to the stator’s 0th breathing mode being excited by the 48th frequency order electromagnetic force. Through theoretical calculation of the air-gap magnetic field and electromagnetic force wave, it is concluded that the 48th order electromagnetic force results from interaction of the rotor magnetic field and slotted core of the stator, and due to stator current harmonics. In this study, it is demonstrated by increasing the air gap by 0.2mm experimentally, the electromagnetic force can be reduced, resulting in the reduction of the motor noise by 5dB.


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