Slavic, J., Javorski, M., Luznar, J., Cepon, G. et al., "Magnetostrictive and Magnetic Sources of Noise in the Electric Motors," SAE Technical Paper 2016-01-1838, 2016, doi:10.4271/2016-01-1838.
In electric motors the working torque results from the magnetic forces (due to the magnetic field). The magnetic forces are also a direct source of structural excitation; further, the magnetic field is an indirect source of structural excitation in the form of magnetostriction. In the last decade other sources of structural excitation (e.g. mechanical imbalance, natural dynamics of the electric motor) have been widely researched and are well understood. On the other hand, the excitation due to the magnetic forces and magnetostriction is gaining interest in the last period; especially in the field of auto-mobility.Due to the broadband properties of the magnetic field (e.g. Pulse-Width-Modulation(PWM), multi-harmonic excitation), the direct structural excitation in the form of magnetic forces is also broadband. It is important to understand the broadband content of this excitation with regards to the broadband structural response which results in the broadband noise of the electric motor. This research presents an experimental approach to the characterization of the magnetic forces due to PWM excitation.The magnetostrictive excitation has long been researched in the time-domain, only. In the last years it was proven the standardized magnetostriction identification approach does not take into account some of the basic structural-dynamics principles and therefore results in wrong conclusions if considered in the frequency domain. This research gives some of the guidelines required for proper identification of magnetostriction in the frequency domain.In the following years it is expected that the effort on magnetostriction- and magnetic-forces- research will significantly decrease the noise of electric motors.