Analysis of electromagnetic acoustic noise excitations

Increasing electrification together with rising demands for comfort leads to high quality requirements regarding acoustic noise emitted from electrical machines. In parallel to the electromagnetic conversion from electrical energy to mechanical energy and vice versa, acoustic force excitations occur as a parasitic effect giving rise to machine vibration and radiated sound. The analysis of audible noise excitations is the key to improve the acoustic performance of electrical machines. Classically, analytical approaches are used, whereas modern numerical approaches promise better accuracy, but typically lack the cause-relationship. Therefore, different combined approaches are developed, including hybrid modeling and a convolution based approach. The transfer function from electromagnetic force excitation to surface velocity and sound pressure decisively determines the sound generation. The simulation of this structural dynamic behavior requires reliable homogenized material parameters as determined in this work. A practical procedure for the experimental identification of the transfer function is developed. In addition to the vibration problem, the radiation characteristic is required to be determined for the pre-calculation of the acoustic sound. Using computationally efficient analytical cylinder models, this work shows a novel modular approach for the online auralization of electrical machines, i. e. for making the simulated sound hearable. This approach can be used to auralize electrical machines in acoustical virtual scenarios. For the practical development of low-noise electrical machines, this work proposes a methodology which uses the discussed analysis and calculation techniques. The focus is set on a structured procedure together with a large collection of influencing and controlling parameters. Motor design rules are presented considering individual machine type aspects. For example, a reduction of 8 dB of the total sound pressure level of a permanent-magnet synchronous machine was achieved by only changing the shape of the surface-mounted magnets. Four practical examples complete this dissertation.