The EVS (Electromagnetic Vibration Synthesis) is a proprietary algorithm of Manatee designed to speed up electromagnetic noise and vibration calculation while giving more physical insights on the e-NVH behaviour of an electrical system.
It consists in decoupling the vibrational characterization of the electric motor structure from the operational electromagnetic excitation, as one would do experimentally using an impact hammer or an electrodynamic shaker to measure Frequency Response Functions (FRF).
As electromagnetic forces due to Maxwell stress can be decomposed in a discrete series of rotating force waves with specific wavenumbers which depends on slot / pole combination and winding pattern, this characterization can be carried by artificially exciting the structure with some specific rotating force patterns at variable frequency in radial and tangential directions. In some cases, one might also have to calculate bending moment or axial force FRF.
Some normalized Frequency Response Functions are then obtained and stored for later use. Once FRF are calculated, the electromagnetic loads are projected on the excitation basis and the vibration response is synthesized without additional calculations. Besides, torque ripple, Unbalanced Magnetic Pull, and radial ripple excitations can be separated in the e-NVH response. Air-borne noise due to stator excitation can also be separated from structure-borne noise due to rotor excitation, similarly to a numerical transfer path analysis.
The EVS method is particularly computationally efficient at variable speed, or during optimization of noise control techniques (skewing, current shaping, pole shaping, notching).
An example of rotating wave Electromagnetic Vibration Synthesis is illustrated here:
EVS assumes linearity of the structural model. FRF calculation do not include gyroscopic effects or strong magneto-mechanical coupling.