Analytical multi-physics methodology for fast acoustic noise prediction of an external rotor SPMSM

The acoustic noise of an external rotor Surface Permanent Magnet Synchronous Machine (SPMSM) is studied using a multi-physical analytical methodology. The magnetic radial forces are calculated from the field solution, which is obtained through numerical conformal mapping, using Maxwell stress tensor. Applied on the rotor at the air gap location, these forces excite the rotor plus housing system and induce forced vibrations. The system is modeled as a ring with equivalent material and geometrical parameters emulating the interaction between the rotor and the housing. The modal characteristics of this simplified model are validated numerically. Finally the acoustic pressure is computed using the radiation of a vibrating infinitely long cylinder. Being fast and efficient to execute, the proposed multi-physics model allows acoustic noise optimization analyses early in the design process of external rotor machines.