The Magnetic Noise of a DC Electric Motor — Modeling of Three-Times-Coupled Electromagnetic, Mechanical and Acoustic Phenomena

Abstract

The sound power level of the magnetic noise radiated from a DC electric motor was numerically estimated for different loading conditions and two motor designs. Since the mechanism of the magnetic noise generation in a DC electric motor can be described as a three-times sequentially coupled problem, three linked — electromagnetic, mechanical and acoustic — numerical models were prepared. In the first phase the electromagnetic model was built to calculate the magnetic forces that excite the structure of the motor using the finite-element method (FEM). In the next phase the exciting magnetic forces were transferred to the structural model where the harmonic analysis was carried out using the FEM. The last phase was to model the acoustics, where the boundary-element method (BEM) was applied. To take account of the complexity of the investigated DC electric motor all three numerical models were three-dimensional (3-D). Finally, the numerical results from all three models were compared with the cogging torque, the vibration and the acoustic measurements, and a reasonable agreement was found.