Electromagnetic Noise Analysis in Single-Phase Brushless Motors Based on Multiphysics Coupling

Electromagnetic noise, as a primary acoustic issue during the operation of brushless DC motors, directly affects the dynamic stability of equipment, user auditory experience, and environmental noise levels. To investigate the influence of load and speed variations on electromagnetic noise in single-phase brushless DC motors, this study established a multi-physics coupled simulation model using ANSYS Maxwell and Workbench. Analyses were conducted on harmonic components of air gap magnetic flux density, electromagnetic vibration responses, and noise spectra under no-load, rated-load, overload conditions, and different rotational speeds, accompanied by modal analysis of the motor stator. When the load increased from no-load to overload, significant variations occurred in electromagnetic force harmonic content. The amplitude of low-order harmonics under overload conditions increased by $\mathbf{8 . 0 6 \%}$ compared to rated-load operation, directly triggering enhanced electromagnetic force wave amplitudes. The surge in electromagnetic force harmonics caused a $150 \%$ increase in stator vibration amplitude relative to no-load conditions, driving a significant rise in high-frequency components within the noise spectrum, with the maximum total sound pressure level reaching 67.971 dB. In the constant-power high-speed range, increased rotational speed induced higher field-weakening current, resulting in a 15.05% growth of electromagnetic force harmonic content compared to 4000 rpm operation. This further intensified the coupling effect between electromagnetic force waves and structural modes, ultimately manifesting as a positive correlation between A-weighted sound pressure level and rotational speed. This research provides theoretical foundations for noise design in brushless DC motors.