The speed and torque of electronically commutated motors can be controlled by pulse width modulation (PWM), which composes current waveforms of the desired fundamental frequency together with a number of higher switching harmonics. The latter enriches the magnetic force spectrum, escalating the vibrations and the noise of electromagnetic origin. The influence of the PWM carrier frequency on the structure borne noise was researched experimentally and numerically. To obtain a clear insight into the physical phenomenon, an experiment with original motor parts was proposed, which enables controlled excitation with PWM, measurement of magnetic forces and noise, and excludes the aerodynamic and mechanical sources of noise. Further, the numerical modeling of structure borne noise at PWM excitation was studied with a multiphysics finite element analysis containing electronic, electromagnetic, structural and acoustic field problems. This approach is computationally inefficient, therefore a method for a fast structure borne noise prediction at PWM excitation was introduced. The latter uses the extended field reconstruction method and modal superposition method to achieve significantly lower computational times and is suitable for parametric studies. Experimental and numerical work shown that PWM switching harmonics can excite structural dynamics and thus increase the total noise. The PWM switching noise can be reduced by appropriate carrier frequency selection in accordance with the structural dynamics.
|
