Mechanical Resonance in Nonoriented Electrical Steels Induced by Magnetostriction Under PWM Voltage Excitation

Acoustic noise in inverter-fed motors can increase if resonance induced by magnetostriction occurs. This paper presents results of measurements of magnetostriction-induced mechanical resonance in nonoriented (NO) steels, commonly used in motor cores, under pulse width modulation (PWM) excitation. The resonant frequency of a strip of NO steels was determined and it was magnetized by PWM voltage waveforms. The PWM switching frequency was chosen to be the same as the sample resonant frequency. The peak-to-peak magnetostriction under PWM excitation was up to 28% higher than that under sinusoidal excitation when an integer multiple of the switching frequency matched the resonant frequency of the sample.