Acoustic noise of sheeted electrical steel inductors in PWM operation — causes and mitigation

Electrical steel inductors are superior in size and cost compared to inductors using alternative core like nanocrystalline or powder materials in applications involving pulse-width modulated currents. However, electrical steel tends to emit more acoustic noise, which can be undesirable. The causes for these acoustic noise emissions, i.e. magnetic forces and magnetostriction, are explained in detail and the particular flux density distribution in sheeted electrical steel inductors a PWM operating is derived. Based on these insights, two methods of reducing the noise of an electrical steel inductor are proposed. One method implies a redesign of the inductor for lower nominal flux density. The other method is based on changing only the mechanical construction of the inductor. It does not affect the main design parameters of an inductor, i.e. inductance and temperature rise, and can thus be applied to existing inductor designs.