PWM inverters producing torsional components in AC motors

Abstract

Voltage source adjustable frequency drives produce voltage spectra capable of exciting torsional components within the bandwidth of a loadpsilas criticals. If not damped, a motorpsilas torsional spectrum may excite the mechanicalpsilas resonant frequencies destroying fan blades or fail couplings and shafts. This paper reports on an oil refinerypsilas induced draft fanpsilas coupling and drive motorpsilas shaft failures. Field torsional data, mechanical and drive models with analyses and simulation data are presented identifying contributing factors. The paper also presents a solution with installation data showing the improvement.