Frequency response of induction motors under forced oscillations

Abstract

This paper analyses the hunting nature of induction motors when driving oscillating loads. Proceeding from the equation of motion of the oscillating system, it is shown that the electrical torque developed by an induction motor has two components; the damping torque and the synchronising torque. Neglecting, at first, the effect of the stator resistance, and limiting the investigation to small oscillations, these two characteristic torques are functions of the mean relative slip and the hunting frequency. Expressions are developed for the frequency responses of the slip, torque and current fluctuations. Resonance frequencies are defined for each fluctuation. The effects of the stator resistance on the damping and sychronsing torques and on the frequency response are shown.