Suppression Control of Speed Variation of the Induction Motor with Fluctuating Load by Repetitive Learning Control

Abstract

Induction motors are robust and inexpensive machines and are widely used for variable speed control because of recent development of electronic technique. In the case that loads of the motors are compressors, pumps, and so on, the constant V/F control of the induction motors is usually employed because it is difficult to install speed sensors and accurate speed control is not required. In such loads, the rotational speed of the motors is considerably fluctuated because the load torque is pulsated. When frequency of the torque pulsation is close to the resonant frequency of the mechanical system, large vibration and acoustic noise are produced especially in low frequency region.
In this paper, authors propose a method to suppress the variation of the rotational speed of the V/F controlled induction motor with a fluctuated load by feedforward compensation using a timing sensor of 1 pulse/rev. considering that the load torque varies periodically. The feedforward data by a period for the compensation is obtained by the learning control based on the repetitive control in which the motor speed is controlled by periodically reflecting the past speed error on the present V/F input to the inverter. Effectiveness of the proposed method is confirmed by approximate analysis, simulations and experiments.