No abstract

Induction motors are robust and inexpensive machines and are used widely for variable speed control because of the recent development of electronic technique. In the case where loads of the motors are compressors, pumps, and so on, the constant VIF control of the induction motors usually is 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 fluctuates considerably because the load torque is pulsated. When the frequency of the torque pulsation is close to the resonant frequency of the mechanical system, large vibration and acoustic noise are produced especially in the low-frequency region. This paper proposes a method to suppress the variation of the rotational speed of the VIFcontrolled 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 VIF input to the inverter. Effectiveness of the proposed method is confirmed by approximate analysis, simulations and experiments.Key words: Induction motor: fluctuating load repetitive learning control: suppression of speed variation. speed closed-loop control and the speed open-loop control [I]. Vector control and slip frequency control can be cited in the former and constant VIF control in the latter. Among these, the vector control is especially excellent and a driving performance comparable to the armature current control of dc machines can be realized. However, the control system also becomes complicated, and highaccuracy sensors for rotational speed, current and voltage are required. On the other hand, the speed control by the constant VIF control can be performed without speed sensor even in the case where sensors are difficult to install because of structure or environment. Therefore, they are used widely for simple speed control in blowers compressors, pumps, and, more recently, in home electrical appliances such as air conditioners.The apparatus which drive the compressors such as in the air conditioners, will, in general, produce a pulsating torque [2] and cause problems in the environment and performance. In general, however, the IS SNO424-7760/93/OOO5-0 1 14 0 1993 Scripta Technica, Inc.