Control apparatus suitable for use in induction motor

Abstract

A gain change-over switch according to the present invention serves to change over at least one of a current loop gain and a velocity loop gain to a value of the gain greater than that in other modes, in the case where a rotational-position control mode is selected as a control mode of the induction motor out of a rotational-speed control mode and a rotational-position control mode or where the rotational-position control mode is chosen and at the same time, a work mode for driving a work piece to work the same is selected, whereby an induction motor is controlled with high accuracy. Further, an exciting change-over switch according to the present invention serves to select a reinforcement exciting circuit for producing the secondary flux in the induction motor, which is greater than that produced by a weakening variable exciting circuit, only in the case where the rotational-position control mode and in the work mode are selected, thereby to control the induction motor with high accuracy. In other modes, the change-over switch serves to select the weakening variable exciting circuit for variably controlling the excitation-component of the primary current to produce the secondary flux corresponding to a torque component developed by the primary current.