JPS57211992A - Controller for induction motor - Google Patents

Abstract

PURPOSE:To perform a brake control with less loss by providing a pattern selecting circuit for sequentially selecting in response to a master circuit for reducing a primary voltage frequency applied to an induction motor and a speed by reducing thyristor firing signals in the prescribed pattern. CONSTITUTION:An induction motor 1 is controlled at its primary voltage through thyristors (THY) 3-6 from AC power sources R-T, and the THY 3-6 are controlled via a mask circuit 38. A signal obtained via a mask signal voltage unit 11 is applied through resistors 13, 16, 19, 22 to operational amplifiers 14, 17, 20, 23, the outputs of which are converted numerical values through Zener diodes 15, 18, 21, 24, and are inputted to a reduction control microcomputer 37. The output of a THY firing pulse phase control circuit 36 is applied to the mask circuit 38. A pattern selecting circuit 39 which operates with the output of a tachometer generator 2 is connected to the computer 37, and a torque direction detecting circuit 26 is also connected. The circuit 38 applies a mask to the signal of the circuit 36 under the control of the computer 37, thereby controlling the reduction of the firing signals of the THY 3-6.