Design and construction of a thyristor chopper controller for speed control of a DC motor

Abstract

The aim of this project is to provide speed control of a 1KW 220 V, D.C. Motor with separately excited field. The motor is coupled to a d.c. generator to provide a variable load. The speed controller involves a thyristor chopper employing the principle of forced commutation. An appropriate chopper circuit was selected and the component values of the power circuit were designed. The gate signals to the thyristors employed were derived from an electronic control circuit which utilises two timer i.c's in a circuit known as “linear ramp control circuit". Closed loop control was effected by providing Speed feedback. Back e.m.f was utilised to provide the speed signal. The speed control loop encloses a current loop for overcurrent protection.