Four-quadrant current-regulated energization of d.c. motor using pulse-width modulation

Claim 1

A current-regulated system comprising, in combination; a D.C. voltage source having a first and a second terminal; a first and a second current supply line respectively connected to the first and second terminal; an inductive load having two terminals; a four-quadrant energizing circuit for the load, comprising a first thyristor connecting the first load terminal to the first supply line, a second thyristor connecting the second load terminal to the second supply line, the polarities of the first and second thyristors being such that when both are conductive they establish a current path for current flow through the load in a first direction, a third thyristor connecting the second load terminal to the first supply line, and a fourth thyristor connecting the first load terminal to the second supply line, the polarities of the third and fourth thyristors being such that when both are conductive they establish a current path for current flow through the load in an opposite second direction; a first transistor connected in the first supply line between the first source terminal and the first and third thyristors; a second transistor connected in the second supply line between the second source terminal and the second and fourth thyristors; negative-feedback current-regulating means regulating the current flowing through the load, including means for generating an error signal indicative of the sense and magnitude of the difference between the actual current flowing through the load and a desired current to be caused to flow through the load, means operative in dependence upon the sense of the difference indicated by the error signal for selecting either the first and second or else the third and fourth thyristors for conduction, means operative for deriving from the error signal an actuating signal which is pulse-width-modulated in dependence upon the magnitude of the difference indicated by the error signal, and means operative in dependence upon the pulse duration and interpulse duration of the actuating signal for rendering alternately conductive and non-conductive the two transistors and the selected two thyristors; and bypass circuit means operative during the non-conduction time intervals of the transistors for diverting current flowing through the inductive load into and through the voltage source without passing through the transistors or the thyristors and in such a direction through the voltage source that the latter opposes this flow of current through the load.