GB1295734A - - Google Patents

Abstract

1295734 Control of AC motors A G SARFATI and G VISCHIANI 10 June 1970 [11 June 1969] 28179/70 Heading H2J [Also in Division D1] Asynchronous motor windings A 1 , A 2 are supplied with A.C. voltages V 1 , V 2 respectively, the former leading in phase, and a network 10 of diodes D 1 -D 3 and SCR's 1-2 provide a connection to the neutral 0. Motor speed control is obtained by adjusting the firing angle of SCR1, SCR2, which are fired simultaneously at mains frequency, SCR2 controlling current in A 2 when V 2 is positive to 0, SCR1 serving to control current in either A 1 , when V 1 is positive to 0, or A 2 , when V 2 is negative to 0, current then flowing via D 1 , SCR1 and D 2 to A 2 . When SCR1, SCR2 are non-conductive winding A 1 receives half wave rectified current via D 1 to brake the motor. Whenever the base of transistor T 1 becomes positive, capacitor C2 is charged via D 5 , rendering T 3 conductive after a delay set by the motor control resistor 9, hence firing the SCR's via T 2 , and R 6 , R 8 respectively. Whenever a voltage is present across monitor 4 controlled optically, transistors T 5 , To conduct, discharging C 2 and cutting off T 3 , T 2 , thus braking the motor. Voltage V 1 must lead V 2 in phase to avoid spurious turning on of T 1 , and Fig. 3 (not shown), displays a circuit in which lamp (13) does not light if V 1 is the leading phase. The system is used in a yarn storage device, Fig. 1 (not shown), see Division D1, and is stopped when the yarn interrupts a light beam providing the voltage across 4. A counter may be fitted to the drum.