GB1223450A - Controlling circuit for ac motor - Google Patents

Abstract

1,223,450. Control of A.C. motors. TOKYO KEIKI SEIZOSHO K.K. 24 Dec., 1968 [30 Dec., 1967 (4)], No. 61396/68. Heading H2J. When a triac TC1 is made conductive, motor windings 103, 104 which are interconnected through capacitor 105, are energized to drive the motor in one direction, the motor being reversed when triac TC2 is triggered. Thyristors S5, S6 are made conductive, when both the triacs TC1, TC2 are non-conductive, whereby the motor windings are supplied with directcurrent for braking. The thyristors S5, S6 may be replaced by a single thyristor. The signal generator 113 may comprise a transformer having its primary winding subjected to the voltage across the capacitor 105 when the motor is driven. The secondary winding of the transformer energizes a bias circuit to prevent conduction of the braking thyristor. When the motor is no longer driven, the voltage across the capacitor drops to zero, whereby the braking thyristor becomes conductive. In another arrangement, two transformers have their primary windings connected in parallel across the triacs TC1, TC2 respectively, whereby the transformers are energized when the triacs become non-conductive. Due to the outputs of the transformers, current passes from a D.C. source through a zener diode to the gate of the braking thyristor. The D.C. source may be formed by rectifying the output of source 101. In a further embodiment, three triacs are non- conductive when there is no input signal two of the triacs being in circuit with the motor, and the other serving to short-circuit, when it conducts, the triggering circuit of the braking thyristor. A diode logic circuit ensures that the third triac conducts when the triacs TC1, TC2 are made conductive. The third triac may be fired through a transformer or capacitor network, the capacitor serving to control the conduction period of the braking thyristor, so dispensing with the safety resistor R1. In a further modification, the conduction angle of the triacs TC1, TC2 is controlled by adjusting the discharging time of a capacitor to regulate the braking current applied to the motor. Another example relates to an arrangement in which a thyristor is rendered conductive to supply direct-current to the motor when triacs TC1, TC2 are non-conductive, thus blocking a further thyristor in series with the motor. The motor may be wound with three phases.