GB1200250A - Circuit arrangements for controlling three-phase asynchronous motors - Google Patents

Abstract

1,200,250. Automatic control of speed. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. March 22, 1968 [March 25, 1967], No.13971/68. Heading G3R. [Also in Division H2] In a system in which a three phase asynchronous motor is controlled for both driving and D.C. braking by controlled rectifiers (thyristors), during driving one phase U at least is energized only through one, half wave, rectifier. This enables an immediate change from driving to braking, whereas in prior art systems braking may be delayed up to 270 degrees to avoid short circuit between supply phases. As shown, for driving, phases V, W are energized through back to back thyristors 3---6, and U is energized through 1 only; for braking, D.C. is applied to U only from all supply phases RST through thyristors 1, 7, 8. Triggering is controlled by a logic circuit Fig. 5 (not shown) in which the polarity of the difference between a tachogenerator voltage and a reference determines whether driving or braking thyristors are fired and the magnitude of the difference selects a point at which a sawtooth waveform (derived from the supply RST) is gated to triggering transformers and thus controls the firing angle. For small motors one of the braking thyristors may be omitted, and/or two driving thyristors 4 and 6, so that each phase is energized for driving with only half wave A. C. In Fig.6 (not shown) the windings are delta connected, one terminal is connected directly to the supply R, another to S through one driving and one braking thyristor and the other to T through a pair of back to back driving thyristors. This energizing arrangement may also be applied to a star connected motor.