GB1513279A - Motor control circuits - Google Patents

Abstract

1513279 Controlling motors; converters VILLAMOS AUTOMATIKA INTEZET 8 Dec 1975 [6 Dec 1974] 50274/75 Headings H2J and H2F A motor control circuit comprises a plurality of controlled rectifiers arranged to supply at least one controlled current and a control circuit for preventing triggering of undesirable combinations of the controlled rectifiers, the control circuit including at least one channel consisting of a current differential transmitter arranged to provide an output signal corresponding to the first derivative with respect to time of the or one of the controlled currents, a shaping unit consisting of a rectifier, a limiter and a low pass filter in cascade connected to the output flow of the transmitter, and a logic network connected to the output of the shaping unit and arranged to detect when the first and second derivatives with respect to time of the controlled current are zero, the logic network being arranged to prevent triggering of the controlled rectifier or rectifiers which are not supplying the controlled current or currents until said first and second derivatives are substantially zero. As shown in Fig. 1, a D.C. motor 1 is driven in one direction from an AC supply via controlled rectifier 2 and on the opposite direction via controlled rectifier 3, under the control of a unit 10, differencing circuits 8, 9, feedback from a shunt 5, adding circuits 6, 7 and triggering units 4, 5. To prevent simultaneous conduction of rectifiers 2, 3, and inductive transducer (transmitter) 11, 12 provides a signal representing the first derivative w.r.t. time of the current supplied to the motor. This signal is applied to a rectifier 13 whose output is applied to an amplitude limiter and integrator R, Z, C. The logic network 14 detects when the integrated signal is zero for a predetermined time, e.g. 4-5 Ás, thus indicating that the first and second derivatives are zero. The outputs of the logic network are applied to the inhibit inputs 26 of the triggering units 4, 5. As shown in Fig. 2, an A.C. motor 20 is supplied by a three-phase supply RST via controlled rectifier networks 21, 23 and 25 for one direction of rotation and via rectifier networks 22, 24 and 25 for the other direction, the rectifier networks being under the control of circuitry as described with reference to Fig. 1. Transmitters 27, 28 are provided in two respective phase lines to the motor, and logic networks 29, 30 are provided and have their outputs connected to the networks 21, 22 and 23, 24 respectively. The transmitters may consist of a Hall generator or a capacitative transmitter connected to an amplifier and differentiating circuit.