GB1253776A - Traction motor control system - Google Patents

Abstract

1,253,776. Chopper control arrangement. WESTINGHOUSE ELECTRIC CORP. 2 April, 1970 [21 April, 1969], No. 15641/70. Heading H2J. [Also in Division G3] Traction motors M1-M4 with fields F1-F4, controlled in both motoring and braking modes by a chopper circuit 20 receiving ON and OFF signals from a control network via leads 74, 66 respectively, are switched between modes by relays A, B, C, such that A1 closes and A4 opens, or vice versa, while A8, B1, A9 and B2 co-operate to ensure that a gate 68, which transmits the ON pulses to the chopper only if opened by a voltage from 92, remains non- conductive throughout the change of mode. The arrangement is shown in the braking mode, and when relay B is energized by switch S, contacts B2-B4 close after B1 opens, and switches A1-A3 close before A9 closes, whence C1, C2 close. The enabling signal to the gate 68 travels via A8 and B1 in the braking mode and via C1, A9 and B2 in the motoring mode. For motoring the motors M1, M2 and M3, M4 are in series pairs, the pairs connected in parallel, and in series with the chopper 20, smoothing reactor 26, and current detector 91, and for braking, armatures 1 and 2, in series with fields 3 and 4 are in parallel with armatures 3 and 4 in series with fields 1 and 2, all shunted by resistor 24, and resistor 22 intermittently shunted by the chopper to control the braking effort. The chopper comprises thyristors 38, 40 and 42, reactor 46 and thyristor 42 providing a by-pass circuit for the initial current, and 40 being operative for quenching. Pulses are supplied via transformers 52 and 54, 52 having mutually isolated secondaries for thyristors 38 and 40. Diode 28 by-passes the back e.m.f. of the motors when their current is switched off. Oscillator 62 provides OFF pulses Pf to the chopper, on lead 66 at regular intervals, and, after a controlled time delay provided by delay 70 in response to control system 86-88, 90, and comparator 80 which may be a differential amplifier, comparing the desired with the actual motor current, a series of ON pulses P n is supplied on lead 74, provided the gate 68 is open. The control scheme of pulses may alternatively be of the variable frequency or ripple control type. Circuit 88 limits the allowable rate of change of the delay, and shapers 72, 64 may be differentiating circuits. Overcurrent protection 98, 100, 102, OL-1, OL-2 may be provided, although C2 may be operated directly by relay A, and overcurrent protection omitted.