GB1216932A - Improvements in motor control systems - Google Patents

Abstract

1,216,932. Automatic control systems. GENERAL ELECTRIC CO. Aug.21, 1968 [Oct. 20, 1967], No.39891/68. Heading G3R. [Also in Division H2] In a speed or torque retroactive control system wherein a D. C. motor is fed from a three-phase supply by a plurality of phase-controlled rectifiers, trains of relatively high frequency pulses (e.g. in the range of 5 khz to 20 khz) are used to gate the controlled rectifiers to avoid commutation due to transients in the supply voltage, and initiation of each pulse train terminates a pulse train in a preceding phase. As shown, D. C. signals proportional to the speed of motor 10 are fed from tachometer 82 and compared with command reference signals at 78 and error signals are amplified by amplifier 84, which has an adjustable feedback network 86 for smoothing out high frequency signals (due to transient operating conditions) to stabilize the system. For quick response to required charges a voltage regulator 88 compares the output from 84 with feedback from 90 which is proportional to the voltage across the armature of motor 10, stabilization being provided by a capacitor 98. The control system can reverse motor 10, and has a regenerative braking mode. Firing signal generators 27 and 34 are energized for forward or reverse drive, respectively, via amplifiers 106 and 108 when the error signal input to differential amplifier 100 is positive or negative, respectively. Each generator 27 and 34 comprises three high frequency pulse generators for the three phases of the bridge circuit rectifiers 36 and 38 respectively, but for clarity these are only shown separately for generator 27 and bridge circuit 36. Initiation of firing pulse trains from generators 28, 30, 32 is synchronized with the A. C. supply (from lines 40, 42, 44) by circuits 62, 64, 66, and interconnections 70, 72, 74 ensure that initiation of pulses in generator 28, for example, terminates the pulses from generator 32. Lockout circuits 124 and 126 ensure that the rectifiers for one direction of motor 10 are not fired while current is still flowing in the other rectifiers, and instantaneous current limiting is provided by circuit 110, as in Specification 1, 207, 553. One embodiment of a suitable pulse generator circuit is described Fig.3 (not shown).