Patent GB-1531346-A (GB)
Title: Regenerative motor control having field and armature coordinating means
IPC: H02P3/14
Filed: 1976-03-31
Abstract: 1531346 Control of DC motors ALLENBRADLEY CO 31 March 1976 [24 April 1975] 12859/76 Heading H2J A separately-excited D.C. motor 22 is controlled to maintain constant a desired operative condition such as torque, tension in a web driven by the motor or speed as shown in Fig. 1, wherein an amplifier 16 produces an error signal of one or other polarity according to that derived by comparing the signals from a reference source 30 and a tachometer 38, the output of amplifier 16 controls the current in the motor field winding 26 through thyristors 54, 56 or 58, 60 controlled through members 62, 64 and controls the current in the motor armature 24 through thyristor bridge 82 controlled by members 94, 98, 108, 110, and the amplifier 16 is controlled by a limiting circuit 74, responsive to a signal from resistor 66 sensing the field current, to limit the error signal during weak field conditions such as starting and during field reversal prior to regenerative braking, this limiting action and the design of the circuit 110 causing the armature current to be reduced to zero during weak field conditions and to be controlled by the error signal during normal conditions to maintain the motor speed at the desired value. As shown in Fig. 2, the output of amplifier 16 is limited by one or other of transistor-diode circuits 208, 210 or 214, 216 according to the signal polarity, which transistors are controlled by the signal from resistor 66 applied to amplifier 220 and also to firing circuit 62 to maintain the field current at a desired value having a maximum established by the setting of potentiometer 64. Absolute value circuit 110 includes an amplifier 304 having a gain of two, an adjustable potentiometer 334 and a further amplifier 322, whose output feeds a regulator 98 receiving a signal of actual armature current from resistor 104 and controlling this current to a desired value having a maximum established by the setting of potentiometer 108. The potentiometer 334 is adjusted to produce a signal equal to the lowest limited output signal of amplifier 16 whereby in conjunction with the signal passed by resistor 332, the gain of amplifier 304 and the selective signal blocking action of diode 314, the output signal of circuit 110 is zero when the signal of amplifier 16 is at its lowest limited value and is subsequently proportional to the amplifier signal but always positive irrespective of the polarity of this signal. At starting the output signal of amplifier 16 is initially limited to its lowest value determined by the characteristics of transistors 210, 216 and thereafter to a progressively increasing value superimposed by the signal from amplifier 220, until the field current reaches a value producing a signal to include the whole output range of amplifier 16, after which the baseemitter junction of transistor 210 or 216 becomes conductive to limit the signal from amplifier 220. During field reversal produced by reduction of the reference signal 30 or an overhauling load, the signal from amplifier 16 is limited to its lowest value until the field current has fallen to zero, after which the abovedescribed operation occurs to produce armature current build-up and regenerative braking. When the motor speed has been reduced sufficiently to change the polarity of the signal to amplifier 16, field reversal and the associated above-described operation are repeated to return the system to its motoring condition. The response of circuit 62 is such that the field current rapidly attains its normal desired value.