GB1478958A - Dc motor systems - Google Patents

Abstract

1478958 Control of D.C. motors SIMMS GROUP RESEARCH & DEVELOPMENT Ltd 18 July 1974 [25 July 1973] 35432/73 Heading H2J A motor control system comprises a D.C. motor having a reversible armature 10 and a plurality of field windings 11 each in series with a respective transistor 12, the series combinations being connected in parallel to form an arrangement in series with the armature 10, Fig. 1 (not shown), all the transistors 12 being simultaneously controlled by a variable mark/ space ratio oscillator 26 and each combination 11, 12 being associated with a circuit such as that shown in Fig. 2, whereby in the event of the current through a particular transistor exceeding a predetermined value, the circuit produces a control signal which is applied to the oscillator to modify its operation to reduce the current through all of the transistors. A controller 28, for example the accelerator of a vehicle driven by the motor, determines the mark-space ratio of oscillator 26 which turns transistors 19, 12 on and off to produce a desired motor speed. The method of connection of the windings 11 and transistors 12 ensures that the winding currents are substantially equal. Each current is sensed by a resistor 15 connected to the input terminals of an operational amplifier 31 which, when the current exceeds a predetermined value, supplies a control signal via diode 36 to the oscillator 26. This signal may either terminate the oscillator cycle and so turn off the transistors 12 until the next cycle, or vary the mark-space ratio of the oscillator to reduce the currents through the windings. Members 12, 19, 31 and their associated circuitry may be mounted on a replaceable panel provided with a warning circuit composed of transformer 17, monostable element 38, 39 and a light emitting diode 37, which flashes when transistor 12 is made conductive and thus indicates correct operation.