Electricity: motive power systems – Series motors
Patent
1986-09-18
1988-03-08
Ro, Bentsu
Electricity: motive power systems
Series motors
318331, 318345C, 318345AB, 318345G, H02K 2308, H02P 762
Patent
active
047301490
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a circuit arrangement controlling the speed of an electric motor.
In a known circuit of this type (DE-OS No. 2,906,388), the series connection of the armature winding of the electric motor and a controllable rectifier is connected between two field winding halves. Arranged in parallel with this series connection is a potentiometer whose pickup is connected to the inverting input of an operational amplifier configured as integrating amplifier. The inverting input of the operational amplifier is located at the terminal of the potentiometer connected directly to an electrode of the controllable rectifier. Arranged in parallel with the field winding portion starting at this reference potential point is a series connection of a capacitor and an ohmic resistor, with the capacitor being connected to the reference potential point. A line leads from the point of connection of the capacitor with the resistor to the inverting input of the operational amplifier. This generates a signal which is proportional to the motor current and is switched in opposition to the signal picked up at the potentiometer. The output of the operational amplifier controls a phase control unit which, in turn, charges the control electrode of the controllable rectifier. A drawback of this circuit arrangement is that the potentiometer for setting the rpm also picks up the voltage drop that builds up during the idle period of the controllable rectifier. To suppress this part of the control voltage present at the potentiometer pickup, since it falsifies the measuring result, a special switch is necessary which short-circuits the control signal at the potentiometer pickup with respect to the reference potential point during the idle time of the controllable rectifier.
SUMMARY OF THE INVENTION
The object underlying the invention is to provide a circuit arrangement of the above-described type which permits readjustment of the rpm in dependence upon the load by simple means.
This object is realized according to the invention by a circuit arrangement for controlling the rpm of an electric motor having series-connected field and armature windings to which a controllable rectifier is connected in series, the rectifier being controlled by a phase control unit as a function of a control signal obtained at the armature winding and conducted through an operational amplifier, wherein one terminal of the armature winding is connected to the inverting input of the operational amplifier, and the other terminal is connected to the non-inverting input of the operational amplifier so that the voltage between the inverting and non-inverting inputs of the operational amplifier is proportional to the voltage across the armature winding, the output of the operational amplifier is connected to one input of a comparator whose second input is connected to a desired value generator, and the output of the comparator is connected to the phase control input of the phase control unit.
In a circuit arrangement according to the invention, a voltage picked up directly at the armature terminals and proportionally changing with the rpm of the armature is passed to the two inputs of the operational amplifier following adaptation to the permissible control data of the operational amplifier. A control voltage corresponding to the armature rpm is then available at the output of the operational amplifier. This voltage is supplied as an actual value to an input of a comparator whose second input is provided with a desired value signal. If the actual value supplied by the operational amplifier is lower than the given desired value, the comparator supplies to the phase control input of the phase control unit a signal which changes the phase control angle via the controllable rectifier so that the change in current flow causes the actual value to be brought close to the desired value. Since the comparator only emits an on or off signal, rapid readjustment of the rpm is achieved. However, to prevent overshooting during the control p
REFERENCES:
patent: 3231808 (1966-01-01), McDaniel
patent: 3705337 (1972-12-01), Grabl
patent: 3868554 (1975-02-01), Konrad
patent: 4259623 (1981-03-01), Moeder et al.
patent: 4481448 (1984-11-01), Bishop
Ro Bentsu
Telefunken electronic GmbH
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