DE1159078B - Arrangement for regulating the armature voltage of a constantly excited DC shunt motor with the aid of transistors - Google Patents

Description

Arrangement for regulating the armature voltage of a constantly excited DC shunt motor with the aid of transistors The invention relates to an arrangement for regulating the armature voltage of a constantly excited DC shunt motor with Using transistors and a power supply transformer with several secondary windings for the power supply of the motor and the electronic control and regulation part. This The control and regulating part consists of control elements for setting a target armature voltage according to the desired engine speed and from control elements for automatic Correct the load-dependent armature actual voltage to the voltage setpoint. The regulation is carried out with square-wave pulses of constant frequency Change the pulse width.

Control arrangements are known. where DC shunted small motors can be controlled with square-wave voltage pulses. A known rule arrangement controls by changing the pulse frequency with a constant pulse width (pulse frequency control). It uses a monostable multivibrator to generate pulses more constant Width, also a switching transistor for comparing the on a potentiometer set anchor tension with the anchor actual tension. If the actual armature voltage drops, so the transistor becomes conductive, its collector voltage drops and thus causes that the multivibrator circuit generating the pulses has two further transistors comes into action. The impulses are then amplified via further transistors and supplied to the motor armature, which is excited by these pulses. Has the anchor tension the armature setpoint tension is reached, the arrangement switches off until the armature actual tension is reached sinks again. This control arrangement generally works with a pulse frequency between 200 and 700 pulses per second. This rule arrangement is unfavorable their complex and expensive construction due to the large number of transistors required.

In another known control arrangement, the pulse width is changed controlled at constant pulse frequency (pulse width control). This rule arrangement However, it is at least as expensive as the aforementioned control arrangement with changeable Pulse frequency. Triangle pulses are used to control a square pulse generator used, which are formed by a multivibrator circuit. For comparison an armature setpoint voltage set on a potentiometer with a speed proportional DC voltage and a tachometer generator, a comparison transistor and your own DC power source provided. The invention is based on the object of a extending over a wide speed range. the simplest and cheapest possible arrangement for regulating the armature voltage of a constantly excited DC shunt motor to create with the help of transistors.

The invention is characterized in that, to control a transistor which generates the square-wave voltage pulses of constant frequency and varying pulse width, the pulse width depends on the armature setpoint voltage set on a potentiometer as a control element and the load-dependent average armature actual voltage, on its base-emitter path a rectified sinusoidal half-wave voltage is applied, which determines the respective pulse width by changing its base potential as a function of the control deviation. To change the basic potential of the control voltage of the transistor, means are provided which raise the basic potential of the control voltage, which is negative compared to zero, into the positive range and expand the control range of the armature voltage in such a way that the motor speed can be set to zero. In order to obtain a particularly simple, high-performance control arrangement, the following are also developed in accordance with the invention. In some cases known measures are used: a) A further transistor working as a variable resistor is provided as an automatic control arrangement, the internal resistance of which depends on the armature setpoint voltage set on a potentiometer and applied to the base of this transistor and the mean armature voltage of the motor, which is smoothed by a capacitor is applied to the emitter of this transistor, depends; b) the collector potential of this transistor, which is dependent on the internal resistance, influences the potential at a voltage divider tap, which is arranged between the collector of this transistor and a resistor connected to it; c) from the voltage divider tap point, a line is connected via a Zener diode, a full-wave rectifier and a secondary winding of the transformer to the base of the transistor generating the square-wave pulses, so that the potential of the rectified sine semicircular control voltage, which determines the width of the square-wave pulses, is influenced by the potential at the voltage divider tap point will; d) the square-wave voltage pulses are amplified in a known manner with the aid of further transistors and form as a result of importing pulses with a width matched to the engine load constantly the armature voltage.

Since when the engine is loaded, the armature voltage only drops as much as for It is necessary to initiate the control process, which then prevents any further drop, the set armature voltage mean value can be constant even with changing loads being held.

In a simple way, the performance of the control arrangement can still can be increased by, as known per se, connecting a choke coil in front of the motor so that the voltages induced by the pulses in the choke coil add to the respective operating voltage. As surge protection for the last The transistor of the pulse amplifier stage is a quenching diode in parallel in a known manner to the choke coil and to the armature so arranged that after locking the last Transistor of the pulse amplifier stage at the end of each pulse induction current flowing flows over the motor armature and thus contributes to the generation of torque.

The circuit diagram of an embodiment of the control arrangement according to the invention is shown in the drawing. It is based on this drawing in the following described in more detail.

A mains connection transformer 1 is to be connected with its primary winding 10 via a fuse 11 and a two-pole switch 12 to an alternating current source. There are four windings on the secondary side of the transformer 1. A winding with terminals 21 and 22 and rectifier bridge 3 generates a full-wave rectified, semi-sinusoidal DC voltage which is applied via a Zener diode 4 between voltage divider tap point A and the base terminal of a transistor 30. A further secondary winding with the connections 23 and 24 and the center connection 25 feeds the excitation winding 200 via a pair of diodes 5 and 6 and the armature winding 204 of a small direct current shunt motor via a choke coil 201, a direction switch 202 and a transistor 50. As overvoltage protection for the transistor 50 , a quenching diode 205 is arranged parallel to the choke coil 201 and to the armature 204 of the motor.

An armature setpoint voltage can be continuously adjusted on a potentiometer 206. The potentiometer supply voltage is taken from a secondary winding with the connections 28 and 29 via a rectifier bridge 71 on a smoothing capacitor 711.

To reduce the engine speed, the armature setpoint voltage is reduced at the potentiometer 206. To increase the engine speed, however, the nominal armature tension is increased.

A further secondary winding with the connections 26 and 27 supplies a negative bias voltage via a rectifier bridge 70 on a smoothing capacitor 701.

The following consideration of the control process is based on the fact that line O has zero potential. It is known that the mean speed of the motor is dependent on its mean armature voltage. The mean armature voltage is specified by the armature setpoint voltage set on potentiometer 206. The armature setpoint voltage is placed between the line O and the base of the transistor 203 . In the control arrangement shown, it is positive with respect to line 0, but is smaller by the value of the control voltage of transistor 203 (for example about 0.1 volts) than the positive mean armature voltage of the motor, smoothed by a capacitor. This is placed between the emitter of transistor 203 and line O and can be varied from about 6 to 60 volts.

The internal resistance of the transistor 203 depends on the nominal armature voltage lying between its base and the conductor O and on the mean actual armature voltage, which lies between its emitter and the conductor 0 and is influenced by the torque of the motor. At high speed and high torque the internal resistance is high, at low speed and low torque it is small. At low speed and high torque and at high speed and low torque as well as at all possible intermediate stages, an internal resistance between these extreme values results.

If the internal resistance of transistor 203 is high, then the voltage drop between emitter and collector is also high and the potential at the collector is strongly negative. Since the potential of the resistor 207 is also negative. so the potential at the voltage divider tap point A is also strongly negative. If, on the other hand, the internal resistance of transistor 203 is small, then the negative potential at the collector is also small, and thus the potential at voltage divider tap point A also becomes smaller, ie the potential at point A shifts towards zero.

This change in potential at point A has an effect on the control process of transistor 30, since between point A and the base of transistor 30 there is the rectified sine semicircular control voltage shifted by the value of the Zener voltage to plus. In order to obtain proper switching and control of the transistor 30 , the following conditions must be observed when choosing the Zener diode: The basic potential of the control voltage must be less than the Zener voltage, and the sum of the control voltage and tap voltage between point A and line O must be greater than be the zener tension.

Are these conditions met? the basic potential of the control voltage is raised so far into the positive range that only the peaks of the sine semicircular control voltage protrude into the negative range and beyond the switching voltage of transistor 30 and cause transistor 30 to open.

This is positive at high engine speeds and high engine loads Basic potential of the control voltage at the base of transistor 30 is small, the sinusoidal voltage half-arcs come far into the negative range and open the transistor 30 for a long time. The square pulses at the collector of the transistor are therefore wide.

This is positive for a low engine speed and low engine load The basic potential of the control voltage at the base of the transistor 30 is large, the sinusoidal tension half-arcs come only a little, d. H. only with the near that Part of the vertex lying in the negative area. The transistor 30 is thereby open only briefly, the pulses at the collector of transistor 30 are therefore narrow.

As is known, by appropriate selection of the transistor 30, a precise Switching, d. H. Pulses with a steep slope can be achieved, so that practical the impulses generated at the collector can be described as rectangular.

These square-wave pulses are amplified by the transistors 40 and 50 in a manner known per se. This amplified voltage, composed of individual rectangles, which is taken from the secondary winding with the terminals 25 and 23- "24, is fed to the armature 204 of the motor and results in the mean actual armature voltage, which is decisive for the respective speed of the motor.

If the mean actual armature voltage drops due to higher loads, after the control process described above, the pulses are wider, and the mean actual armature voltage then rises again to the value. that she had before the load increase on the engine.

If, on the other hand, the load decreases, the mean actual anchor voltage increases, because the motor then acts as a generator due to its constant excitation. The control process is now reversed, the impulses become narrower and the middle one The actual armature voltage thus drops back to the original value.

As already mentioned, a change in load affects the actual armature stress not fully off, but only as far as necessary to initiate the control process which then prevents any further voltage change.

A change in the armature voltage at the potentiometer 206 effects the same control process as a change in load; an increase in the armature setpoint tension acts like an increase in the load, a decrease in the armature setpoint tension acts like a decrease in the load on the motor. Before the motor armature, a choke coil 201 is connected in a known manner, which takes over the difference between the rectified secondary voltage of the transformer 1 and the average armature actual voltage and generates a counter voltage. At the end of each pulse. At the moment when the transistor 50 suddenly blocks, a voltage arises in the choke coil which is added to the rectified voltage. So that this voltage cannot be dangerous to transistor 50, a quenching diode 205 for overvoltage suppression is arranged in a known manner in parallel to choke coil 201 and the armature, whereby the induction current flowing after the transistor 50 is blocked is inevitably passed through the armature 204 of the motor and so contributes to torque generation.

Claims (3)

PATENT APPLICATION: 1. Arrangement for regulating the armature voltage of a constantly excited DC shunt motor with the help of transistors and a mains connection transformer with several secondary windings for the power supply of the motor and the electronic control and regulating part as well as with control elements for setting a nominal armature voltage according to the desired motor speed and with control elements for automatically correcting the load-dependent Ankeristspannung to the voltage target value, wherein the control with rectangular pulses of constant frequency is accomplished by changing the pulse width, characterized in that to control a transistor (30) which generates the square-wave voltage pulses of constant frequency and a varying pulse width , the pulse width depending on the armature setpoint voltage set on a potentiometer (206) as a control element and the load-dependent mean actual armature voltage, at its base-emitter line ke a rectified sinusoidal semicircular voltage is applied, which determines the respective pulse width by changing its basic potential as a function of the control deviation. 2. Control arrangement according to claim 1, characterized in that means (4) are provided. which is the negative basic potential of the Raise the control voltage of the transistor (30) into the positive range and the control range the armature voltage in such a way that the motor speed down to the value zero is adjustable. 3. Control arrangement according to claim I and?, Characterized by the application of the following, partly known measures: a) that a further transistor (203) operating as a variable resistor is provided as an independent control arrangement, the internal resistance of which is different from that set on a potentiometer (206) , at the base of this transistor (203) applied armature target voltage and from the mean armature voltage of the motor smoothed by a capacitor. which is applied to the emitter of this transistor (203). depends, b) that the internal resistance-dependent collector potential of this transistor (203) influences the potential at a voltage divider tap point (A) which is arranged between the collector of this transistor (203) and a resistor (207) connected to it, e) that of the Voltage divider tap point (A) a line via a Zener diode (4), a full-wave rectifier (3) and a secondary winding of the transformer (1) is connected to the base of the transistor (30) generating the square-wave pulses, so that the potential of the rectified sine semicircular control voltage, the determines the width of the rectangular pulses, is influenced by the potential at the voltage divider tap point (A). d) that the square-wave voltage pulses are amplified in a known manner with the aid of further transistors (40, 50) and form the armature voltage as a sequence of pulses with a width constantly adapted to the motor load. Documents considered: German Auslegeschrift No. 1021025; "Electronics", 1959, No. 6, pp. 179 to 182.