DE2042721B2 - DC shunt motor reversing circuit - has field winding in transistor bridge and capacitor in supply lead aiding current reversal - Google Patents

Abstract

A reversing d.c. shunt motor uses field reversal to obtain reversed rotation. The inductive field winding (L) lies in the diagonal of a four transistor (Q1-Q4) bridge fed from a d.c. supply (P). Current flow, and hence field polarity, depends on which pair of transistors is conducting. Each transistor is bridged by a flywheel diode (D1-D4). Rapid field reversal is obtained by placing a capacitor (C) in the d.c. supply to the bridge, the capacitor and field inductance forming a series resonant circuit. When the transistors switch off, stored energy is transferred from the field to the capacitor where it is available again to boost the current when the opposite bridge arms subsequently turn on.

Description

25th

The invention relates to a circuit arrangement for the accelerated reversal of the direction of the current through one in the diagonal branch of a DC-fed bridge circuit consisting of four transistors switched-on inductance, in particular the current through the field winding of a direct current shunt motor, wherein in each bridge branch of the emitter-collector path of the transistor one in Opposite direction to the emitter-collector path current-permeable freewheeling diode is connected in parallel

In addition to direct current shunt motors, the invention can also be used advantageously in deflection coils for the Magnetic beam deflection in cathode ray tubes, electron microscopes or others with charge carrier beams working facilities as well as for quick polarity reversal of solenoid valves and at inductive controls are used.

It is known that the direction of rotation of a shunt motor can be reversed either by reversing the armature current direction or by reversing the excitation field. While the reversal of the armature current is often used, in the case of reversal of the direction of rotation by reversing the polarity of the field current, the high time constant T = - = - of the field is available

R.

against a rapid change of direction of rotation. This time constant can be an order of magnitude higher than the mechanical time constant of the armature. Circuits with field reversal have therefore hardly found their way into control technology. Your transition behavior for sudden speed commands is too slow. On the other hand, a circuit in which the excitation field is reversed to reverse the direction of rotation has the advantage that the speed and direction of rotation can be controlled separately from one another, for example the speed by pulsed control of the armature current and the direction of rotation, as mentioned, by reversing the excitation field. Since the armature current is usually substantial, e.g. B. is a hundred times greater than the field current, a circuit for field reversing can be built with components with a significantly lower current-carrying capacity and the cost of cooling the components can be reduced.

From AEG-Mitteilungen Vol. 50 (1960), pp. 49-53, in particular Figure 5 on page 51, there is a circuit arrangement known according to the generic term of the claim. The object of the invention is at a to enable such a control circuit to accelerate the field reversal.

From DT-OS 18 11 709 there is also an electrical one Directional drive known, in which one disrupts the drive control as a result of a reversal of the direction of rotation seeks to avoid the field reversal that can only be achieved relatively slowly by reducing the armature current or the armature voltage is tracked directly to the excitation current or the excitation voltage, including the control loop an armature circuit and an excitation circuit are subordinate, with the actual value of the excitation current determines the nominal value of the armature current. Such a circuit arrangement is quite complex.

In contrast, the solution to the above-mentioned object leads to that characterized in the patent claim Invention to an extremely simple circuit structure.

In the circuit according to the invention, the series resonance of inductance and capacitor a rapid field dismantling and conversion achieved. When turning off the previously current-permeable, move diagonally opposite transistors migrates the magnetic energy stored in the inductance in the form electrical energy via the diodes into the capacitor and is stored there. This increases the when the voltage is subsequently switched on again, the voltage at the bridge circuit is increased by the voltage at the capacitor, so that the field is built up faster when it is switched on again.

The invention is explained below with reference to an embodiment shown in the drawing. The transistor bridge circuit consists of four transistors Qi to Q 4, in whose diagonal branch DB the inductance L, for example the field winding of a direct current shunt motor, is switched on. A diode Di to DA is connected in parallel to each of the emitter-collector paths of the four transistors. Corresponding control signals are fed to the base electrodes of the transistors, which are used as control electrodes, via input terminals K 1 to KA , so that the current from positive pole P of the direct current source first passes through diode D 5 and then either via transistor Q 1, inductance L and transistor Q 3 flows to ground, i.e. based on the circuit diagram from left to right through the inductance L, or, if the transistors Q 2 and QA are switched through, flows through them and thus from right to left through the inductance L. Between the upper direct current feed point A of the bridge circuit and the positive terminal P of the direct current source, apart from the diode D 5 , the capacitor C , which is parallel to this, is also switched on.

Assuming first that the steady field current flows through the transistors Q 1 and Q 3, and these are then blocked , the magnetic energy stored in the inductance L tries to keep the current flowing in the previous direction. The only way to do this is via the diodes DA and D2 , via which the capacitor C is charged with the specified polarity. The voltage on the capacitor C is thus added to the voltage of the direct voltage source of, for example, 28 V. As soon as the field of the inductance L is reduced, the current flow stops

Although capacitor C is on, it remains charged to 1000 V, for example, because diode D 5 is only conductive in the opposite direction to the capacitor voltage

If the transistors Q 2 and <? 4 are now switched on, this increased voltage drives a current in the opposite direction through the inductance L via these two transistors, whereby a field quickly builds up in the opposite direction, which together with the armature field of the Motor first brakes the armature and then rotates it in the opposite direction. The recharging time t, which elapses until the magnetic energy of the inductance L is transferred to the capacitor C in the form of electrical energy, results from the relationship t-π · J / LC and becomes shorter the smaller the capacitor C is. On the other hand, this capacitance must not be too small, because the self-induction voltage that develops at the inductance during charge reversal is proportional to the value | / L / C, ie, the greater the lower the capacitance C is. However, the high-voltage transistors available today, as they were specially developed for line deflection stages in television sets, are able to process collector-emitter voltages of over 1000 V, so that no difficulties arise in this regard.

1 sheet of drawings

Claims (1)

Claim: Circuit arrangement for accelerated reversal of the direction of the current through an inductance switched on in the diagonal branch of a DC-fed bridge circuit consisting of four transistors, in particular the current through the field winding of a direct-current shunt motor, with one in each bridge branch of the emitter-collector path of the transistor in the opposite direction to the emitter -Collector path current-permeable freewheeling diode is connected in parallel, characterized in that between the one direct current feed point (A) of the bridge circuit (Qi-Q 4) and the associated terminal (P) of the direct current source, the parallel connection of a forward-polarized diode (DS) and a capacitor (C) forming a series resonant circuit together with the inductance (L) is switched on