EP0169488A2 - Transformer circuit - Google Patents

Abstract

To reduce power loss, weight and switching times, a transformer circuit comprises at least one actuating unit (144), in which the first winding (9) of a transformer (8) connects an input connection (2) to an output connection (5). Switches (150 to 153) can be used to apply either the input voltage or the output voltage of the actuating unit to a further winding (11) of the transformer, as a result of which a voltage (AU) induced in the first winding is additively or subtractively impressed on the input voltage. The further winding can be connected in parallel with the anti-parallel winding sense to the first winding or short-circuited, whereby the output voltage becomes equal to the input voltage. If the circuit of the further winding is opened, the first winding throttles the load current. For a quick changeover, all switches are briefly closed at the same time, a current limiting circuit (157) limiting the short-circuit current. V-MOS transistors as switches further shorten the switching times. Two or more control units can be connected in series and serve as a voltage constant or voltage regulator with a sensor arrangement, a comparator arrangement and a switch control.

Description

The invention relates to a transformer circuit according to the preamble of claim 1.

Such transformer circuits are used, with the aid of at least one actuating unit, which can be brought into different switching states, to change the amplitude of an AC supply voltage emitted by a voltage source, if necessary, before it is applied as a load AC voltage to a consumer.

Such a transformer circuit is known for example from DE-OS 25 00 065. This circuit comprises a single control unit with a transformer, the primary winding of which is fed by the supply voltage emitted by the voltage source. Several taps are provided on the secondary winding, which can be optionally connected to the lines leading to the load by means of automatically controllable switches. This ensures that the same AC voltage amplitude is always supplied to the load even when the circuit is connected to voltage sources which emit different AC voltages with respect to the amplitude.

However, this known arrangement has a number of disadvantages. The entire power supplied to the load must be passed on via the magnetic field of the transformer. The dimensioning of the transformer must therefore be adapted to this total power and it there are correspondingly high losses. If the load consumes very high powers, the transformer must be designed very large and moreover cooled, which leads to considerable manufacturing and operating costs. In addition, the known circuit is not suitable for switching frequently and quickly in order to keep the load voltage at least approximately constant despite corresponding changes in the amplitude of the supply voltage. If one were to operate the known arrangement in this way, considerable problems would also arise from the fact that the total power supplied to the load flows through the changeover switches. On the one hand, these switches would have to be operated under load and, on the other hand, special measures would have to be taken to prevent the power supply from being interrupted during the switchover.

In contrast, the invention has for its object to provide a transformer circuit of the type mentioned, with the help of which the amplitude of the supply voltage emitted by the voltage source can be changed in a simple and quick manner and with extremely low energy losses.

To achieve this object, the invention provides the features set out in claim 1.

These measures are based on the consideration that in many applications the required change in the amplitude of the supply voltage emitted by the voltage source is only a comparatively small percentage, for example of + 25% of the amplitude. Therefore, according to the invention, the main part of the power of the load is supplied via the first winding of the transformer in a galvanic way, whereby due to the low number of turns of this winding and low frequencies with which high powers are delivered to loads, the inductance of this first winding produces only a very small voltage drop with correspondingly small losses, which moreover occur in an increased manner in the case of conventional transformer circuits.

According to the invention, the at least one control unit of the transformer circuit can be brought into at least one switching state by applying a control voltage U _s to the further winding, in which a voltage .DELTA.U _{1 is} induced in the first winding of the transformer additional winding with respect to the first winding added to or subtracted from the input voltage, so that the following applies to the output voltage U _{A, which} is different from the input voltage:

The relative size of ΔU ₁ with respect to the control voltage U _{s is given} by the turns ratio w ₁ / w _{w of} the first winding of the transformer for further winding:

The turn ratio w _{1 /} w _w is here substantially less than 1 and is preferably in the range from 1: 7 to 1: 200. In addition, the current that flows through the further winding in the first switching state is to be matched to the nominal load current that flows through the first winding of the transformer so that, for a given turns ratio, the fluxes of both windings are approximately the same in amount and such an angular displacement mutually sen that the magnetic flux, which results in the transformer core, leads to the desired induced additive or subtractive voltage drop ΔU ₁ at the first winding of the transformer. It can be seen that under these conditions the induced voltage drop Δ U _{1 is} largely independent of the load current, so that a constant difference between the input and output voltage of the actuator can be maintained even if the load current fluctuates in relation to its nominal value.

A major advantage of this arrangement is that the magnetic coupling of the transformer is only the small part of the power that is required for the induced change in amplitude. This significantly reduces the energy losses caused by the inductive energy transfer from one transformer winding to the other. The transformer can thus be dimensioned correspondingly smaller and the effort required for cooling the transformer can be reduced. The switches, which can be used to apply the control voltage to the further winding of the transformer, also result in only a small part of the total power, so that the switches are loaded far less even with frequent switching operations. moreover, semiconductor switches, e.g. Triacs or switches constructed from V-MOS transistors are used which enable switching to be carried out considerably faster than the mechanical switches used in such cases according to the prior art. A complete interruption of the energy supply to the load during switching cannot occur in principle, since the galvanic connection between the load and the voltage source is constantly maintained via the first winding of the transformer.

For a universal usability of such an actuating unit, it is expedient to ensure that even in the periods in which the actuating unit is not in the first switching state, the magnetization of the transformer core is not essentially caused by the flooding of the first winding alone. This can e.g. done by an auxiliary winding in the periods in which the further winding is not. is connected to a control voltage, with the help of switches e.g. is short-circuited. By appropriately dimensioning the number of turns and the current which then flows through the auxiliary winding, the through-flow of this auxiliary winding can be adjusted so that no significant induced voltage drop occurs at the first winding.

In the periods in which the auxiliary winding is short-circuited, the output voltage of the actuating unit is approximately equal to the input voltage. However, this equality can only be achieved approximately and the equipment required for this is comparatively large.

• A) Stelleinheit mit einer einzigen weiteren Wicklung, an die zwei Steuerspannungen anlegbar sind.

However, the at least one control unit of the transformer circuit can preferably be brought into different switching states by applying different control voltages to one or more further windings, as will be explained below for various embodiments:

• A) control unit with a single further winding to which two control voltages can be applied.

The switching state in which such an actuating unit is located when the first control voltage U _S1 is applied is referred to as the first switching state, which is determined by the above Equations (1) and (2) are described, so when the second control voltage U _{S2 is applied} to the further winding under the same conditions as above, a second switching state results, in which a defined second voltage drop AU2 at the first, largely independent of the load current Winding is induced. In this case, the following applies to the output voltage U _A :

In this case, ΔU ₂ depends on the control voltage U _S2 also according to equation (2) above.

The control voltages used are preferably the input voltage U _E and the output voltage U _{A of} the actuating unit, to which the further winding is galvanically connected with the aid of the switch, taking into account the sense of the winding, in such a way that the induced voltage ΔU _{1 is} added to the input voltage and the other induced voltage ΔU ₂ subtracted from the input voltage U _E.

und im zweiten Schaltzustand

The following therefore applies to the output voltage U _A in the first switching state

and in the second switching state

und

miteinander verknüpft, wenn w₁ die Windungszahl der ersten Wicklung und w die Windungszahl der weiteren Wicklung des Transformators ist.However, these two inducible voltages ΔU ₁ and ΔU ₂ cannot be selected independently of one another. Rather, they are according to the equations

and

linked to one another if w _{1 is} the number of turns of the first winding and w is the number of turns of the further winding of the transformer.

So that an unchanged transmission of the amplitude of the input voltage of the control unit to the output connections of the control unit is also possible, the control unit can be brought into a third switching state in which no voltage is induced in the first winding of the transformer. So that the first winding does not develop a throttle effect with a correspondingly high voltage drop in this third switching state, care must be taken that the magnetization of the transformer core is not essentially caused by the flooding of the first winding alone. This can be done in various ways, as will be explained in more detail below. It is essential that in this third switching state only an extremely low voltage drops at the first winding of the transformer, so that with a good approximation the output voltage of the actuating unit is equal to the input voltage:

Because of the small voltage drop across the first winding, only a small voltage is induced in the further winding, so that the short-circuit current flowing in the circuit of the further winding remains small and causes very little power loss.

A first possibility for realizing the third switching state is to provide a switch, with the aid of which a further winding can be short-circuited, whereby it is disconnected from all control voltages at the same time.

In order not to overload the transformer, it must be ensured that the short-circuit switch is only closed when the switches used to apply the control voltages are open. It must also be ensured that the switches serving to apply the one control voltage are only closed when the switches which are used to apply the other control voltage are opened, and vice versa.

In order to make a simultaneous closing of these switches impossible, the switching state of each switch is monitored with the aid of an associated sensor unit and a closing command for a previously open switch is suppressed by a blocking circuit if the output signal of the sensor unit of the other switches indicates that one of these other switches is still closed.

It is desirable that when switching from one switching state to the other, the output voltage U _{A of} the actuating unit changes as quickly and as "smoothly" as possible, ie without strong fluctuations in the absolute amplitude of the output AC voltage up or down from its old to the new amplitude value. However, this cannot be optimally achieved in the embodiment in which the third switching state is produced by short-circuiting the further winding, since certain switching criteria must be observed for the closing and opening of the switches, which make it impossible to derive from an amplitude value Switching the output voltage to another so quickly that the amplitude value is reached in a stable manner after less than a full oscillation period of the load AC voltage.

It is therefore preferably provided to produce the third switching state by electrically connecting the further winding of the transformer to the first winding in parallel in such a way that a short-circuited transformer is obtained with two windings wound antiparallel to its core and connected to the same voltage. The currents that flow in the two antiparallel windings each try to build up a magnetic field in the core of the transformer; however, these fields face each other and essentially cancel each other out. The leakage inductance and the ohmic resistance of the first winding through which the load current flows are very small. The voltage drop occurring at it is therefore very small and the above equation (8) applies with a good approximation. The current flowing through the further winding is correspondingly small, since the further winding has a significantly higher impedance than the first winding of the transformer. As a result, the load current flows practically exclusively through this first winding.

In principle, four switches are sufficient for a transformer which has only a single additional winding in order to be able to bring the relevant actuating unit into the three different switching states mentioned.

If no further measures are taken, care must also be taken in this case to ensure that the input voltage and / or the output voltage of the actuating unit is not short-circuited by simultaneous closing of corresponding switches, as a result of which an inadmissibly high short-circuit current would flow. However, this would mean that here again certain switching criteria would have to be observed for the opening and closing of the switches, which would be achieved when changing from one switching state to another would delay the new amplitude value.

To avoid this, the use of one or more current limiting circuits is provided in particularly preferred embodiments of the actuating unit according to the invention.

In the case of a transformer comprising only a single additional winding, the third and fourth switches, i.e. the two switches with which the two ends of the further winding can be connected to the connecting connecting conductor of the actuating unit, for example themselves each be designed as a current limiting circuit in such a way that they do not let any current through at all in the open state and the current flowing through them in the closed state only oppose a very small, constant resistance as long as this current remains below a predetermined limit value, but prevent the current from rising above this limit value.

The transition from the first to the second switching state or from the second to the first switching state then takes place simply in such a way that the two switches opened in the previous switching state are also closed, which corresponds to a transition to the third switching state, and only then do the switches opened, which must be open in the new switching state. Because of their current limiting properties, the third and fourth switches prevent impermissibly high short-circuit currents from flowing in the third switching state.

Another possibility for a transformer with a single further winding is that the third and fourth switches, ie the two switches with which the two ends of the further winding can be connected to the connecting connecting conductor of the actuating unit, do not lead directly to this connecting connecting conductor. Instead, the third and fourth switches are directly electrically connected to one another by a further conductor and a circuit arrangement is provided between this further conductor and the connecting connecting conductor, which on the one hand connects the two conductors in an electrically conductive manner and on the other hand the flow of an impermissibly large current of one of these two conductors prevented on the other. In the simplest case, this circuit arrangement can be a switch which is always opened when the actuating unit is to be brought into its third switching state, in which an impermissibly high short-circuit current would otherwise flow via this switch. However, such switches can only be opened at very specific times, so that the optimum switching speed cannot yet be achieved with them.

Instead of this, an automatically operating current limiting circuit is preferably used as the circuit arrangement, which opposes the current flowing through it with only a very small, constant resistance, as long as this current is less than a predetermined limit value. However, if the current approaches this limit too much, the current limiting circuit steadily increases its resistance so that the current cannot exceed the predetermined limit. In contrast to a simple switch that opens when you open it flowing current abruptly limited to zero, this continuous limiting process has the advantage that there are no voltage peaks in the output voltage of the actuator. The limit value is chosen so that it is only slightly greater than the current which must flow through the further winding in the first or second switching state and also through the current limiting circuit lying in series with the further winding in these two switching states.

In this arrangement, since the further conductor, which connects the third and fourth switches to one another, would short-circuit the further winding if the third and fourth switches are closed at the same time, the transition from the first to the second switching state is preferably carried out here in such a way that first the second switch is closed, which connects the second end of the further winding to the output end of the first winding. Since in the first switching state the first switch is closed, which connects the first end of the further winding with the input-side end of the first winding, and since this first switch initially remains closed, the two windings are temporarily electrically parallel to one another and the actuating unit is located in the third switching state. The current limiting circuit prevents an inadmissibly high short-circuit current from flowing through the closed second switch and the fourth switch, which is also still closed and which connects the second end of the further winding to the further conductor and thus also to the connecting connecting conductor. The switching process is then continued in such a way that the fourth switch is opened and then the third switch is closed, which connects the first end of the further winding to the further conductor. Even with this switch position, the actuating unit is in the third switching state, since the first and the second switch are still closed. An impermissibly high short-circuit current could now flow through the first and third switches, but this is prevented again by the current limiting circuit. Finally, the first switch is then opened so that the actuating unit changes to the second switching state.

The same applies to switching from the second to the first switching state.

If the actuating unit is not to be kept in the third switching state temporarily, but for a longer period of time, the current limiting circuit can advantageously be designed in such a way that it can be switched to at least one second current limiting value, which is substantially lower than the first current limiting value, preferably equal to zero. In this way, the further winding lying parallel to the first winding of the transformer is practically completely separated from the input voltage U _E and there is no longer any short-circuit current at the connecting connecting conductor.

An automatically operating current limiting circuit has the advantage over a switch, in addition to the already mentioned avoidance of switching peaks, that it prevents the current flowing through it from exceeding the predetermined limit value without any delay.

According to a particularly preferred embodiment, it is provided that the limit value to which the current limiting circuit limits the current flowing through it not only to and fro between two values switched but can be changed continuously in a predetermined range. This makes it possible, on the one hand, to limit the short-circuit current flowing in the third switching state to an uncritical value and, on the other hand, to control or regulate, if necessary, the currents flowing through the relevant further winding in the first or second switching state.

If triacs are used as switches, which are known to be closed at any point in time but can only be opened when the current flowing through them is zero, no special additional criteria with regard to the switching point need to be taken into account in the switching processes described above.

For the various embodiments of actuating units according to the invention with a transformer with a single further winding, the following time sequences result when switching over:

If an actuating unit comprises a transformer with a single further winding and four switches, of which the first and second are designed as triac and the third and fourth as current limiting circuits, then when switching from the first (second) to the second (first) switching state the to switches open at the start of switching, ie the second (first) and third (fourth) switch are closed immediately and without any delay, as a result of which the actuating unit changes to the third switching state. To get from this into the second (first) switching state, the first (second) and fourth (third) switch must be opened. Since it is assumed here that the first (second) switch is a triac, this is only possible if it is and the short-circuit current flowing through the winding has a zero crossing. This leads to a time delay, which in the worst case can be half a period of the alternating current. This applies in the same way if the control unit not only briefly passes through the third switching state during the transition from the first to the second or from the second to the first switching state, but has also been in the third switching state for a long time and is brought into the first or second switching state by the latter should.

The following effect also occurs with all of these transitions whenever the third switching state is exited: After opening the switch, in the first or second switching state, a current flows through the further winding, which is then connected to its control voltage, from a completely different voltage source as the short-circuit current, namely driven in the first switching state by the input voltage of the actuating unit and in the second switching state by the output voltage of the actuating unit; depending on the load current, this current is out of phase with the short-circuit current flowing before the switch opens, ie as a rule these two currents are not in phase. Thus, when using triacs during the transition from the third to the second or first switching state in the further winding which is then connected to the control voltage, there is a strong change in the current flowing through this further winding, which is reflected in the output voltage of the actuating unit by a voltage spike on the first half-wave following the opening of the relevant switch. Only the second following half-wave then has the exact new amplitude value and no longer has any overshoots or voltage peaks. With all of these switching processes, in connection with the above-mentioned waiting time until the next zero crossing of the short-circuit current occurs, a total switching time that is too long for certain applications can result.

The situation is even more unfavorable for an actuating unit in which the transformer has a single further winding and in which all four switches are designed as triacs. As already described above, when switching from the first (second) switching state to the second (first) switching state, the two switches that were open until the start of the switching process, namely the second (first) and the third (fourth) switch, must not be closed at the same time. Rather, only the second (first) switch may be closed here initially; then the fourth (third) switch must be opened, which is only possible when using triacs at the next zero crossing of the current flowing through this switch. The third (fourth) switch can then be closed with a certain time safety margin and only then is it possible to open the first (second) switch, for which a zero current crossing must again be waited for. When switching from the first to the second switching state or vice versa, a waiting time of two half-periods can result in the worst case. If the actuator is held in the third switching state for a long time, the third and fourth switches can be opened. If a transition to the first (or second) switching state is then to take place, the fourth (third) switch must first be closed, which can happen at any time; then the second (first) switch is opened, for which a zero current crossing must again be waited for.

Since the short-circuit current and the current which flows through the further winding in the new switching state are usually phase-shifted with respect to one another in these cases, the voltage peak described above again occurs on the first half-wave of the output voltage, which follows the last switching step of the entire switching process . This results in total changeover times which are as long in the transition from the third to the first or second switching state as in the first embodiment of an actuating unit according to the invention, and which are even longer in the transition from the first to the second or from the second to the first switching state .

If you want to make the switching processes even faster in these embodiments, the invention provides instead of using triacs electronic switches which can not only be closed at any time but also opened again. For this purpose, for example, V-MOS transistors are available, of which two each have to be connected in series with their source-drain paths with opposite polarity in order to set up an AC voltage switch. With these switches, there are no waiting times until the next zero current crossing. In addition, a switching criterion that is independent of the zero crossing of the short-circuit current can be used for the opening processes, which each lead from the third switching state to the first or second switching state, which leads to the smallest possible change in the current in the further winding lying on its control voltage after the switching process . If, for example, the point in time at which the current which flows through the further winding connected to its control voltage after the switchover process reaches its zero crossing is used as the switching point in time has, it can be achieved that already in the first half-wave that follows this switching process, the output voltage of the actuating unit has exactly the new amplitude value without voltage peaks or voltage dips.

_D a in the intermediate period in which the actuating unit is in the third switching state, a different current flows through the further winding than when the further winding in the new switching state is connected to its control voltage, according to the invention the time interval of the zero crossing of the last-mentioned current measured and stored at an earlier point in time from the zero crossing of the input AC voltage, in which the actuating unit is in the relevant switching state. With the help of this stored value, the above-mentioned favorable switching time can then be determined on the basis of a zero crossing of the input AC voltage.

Thus, the times that elapse between the initiation of a switching process and the point in time at which the output voltage stabilizes its new amplitude value, i.e. reached without impressed voltage peaks or dips. If the actuating unit is in the first or second switching state and a switchover to the second or first switching state is necessary, then in the embodiments equipped with V-MOS transistors as switches, the first half of the change occurring in the output voltage can occur at any time immediately and carry out the second half of this change within a half period of the AC voltage to be switched.

Such a change or influencing of the output voltage in two very quick successive steps is extremely advantageous, because in spite of the high speed with which the new state is reached, the system has enough time to switch from one switching state to the other without switching peaks and overshoots switch.

A fourth switching state can be produced for an actuating unit, the transformer of which has only a single further winding, in that the switches of the actuating unit are actuated in such a way that the circuit of the further winding has a high resistance value, which, even after being transformed down, on the side of the first Winding provides a high resistance value. In this switching state, the entire magnetization of the transformer core is caused by the flooding of the first winding. A voltage drop dependent on the size of this flow and thus on the size of the load current then occurs at the first winding. This throttling effect of the first winding in the fourth switching state can be used to limit the power supplied to the load to a safe level when a short circuit occurs at the load.

B) Actuator with two more windings

According to a second embodiment, however, the transformer can also have two further windings, the flooding and winding conditions for the first winding meet the same conditions as those specified above for the further winding. In this case, the actuating unit is brought into the first switching state in that a control voltage is only applied to the first further winding; in the second switching state In contrast, the actuating unit is brought about in that a control voltage is applied only to the second further winding.

Preferably, the number of turns, the control voltages and the sense of winding of the two further windings with respect to the first winding are chosen so that the amplitudes of the two inducible voltages ΔU ₁ and ΔU ₂ are approximately the same size, but the two inducible voltages have opposite signs on the Input voltage U _{E can be} impressed. In this case, the two equations (4) and (5) above again apply to the first and second switching states.

und

Wählt man w_w1 und w_w2 beispielsweise so, daß

gilt, so lassen sich zur Eingangsspannung U_E genau symmetrisch liegende Ausgangsspannungen U_A+ und U_A- erzielen. Alternativ hierzu kann aber auch gewünschtenfalls die aus den Gleichungen (9) und (10) ersichtliche Asymmetrie zwischen +ΔU₁ und -ΔU₂ noch verstärkt werden.The control voltages can indeed be generated in various ways and applied to the further windings. However, in the first switching state, the first further winding is preferably directly galvanically connected to the input voltage U _{E of} the actuating unit with the aid of the switches, while in the second switching state the second further winding is directly galvanically connected to the output voltage U _{A of} the actuating unit, so that in both Switching states receives an autotransformer arrangement. One of the two further windings is used exclusively as an adding winding and the other is used exclusively as a subtracting winding. Thus, only an additive induced voltage + ΔU ₁ and a subtractive induced voltage -AU2 are also available. However, these two voltages are not necessarily linked to one another via the above equations (6) and (7), since a separate number of turns w _w1 and w _w2 can be selected for each of the two further windings. The equations apply here to the impressable induced voltages:

and

If you choose w _w1 and w _w2, for example, that

applies, output voltages U _A + and U _A - which are exactly symmetrical to the input voltage U _E can be achieved. Alternatively, if desired, the asymmetry between + ΔU ₁ and -ΔU _2, which can be seen from equations (9) and (10), can also be increased.

In addition, this embodiment allows one end of each of the two further windings to be firmly connected and only the other end to be either electrically conductively connected to the input or output voltage or separated from it with the aid of a switch. So fewer switches are needed.

As already mentioned, such a transformer circuit is particularly advantageous if the voltages to be induced + ΔU ₁ and - ΔU _{2 make up} only a comparatively small percentage of the input voltage U _E. The bond ratios w ₁ / w _w b ^{between w} ₁ / ^w _w1 and w1 / ww2 are therefore generally less than 1 and are preferably in a range from 1: 3 to 1: 200.

This second embodiment can also be constructed in different variants, which produce a enable third switching state, in which the output voltage of the actuating unit is practically the same as the input voltage, in different ways.

A first possibility is that switches are provided, by means of which the two further windings can each be short-circuited. Here too, special measures must be taken to avoid overloading the transformer, which ensure that the switch or switches used to apply a control voltage are closed only for one of the two further windings. For the preferred embodiment with two further windings, one of which is hard-wired as an adding winding and the other hard-wired as a subtracting winding, this means that the two switches are not operated overlapping. It must also be prevented that a control voltage is applied to one or both further windings while the associated short-circuit switch is closed.

To make simultaneous closing of the switches in question impossible, the switching state of each switch is also monitored here with the aid of an associated sensor unit and a closing command for a previously open switch is suppressed by a blocking circuit if the output signal of the sensor unit of the other switches indicates that one this other switch is still closed.

So that when switching from one switching state to the other, the lowest possible energy losses and the smallest possible switching peaks occur, it is necessary in this variant to switch the switches at certain phase angles or in certain phase angle ranges of the magnetic River that penetrates the first winding of the transformer to open or close. These phase angles or phase angle ranges are chosen so that this magnetic flux changes little as a result of the opening or closing process.

However, this leads to switching criteria that delay the switching from one switching state to another in such a way that the new amplitude value of the output voltage cannot be reached stably within an oscillation period of the load alternating voltage.

Therefore, in a second variant of a transformer, which has two further windings, each of which is connected at one of its two ends to the front or rear end of the first winding as seen from the voltage source, one is provided in order to achieve the third switching state these two further windings are connected in series with the first winding in parallel; these two further windings lying in series with one another can be regarded as a single winding which has a continuous winding direction.

A short-circuited transformer is again obtained with two windings wound antiparallel on the core and connected to the same voltage. The currents in these antiparallel windings try to build up opposing magnetic fields in the core of the transformer, which essentially cancel each other out. The above equation (8) applies again. The current flowing through the two further windings lying in series with one another is very small, since these further windings have a significantly higher impedance than the first winding. The load current therefore flows almost exclusively through the first winding.

In principle, three switches are sufficient in such a transformer, which has two further windings of the type specified above, in order to be able to bring the relevant actuating unit into the three different switching states mentioned.

If no further measures are taken, care must also be taken here that the input voltage of the actuating unit is not applied to the further windings connected in parallel with the first winding, in which an impermissibly high short-circuit current would then flow, by simultaneously closing the switches. However, this would mean that here again certain switching criteria would have to be observed for the opening and closing of the switches, which would delay reaching the new amplitude value when changing from one switching state to another.

To avoid this, the use of a current limiting circuit is preferably provided here.

Preferably, the two switches, with which the two free ends of the two further windings can be connected to the connection connecting conductor, are likewise connected directly to one another in a galvanically conductive manner by a further conductor, and there is a circuit arrangement between the further conductor and the connecting connecting conductor Provided above under A) type, which is preferably again formed as a current limiting circuit.

Here, too, the previously open switch is first closed during the transition from the first to the second switching state or from the second to the first switching state, as a result of which the actuating unit temporarily changes to the third switching state; the current limiting circuit in turn prevents the flow of an impermissibly high short-circuit current. A short time later, the switch which was closed in the previous switching state is opened, as a result of which the control unit changes to the new switching state.

The statements made above under A) about the preferred design and control of the current limiting circuit apply here in a corresponding manner.

For the switching from one switching state to another, the following time sequences result in the present embodiment:

In the worst case, when using triacs as switches, a half-period must also be waited until the corresponding switch can be opened when changing from the third to the first or second switching state. It is again irrelevant whether the actuating unit has been in the third switching state for a long time or whether it briefly runs through when switching from the first to the second or from the second to the first switching state.

Here, too, when switching to the first or second switching state, the current which flows through the further winding after the switching process has ended, which is due to its control voltage in the new switching state, is phase-shifted with respect to the short-circuit current previously flowing through this winding, so that the same disturbing voltage peak results as in the embodiments described above.

To carry out the switching processes more quickly, it is also possible here to use electronic switches instead of triacs, which, for example, each consist of a series connection of two V-MOS transistors and can be closed and opened at any time.

Again, the waiting times until the next current zero crossing no longer apply and the switching criterion described above, which is independent of the zero crossing of the short-circuit current, can be used if a switch has to be opened to transition from the third switching state to the first or second switching state.

Again, a point in time is used as the switching time at which the current which flows through the further winding connected to its control voltage after the switching process has its zero crossing. Since a different current flows through the two further windings in the third switching state than when the corresponding further winding is connected to its control voltage in the new switching state, the time interval between the zero crossing of the last-mentioned current and the zero crossing of the input AC voltage is also in a previous one Period measured and the measured value saved. With the help of this stored value, the above-mentioned favorable switching time can then be determined again.

Thus, the time periods required for the switching processes can also be made extremely short. If the actuating unit is in the first or in the second switching state and a switchover to the second or first switching state is necessary, it can be switched off in the case of V-MOS transistors permitted embodiments carry out the first half of the change occurring in the output voltage immediately at any time and the second half of this change within a half period of the AC voltage to be switched.

Such a change or influencing of the output voltage in two very quick successive steps is extremely advantageous, because in spite of the high speed with which the new state is reached, the system has enough time to switch from one switching state to the other without switching peaks and overshoots switch.

Such a change, which takes place in two steps, is however not possible with a single actuating unit if it is already in the third switching state and is to be brought out of this into the first or second switching state. Although it only changes the output voltage by half the maximum possible change, this half must be managed in a single step.

If, for a given input voltage of the control unit, more than three different output voltages are to be optionally available in succession at the output connections, the transformer can indeed have several further windings, each of which can have different numbers of turns. These number of turns can be within the above-mentioned range from 1: 3 to 1: 200, but should only differ from each other to such an extent that if the associated voltage is applied to the further winding with the smallest number of turns, none in the other further windings excessive voltages are induced. A corresponding number of switches can be provided, with the aid of which each of these windings can be connected to or disconnected from a control voltage. It is also possible to apply a control voltage to only one or to two or more of the further windings at the same time.

C) Actuator with another winding to which more than two control voltages can be applied.

A preferred possibility, according to the invention, of optionally providing more than three different output voltages in succession at the output of a single actuating unit, is alternatively one of a plurality of control voltages U _S1 , ..., to the at least one further winding with the aid of switches. US2q anz place ^u-, which differ at least partially in amplitude from each other. Q is any integer greater than 1.

To generate these control voltages ^U _S1 , ..., U _S2q , an AC voltage _source is preferably used which has a plurality of taps, between which different tap voltages U _X1 , ..., U _{XP are} constantly available and can be tapped off. p is also an integer greater than 1 and preferably less than q. With the help of switches, these tap voltages can be applied either individually or in groups added as control voltages to the further winding of the transformer.

It is an essential aspect of the invention to provide a transformer circuit which is digital in a predeterminable change range + ΔU _max Allows changing the voltage applied to a load and thus the power delivered to the load. In special cases, the change range can only be positive or only negative; ie only the additive or only the subtractive impression of induced voltages AU on the input or supply voltage may be required. In the following, however, the general case of a change range ± ΔU _{max that is} symmetrical to the change zero (input voltage equals output voltage) is explained.

und

A digital change in the output voltage in this range ⁺ ΔU _max is understood to mean that there is a smallest voltage change that can be impressed both on the positive and on the negative side + ΔU _min or - ΔU _min and that q can be positively impressed in the positive part of the change range Voltages - ΔU ₂ (ν = 1, ..., q) and in the negative part of the change range q negative impressable voltages - ΔU (ν = 1, ..., q) are available, whereby the following applies:

and

This means that in the positive as well as in the negative part of the change range, any voltage that can be impressed + ΔU _{2 is} an integer multiple of the associated smallest voltage that can be impressed + Δ _Umin and that ₂ can assume all integers between 1 and q. The greatest possible inducible voltage in each direction is also the limit of the range of change:

It can be seen that the range of change can be varied both by choosing the smallest change ± ΔU _min and thus the step size, and by choosing the number q of cuts. However, an increase in the step size leads to a reduction in the accuracy with which the load voltage U _L can be kept constant at a predetermined value, for example when using the transformer circuit according to the invention. On the other hand, an increase in q means an increase in the technical outlay. When defining the quantities q and ± ΔU _min, an optimization tailored to the respective application must be carried out.

The amplitudes of + Δ U _min and - Δ U _min are preferably at least approximately the same size, so that the following also applies at least approximately to the other inducible voltages:

In a corresponding manner, the control voltages U _Sν to be applied to the further winding are digitally structured in accordance with the invention, ie there is a smallest control voltage U _Smin which leads to the impressing of the smallest induced voltage ΔU _min , and the other control voltages are integral multiples of this smallest control voltage :

whereν again runs through all values from 1 to q. In order to be able to cover the above-mentioned symmetrical change range ⁺ ΔU _max with 2q steps, only q control voltages U _{S2 have to be} provided, since with the help of the switches each voltage tapped from the AC voltage source can be applied to the further winding in two different ways so that in one of the two cases the winding direction of the further winding with respect to the first winding of the transformer "is just opposite to the winding direction in the other case. As a result, the induced voltage .DELTA.U is in one case additively and in the other case subtractively applied to the input voltage of the actuating unit.

Here, too, there is again the possibility of short-circuiting the further winding, so that the output voltage of the actuating unit is equal to the input voltage, or to interrupt the circuit of the further winding in order to limit the load current due to the resulting choke effect of the first winding.

To generate the q control voltages U _S2 , it is not necessary according to the invention to provide q + 1 taps at the AC voltage source in such a way that a tap voltage U _Xmin corresponding to the smallest control voltage U _Smin drops between all immediately adjacent taps.

Rather, the amplitudes of the tap voltages are graded according to a suitable code so that, with a minimum number of taps (and thus also a minimum number of switches), all required control voltages U _{Sν can be combined} by additively combining several tap voltages, unless they are directly one of the voltages correspond to that between two be neighboring taps are available. Thus, the smallest control voltage U _Smin is available, at least one pair must., _Hen be provided for by adjacent taps between which U _Xmin U _Smin falls from a ^voltage riffs ^g. Between the other pairs of adjacent taps, tap voltages can then be at least partially provided, which, according to the code mentioned above, are integer multiples of the smallest tap voltage U _Xmin different from 1. The cheapest code here is the pure binary code, in which each tap voltage occurs only once, and the tap voltages 1 in succession between successive tap pairs. U _Xmin , 2nd U _Xmin , 4th U _Xmin , 8. U _Xmin etc. fall off.

However, the use of this code assumes that pairs of taps that are not required for the additive composition of a control voltage U _Sν that is just required can be short-circuited without further notice.

In a preferred according alternating voltage source, consisting of an additional transformer arrangement having a winding consists, to which an alternating voltage is applied and which is divided into a plurality of winding sections, bgreifen between which the taps to the _A of the Abgriffsspannun ^g en U _X1, ... , U _XP are brought out, the above-mentioned condition for the use of a pure binary code does not exist. For this reason, a code is preferably used here which allows any control voltage required to be tapped from a group of taps which follow one another immediately, unless it can be tapped directly from a single tapping pair. In space common, this means that at least the smallest waste oltage griffss ^p U _{Xmin 'in} some cases, but also some of the integral multiples thereof repeatedly need to be tapped. For example, for the generation of eight control voltages
1st U _{Smin '} 2nd U _Smin' ..., 8th U _Smin
four winding sections can be provided on the winding of the additional transformer arrangement, the number of turns of which are selected such that the tapping voltages are in turn at the taps
_1UXmin , _2UXmin , _4UXmin , 1. U _Xmin
drop, where U _Xmin = U _Smin . _M sees that the control voltages 1. U _Smin . 2nd U _Smin and 4th U _Smin can be tapped directly at the first or second or third winding section (counted from the left in the above row) while the control voltage ^3. U _Smin over a combination of the first and second winding section, the control voltage 5. U _Smin over a combination of the third and fourth winding section, the control voltage 6. U _Smin over a combination of the second and third winding section, the control voltage 7. U _Smin over a combination of the first, second and third winding section and the control voltage 8. U _Smin can be tapped over the combination of all four winding sections. However, the code just given as an example is not the only possible one with this number of required control voltages and four available winding sections. For example, all eight control voltages can also be tapped if the integer multiples of the smallest tapping voltage correspond to code 1,3,2,2.

The number of turns of the winding sections is preferably selected such that the tap voltage 1 at the section lying at one of the two ends of the row of winding sections. UXmin and at the section that lies at the opposite end, the tap voltage 1. U _Xmin can be _tapped directly, as is the case with the first of the two examples above.

It is essential that the code is always selected so that all the required control voltages U _S2 are available with a minimum number of winding sections or taps. In addition, if possible, the maximum alternating voltage that can be tapped across the combination of all winding sections should be the same or at least not significantly greater than the maximum required control voltage U _Smax .

The additional transformer arrangement preferably consists of only a single winding which is divided into the different sections and at the extreme ends of which a corresponding AC voltage is applied. For this purpose, for example, the input or output voltage of the actuating unit itself can be used.

In order to be able to use a transformer circuit, which consists of a single actuating unit, on the further winding of which different control voltages can be applied with the aid of switches in the manner just described, as voltage constants and / or voltage regulators, the invention further provides that the voltage applied to the load Voltage U _{L is} measured with the aid of a sensor arrangement that a comparator receives the output signal ^compares the ^{sensor arrangement} with a reference value U _ref , which represents the nominal value S of the load voltage, and that a switch control is provided which controls the switches on the basis of the difference signal emitted by the comparator arrangement in such a way that those induced in the first winding of the transformer Counteract changes in voltage Δ U _{ν of} any fluctuations in the load voltage U _L and compensate for these fluctuations.

If it is desired to be able to provide more than three different load voltages in succession for a given supply voltage Uv, it is advantageous, as an alternative to the one-stage arrangement just described, to provide a transformer circuit in which two or more stages, each of which can consist of one or more control units, are connected in series to one another such that at the first stage, the supply voltage U _v as an input voltage U _e is applied, the output voltage U _A is applied to this first stage as an input voltage U _e to the second stage, etc., and that the output voltage of the last stage of the Load is supplied as a load voltage U _L. Seen from the voltage source, the first windings of the transformers of all stages are in series with each other and with the load.

The stages connected in series with one another can each consist of a single actuating unit which is designed with one or more, in particular two further windings, and according to one of the embodiments described above, at least into the equations (4), (5) and ( 8) defined three different switching states can be brought.

As an alternative to this, the stages of such a transformer circuit can also each consist of two actuating units connected in series, which are combined to form a pair of actuating units.

wenn U_EP die Eingangsspannung des Stelleinheiten-Paares ist.This should be understood to mean the following: These are two actuating units, which also have two further windings, one of which is used as an additive and the other as a subtracting winding. The two transformers are dimensioned in such a way that each of the two actuating units, both in an adding and in a subtracting manner, is able to effect approximately half of the total voltage change that is to be applied by the actuating pair. For example, if the pair of actuating units should be able to change its input voltage U _EP by + ΔU _P , then each of the two actuating units can change the input voltage of + ΔUp / 2 supplied to it on its own. If each of the two actuating units is in its first switching state, this is referred to as the first switching state combination of the actuating unit pair and it applies to the output voltage of the actuating unit pair

when U _{EP is} the input voltage of the actuator pair.

If each of the two actuating units is in its second switching state, this is referred to as the second switching state combination of the actuating unit pair, and it applies

Furthermore, the turn ratios of the two transformers are matched to one another in such a way that the effects of the two actuating units compensate one another when the actuating unit pair is in a third switching state combination; In this third switching state combination, for example, the first actuating unit closer to the supply voltage source is in the first and the second actuating unit in the second switching state. It then applies to the output voltage of the actuator pair

It is of great advantage that the losses that occur in the control units are extremely low in all three switching state combinations. In particular, the unchanged transmission of the input voltage to the output of the pair of actuators in the third switching state combination is practically loss-free.

In comparison to an actuating unit, which alone can assume the three switching states corresponding to equations (4), (5) and (8), such an actuating unit pair has the advantage that only half of those for each actuating unit The relevant voltage or power change must be applied. Although two transformers are required, they can also be dimensioned considerably smaller and lighter in accordance with half the power. This is particularly advantageous for the manufacture, transport and spare parts management of transformer circuits for high performance.

In general, the fourth switching state combination remains unused for a pair of actuating units, in which the first actuating unit is in the second switching state and the second actuating unit is in the first switching state. The information just given can be summarized in the following Table 1:

Basically, it is not necessary here that each of the two control units of the control unit pair can be brought into the third switching state on its own.

However, in the case of a pair of actuating units, each of the two actuating units is preferably designed such that the one further winding or both further windings can be connected in parallel with the first winding, ie each of the two actuating units can be brought into the third switching state on its own; one sees the current limiting circuit or current limiting circuits mentioned above in each setting unit Before, V-MOS transistor switches can be used to carry out an extraordinarily fast, multi-step switching from each switching state combination of the actuating unit pair to any other switching state combination.

For example, if the pair of actuating units is to be moved from the second switching state combination (U _AP2 = U _EP - Δ U _P ) to the third switching state combination (U _AP3 = U _EP ), this can be done with such a pair of _actuating units without delay in that the switch is closed in both actuating units, the closing of which brings the actuating unit by itself into its third switching state, as described above. This results in a further switching state combination which is equivalent to the third switching state combination described above with regard to the output voltage U _{AP of} the pair of actuating units. So UAP3 '= U _EP also applies here. This change in the output voltage by ΔU _P can take place at any time and the output voltage passes from the old voltage value U _AP2 to the new voltage _value U _AP3 'practically without delay.

The same applies to a transition of the pair of actuators from the first switching state combination (U _AP1 = U _EP + Δ ^U _P ) to the further switching state combination.

However, if the output voltage U _{AP is to} remain the same as the input voltage U _EP for a longer period of time, it is expedient to switch the actuating unit pair from this further switching state combination into the third switching state combination described above. This takes place at the most convenient times in that by opening the corresponding switch, the first actuating unit is brought into its first switching state and the second actuating unit is brought into its second switching state. The output voltage of the pair of _{actuators changes} from ^U _AP3 ' ^{= U} _EP to ^U _AP3 ^{= U} _EP , so it practically does not change.

The third switching state combination has the advantage over the other switching state combination that, if necessary, a transition to the first or the second switching state combination can take place in two equally large change steps, the first of which can be carried out without any delay, that the second or the first actuating unit is brought into its third switching state by closing the switch in question. As a result, the output voltage of the _{actuator unit} pair instantaneously changes from U _Ap3 = U _E to U _E + ΔU _P / 2 or U _E -ΔU _P / 2. At the next favorable time, which occurs at the latest within the next half cycle of the AC voltage, the second or the first actuating unit is then brought from the third into the first or the second switching state, as a result of which the actuating unit pair changes into the first or second switching state combination , in which U _Ap1 - U _E ⁺ ΔU _p / 2 + ΔU _P / 2 ^{or U} _AP2 ⁼ UE - ΔU _P / 2 - ΔU _P / 2 applies.

The transition from the first to the second or from the second to the first switching state combination likewise takes place in two steps, of which the first can be carried out immediately and the second at the latest within the next half cycle of the AC voltage. In this case, the first step consists in bringing both actuating units into their third switching state simultaneously by closing the corresponding switches; in the second step, the the control units are converted into their second or first switching state by opening the corresponding switches.

If a transformer circuit consisting of one or more such pairs of actuating units (which can then cause different voltage changes) is used as a voltage regulator or voltage constant, it can also be used to meet the extremely high requirements in terms of switching speed and switching accuracy, such as those used in the Power supply of data processing systems are provided.

In order to be able to cover a larger range of output voltage values in small voltage steps, it is advantageous to have several stages which either consist of individual actuating units, each of which can be brought into the third switching state, or consist of the actuating unit pairs described above

so werden die Spannungsdifferenzen der anderen Stufen so gewählt, daß sie in etwa gleich + 3A%, ± 9A% usw. der Versorgungsspannung U_v sind.(whereby both types can be mixed in an arrangement), to be connected in series and to select the voltage differences ± ΔU ₁ , ..., ± ΔU _n , which can produce n such stages, differently from one another. It is particularly advantageous if the percentage values that result when each of these voltage differences is divided by the supply voltage divided by 100 are in relation to one another in the form of integer powers of three. This applies to the smallest voltage difference ⁺ ΔU _min that can be generated by one of the stages:

so the voltage differences of the other stages are chosen so that they are approximately equal to + 3A%, ± 9A% etc. of the supply voltage U _v .

If, for example, three stages are connected in series in a transformer circuit, and if the three switching states or switching state combinations mentioned above are used for each stage, twenty-seven combinations of switching states are possible for the entire transformer circuit, one of which has almost the supply voltage output by the voltage source unchanged amplitude can get to the load, while thirteen combinations increase the amplitude of the supply voltage by approximately integer multiples of A% and thirteen combinations decrease this amplitude by approximately integer multiples of A%. This is shown in more detail in Table 2.

In der mittleren Spalte bedeutet ein "+", daß sich in der betreffenden Stufe die eine Stelleinheit bzw. beide Stelleinheiten eines Paares im ersten Schaltzustand befinden, so daß die Amplitude der Versorgungsspannung um 9A%, 3A% oder A% vergrößert wird, während ein "-" eine entsprechende Verkleinerung bedeutet und "O" den dritten Schaltzustand einer einzelnen Stelleinheit bzw. die Schaltzustands-Kombination 3 (siehe Tabelle 1) des betreffenden Stelleinheiten-Paares symbolisiert, in dem bzw. in der die Amplitude der Eingangs-Wechselspannung unverändert weitergegeben wird. In der rechten Spalte sind die durch die jeweilige Kombination der Schaltzustände aller Stufen erzielbaren Gesamtänderungen der Amplitude wiedergegeben. Dabei sind nur gerundete Werte angegeben, die nicht berücksichtigen, daß sich die Eingangsspannung der näher bei der Last angeordneten Stufen in Abhängigkeit vom Schaltzustand der vorausgehenden Stufen ändern kann.In the left column of this table, the consecutive number n of the respective combination of switching states is shown, whereby the superscript "+" or "-" indicates whether it is a combination that leads to an enlargement ("+" ) leads to the amplitude of the supply voltage or a combination that lowers the supply voltage ("-").

In the middle column, a "+" means that one or both actuating units of a pair are in the first switching state in the relevant stage, so that the amplitude of the supply voltage is increased by 9A%, 3A% or A% while a "-" means a corresponding reduction and "O" symbolizes the third switching state of an individual control unit or the switching state combination 3 (see Table 1) of the relevant control unit pair, in which or in which the amplitude of the input AC voltage is passed on unchanged becomes. The right column shows the total changes in amplitude that can be achieved by the respective combination of the switching states of all stages. Only rounded values are given, which do not take into account that the input voltage of the stages closer to the load can change depending on the switching state of the preceding stages.

It can be seen that the amplitude change takes place with the aid of such a transformer circuit according to the invention in discrete steps, the step width from one switching state combination to the next always being approximately equal to A% of the respective supply voltage.

If a stage is made up of two actuating units that form a pair, as an alternative to the arrangement just explained, only two switching state pairs can be used for each actuating unit pair. Combinations are used, for example the switching state combination O, in which the output voltage is equal to the input voltage, and the combination “-”, in which the output voltage is n. _A % lower than the input voltage, where n is one for each pair of actuating units takes another integer value. For this application, it is possible to construct the pairs of actuators so that they can only assume these two switching state combinations. This can be done in such a way that, for example, the front actuating unit of each pair has a hard-wired, non-switchable further winding that permanently induces, for example, a negatively impressed voltage - (n / 2) · A%, while the second actuating unit has an adding and has a subtracting further winding, which can alternatively be switched such that they either induce a voltage of + (n / 2) .A% or of - (n / 2) _' A%, which in connection with the induced voltage - ( n / 2) · A% of the front actuator results in either a change in voltage O or - nA%. Correspondingly, control unit pairs can also be provided, which can only assume the two switching state combinations O and + n · A%.

In all these cases, the change in the output voltage of the entire transformer circuit with respect to the input voltage does not take place according to the ternary code shown in Table 2, but according to a binary code. To cover the same voltage change range, more actuator pairs are required than with the ternary code; However, there are applications in which the input voltage is to be changed in only one direction based on an overall change O and / or the voltage change range is not large. Then he can The advantage of a purely binary control may outweigh the increased need for control units.

Regardless of how many stages are connected in series and whether a binary or a ternary or another code is used, it is a salient feature of a transformer circuit according to the invention which is constructed in such a way that it allows a gradual or digital influencing even of very large powers. In contrast to analog systems, it has an extraordinarily high regulating or control speed. The accuracy achieved in each case essentially depends only on the number of actuating units or stages used.

However, the typical and preferred application of a transformer circuit according to the invention consisting of two, three or more stages does not consist in the fact that nine, twenty-seven or more output voltages should be able to be generated one after the other starting from a fixed supply voltage originating from a voltage source.

Rather, the use of such a transformer circuit as a voltage constant and / or voltage regulator is provided in a particularly preferred application. This means that either the nominal value of the supply voltage Uv emitted by the voltage source or another voltage value can be selected as the target value S _L for the voltage supplied to the load. However, such a different setpoint must lie within the change range of the transformer circuit according to the invention. If it is very close to the limit of this change range, the load voltage U _L can only be regulated in the case of deviations from the set value S in one direction possible. However, this is completely sufficient in cases where deviations in the other direction do not occur.

In the following, the application as a symmetrical voltage regulator is explained in more detail, with the aid of which the amplitude of the load voltage supplied to a load is prevented from deviating from a predetermined desired value S _L by more than + δ%, which is equal to the nominal value of the supply voltage U _V , which can fluctuate in a much larger range, for example by a maximum of ± Δ% of the nominal value.

For this purpose, a circuit arrangement according to the invention comprises, in addition to a transformer circuit with a corresponding number of stages, a sensor arrangement which measures the amplitude of the supply voltage and / or the amplitude of the load voltage, a comparator arrangement which compares the sensor signal or signals with one or more reference values and, in the event of deviations, corresponding difference signals generates, as well as a switch control that compares these difference signals, for example, with a permanently programmed table of difference signal values. From this comparison, the switch control determines the combination n or n of switching states (see Table 2) that is required to compensate for the deviation of the supply voltage from the nominal value, so that the load voltage remains within the specified range S _L f%.

It is now assumed that the amplitude of the supply voltage initially corresponds to the nominal value and thus also to the nominal value S _L , but then increases over time from this nominal value Dimensions deviate upwards, for example: In this case, the switch control must be in time for the switching state combination n = O (see table 2), in which the load voltage U _{L is} equal to the supply voltage U _v , in time for the switching state combination n = 1 ^- , continue to increase to the combination n = 2 ^- etc. As a result, a corresponding integer multiple of A% is subtracted from the supply voltage and the load voltage is thus kept in the desired range S _L ± δ%.

With a continuously increasing positive deviation, the transition from the nth combination to the (n + 1) ^- th combination takes place at a certain switching threshold SW _n - / (n + 1) ^- that is to say a fixed amplitude value of the supply voltage. If the positive deviation steadily decreases again, the transition from the (n + 1) th combination to the n th combination of switching states takes place at the same switching threshold in the opposite direction. It is advantageous to separate the last two switching thresholds from one another by means of a small voltage difference. The "hysteresis" achieved in this way prevents an excessive switching cycle in cases in which the supply voltage U _V has a value for a long time which is equal to a switching threshold and fluctuates slightly around this value.

The same applies to negative deviations in the amplitude of the supply voltage from the nominal value only that the switching thresholds are denoted by SW _n + _{/ (n + 1)} +, because in this case with increasing deviations downwards from the additive imprint of n times the minimum Amplitude change A% to additively impress (n + 1) times A% above must be gone to achieve the desired constancy of the amplitude of the load voltage.

weiterhin gilt |U_LVOR-U_Lnach| U_Lnach| = A·S. 100. Der Prozentwert A ist zwar konstant, ist aber nicht auf den Sollwert S_Lsondern auf die Amplitude der Eingangsspannung der jeweiligen Stufe bezogen. Somit ist die Größe von U_Lvor und U_Lnach davon abhängig, von welcher Kombination von Schaltzuständen ein Übergang zu einer benachbarten Kombination erfolgt.With each transition from a combination of switching states to an adjacent combination, the amplitude of the load voltage changes abruptly by approximately A%. The switching thresholds are preferably set such that when the amplitude of the supply voltage passes the value of the switching threshold in question without a sudden change, the amplitude _values U _Lvor and U _{Lnach are} symmetrical to the setpoint. It is U _Lvor the amplitude of the load voltage before the _U mschalt- process and U _{L after} the amplitude of the load voltage by the switching operation. The following should therefore apply with the best possible approximation:

| U _{LVOR -U Lnach} | also applies U _Lnach | = A · S. 100. The percentage value A is constant, but is not related to the target value S _L but to the amplitude of the input voltage of the respective stage. The size of U _Lvor and U _{Lnach therefore} depends on which combination of switching states a transition to an adjacent combination takes place.

The above equation (14) can be maintained in any case by suitable selection of the switching thresholds SW. It is also possible according to the invention to ensure by a corresponding choice of A that U _Lvor and U _{Lnach lie} within the amplitude range specified by the desired control accuracy S _L + δ%, the percentage value being related to the setpoint value S _L = 100%.

When determining the value of A, it should be taken into account that on the one hand A should be as large as possible, so that as few actuators as possible are required to cover a given fluctuation range Δ, but on the other hand A should not be chosen too large, because otherwise the desired control accuracy J is not can be observed. According to the invention, A is preferably chosen so that it is between 1.6 ∫ and 1.8 ƒ.

It should be pointed out again here that the switching thresholds can be used regardless of whether the circuit arrangement works as a voltage constant or as a voltage regulator, i.e. whether the load voltage U _{L is kept} at a setpoint value S _L which is equal to the nominal value of the supply voltage emitted by the voltage source or at a target value that differs from this nominal value.

The use of these switching thresholds is also independent of whether the supply voltage or the load voltage is measured with the sensor arrangement. In the first case, the difference between the above switching thresholds and the desired value S _{L can be contained} directly in the table used by the switch control, with which the difference signal supplied by the comparator is compared. In the second case, the switch control must determine from the approximation of the amplitude of the load voltage to one of the values U _Lvor and U _Lnach and / or knowledge of the currently valid combination of switching states, to which switching threshold the supply voltage is approaching and which switchover must therefore be carried out .

Another possibility is that the sensor arrangement measures the amplitude of the alternating voltages in front of and behind the transformer circuit. The changes in both the supply voltage Uv and the load voltage U _{L are then} detected and evaluated in such a way that the switches of the actuating units are controlled in such a way that the amplitude of the voltage supplied to the load is as constant as possible.

A transformer circuit according to the invention can advantageously be used in multiphase systems with or without a neutral conductor. In the first case, at least one control unit is provided for each phase, the first winding of which lies in the respective phase conductor in such a way that the load current flowing on this phase conductor flows through it, while the connecting connecting conductor of each control unit with the neutral conductor of the multiphase system connected is.

If the multiphase system does not have a neutral conductor leading from the voltage source to consumption, the first windings of the actuating units which are provided for a specific phase are switched back into the phase conductor and all the connecting connecting conductors are connected to one another, thereby creating an artificial zero -Conductor is formed, which can be at any potential.

Finally, in the case of a multi-phase system without a neutral conductor, the actuating units provided for the different phases can be arranged in a daisy chain.

• Fig. 1 eine Transformatorschaltung, bei der zwischen Spannungsquelle und Last eine Stelleinheit angeordnet ist, die gemäß einer ersten Ausführungsform einen Transformator mit einer einzigen, kurzschließbaren weiteren Wicklung besitzt,
• Fig. 2 eine Transformatorschaltung, bei der zwischen Spannungsquelle und Last eine Stelleinheit angeordnet ist, die gemäß einer zweiten Ausführungsform einen Transformator mit zwei jeweils kurzschließbaren weiteren Wicklungen besitzt,
• Fig. 3 einen Ausschnitt aus Fig. 2, der die Einzelheiten einer Sensoreinheit wiedergibt,
• Fig. 4 zwei miteinander in Reihe geschaltete Stelleinheiten, die ein Stelleinheiten-Paar bilden und von denen jede gemäß einer dritten Ausführungsform einen Transformator mit zwei nicht kurzschließbaren weiteren Wicklungen besitzt,
• Fig. 5 eine als einphasiger Spannungskonstanter aufgebaute Transformatorschaltung mit drei in Reihe geschalteten Stufen,
• Fig. 6 eine weitere Ausführungsform eines Spannungskonstanters für ein 3-Phasen-System,
• Fig. 7 eine Ausführungsform, bei der eine einzige Stelleinheit in eine Vielzahl von Schaltzuständen gebracht werden kann und als Spannungsregler Verwendung findet,
• Fig. 8 eine weitere Ausführungsform einer Stelleinheit für eine Transformatorschaltung gemäß der Erfindung, bei der der Transformator nur eine einzige weitere Wicklung aufweist, die zur ersten Wicklung parallelgeschaltet werden kann,
• Fig. 9 eine Ausführungsform einer Stelleinheit für eine Transformatorschaltung gemäß der Erfindung, bei der der Transformator zwei weitere Wicklungen umfaßt, die miteinander in Reihe zur ersten Wicklung parallelgeschaltet werden können,
• Fig. 10 den Aufbau einer Strombegrenzungsschaltung, wie sie bei den in den Fig. 8 und 9 wiedergegebenen Stelleinheiten Verwendung findet, und
• Fig. 11 ein Diagramm zur Erläuterung der Wahl der günstigsten Schaltzeitpunkte beim Übergang von einem Schaltzustand in einen anderen.

The invention is described below using exemplary embodiments with reference to the drawing; in this shows:

• 1 is a transformer circuit, in which a control unit is arranged between the voltage source and the load, which according to a first embodiment has a transformer with a single, short-circuitable further winding,
• 2 shows a transformer circuit in which an actuating unit is arranged between the voltage source and the load, which according to a second embodiment has a transformer with two further short-circuitable windings,
• 3 shows a detail from FIG. 2, which shows the details of a sensor unit,
• 4 two actuating units connected in series, which form a pair of actuating units and each of which, according to a third embodiment, has a transformer with two further windings which cannot be short-circuited,
• 5 shows a transformer circuit constructed as a single-phase voltage constant with three stages connected in series,
• 6 shows a further embodiment of a voltage constant for a 3-phase system,
• 7 shows an embodiment in which a single actuating unit can be brought into a multiplicity of switching states and is used as a voltage regulator,
• 8 shows a further embodiment of an actuating unit for a transformer circuit according to the invention in which the transformer has only a single further winding which can be connected in parallel with the first winding,
• 9 shows an embodiment of an actuating unit for a transformer circuit according to the invention, in which the transformer comprises two further windings which can be connected in parallel with one another in series with the first winding,
• Fig. 10 shows the structure of a current limiting circuit, as used in the control units shown in Figs. 8 and 9, and
• 11 is a diagram for explaining the selection of the cheapest switching times when changing from one switching state to another.

1 shows an AC voltage source 1, which emits a supply voltage U _v , which is fed to the input connections 2, 3 of an actuating unit 4 as an input voltage U _E. An output voltage U _A appears at the output connections 5, 6 of the actuating unit 4 and is supplied to a load 7 as a load voltage U _L.

With the help of the actuating unit 4 according to the invention, the amplitude of the output voltage U _{A can be changed} compared to the amplitude of the input voltage U _E. For this purpose, the control unit 4 comprises a transformer 8, the first winding 9 of which is connected between the input connection 2 and the output connection 5, while the input connection 3 is connected directly to the output connection 6 by means of the connection connecting conductor 10. In this way, seen from the voltage source 1, the first winding 9 is connected in series with the load 7.

The transformer 8 has a further winding 11 which is magnetically coupled to the first winding 9 via the iron core 12 of the transformer 8. With the two ends 13, 14 of the further winding 11, two switch pairs 15, 16 and a short-circuit switch 17 are connected.

With the help of the two pairs of switches 15, 16 and the short-circuit switch 17, the actuating unit 4 can be brought into four different switching states. In the first switching state, in which the switch pair 15 is closed and the switches 16, 17 are open, the input voltage U _{E is} applied to the further winding 11. The winding direction of the windings 9, 11 defined by the points 19, 20 is selected such that the voltage ΔU ₁ , which in this first switching state is caused by the further winding 11 in the first winding 9 is induced, added to the input voltage U _E. The voltage is thus obtained between the output connections 5, 6 of the control unit

As already mentioned, the value, ie the absolute amplitude of the induced voltage ΔU _{1, is} determined by the turn ratio w _{1 /} w _{w of} the first winding 9 to the further winding 11 according to the equation ΔU ₁ = w _I U _E / ^w _w .

Für die induzierte Spannung gilt in diesem Fall Δ^U ₂ = W₁U_E/(W_W ⁺ w₁). Da das Windungsverhältnis der ersten Wicklung 9 zur weiteren Wicklung 11 erfindungsgemäß typischerweise kleiner 1 : 7 ist, ist also die im zweiten Schaltzustand induzierte Spannung ΔU₂ immer etwas kleiner als die im ersten Schaltzustand induzierte Spannung ΔU₁. Allerdings kann in der Praxis die mit der Schaltungsanordnung nach Fig. 1 im ersten Schaltzustand erzielbare Vergrößerung der Ausgangsspannung U_A gegenüber der Eingangsspannung U_E mit sehr guter Genauigkeit gleich der im zweiten Schaltzustand erzielbarenIn the second switching state, which is shown in FIG. 1, the switches 15 and 17 are open and the switch pair 16 is closed, as a result of which the output voltage U _{A of} the actuating unit 4 is applied to the further winding 11. At the same time, the winding direction of the further winding 11 is reversed compared to the first switching state. As a result, the voltage ΔU ₂ , which is induced in the first winding 9 of the transformer 8 in this switching state, is subtracted from the input voltage U _Er, so that the following are obtained at the output 5, 6:

In this case, Δ ^U ₂ = W ₁ U _E / (W _W ⁺ w ₁ ) applies to the induced voltage. Since the turn ratio of the first winding 9 to the further winding 11 is typically less than 1: 7 according to the invention, the voltage ΔU ₂ induced in the second switching state is always somewhat smaller than the voltage ΔU ₁ induced in the first switching state. In practice, however, the increase in output voltage U _{A that} can be achieved with the circuit arrangement according to FIG. 1 in the first switching state compared to the input voltage U _{E can be achieved} with very good accuracy, similar to that which can be achieved in the second switching state

Voltage reduction are set, since the first winding 9 represents a complex resistor for the load current flowing from the voltage source 1 to the load 7. Since the first winding 9 generally comprises very few turns, this resistance is small, but it does lead to a certain voltage drop, which is independent of the switching state of the actuating unit 4. The value of U _A in both switching states is therefore slightly below the values that result from the simplified equations above. The output voltages that can be achieved in the two switching states are therefore symmetrical to the input voltage with good accuracy:

In a third switching state of the actuating unit 4, the two switch pairs 15, 16 are open and the short-circuit switch 17 is closed. The circuit, thus short-circuited, further winding 11 has a very small resistance, which, due to the fact that the turns ratio w 1 / ww is significantly smaller than 1, appears to be correspondingly transformed down on the side of the first winding 9. As a result, the first winding 9 in this switching state represents an extremely small resistor for the load current, to which practically no voltage drops, so that the following applies with very good approximation:

or

Because of the extremely low voltage drop across the first winding 9, only a low voltage is induced in the further winding 11, so that despite the short circuit, only a relatively small short-circuit current flows through the further winding 11. The losses that occur here can be kept far below 1% of the power delivered to the load 7.

Since the losses occurring in the actuating unit 4 are also well below 1% of the load power in the first two switching states, such a transformer circuit forms an extraordinarily advantageous possibility of providing three different output voltages U _A digitally starting from a given input voltage U _E.

In a fourth switching state, all switches 15, 16, 17 are open. The circuit of the further winding 11 then has an almost infinitely high resistance value which, even after step-down transformation on the side of the first winding 9, provides a high resistance value, so that a voltage drop which depends on the magnitude of the load current occurs at the first winding. This throttling effect of the first winding 9 in the fourth switching state can be used to limit the power supplied to the load to a safe level at least until a short circuit occurs at the load until further switch-off measures have been taken.

The two pairs of switches 15 and 16 and the short-circuit switch are actuated by a switch control 23 which, via lines 25, 26 and 27, switches 15, 16 and 17, which can be formed, for example, by triacs. controlled in the required manner. It is ensured that the switches 15, 16 and 17 are never closed at the same time and, on the other hand, the periods in which the switch is made from one switching state to another are kept as short as possible. In the event of a transition from the first or second switching state to the third or vice versa, the switch pairs 15 or 16 must be opened shortly before the time or closed shortly after the time in which the short-circuit switch 17 is closed or opened. During a transition from the first to the second or from the second to the first switching state, an almost simultaneous closing and opening of the switch is not favorable, as will be explained in more detail below. Rather, a short time interval is maintained between the opening of the previously closed switch pair and the closing of the previously open switch pair.

In order to prevent the output voltage U _{A from} collapsing in these short switching intervals due to the above-described choke effect of the first winding 9, the transformer 8 in the exemplary embodiment shown in FIG. 1 has its own short-circuit winding 28, which with the aid of of a switch 29, which is parallel to it, can be short-circuited. This switch 29 is controlled by the switch controller 23 via a line 30 and is only closed for those periods during which the two switch pairs 15, 16 are temporarily open simultaneously when switching from one switching state to the other.

FIG. 2 shows a transformer circuit with an actuating unit 34, the structure of which differs from that of the actuating unit 4. The function of the Actuating unit 34 is basically the same as that of actuating unit 4.

The actuating unit 34 in turn comprises a transformer 8, the first winding 9 of which is connected between the input terminal 2 and the output terminal 5, while the other input terminal 3 is directly electrically connected to the other output terminal 6 via the terminal connecting conductor 10.

In contrast to the actuating unit 4 from FIG. 1, in the present case the transformer 8 has two further windings 35, 36, one end of which, as an additional winding 35, is firmly connected at one end to the end of the first winding 9 in a galvanically conductive manner, which is directly electrically connected to the input terminal 2, while the other end of the adding winding 35 can be connected to or disconnected from the connecting connecting conductor 10 with the aid of a switch 37. The other of the two further windings is fixed as a subtracting further winding 36 with one end and is directly galvanically conductively connected to the end of the first winding 9, which is directly galvanically conductively connected to the output terminal 5 of the actuating unit 34, while the other end of the subtracting another winding 36 can be connected or disconnected from the connecting connecting conductor 10 with the aid of a switch 38. The sense of winding of the three windings 9, 35 and 36, which are magnetically coupled to one another via the core 12, is identified by points 19, 20 and 21. It is selected so that the voltage Δ U ₁ , which is induced in the first winding 9 by the adding winding 35 when the switch 37 is closed, is added to the input voltage U _E , and that the voltage 0 U2, which is generated when the switch 38 is closed from the subtracting Winding 36 is induced in the first winding 9, subtracted from the input voltage U _E.

A short-circuit switch 31, 32 is arranged parallel to each of the two further windings 35, 36, which short-circuits the associated further winding 35 or 36 in the closed state. The two short-circuit switches 31, 32 are controlled via a line 33 so that they are always open or closed at the same time. The switches 31, 32, 37 and 38 are controlled so that either only the switch 37 or only the switch 38 or only the switches 31, 32 are closed. The actuating unit 34 can thus be brought into the same three switching states as described above for the actuating unit 4. Also, the actuator can 34 by opening all the switches 31, 32 are brought into a corresponding fourth switching state, 37 and 38, the non-operating state e-called "normal" _B is used, but in the case of a load short-circuit for limiting the load-short-circuit current are used can .

Basically, it would be sufficient to provide only one short-circuit switch 31 or 32 and to close it in order to produce the third switching state. However, if both other windings 35, 36 are short-circuited, only half the short-circuit current flows in each of the windings 35, 36, which enables a smaller dimensioning. _Whether this outweighs the disadvantage of a second short-circuit switch is an optimization question that has to be decided in a specific individual case.

In any case, one switch is less required in the exemplary embodiment according to FIG. 2 than in the exemplary embodiment in FIG. 1, whereby the disadvantage of a second further winding is largely compensated for.

. ^U _E + .DELTA.U ₁ and ^U _A2 = UE - - .DELTA.U ₂ also not the embodiment shown in Figure 2 so that here so the two output voltages U _A1 offers the possibility Δ U ₁ independently within certain limits of Δ U ₂ to choose more necessarily must be symmetrical to the input voltage U _E.

In the present exemplary embodiment, too, a switch controller 23 is provided, which outputs the control signals for the switches 37, 38 and 31, 32 via the lines 25, 26, 27. However, the lines 25, 26, 27 are not connected directly to the switches 37, 38, 31, 32, but are each connected to an input of an AND gate 39, 40, 41, the other inputs of which are controlled by sensor units 42. Each of the sensor units 42 has two input connections, with the aid of which it queries the voltage drop across the associated switch 37, 38 or 31. The purpose of these sensor units 42 and the AND gates 39, 40, 41 is to ensure that each of the two switches 37, 38 or the two switches 31, 32 can only be closed by a corresponding signal from the switch control 23 if the other switches have been opened beforehand.

If, for example, as shown in FIG. 2, the switch 37 of the actuating unit 34 is closed, then no voltage drops across this switch 37. Therefore, the associated sensor unit 42 generates a logic O signal at its output, which blocks the AND gates 40, 41 and prevents a closing signal from switch controller 23 from reaching switches 38 and 31, 32. These switches can therefore only be closed when the switch 37 has been opened, which is indicated by the sensor unit 42 by supplying the AND gates 40, 41 with a logic 1. The same applies in reverse naturally also for querying the closed state of the switches 38 and 31, 32 by the associated sensor units 42 and a corresponding blocking or release of the AND gate 39.

If triacs are used as switches 37, 38, 31, 32, these can of course not be controlled directly by the AND gates 39, 40, 41, but there is one between the output of these AND gates and the gate electrode of the triacs of the usual triac drive circuits is provided, which is omitted in Fig. 2 for the sake of clarity. The sensor circuits 42 are described in more detail below with reference to FIG. 3.

If the switching unit 34 shown in FIG. 2 is to be changed from the first switching state to the second or from the second switching state to the first, the previously closed switch 37 or 38 must be opened and the previously opened switch 38 or 37 must be closed a short time later will. The output voltage U _{A of} the actuating unit 34 should change from the old to the new amplitude value as quickly as possible and without the occurrence of additional voltage peaks or voltage dips. To achieve this, it is expedient to open the previously closed switch 37 or 38 when the current flowing through the associated winding 35 or 36 has a zero crossing. If a triac is used as switch 37 or 38, this results in the opening of the switch at the right time, that is to say automatically when the current crosses zero by preventing re-ignition in the other direction after the triac has self-extinguished when the current crosses zero. A previously opened switch 38 or 37 is preferably closed at such phase angles of the magnetic flux passing through the winding 9, in which the change in this magnetic flux caused by the closing of the switch 38 or 37 is as small as possible. The phase angle of the magnetic flux, at which this criterion is met, depends on the load current, so that it cannot be given an exact value, but only a range. For the switch 37, this area is in the vicinity of the zero crossing of the magnetic flux, while for the switch 38 it is in the vicinity of the maximum of the absolute value of this magnetic flux.

To determine the most favorable closing times for the switches 37 and 38, the transformer 8 has a fourth winding, which serves as a sensor winding 43. When switches 37 and 38 are open, a voltage is induced in this sensor winding which has a constant phase shift with respect to the magnetic flux in the winding 9 which is independent of the load. This phase shift is constantly equal to 90 °, so that the switch 37 must always be closed in the area of the absolute maximum of this voltage and the switch 38 in the area of a zero crossing of this voltage. The information required for this is supplied to the switch control 23 from the winding 43 via the lines 44.

An example of the sensor units 42 shown only schematically in FIG. 2 is explained below with reference to FIG. 3. 3 shows only the two connecting lines to the actuating unit 34, which supply the voltage dropping at the associated switch, for example at the switch 37, from above, and the line which, at the bottom, supplies the control signal for the two AND gates of the other switches, for the AND gates 40, 41 of the switches 38 and 31, 32.

The AC voltage dropping across the switch 37 in the open state is rectified with the aid of a rectifier 46, the DC voltage outputs of which are connected to one another via a resistor 47 and a photodiode 48 of an optocoupler 49. A phototransistor 50 of the optocoupler 49 is connected on the one hand via a resistor 51 to a supply voltage V and on the other hand directly to ground. The voltage which can be tapped off from the ground between the collector of the phototransistor 50 and the resistor 51 is fed via a line 52 to an inverter 53, the output of which is connected to the output line leading to the AND gates 40, 41 which carry the closing signals can come, release or block from the switch control 23 via the lines 26, 27.

If the switch 37 is open, the rectifier 46 generates a direct voltage from the alternating voltage then dropping at the switch 37, which causes the diode 48 of the optocoupler 49 to light up. The "low" signal then emitted by the phototransistor 50 is inverted by the inverter 53 into a "high" signal, which the AND gates 40, 41 enable.

In contrast, if the switch 37 is closed, no AC voltage drops across it and the rectifier 46 does not generate any DC voltage. As a result, the diode 48 of the optocoupler does not light up and the phototransistor 50 emits a "high" signal, which is inverted by the inverter 53 into a "low" signal for blocking the AND gates 40, 41.

4 shows two actuating units 54, 54 ', which have an identical structure, which differs from the structure of the actuating unit 34 shown in FIG. 2 only in that the two short-circuit switches 31, 32 are omitted. As a result, the AND gate 41 from FIG. 2, which controls these two switches 31, 32, and the one of the three sensor units 42, which queries the switching state of the switches 31, 32, are also omitted. The two remaining AND gates 39, 40 accordingly only require two instead of three signal inputs. Otherwise, the basic structure of the actuating units 54, 54 'is the same as that of the actuating unit 34 and the corresponding parts are provided with the same reference numerals.

The two actuating units 54, 54 'are connected in series with one another, ie the output voltage U _A appearing at the output connections 5, 6 of the actuating unit 54 is fed directly to the input connections 2', 3 'of the actuating unit 54' as the input voltage U _{E '} . _In addition, the input connections 2, 3 of the control unit 54 are supplied with the supply voltage U _v output by the voltage source 1 as input voltage and the output voltage output at the output connections 5 ', 6' of the control unit 54 'is applied to the load 7 as the load voltage U _L , the first two windings 9, 9 'of the two transformers 8, 8' seen from the voltage source 1 with the load 7 in series.

The fact that the two actuating units 54, 54 'have no short-circuit switches means that each of them can only be brought into three of the four switching states defined above. If the fourth switching state, in which the switches 37, 38, 37 ', 38' are all open, is left aside only for the emergency of a load short circuit, then only operating switching states remain for each of the two actuating units 54, 54 ' the first two switching states in which they can be brought independently of each other.

This results in a total of four different switching state combinations for the transformer circuit shown in FIG. 4.

Due to the absence of the third switching state in each case, each of the two control units 54, 54 'can only input the input voltage U _E or U _E to them with a changed amplitude, ie either with an additive or a subtractive voltage change + ΔU ₁ or - ΔU ₂ or Pass on + ΔU ₁ 'or - ΔU ₂ '. Since the turn ratios of the further windings 35, 36 and 35 ', 36' to the associated first winding 9, 9 'can in principle be determined independently of one another, a total of four different load voltages U _L can be generated for a given supply voltage Uv.

Preferably, however, these turns ratios to form a pair of actuators are set so that the percentage increase in the output voltage U _{AP of} the pair compared to the input voltage U _{EP of} the pair, which results when the switches 37, 37 'are closed, is equal to the percentage decrease in the output voltage U _{AP is} compared to the input voltage U _EP , which results when the switches 38, 38 'are closed, and that the output voltage U _{AP is,} with great accuracy, equal to the input voltage UEP when the switches 37 and 38' are closed, that is to say the front, ie Actuator 54 located closer to voltage source 1 is in the first switching state and rear actuating unit 54 'is in the second switching state. With this special switching state combination, the effects of the two actuating units 54 and 54 'mutually cancel each other out, so that the AC voltage emitted by the voltage source 1 is applied to the load 7 is practically unchanged. It is of particular importance that this unchanged transmission of the input voltage of the actuator pair to the output takes place almost without loss, so that even if one connects several such actuator pairs in series, an efficiency of more than 99% can be achieved.

The pair of actuating units thus has four combinations of switching states, three of which correspond to the three switching states of the individual actuating units 4 and 34 described above:

The fourth switching state combination remains unused. With regard to the switching options, the function of such a pair of actuating units 54, 54 'is practically the same as the function of an individual actuating unit 4 or 34.

However, a pair of actuators offers the advantage that, given the size of the voltage to be applied and thus the power to be switched, each of the two actuators can only handle half of this switching power must and can therefore be dimensioned accordingly smaller. Although one more transformer is required, the two transformers 8, 8 'of the actuating unit pair 54, 54' together are only slightly larger and heavier than the one transformer 8 of an actuating unit 4 and 34, respectively, with the same switching capacity. A single actuating unit 54 or 54 'is in any case considerably smaller and lighter than an actuating unit 4 or 34, ie there are smaller and lighter subunits, which has considerable structural advantages in arrangements in which a large number of such actuating units or actuating unit pairs are connected in series brings. Transport is also much easier if you can break down such a system into several smaller and lighter sub-units. Two smaller units also have the advantage that they lead to smaller losses than a single unit with the same switching capacity.

To achieve particularly high switching speeds, such a pair of actuating units can also be constructed from two actuating units 174, 174 ', as will be described below with reference to FIG. 9.

5 shows a transformer circuit which serves as a single-phase voltage constant for the voltage U _L supplied to the load 7. It is assumed that a set value S _{L is} specified for the amplitude of the alternating voltage supplied to the load 7, which is set to 100% below, and from which the voltage actually applied to the load 7 may deviate by a maximum of + δ% . It is further assumed that the Versorgungsspan- supplied from the AC power source 1 is a representation _nu ng _Uv in its amplitude by A +% of nominal value _Vnom U. In principle, the setpoint S _L the load voltage U _{L is} equal to the nominal value U _{Vnenn of} the supply voltage U _v or different from this nominal value. It is a particular advantage of the transformer circuit according to the invention that it enables the load voltage U _L to be regulated to a desired value S _L , which is, for example, at or near the limit of the intended control range. However, this is only useful if deviations in the supply voltage can only occur in one direction. If, for example, the supply voltage is generated from a battery arrangement with the aid of an inverter, this requirement is met without further ado, since the direct battery voltage and thus also the amplitude of the alternating voltage generated therefrom only prolonged operation with progressive discharge of the battery arrangement, but not can increase.

In the following, however, the first case (U _Vnom = S _L ) is considered and assumed that Δ >> δ, so that the amplitude of the supply voltage U _{V must be} regulated to the setpoint S _L.

For this purpose, a transformer circuit according to the invention is provided between the voltage source 1 and the load 7, which consists of three stages 55, 56, 57 connected in series with one another, each of which is operated either by an actuating unit 4, 34, 144 or 174 according to FIG. 1 , 2, 8 or 9 or can be formed by a pair of actuating units 54, 54 'according to FIG. 4 or by a pair of actuating units which is constructed from two actuating units 174, 174' according to FIG. 9. Steps 55, 56, 57 are controlled with the aid of a switch control 23, which is connected to each step 55, 56, 57 via a pair of lines 61, 62 connected is. Depending on whether the stages 55, 56, 57 are formed by an actuating unit 4, an actuating unit 34, an actuating unit 144, an actuating unit 174, an actuating unit pair 54, 54 'or an actuating unit pair 174, 174', these line pairs symbolize , lines 25, 26, 27 and 30 (see FIG. 1), lines 25, 26, 27 and 44 (see FIG. 2), lines 158, 159, 160, 161 and 30 (see FIG 8), lines 163, 164, 165 and 30 (see FIG. 9), lines 26, 27, 44, 26 ', 27' and 44 '(see FIG. 4) or twice lines 163, 164, 165 and 30 (see Fig. 9).

The switch control 23 issues the switching commands to the switches of the stages 55, 56, 57 via the lines 61 and receives the information generated by the sensor windings 43 about the phase position of the magnetic flux in the first windings 9 of the transformers 8 and thus via the lines 62 the favorable closing times and periods for the switches. Furthermore, a first comparator 63 is provided, which receives a reference _voltage U _ref1 at one of its two inputs, which represents the setpoint S _L for the load voltage U _L. The other of its two inputs is supplied with the output signal of a first sensor 64, which measures the load voltage U _L. Upper line 65, the comparator 63 outputs a differential signal to the switch controller 23, which indicates whether and how far the load voltage U _{L L} S deviates from the setpoint. Before this deviation comes out of the permissible range + 6 _% , the switch controller 23 changes the switching states of stages 55, 56, 57, which then impress a new amplitude change on the supply voltage U _V and thus the load voltage U _L within the permissible control range Hold ± δ%. Moreover, a second comparator 66 is provided which ^r- a nominal value _Vnom the U Ve supply voltage Uv corresponding reference voltage U _ref2 to the output signal of a second probe 67 compares precisely of this supply voltage U _v is measured. The differential signal emitted by the second comparator 66 is likewise fed via line 68 to the switch control 23, which can thus operate not only in the control mode but also in the control mode or in a combination of both. This offers the advantage that in the event of a short circuit on the load side, ie with U _L = O, the switch control can recognize the fault from the fact that Uv is still different from zero and does not attempt to regulate the load voltage U _L ; instead, it can bring the control units of all stages into the fourth switching state defined above, in which the first windings 9 of all the transformers 8 exert a strong choke effect and thus limit the load short-circuit current. The switch controller 23 preferably comprises a microprocessor for processing the information coming in via the lines 62, 68 and 65 and for converting this information into corresponding switching commands.

As already mentioned, the stages 55, 56, 57 are constructed in such a way that each stage increases the input voltage supplied to it in a first switching state or in a first switching state combination by a predetermined percentage, in a second switching state or in a second switching state -Combination reduced by approximately the same percentage rate and passed on unchanged in a third switching state or in a third switching state combination. In this sense, the following always, if not expressly from Actuator pairs are discussed, switching state combinations also referred to simply as the first, second or third switching state.

Für ein Ausführungsbeispiel, bei dem jede Stufe 55, 56, 57 von einem Stelleinheiten-Paar 54, 54' bzw. 174, 174' gebildet wird, ist dies in Tabelle 3 nochmals genauer für den Fall dargestellt, daß + A%_%w + 1% gewählt wird, so daß sich für das Stelleinheiten-Paar der mittleren Stufe 56 eine mögliche Amplitudenänderung von ca. + 3% der diesem Paar zugeführten Eingangsspannung und für das Stelleinheiten-Paar der vordersten Stufe 55 eine mögliche Amplitudenänderung von ca. + 9% ergibt.The specified percentages by which the individual stages can change the input voltage supplied in each case differ from stage to stage and are preferably approximately in relation to one another in the form of integer powers of three. In the exemplary embodiment shown in FIG. 5, the last stage 57, which is closest to the load 7, can change the input voltage supplied to it, for example, by + A% or pass it on almost unchanged. The middle stage 56 can change the input voltage supplied to it by approx. + 3A% or pass it on almost unchanged and the foremost stage 55 closest to the voltage source 1 can change the input voltage supplied to it by approx. + 9A% or pass it on almost unchanged.

Is formed for one embodiment, wherein each stage 55, 56, 57 by an adjusting unit pair 54, 54 'or 174, 174', shown in Table 3 again in greater detail for the case in which + _A%% w + 1% is selected so that there is a possible amplitude change of approx. + 3% of the input voltage supplied to this pair for the actuator unit pair of the middle stage 56 and a possible amplitude change of approx. + 9% for the actuator unit pair of the foremost stage 55 results.

As can be seen from Table 3, in order to achieve a change in the respective input voltage of a pair of actuating units that is as symmetrical as possible, the percentage voltage changes that can be achieved by the individual further windings are selected at least partially differently.

For the pair of the foremost stage 55, the additive winding of the actuating unit 54 or 174 can effect a change of + 4.5%, while the subtracting winding can bring about a change of - 4.9%, and the additive one or subtracting winding of the actuating unit 54 'or 174' can impress a change of + 4.4% or - 4.2% on the input voltage of this rear actuating unit 54 'or 174' of stage 55.

These percentage values are selected by a corresponding choice of the turn ratios so that the total changes shown in Table 3 on the right result for the three switching states used in the first stage, which are + 9.1%, -8.9% and + 0.1% . These three values are chosen to be 0.1% higher than the target + 9%, - 9% and 0%. This compensates for the voltage drop that occurs when the load current flows due to the remaining throttle effect on the relevant first turns of these two positions units 54, 54 'or 174, 174' results.

The same applies to level 56, with values that are about 0.02% to 0.03% higher, as can be seen in Table 3 without any problems.

Bei der Kombination n = O befinden sich alle drei Stelleinheiten-Paare in dem eben geschilderten Zustand und man entnimmt der ganz rechten Spalte der Tabelle 4, daß das Verhältnis von Lastspannung U_L zur Versorgungsspannung U_v in diesem Fall gleich 1,0014 also praktisch gleich 1 ist.In Table 4, similar to Table 2 on the left, the twenty-seven switching state combinations are listed again, which can be achieved with a transformer circuit comprising three actuator unit pairs according to FIG. 5, if only three switching state combinations are used for each actuator unit pair. In addition, Table 4 shows for each actuating unit 54, 54 'of the three actuating unit pairs whether the adding or subtracting winding is connected to the associated input or output voltage. A "1" means that the relevant further winding is connected to the associated voltage, while an "O" indicates that the winding can be opened by opening the relevant switch 37, 37 'or 38, 38' from the connecting connecting conductor 10 ( see Fig. 4) separately and therefore not connected to the input or output voltage. The number combination 1001 for a pair of actuating units thus means that in the front actuating unit, ie closer to the voltage source 1, the additive winding is switched on and the subtracting winding is switched off, while in the rear actuating unit arranged closer to the load 7, the additive winding switched off and the subtracting winding is switched on. A pair of actuators identified in this way is therefore in the third switching state combination defined above, in which the effects of the front and rear actuators virtually cancel each other out, so that the input voltage appears at the output of the actuator pair with an almost unchanged amplitude.

With the combination n = O, all three pairs of actuating units are in the state just described and it can be seen from the right-hand column of Table 4 that the ratio of load voltage U _L to supply voltage U _v in this case is 1.0014, which is practically the same 1 is.

In contrast, for example, when n = 13 ^+, all three pairs of actuating units are in a state in which the adding winding is switched on in both actuating units (first switching state combination identified by 1010). The right column shows that the load voltage U _L is 13.52% greater than the supply voltage U _v .

The switch controller 23 selects this combination when the supply voltage U _V has dropped significantly compared to the setpoint.

liegt an der unteren Grenze von 99,5% (bezogen auf den Sollwert) und somit innerhalb des zulässigen Bereichs. Für die Schaltzustands-Kombination n = 13^- gilt entsprechend, daß hier die Versorgungsspannung U_V auf 114,84% des Sollwerts angestiegen sein kann, ohne daß die Lastspannung

die obere Grenze 100,5% des zulässigen Bereichs übersteigt.If one assumes that the deviation% of the load voltage from the setpoint S, which is set to 100% here, may not exceed + 0.5%, the supply voltage U _v can drop to 87.65% of this setpoint because the transformer circuit according to the invention can raise this reduced supply voltage U by 13.52% (based on U _V = 100%); the resulting value for the load voltage of

lies at the lower limit of 99.5% (based on the setpoint) and thus within the permissible range. For the switching state combination n = 13 ^{- it} applies accordingly that here the supply voltage U _V can have risen to 114.84% of the target value without the load voltage

the upper limit exceeds 100.5% of the permissible range.

The same can be achieved for all other switching state combinations n. In this case, it is preferable to always switch from one switching state combination to the _other at values of the supply voltage U _v in which the amplitude of the load voltage U _L before switching and the amplitude of the load voltage U _L after switching are approximately symmetrical to setpoint value S _L [ see equation (14) _7 above. It follows from the above values that, in this exemplary embodiment, fluctuations in the supply voltage U _v from + Δ = + 14.84% (based on the setpoint S = 100%) to -Δ = - 13.35% (also based on S = 100%) can be compensated so that the load voltage U _L only fluctuates within a range of S + 0.5%.

The same applies, albeit to a limited extent, if the stages 55, 56, 57 are formed by a pair of actuating units comprising two actuating units 174, 174 'according to FIG. 9 or by individual actuating units 4, 34 and 144, respectively.

If a larger fluctuation range ± Δ% is to be detected, either the minimum amplitude change A must be increased, which is at the expense of the control accuracy δ, or the number of stages must be increased. It can be useful to add a level whose The change range is not equal to the next integer power of three from A, so here is not equal to + 27A, but is only an integer multiple less than 27 of A, which is so large that if all four stages are in the same direction, i.e. all additive or all act subtractive, the required fluctuation range + ä can just be covered.

Fig. 6 shows a modification of the circuit arrangement according to the invention, as it can be used to control the voltage output by a three-phase network.

As can be seen from FIG. 6, a transformer circuit 75, 76, 77 according to the invention is provided for each of the three phase conductors R, S and T, each of which is constructed in the same way as the transformer circuit in FIG. 5. It therefore exists each of these three transformer circuits 75, 76, 77 from three stages 55, 56, 57 connected in series, each of which here consists of a pair of actuating units 54, 54 'and 174, 174' and can assume four different switching states. The AC voltage on each of the three phase conductors R, S and T can thus be subjected to change amounts which are in a ratio of 1: 3: 9 to each other, or the AC input voltage can be passed on unchanged or the load current can be throttled.

In order to be able to bring the stages of the transformer circuits 75, 76, 77 into the three different switching states as required, each of the transformer circuits 75, 76, 77 is not only with its associated phase conductor R, S or T, but also with the zero -N conductor connected. A three-phase network 80 is used here as the voltage source.

The voltage amplitudes supplied by the network 80 on the individual phase conductors R, S, T are continuously measured with the aid of a sensor arrangement 81, which supplies the three measurement signals to a comparator arrangement 82. There, the measurement signals are compared with a common reference value U _ref . Alternatively, a separate reference value can also be specified for each phase conductor R, S and T.

The comparator 82 generates a separate difference signal for each of the three phase conductors R, S, T, which is fed to a switch controller 83. This controls via the line groups 85, 86, 87, the switches of the stages 55, 56, 57 in each of the transformer circuits 75, 76, 77 in the manner as has been explained in detail above. Of course, here too, each control unit is connected to the switch control 83 via several lines, as shown in FIGS. 1, 2, 4, 8 and 9. For the sake of simplicity, however, these lines have only been shown in FIG. 6 as a single bidirectional line.

The output of each transformer circuit 75, 76, 77 is formed by a phase conductor R _K , S _K or T _{K '} , the letter "K" indicating that an AC voltage with a constant amplitude is available on these phase conductors. These voltages can either be applied together to a single load that requires a three-phase current, or different loads, each of which only has to be operated with a 1-phase alternating current.

Alternatively, the sensor arrangement 81 can also be designed in a multi-phase system in such a way that it measures the AC voltages supplied to the phase conductors R _K , S _K , T _K of the loads.

With greater demands on the control accuracy or with even larger control ranges, more than three stages can also be provided for the transformer circuits 75, 76, 77. Analogously to FIG. 6, the circuit arrangement according to the invention can also be used in multiphase systems which comprise fewer or more than three phases.

7 shows a further embodiment of a transformer circuit according to the invention, which comprises only a single actuating unit 94. As in the exemplary embodiment shown in FIG. 1, a supply voltage U _v , which comes from a voltage source 1, is also supplied to the input connections 2, 3 of the actuating unit 94 as the input voltage U _E. An output voltage U _A appears at the output connections 5, 6 and is supplied to a load 7 as a load voltage U _L. Furthermore, the actuating unit 94 comprises a transformer 8, the first winding 9 of which is connected between the input terminal 2 and the output terminal 5, while the other input terminal 3 is directly electrically conductively connected to the second output terminal 6 by means of the connecting connecting conductor 10. The transformer 8 also has a further winding 11 which is magnetically coupled to the first winding 9 via the iron core 12 of the transformer 8.

In contrast to the exemplary embodiment in FIG. 1, the actuating unit 94 of the present exemplary embodiment can be brought not only into four but into thirty-four different switching states, so that it is possible to make a total of thirty-two different amplitude differences between the input voltage U _E and the output voltage U _A to produce the one control unit 94, to make the input voltage U _E unchanged at the output connections 5, 6 available or to throttle the load current in the event of a short circuit on the load.

This great possibility of variation allows the transformer circuit shown in FIG. 7 to be used as a voltage regulator and / or voltage constant similar to the transformer circuits in FIGS. 5 and 6.

FIG. 7 shows the use as a voltage regulator, in which the output voltage U _{A of} the actuating unit 94, which here is equal to the load voltage U _L, is in turn fed to a sensor arrangement 64 via lines 95, 96. The sensor 64 transmits a measurement signal to a comparator 63, which compares this measurement signal with a reference voltage U _ref , which corresponds to the target value S _{L of} the load voltage U _L. Via line 65, the comparator 63 passes a difference signal representing the difference between the measurement signal and the reference voltage U _ref to a switch controller 23, which controls a switch group 98 consisting of fourteen switches via lines 97 in order to bring the actuating unit 94 into the different switching states , as will be explained in more detail below.

In order to be able to bring the actuating unit 94 into thirty-two further switching states in addition to the two switching states in which the further winding 11 is either short-circuited or completely open, thirty-two control voltages U _S1 to U _S32 must be applied to the further winding 11, which according to the invention can be generated using a single AC voltage source 100.

The AC voltage source 100 is formed by an additional transformer arrangement 101, which in the present case Case consists of six winding sections 104 to 109 electrically connected in series, which are magnetically coupled to one another via a common transformer core 111.

The one end of the group consisting of the winding sections 104 to 109 series circuit is electrically directly conductively connected to one pole of the AC voltage source 1, is connected to the well, the input terminal 3 of the actuating unit 94, which via the terminal-Verbindun ^g s-conductor 10 directly electroplated is conductively connected to the output terminal 6 of the actuating unit 94. The other end of the series circuit consisting of the winding sections 104 to 109 is connected via a line 114 to the second output connection 5 of the actuating unit 94. Thus, the output voltage U _{A of} the actuating unit 94 is present at the series connection of the winding sections 104 to 109.

The series connection of the winding sections 104 to 109 has seven taps 121 to 127, of which the taps 121 and 127 are connected to the two outer ends of the series connection, while the taps 122 to 126 are each led out between two adjacent winding sections.

Each of the taps 121 to 127 is connected to a pair of on / off switches from the switch group 98. In the closed state, one switch of each pair of switches connects the associated tap to a line 129 which is connected to the lower end of the further winding 11 in FIG. 7. The other switch of each pair, in the closed state, connects the associated tap to a line 130 which connects to the other end of the further winding 11 in Connection is established. As already mentioned, all the switches in the switch group 98 are controlled by the switch control 23 via the lines 97 in such a way that the control voltage U _S1 to U _S32 which is just required is always present at the further winding 11, or that the two switches of any pair are closed simultaneously are to short circuit the further winding 11, or that all switches 98 are open to throttle the load current.

For a symmetrical control of the load voltage U _L around the target value S _L , the actuating unit can be brought into thirty-two different switching states, sixteen of which are used to additively impress the respectively induced voltages ΔU ₁ to ΔU ₃₁ and sixteen to negatively impress the respectively induced voltage ΔU ₂ to 4U32 are provided. The amplitude of each positively impressed voltage is equal to the amplitude of a corresponding negatively impressed voltage.

Since the sign of the stamping results from the winding direction with which the further winding 11 is connected to a control voltage, only sixteen control voltages U _S1 to U _S16 with different amplitudes are required, since the further winding 11 with the aid of the switches 98 with two Different directions of the winding sense can be placed on the different taps 121 to 127.

In order to be able to tap the sixteen different control voltage amplitudes, the number of turns of the winding sections 104 to 109 are matched to one another according to a code which is optimized so that on the one hand the smallest possible number of winding sections 104 to 109 and thus also taps 121 to 127 and switches 98 is needed, and that on the other hand, the maximum required control voltage U _{Smax can be tapped} between the most distant taps 121 and 127.

According to this optimized code, the winding section 109 has a number of turns such that when the output voltage U _{A of} the actuating unit 94 is applied to the series connection of all the winding sections 104 to 109, a tap voltage 1 of this winding section 109. U _{Xmin can be} tapped, which corresponds to the smallest required control voltage U _Smin .

By simultaneously closing the upper switch of the switch pair 132 in FIG. 7 and the lower switch of the switch pair 131, the smallest control voltage U _Smin required can be applied to the further winding 11 in such a way that the voltage thereby induced in the first winding 9 of the transformer 8 ΔU _{min is} impressed on the input voltage UE subtractively. Instead be the lower one in Fig. 7 switch the couple 132 and the upper switch of the pair closed 131 simultaneously, is located on the further winding 11 has the same smallest control voltage U _Smin number, but the winding direction of the other _W is ick- lung 11 relative to the previous case inverted, so that now the induced voltage ΔU _{min is} additively impressed on the input voltage U. The same also applies to the control voltages that can be tapped between any other taps 121 to 127.

According to the optimized code, the number of turns of the other winding sections 104 to 108 are selected such that the following tap voltages are available between adjacent taps 121 to 126:

Together with the tension 1. U _Xmin at tap pair 126, 127, this gives the possibility of all control voltage amplitudes of 1. U _Smin to 16. U _Tapping either directly at taps that are immediately adjacent or between taps that are further apart, as shown in Table 6 below:

It can be seen that the optimized code is also characterized here in that 1 times the minimum tapping voltage U _{Xmin can be tapped} at one winding section 109 at the end of the series _connection and 2 times U _Xmin at the winding section 104 at the other end is.

In order to obtain the same conditions as in the embodiment shown in FIG. 1, it can be provided in the embodiment shown in FIG. 7 that the line 114 is not firmly connected to the line 95 at point 140. Instead, two push-pull switches can be arranged here, with the help of which the end of the line 114 which is remote from the series connection of the windings 104 to 109 via corresponding lines either with the line leading from the output connection 5 to the load 7 or with the line from the voltage source 1 to the input terminal 2 leading line can be connected. These switches are then also controlled by the switch controller 23 in order to apply either the input voltage U _E or the output voltage U _{A of} the actuating unit 94 to the series connection of the windings 104 to 109. The former preferably takes place when a voltage .DELTA.U ₁ ..., .DELTA.U _{31 is to be} induced in the first winding 9 by a corresponding control voltage U _S1 '... U _S31 applied to the further winding 11 additively impresses the input voltage U _E. By contrast, the line 114 is preferably connected to the output voltage U _A when a voltage Δ U ₂ ... ΔU _{32 is to be} induced in the first winding 9, which is subtractively impressed on the input voltage U _E.

FIG. 8 again shows a single actuating unit 144, which is constructed similarly to the actuating unit 4 from FIG. 1 and is connected in the same way to change the amplitude of an AC voltage between an AC voltage source 1 and a load 7. Circuit parts in Fig. 8, which are present in the same way in Fig. 1, again have the same reference numerals. In particular, also in FIG. 8 the transformer has only a single further winding 11, which is magnetically coupled to the first winding 9 via the iron core 12 of the transformer 8. Two switches 150, 152 and 151, 153 are connected to the two ends 13, 14 of the further winding 11.

If the switch 150 is closed, it connects the end 13 of the further winding 11 to the input terminal 2, to which the one end of the first winding 9 is also connected. If the switch 151 is closed, it connects the other end 14 of the further winding 11 to the output terminal 5, to which the other end of the first winding 9 is connected.

If the switch 152 is closed, it connects the end 13 of the further winding 11 to a line 155, with which the switch 153 also connects the other end 14 of the further winding 11 in the closed state. A circuit arrangement 157 is provided between the line 155 and the connecting connecting conductor 10, which can be a simple controllable off / on switch, but is preferably formed by a current limiting circuit, as will be explained in more detail below with reference to FIG. 10 .

With the help of the switches 150 to 153, the actuating unit 144 can be brought into four different switching states. In the first switching state, in which the switches 150 and 153 are closed, the input voltage U _{E is} applied to the further winding 11 and the current limiting circuit 157 lying in series therewith. Since the limit value to which the current limiting circuit 157 limits the current flowing through it is selected to be greater than the current which flows through the further winding 11 in this first switching state, the voltage drop across the current limiting circuit 157 is very small and it is practically the whole Input voltage U _E at the further winding 11 as a control voltage. The winding direction of the windings 9, 11 defined by the points 19, 20 is selected such that the voltage Δ U ₁ , which is induced in this first switching state by the further winding 11 in the first winding 9, is added to the input voltage U _E. The voltage is thus obtained between the output connections 5, 6 of the control unit

The absolute amplitude of the induced voltage ΔU ₁ is determined by the turns ratio w _{1 /} w _{w of} the first winding 9 to the further winding 11 according to the equation AU1 = w ₁ U _E / w _w .

In the second switching state, which is shown in FIG. 8, the switches 150 and 153 are open and the switches 151 and 152 are closed, as a result of which the output voltage U _{A of} the actuating unit is connected to the further winding 11 and the current limiting circuit 157 which is in series with it again 144 is laid. Since the current flowing through the further winding 11 in this second switching state is approximately equal to the current flowing through the further winding 11 in the first switching state, this current is also below that

Limit value of the current limiting circuit 157, so that its resistance is very small even in this second switching state and practically the entire output voltage U _A is applied to the further winding 11. The winding direction of the further winding 11 is reversed compared to the first switching state. As a result, the voltage .DELTA.U _2, which is induced in this second switching state in the first winding 9 of the transformer 8, is subtracted from the input voltage _U. , so that you get at the output 5, 6:

In this case, ΔU ₂ = w ₁ U _E / (w _w + w ₁ ) applies to the induced voltage. The voltage ΔU ₂ induced in the second switching state is therefore somewhat smaller than the voltage ΔU ₁ induced in the first switching state.

In a third switching state of the actuating unit 144, at least the two switches 150 and 151 are closed, so that the further winding 11 with antiparallel winding direction to the first winding 9 and electrically parallel to this first winding 9 is at the same voltage as this. In this switching state, the transformer 8 is therefore short-circuited and the currents flowing in the two antiparallel windings 9, 11 each try to build up a magnetic field; however, these fields face each other and almost cancel each other out.

The leakage inductance of the first winding 9 can be kept so low that the first winding 9 the load current flowing through it in this circuit state only opposes their very small ohmic resistance, whereby the voltage drop occurring at the first winding 9 is very small. This means that applies in this third switching state

Only the slight voltage drop across the first winding 9 is available as the driving voltage for the short-circuit current flowing through the further winding 11, so that the short-circuit current through the further winding 11 also remains very low. Since the impedance of the further winding 11 is considerably greater than that of the first winding 9, the load current flows practically exclusively through the first winding 9.

If it is always ensured that the switches 152, 153 are both open when the switches 150, 151 are closed, the current limiting circuit 157 can be dispensed with, ie the conductor 155 can be connected directly to the connecting connecting conductor 10 in a galvanically conductive manner. However, this has the consequence that when switching from, for example, the second switching state shown in FIG. 8 to the first switching state, the switches 151, 152 must first be opened, and the switches 150 only when these switches are open with certainty , 153-can be closed. If all four switches 150 to 153 were closed at the same time in the absence of a current limiting circuit 157, both the input voltage U _E and the output voltage U _{A would be} short-circuited, which would lead to impermissibly high short-circuit currents and to an undesirable breakdown of these voltages.

Without a current limiting circuit 157, the previously closed switches would first have to be opened when changing from one switching state to the other, which, if triacs were used as the switch, would only be possible when the current flowing through them was zero, and those for the new switch state to be closed switch to be closed, for which certain times would have to be waited again, in which this switching process results in the lowest possible switching peaks in the output voltage U _A. Overall, this means that the new amplitude value is available in a stable manner at the earliest after one and a half to two periods of the AC output voltage U _A.

To accelerate the switching processes, it is therefore advantageous to provide the current limiting circuit 157. In the case of a switchover process by which the actuating unit is to be switched from the second switching state shown in FIG. 8 to the first switching state, for example, the actuating unit 144 is first brought into the third switching state, which is done by closing the first switch 150. A short time later, the third switch 152 is then opened and the fourth switch 153 is then closed. The actuating unit remains in the third switching state since the first switch 150 and the second switch 151 are closed during this time. Short-circuiting of the two windings 9 and 11 by the further conductor 155 is avoided in that the two switches 152 and 153 are not closed at the same time. During the entire time in which the actuating unit 144 is in the third switching state, the current limiting circuit 157 prevents the flow of an inadmissibly large short-circuit current from the connection 5 or connection 2 to the connection connecting conductor 10 via the simultaneously closed switches 151, 153 or the simultaneously closed switches 150, 152. The switch 151 is then opened as the last step of the switching process, as a result of which the actuating unit changes from the third switching state to the first switching state.

The same also applies to a switching process that leads from the first to the second switching state.

In the switching processes just described, the actuating unit 144 also briefly passes through the third switching state whenever it is intended to change from the first to the second or from the second to the first switching state. If the actuating unit 144 is to be kept in the third switching state for a longer period of time, the switches 152 and / or 153 are opened so that no more currents can flow from the input connection 2 or from the output connection 5 to the connection connecting conductor 10, and the power loss is thus further reduced .

In a fourth switching state, all four switches 150 to 153 are open, so that the circuit of the further winding 11 has a high resistance value, which provides a high resistance value even after transformation down on the side of the first winding 9. A voltage drop dependent on the size of the load current thus occurs at the first winding. This throttling effect of the first winding 9 in the fourth switching state can be used to limit the power supplied to the load to a safe level at least until a short circuit occurs at the load until further switch-off measures have been taken.

The switches 150 to 153 are actuated by a switch control 23, which controls the switches via lines 158, 159, 160 and 161. The switch controller 23 can obtain the information required for this from a comparator (not shown in FIG. 8), which compares the load voltage U _L and / or the supply voltage U _v with target values and, in the event of deviations, outputs corresponding differential signals, as described in detail above. Furthermore, the transformer 8 of the actuating unit 144 comprises a short-circuit winding 28 which can be short-circuited with the aid of a switch 29 which is parallel to it. This switch 29 is also controlled by the switch control 23 via a line 30. According to the invention, this only occurs when certain faults occur in the switches 150 to 153 or in the current limiting circuit 157, as will be explained in more detail below.

As an alternative to the embodiment just described, the current limiting circuit 157 in the actuating unit 144 can be omitted without the delays in the switching process mentioned above having to occur. This is achieved in that the two switches 152, 153, which are then directly connected again to the connecting connecting conductor 10, are each designed as a current limiting circuit, the limit value of which can be switched back and forth between the value zero and a value other than zero . If such a current limiting circuit is switched to the limit value zero, this corresponds to the open state of a switch. If, on the other hand, it is switched to the limit value other than zero, it only opposes the current flowing through it with a very small, constant resistance as long as this current remains significantly below the limit value. This limit becomes so chosen that it is greater than the current that must flow through the further winding 11 and the relevant switch 153 or 152 in the first or in the second switching state.

A circuit arrangement which has the properties just described is explained in more detail below with reference to FIG. 10.

In the case just described, the switchover from the first to the second switching state or from the second to the first switching state takes place in such a way that the two previously open switches are closed simultaneously and a short time later the two switches which are open in the new switching state are opened simultaneously have to. If switches 150 and 151 are implemented with the help of triacs, this opening process must be used to wait until the next zero crossing of the current which flows through the relevant switch 150 or 151 before opening.

In this embodiment too, the actuating unit can be brought into the fourth switching state by opening all four switches 150 to 153 simultaneously.

FIG. 9 shows a transformer circuit with an actuating unit 174, the structure of which differs from that of the actuating unit 144, but which in principle has the same functions.

The actuating unit 174 in turn comprises a transformer 8, the first winding of which is connected between the input connection 2 and the output connection 5, while the other input connection 3 is connected via the on final connecting conductor 10 is directly electrically conductively connected to the other output terminal 6.

Similar to the control unit 34 in FIG. 2, the transformer 8 here also has two further windings 35, 36, of which the one as an additional winding 35 is firmly connected at one end to the end of the first winding 9 in a galvanically conductive manner is directly electrically connected to the input terminal 2, while the other end of the adding winding 35 can be connected or disconnected from a line 185 by means of a switch 180, which in turn is connected to the connecting connecting conductor 10 via a current limiting circuit 157. The other of the two windings is fixed as a subtracting further winding 36 with one end and is directly galvanically conductively connected to the end of the first winding 9, which is directly galvanically conductively connected to the output terminal 5 of the actuating unit 174, while the other end of the further subtracting Winding 36 can be connected or disconnected from line 185 by means of a switch 181. The sense of winding of the three windings 9, 35 and 36, which are magnetically coupled to one another via the core 12, is identified by points 19, 20 and 21. It is selected so that the voltage ΔU _{1 '} which is induced by the further winding 35 in the first winding 9 when the switch 180 is closed is added to the input voltage U _E (first switching state), and that the voltage ΔU ₂ ' is the closed switch 181 is induced by the further winding 36 in the first winding 9, subtracted from the input voltage U _E (second switching state). Here too, the limit value of the current limiting circuit 157 is selected to be greater than the currents which are generated in the first switching state by the adding winding 35 or in the second switching state by the subtracting one Winding 36 flow. Thus, in these two switching states, the resistance of the current limiting circuit 157 is practically negligible and the total input voltage U _E or the total output voltage U _{A is applied} to the adding winding 35 or to the subtracting winding 36.

In order to be able to bring this actuating unit shown in FIG. 9 into the third switching state, it is necessary to close the two switches 180 and 181 at the same time, as a result of which the two further windings 35, 36 are connected in series with one another with the same winding sense and with an anti-parallel winding sense are connected in parallel to the first winding 9. Since the two further windings 35, 36 can be regarded as a single winding in this switching state, the same switching state is obtained as that described above as the third switching state of the actuating unit 144 from FIG. 8, and the input voltage U _E also becomes here passed on virtually unchanged to the output of the control unit.

So that in this third switching state the input voltage U _{E is not present} at the further winding 35 in the short-circuit and drives an impermissibly high short-circuit current from the input terminal 2 to the input terminal 3, a current limiting circuit 157 is again provided here between the conductor 185 and the connecting connecting conductor 10 , which could in principle be replaced by a controllable on / off switch. However, protection times would then have to be introduced and special verification circuits would have to be provided for switching from one switching state to the other, so that it can be excluded with absolute certainty that switches 180 and 181 are operated simultaneously be closed as long as the switch connecting lines 185 and 10 is closed. A current limiting circuit is therefore preferably used again as circuit arrangement 157, which automatically and without time delay prevents a further increase in the current flowing through it if this current threatens to exceed a predetermined limit value.

The actuating unit 174 can also be brought into a fourth switching state, as shown in FIG. 9. In this switching state, the two switches 180 and 181 are opened at the same time, as a result of which a strong throttling action of the first winding 9 occurs again, which can be used to limit the short-circuit current in the event of a load short circuit.

Switching from the first to the second or from the second to the first switching state also takes place here in such a way that the one of the two switches 180, 181 that was previously open is closed, and only then is the switch closed until then opened. The actuating unit 174 therefore also briefly passes through the third switching state with each transition from the first to the second or from the second to the first switching state.

So that when the third switching state is to be maintained for longer times, the power loss can be kept particularly small, it is provided in this embodiment that the current limiting circuit 157 is controlled via two lines 163 by the switch controller 23 so that its limit value is significantly smaller Value, preferably takes the value zero. The current limiting circuit 157 then acts. an open switch and practically only the very small short-circuit current flows, which is driven by the small voltage drop across the first winding 9 in the two further windings 35, 36.

The switches 180, 181 are controlled by the switch controller 23 via the lines 164, 165.

The transformer 8 of the actuating unit 174 also has a short-circuit winding 28 which can be short-circuited via a switch 29 which is controlled by the switch controller 23 via a line 30.

• 1. Kurzschluß im Schalter 180 oder 181: Ein solcher Kurzschluß bedeutet, daß sich der betreffende Schalter nicht mehr öffnen läßt, die Stelleinheit also dann, wenn sie nicht gemäß der Erfindung ausgebildet wäre, ständig im ersten bzw. zweiten Schaltzustand bleiben würde. Nimmt man an, daß z.B. der Schalter 180 ständig geschlossen ist, so kann aufgrund des Vorhandenseins der Strombegrenzungsschaltung 157 in all den Fällen, in denen keine additive Aufprägung der in der Wicklung 9 induzierten Spannung gewünscht wird, der Schalter 181 geschlossen und die Strombegrenzungsschaltung 157 auf den kleineren Grenzwert geschaltet werden. Die Stelleinheit geht dann also in den dritten Schaltzustand über und gibt die Eingangsspannung unverändert am Ausgang ab. Wird der Schalter 181 wieder geöffnet und die Strombegrenzungsschaltung 157 wieder auf den größeren Grenzwert zurückgeschaltet, so geht die Stelleinheit wieder in den ersten Schaltzustand über. Sie kann also trotz der Störung immer noch zwischen dem ersten und dem dritten Schaltzustand hin- und hergeschaltet werden und die Amplitude der Ausgangsspannung U_A in entsprechender Weise verändern. Der zweite Schaltzustand kann in einem solchen Fall allerdings nicht mehr hergestellt werden. Entsprechendes gilt, wenn ein Kurzschluß im Schalter 181 auftritt, der Schalter 180 aber funktionsfähig bleibt. In diesem Fall kann die Stelleinheit 174 zwischen dem zweiten und dritten Schaltzustand hin- und hergeschaltet werden, den ersten Schaltzustand aber nicht mehr einnehmen.
• 2. Gleichzeitiger Kurzschluß in den Schaltern 180 und 181:
  • In diesem Fall wird die Strombegrenzungsschaltung 157 auf den kleineren Grenzwert geschaltet und die Stelleinheit bleibt auf Dauer im dritten Schaltzustand, in dem die Ausgangsspannung gleich der Eingangsspannung ist. In den ersten oder zweiten Schaltzustand kann sie dann allerdings nicht mehr gebracht werden.
• 3. Sollte ein Kurzschluß gleichzeitig in den beiden Schaltern 180 und 181 und in der Strombegrenzungsschaltung 157 auftreten, so würde zunächst ein sehr hoher Kurzschlußstrom vom Anschluß 2 zum Anschluß 3 fließen. Für diesen Fall ist mit der Strombegrenzungsschaltung 157 eine Sicherung 167 in Reihe geschaltet, die dann durchbrennt und somit die Verbindung zwischen den Leitungen 185 und 10 endgültig unterbricht. Wegen des Kurzschlusses in den beiden Schaltern 180 und 181 befindet sich die Stelleinheit dann im dritten Schaltzustand.
• 4. Leitungsunterbrechung in der Strombegrenzungsschaltung 157:
  • Läßt die Strombegrenzungsschaltung 157 aufgrund einer Störung keinen Strom mehr fließen, so werden die Schalter 180 und 181 durch die Schaltersteuerung 23 permanent geschlossen und die Stelleinheit 174 wird auf Dauer in dem sich so ergebenden dritten Schaltzustand gehalten.
• 5. Leitungsunterbrechung in einem der Schalter 180 bzw. 181 Läßt sich einer der beiden Schalter 180, 181 nicht mehr schließen, so würde immer dann, wenn der jeweils andere Schalter geöffnet werden muß, die oben geschildete starke Drosselwirkung der Wicklung 9 eintreten. Wegen des Spannungsabfalls, der in diesem Zustand an der Drossel 9 auftritt, würde ein Spannungskonstanter oder Spannungsregler, in dem eine Stelleinheit diese Störung zeigt, praktisch seine Funktion nicht mehr ausüben können. Um dies zu verhindern, ist die Kurzschlußwicklung 28 vorgesehen, deren Schalter 29 dann geschlossen wird. Damit befindet sich die Stelleinheit 174 wieder im dritten Schaltzustand; sie kann somit weiterhin zwischen dem dritten Schaltzustand und dem einen der beiden anderen Betriebs-Schaltzustände hin- und hergeschaltet werden.

Because of the construction according to the invention, it is possible in certain malfunctions to keep the actuating unit 174 at least partially functional or at least to control it in such a way that it outputs its input voltage unchanged at the output connections 5, 6. If the control unit forms a link in a longer chain of control units which are used overall as voltage constants, at least the other control units remain functional and the entire transformer circuit can maintain its control or regulating function, albeit to a limited extent. This is explained below for some typical malfunctions:

• 1. Short circuit in switch 180 or 181: Such a short circuit means that the switch in question can no longer be opened, that is to say if the control unit were not designed in accordance with the invention, it would always remain in the first or second switching state. Assuming that, for example, switch 180 is permanently closed, the presence of the current limits may result in tion circuit 157 in all cases in which no additive impressions of the voltage induced in the winding 9 is desired, the switch 181 is closed and the current limiting circuit 157 is switched to the smaller limit value. The control unit then changes to the third switching state and outputs the input voltage unchanged at the output. If the switch 181 is opened again and the current limiting circuit 157 is switched back to the larger limit value, the actuating unit returns to the first switching state. In spite of the fault, it can therefore still be switched back and forth between the first and the third switching state and change the amplitude of the output voltage U _A in a corresponding manner. In such a case, however, the second switching state can no longer be established. The same applies if a short circuit occurs in the switch 181, but the switch 180 remains functional. In this case, the actuating unit 174 can be switched back and forth between the second and third switching states, but can no longer assume the first switching state.
• 2. Simultaneous short circuit in switches 180 and 181:
  • In this case, the current limiting circuit 157 is switched to the smaller limit value and the actuator remains permanently in the third switching state, in which the output voltage is equal to the input voltage. However, it can then no longer be brought into the first or second switching state.
• 3. If a short circuit occurs simultaneously in the two switches 180 and 181 and in the current limiting circuit 157, a very high short circuit current would initially flow from the connection 2 to the connection 3. In this case, a fuse 167 is connected in series with the current limiting circuit 157, which then blows and thus finally interrupts the connection between the lines 185 and 10. Because of the short circuit in the two switches 180 and 181, the actuating unit is then in the third switching state.
• 4. Line interruption in the current limiting circuit 157:
  • If the current limiting circuit 157 no longer allows current to flow due to a fault, the switches 180 and 181 are permanently closed by the switch controller 23 and the actuating unit 174 is kept permanently in the third switching state which results in this way.
• 5. Line interruption in one of the switches 180 and 181, if one of the two switches 180, 181 can no longer be closed, the strong throttling effect of the winding 9 would occur whenever the other switch had to be opened. Because of the voltage drop that occurs at the choke 9 in this state, a voltage constant or voltage regulator would be used an actuator shows this malfunction, can practically no longer perform its function. To prevent this, the short-circuit winding 28 is provided, the switch 29 is then closed. The actuating unit 174 is thus again in the third switching state; it can thus be switched back and forth between the third switching state and one of the other two operating switching states.

The malfunctions just described can also occur in the actuating unit 144 shown in FIG. 8 and, due to their construction according to the invention, can be partially overcome in a manner similar to that just described. Of course, a fuse 167 can also be provided in the actuating unit 144 shown in FIG. 8, which is connected in series with the current limiting circuit 157.

FIG. 10 shows a current limiting circuit 157, as can be used in the actuating units 144, 174 in FIGS. 8 and 9.

This current limiting circuit has two current connections 187, 188, one of which is connected directly to line 155 or line 185 and the other to the connecting connecting conductor 10 in a directly electrically conductive manner. A series circuit is arranged between the two current connections 187, 188 and consists of the source-drain path of a first V-MOS transistor 190, two resistors 192, 193 and the source-drain path of a second V-MOS transistor 191 . Parallel to this series connection are between the two power connections 187, 188 two diodes 198, 199 connected in series with one another, whose forward directions are opposite to each other. The connection point 196 of the two diodes 198, 199 is electrically connected to the connection point 195 of the two resistors 192, 193.

Since each of the two transistors 190, 191 has a diode characteristic, i.e. its blocking effect can only develop in one direction, the two transistors 190, 191 are arranged so that their forward directions are parallel to the forward direction of the diodes 198 and 199 lying in the parallel branch and thus opposite to each other. As a result, an alternating current can also be limited in the required manner with the aid of this current limiting circuit 157.

The diodes 198, 199 are selected so that the voltage drop across them when the rated current flows is smaller than the corresponding voltage drop across the parallel V-MOS transistor 190 and 191, respectively. Since each diode 198 and 199 is not only the one parallel to it V-MOS transistor 190 or 191 but also bypasses its associated series resistor 192 or 193, the half-waves of the alternating current to be limited either flow via diode 198 and further via resistor 193 and V-MOS transistor 191 or via the diode 199 and further via the resistor 192 and the V-MOS transistor 190. As a result, on the one hand, the alternating current in each half-wave can be limited as required by one of the two V-MOS transistors 190 and 191; on the other hand it is avoided that the half-waves also the second Resistor and the second V-MOS transistor must flow through, which are only necessary for limiting the half-waves with the other sign. The power loss occurring in the current limiting circuit 157 can thus be kept particularly small.

The gate voltage for the two transistors 190, 191 supplied from the switch controller 23 via the two lines 163 is applied between the connection point 195 of the two resistors 192, 193 and the two gate connections of the transistors 190, 191. As a result, the voltage that drops across resistors 192, 193 when a current flows between terminals 187 and 188 is subtracted from the gate voltage. The size of this gate voltage is selected so that the current flowing from one of the two connections 187, 188 to the respective other connection cannot exceed a predetermined limit value.

In the case described above that the current limiting circuit 157 is to be switched to a second, smaller limit value which is practically zero, the gate voltage supplied via the lines 163 is chosen to be so low that it is below the threshold voltage U _{TH of} the V- MOS transistors 190, 191, which thus practically no longer allow current to flow through their source / drain path.

As already mentioned, switches 150 to 153 or 180 and 181 triacs can be used as switches. However, this means that these switches can only be opened when the current flowing through them passes through a zero crossing. It has already been pointed out that according to the invention, switches which are initially open until then are closed when changing from one switching state to the other. Then Both the actuating unit 144 and the actuating unit 174 are each in their third switching state. The respective short-circuit current then flows through the switches 150, 151 or 152, 153 or 180, 181 and it can only be switched to the subsequent first or second switching state when this short-circuit current passes through a zero crossing.

If the switch in question is then opened, the further winding 11 or one of the two further windings 35, 36 is connected to its control voltage U _E or U _A , which as a rule attempts to force the flow of a current against the current flowing up to that point Short-circuit current is out of phase, that is, at the point in time at which the respective switch is opened, has no zero crossing.

11 shows a diagram of the curve of an oscillation period of the input voltage U _E , the short-circuit current I _K flowing in the third switching state, the current 1 ₁ flowing in the first switching state and the current 1 ₂ flowing in the second switching state. The amplitude of the short-circuit current I _{K is} shown greatly enlarged for the sake of clarity.

It should be expressly pointed out that the three currents I _K , I ₁ and I ₂ cannot flow at the same time, since the actuating unit 144 or 174 can only ever be in one of the three switching states.

For the following considerations it is now assumed that the actuating unit 144 or 174 is in the third switching state, from that during the first half period of the input voltage U _E shown in FIG. 11, that is to say between the times t ₁ and t ₄ in the first switching state should be transferred. For this purpose, switch 151 must be opened in the embodiment according to FIG. 8 and switch 181 in the embodiment according to FIG. 9. Since these switches are traversed by the short-circuit current I _K , if they are implemented with the aid of triacs, they can only be opened at the time t ₄ at which the short-circuit current I _K passes through a zero crossing. It can be seen from FIG. 11 that at this point in time the current I ₁ , which should flow through the further winding 11 or the further winding 35 immediately following the opening of the switch, has a value which is equal to the zero crossing value of the short-circuit current I _{K '} which flowed through this further winding 11 or 35 before opening is considerably different.

It is clear that the current flowing through the further winding 11 or 35 in the new switching state cannot jump abruptly from zero to the actually required value I _S. Instead, a compensation current I _{G is} induced in the transformer, the value of which is initially equal to -I _S and which decays exponentially over a longer period of time. It can take several oscillation periods of the input voltage U _E until this compensation current I _{G has} completely disappeared.

The compensation current I _{G is} added to the current driven by the input voltage U, through the further winding 11 or 35. Since the transformer 8 is dimensioned so that the current which normally flows through a further winding connected to its control voltage is just below of the saturation limit, the transformer is driven into saturation by this compensation current I _G. This has the consequence that there is a voltage drop in the switching process just described, the leads to the fact that the transition from the old to the new voltage amplitude is not completely smooth, but that voltage peaks are impressed on the first half-wave of the output voltage U following the switching operation.

In order to avoid this disruptive effect, the invention provides that switches 150 to 153 and 180, 181 also be constructed with V-MOS transistors instead of triacs, two of which are again connected in series with opposite polarity. These transistors have the advantage that the switch they form can be opened regardless of the size of the current flowing through them. It is therefore no longer necessary to wait for the next zero crossing of the short-circuit current I _K , but the transition from the third to the first or second switching state can take place at a much more favorable time.

As can be seen from FIG. 11, the optimal switching times would be the times t ₂ or t ₃ 0 because in them the short-circuit current I _K which flows in the other windings in question before the switching is equal to the current which after the switching process in the each additional winding should flow.

Since these ideal times t ₂ and t ₃ are very difficult to measure from a measurement point of view, they can be approximately replaced by times t ₂ 'and t ₃ ', in which the current which the further winding in the first or in the second Switching state flows through, has a zero crossing. These replacement times t ₂ 'and t ₃ ' are not too far away from the ideal times t ₂ and t _3, respectively. Since, as already mentioned, the Amplitude is greatly exaggerated by I _K in Fig. 11, is the use of at equivalent time points t ₂ 'and t _3' required power change also not particularly great.

Since the time intervals τ ₁ and τ ₂ , which have the replacement times t ₂ 'and t ₃ ' from the nearest zero crossing of the input voltage U _E , are load-dependent, they cannot be stored once and for all in the switch control 23. Instead, they are measured whenever the actuator 144 or 174 is in the first or second switching state, and the measured values are stored. If the next switch is to be made from the third switching state to the first or second switching state, the switching time t ₂ 'can be started on the basis of the time that has elapsed since the zero crossing t _{1 of} the input voltage U _E , which is to be followed by the switching process. or the switching time t ₃ 'can be easily specified.

These measures make it possible for the output voltage of the actuating unit to pass through the new amplitude value in a completely undisturbed manner at the next half-oscillation.

A control unit, which is equipped with V-MOS transistor switches and a current limiting circuit 157 and which applies a voltage change + AU to its input voltage in the first switching state and causes a voltage change of -ΔU in the second switching state, from the first to the second switching state or reversed, the total voltage change 2ΔU that occurs can be carried out in two steps; the first step in which the output voltage is changed by (ΔU) takes place immediately ie simultaneously with the generation of the switchover signal. This is done in that the control unit is switched to the third switching state by closing one or more switches that were open until then. The second half of the required change is then accomplished within a period of time, which in the worst case is equal to half an oscillation period of the input voltage U _E. Assuming that U _{E has} an oscillation frequency of 50 Hz, the overall change can be accomplished within a maximum of 10 ms. Then the output voltage U _{A has a} stable new value.

The same also applies if an actuating unit is to be switched to the first or second switching state after it has been in the third switching state for a long time. Since only one or two switches have to be opened during such a transition, after the changeover signal has been generated it is only necessary to wait until the next favorable switching time t ₂ 'or t ₃ ' occurs. Since each of these points in time is available twice per AC voltage period, a time period corresponding to the length of a half cycle of the AC voltage must therefore be waited in the worst case before switching can take place. Although the change in the output voltage takes place in a single step, the magnitude of this change is only half the size of the total change which is made during the transition from the first to the second or from the second to the first switching state.

A particularly quick and precise switchover occurs when two of the actuating units 174 described above are connected in series to form a pair of actuating units.

Claims (46)

1. A transformer circuit for generating an adjustable load voltage on a load from a supply voltage which is supplied by a voltage source, the transformer circuit comprising at least one actuating unit which has two input connections for applying an AC input voltage, two output connections for outputting an AC output voltage, one with the Transformer connected to input and output connections and switches which can be actuated to change the amplitude of the AC output voltage of the actuating unit, characterized in that one (3) of the two input connections (2, 3) of the actuating unit (4 ;, 34; 54; 94 ; 144; 174) through a connection connecting conductor (10) with one (6) of the two output connections (5, 6) is directly electrically connected, that between the other input connection (2) and the other output connection (5) a first winding (9) of the transformer (8) is switched, and that the transforma gate (8) at least one further winding (11; 35), whose turns ratio (w _{w /} w ₁ ) to the first winding (9) is greater than 1 and to which with the help of the switches (15, 16; 37; 98; 150, 153; 180) at least a first control alternating voltage can be applied in order to induce a first voltage (a U1) in the first winding (9), which impresses itself on the input AC voltage (U _E ) in such a way that the amplitude of the output AC voltage varies by the amplitude of the induced voltage (ΔU ₁ ) Amplitude of the input AC voltage (U _E ) differs. 2. Transformer circuit according to claim 1, characterized in that the at least one further winding (11) with the aid of switches (15; 150, 153) a first control alternating voltage can be applied in order to induce in the first winding (9) a voltage (ΔU ₁ ) which is additively impressed on the input alternating voltage (U _E ), and that to the at least one further winding (11) with the aid of A second control alternating voltage can be applied to switches (16; 151; 152) in order to induce a voltage (d U2) in the first winding (9) which is subtractively impressed on the alternating input voltage (U _E ). 3. Transformer circuit according to claim 2, characterized in that the first control voltage is the input AC voltage (U _E ) of the control unit (4; 144) and that the second control voltage is the output AC voltage (U _A ) of the control unit (4; 144). 4. Transformer circuit according to claim 2 or 3, characterized in that the at least one further winding (11) can be short-circuited with the aid of a switch arrangement (17) in order to make the voltage drop across the first winding (9) through which the load current flows as close as possible to zero, so that the amplitude of the output voltage (U _A ) is equal to the amplitude of the input voltage (U _E ) of the actuating unit (4). 5. Transformer circuit according to claim 2, characterized in that one end (13) of the at least one further winding (11) can be connected directly to the input connection (2) of the actuating unit (144) with the aid of a first switch (150), to which the first winding (9) is connected, that the other end (14) of the at least one further winding (11) can be connected directly to the output connection (5) of the actuating unit (144) with the aid of a second switch (151) which the first winding (9) is connected, that each of the two ends (13, 14) of the at least one further Winding (11) can be connected to the connecting connecting conductor (10) via a third switch (152) or a fourth switch (153), and that the actuating unit (144) can be connected using these switches (150, 151, 152, 153) can be brought into the following three switching states: - A first switching state in which the at least one further winding (11) is connected to the input voltage (U _E ) of the actuating unit (144) with such a sense of winding that the voltage thereby induced in the first winding (9) (ΔU ₁ ) additively to the input voltage (U _E ), - A second switching state in which the at least one further winding (11) is connected to the output voltage (U _A ) of the actuating unit (144) with a winding sense such that the voltage (AU2) induced thereby in the first winding (9) subtractively impresses on the input voltage (U _E ), and - A third switching state in which one end (13, 14) of the at least one further winding (11) is electrically conductively connected to one end of the first winding (9), whereby the at least one further winding (11) together with the first closed switch (150) and the second closed switch (151) forms a current path parallel to the first winding (9), as a result of which the resulting magnetic flux in the core (12) of the transformer (8) is at least approximately equal to zero and thus the output voltage (U _A ) the actuator (144) is equal to the input voltage (U _E ). 6. Transformer circuit according to claim 5, characterized in that the third and fourth switches (152, 153) are each designed in the manner of a current limiting circuit in such a way that, in the closed state, the current flowing through them oppose only a small, constant resistance, as long as this current is smaller than a predetermined limit value and that this limit value is selected somewhat larger than the current which flows through the further winding (11) in the first or in the second switching state. 7. Transformer circuit according to claim 5, characterized in that the third and fourth switches (152, 153) are directly electrically connected to one another by a further electrical conductor (155), that between the further electrical conductor (155) that the connects the third and fourth switches (152, 153) to one another, and the connection connecting conductor (10) is provided with a circuit arrangement (157) which connects the two conductors (155, 10) in an electrically conductive manner and prevents the flow of an impermissibly large current, that the switching from one switching state to another takes place in such a way that the third and fourth switches (152, 153) are never closed at the same time, and that the current path (152, 155, 153) that connects the two ends (13, 14) of the another Wiclung (11) connects to each other when the third and fourth switches (152, 153) are closed at the same time, has an electrical resistance value that is greater than the ohmic resistance of the we iteren Wiclung (11). 8. Transformer circuit according to claim 1, characterized in that one of a plurality of control voltages (U _S1 , ..., ^U _S32 ) can be applied to the at least one further winding (11) with the aid of switches (98) at least partially different in amplitude from each other to _lun in the first Wick- g ₍₉₎ each selectively a voltage (.DELTA.U _1, ..., .DELTA.U ₃₂₎ to induce which the input AC voltage (U _e) the actuator (94) so impressed that the amplitude of the AC output voltage (U _A ) differs from the amplitude of the AC input voltage (U _E ) by the amplitude of the respectively induced voltage (ΔU ₁ , ..., ΔU ₃₂ ). 9. Transformer circuit according to claim 8, characterized in that the at least one further winding (11) can be short-circuited with the aid of the switch arrangement (98) in order to make the voltage drop across the first winding (9) through which the load current flows as zero as possible, so that the amplitude of the output voltage (U _A ) is equal to the amplitude of the input voltage (U _E ) of the actuating unit (94). 10. Transformer circuit according to claim 8 or 9, characterized in that the plurality of control voltages (U _S1 , ..., U _S32 ) in two groups ( ^U _S1 , U _{S3 '} ... U _S31 and ^US2 ' U _S4 , .. ., US32) ^are divided ^so that the control voltages belonging to the same group all have different amplitudes, while each control voltage (U _S1 , U _S3 , ..., U _S31 ) from the one group of a control voltage (U _S2 "U _{S4 '} ..., U _S32 ) from the other group is at least approximately the same in terms of amplitude that the control voltages (U _S1 . U _S3' ..., ^U _S31 ) of the one group are connected to the at least one further winding (11) it can be applied that the voltages induced thereby (ΔU ₁ , ΔU ₃ , ..., ΔU ₃₁ ) additively to the input voltage (U _E ) of the actuating unit (94) and that the control voltages (U _S2 , .. ., U _S32 ) of the other group can be applied to the at least one further winding (11) in such a way that the voltages (ΔU ₂ , ΔU ₄ , ..., ΔU ₃₂ ) subtractively on the input voltage (U _E ). 11. Transformer circuit according to one of claims 8 to 10, characterized in that an AC voltage source (100) is provided which has a plurality of taps (121, ..., 127) on which a plurality of tap alternating voltages (U _X1 , ..., U _X6 ) are available, the amplitudes of which are selected such that each of the control voltages (US1, ..., U _S32 ) either equals one of these tap alternating voltages or the sum of several of these tap alternating voltages (U _X1 , ..., U _X6 ), and that at least one of the two ends of the further winding (11) can optionally be connected to various of these taps (121, ..., 127) with the aid of switches (98). 12. Transformer circuit according to claim 11, characterized in that the control voltage (US _min ) required to induce the smallest desired non-zero voltage (ΔU _min ) in the first winding (9) of the transformer (8) as the smallest AC tap voltage (UX _min ) can be tapped from at least one pair of taps (126, 127) of the AC voltage source (100) which are directly adjacent to one another, such that the tapping AC voltages (U _X1 ,...) which can be tapped between the other pairs of taps (121, ..., 126) which are directly adjacent to one another. .., U _X5 ) are either equal to this smallest tap alternating voltage (U _Xmin ) or equal to an integer multiple of this smallest tap alternating voltage (U _Xmin) , and that the number of taps (121, ..., 127), the number of tap pairs ( 126, 127; 122, 123) between which the smallest AC tap voltage (U _Xmin ) can be tapped, and the sizes of the integer multiples of the smallest AC tap voltage (U _Xmin ) ', the taps (121, 122; 123, 124; 124, 125; 125, 126) can be tapped, are selected so that with a minimum number of Taps (121, ..., 127) a specifiable maximum control voltage range (U _Smax )) can be covered in unit steps of the smallest tap AC voltage (U _Xmin ). 13. A transformer circuit according to claim 12, characterized indicates overall that the number of taps (121, ..., 127), the number of Abgriffspaare (126, 127) 122, 123) between which the smallest Abgriffswechselspannun ^g (Uxmin) can be tapped, and the sizes of the integer multiples of the smallest tap alternating voltage (U _Xmin ), which can be _tapped between the other pairs of taps immediately adjacent to one another, are selected such that the maximum voltage that can be tapped at the AC voltage source (100) is the same is the maximum control voltage (U _Smax ) required to induce the desired maximum voltage (ΔU _max ) in the first winding (9) of the transformer (8). 14. Transformer circuit according to one of claims 11 to 13, characterized in that the alternating voltage source (100) is a winding of an additional transformer arrangement (101) to which an alternating voltage is applied and which in several winding sections (104, ..., 109 ) is divided, between which the taps (121, ..., 127) for tapping the tap alternating voltages ( _{UX1 '} ..., _UX6 ) are led out, and that the alternating voltage that can be applied to the winding of the additional transformer _arrangement (101) is the input voltage (U _E ) or the output voltage (U _A ) of the actuating unit (94). 15. Transformer circuit according to claim 1, characterized in that the transformer (8) has at least two further windings (35, 36), to each of which with the aid of the switches (37, 38; 180, 181) Control AC voltage can be applied in order to induce a voltage (ΔU ₁ or ΔU ₂ ) in the first winding (9) which is impressed on the input AC voltage (U _E ). 16. Transformer circuit according to claim 15, characterized in that a control voltage can be applied alternately to the two further windings (35, 36), and that by applying a control voltage to the one further winding (35) in the first winding ( 9) induced first voltage (ΔU ₁ ) has an amplitude whose absolute amount is approximately equal to the absolute amount of the amplitude of the second voltage (ΔU ₂ ) induced in the first winding (9) by applying a control voltage to the other further winding (36) . 17. Transformer circuit according to claim 16, characterized in that the two induced voltages (ΔU ₁ , ΔU ₂ ) can be impressed on the input voltage (U _E ) with opposite signs, so that the amplitude of the AC output voltage (U _A ) in one Is equal to the sum (U _E + ΔU ₁ ) and in the other case to the difference (U _E - 6U2) of the amplitudes of the input AC voltage (U _E ) and the relevant induced voltage (ΔU ₁ , ΔU ₂ ), and that to additively impress an induced voltage (ΔU ₁ ) the input alternating voltage (U _E ) of the actuating unit (34; 54, 54 '; 174) and for subtractively impressing an induced voltage (AU2) the alternating output voltage (U _A ) of the actuating unit (34; 54 , 54 '; 174) is used as the respective control AC voltage. 18. Transformer circuit according to claim 17, characterized in that the transformer (8) comprises two further windings (35, 35 ', 36, 36'), of which one is used only as an additive winding (35, 35 '), the first end of which is permanently galvanically connected directly to one (2) of the two input connections (2, 3) of the actuating unit (34; 54, 54'; 174), and the second end of which can be conductively connected or disconnected from the connecting connecting conductor (10) by means of a switch (37, 37 '; 180), and of which the other is only used as a subtracting winding (36, 36') , which is permanently connected at its first end to one (5) of the two output connections (5, 6) of the actuating unit (34; 54, 54 '; 174) in a direct, electrically conductive manner; while its second connector can be conductively connected or disconnected from the connecting connecting conductor (10) with the aid of a switch (38, 38 '; 181), and that the turn ratio of the first winding (9) of the transformer (8) has to be added Winding (35, 35 ') is approximately equal to the turns ratio of the first winding (9) to the subtracting winding (36, 36'). 19. Transformer circuit according to one of claims 15 to 18, characterized in that the two further windings (35, 36) can be short-circuited at the same time with the aid of switches (31, 32) in order to reduce the voltage drop across the first winding (9) through which the load current flows. as zero as possible so that the amplitude of the AC output voltage (U _A ) is equal to the amplitude of the AC input voltage (U _E ) of the actuating unit, that the two switches (37, 37 ', 38, 38'), which are used to apply a control AC voltage to one of the two further windings (35, 35 ', 36, 36') are used, can be operated exclusively and between the connecting connecting conductor (10) and the relevant end of the associated further winding (35, 35 ', 36, 36 ') are arranged so that a sensor unit (42, 42') is arranged on each of the two switches (37, 37 ', 38, 38'), which emits a signal which the Switching state of the associated switch (37, 37 ', 38, 38'), and that each of the two switches (37, 37 ', 38, 38') is assigned a blocking circuit (39, 39 ', 40, 40'), which, depending on the signal emitted by the sensor unit of the other switch (39, 39 ', 40, 40'), prevents the switch (39, 39 ', 40, 40') assigned to it from closing the other switch (39, 39 ', 40, 40') is closed. 20. Transformer circuit according to one of claims 15 to 19, characterized in that a sensor device for detecting the phase profile of the magnetic flux in the first winding (9) is provided that the switches (37, 38, 37 ', 38'), each serve to apply a control voltage to the further winding (35, 36, 35 ', 36'), depending on the measurement signal of the sensor device, can only be closed at those phase angles of the magnetic flux in the first winding (9) at which this closing is as possible as possible leads to a small change in this magnetic flux, and that these switches (37, 38, 37 ', 38') are only opened at the zero crossing of the current flowing through the further winding (35, 36, 35 ', 36'). 21. Transformer circuit according to claim 20, characterized in that the transformer (8) has a short-circuit winding (28) which can be short-circuited with the aid of a switch (29), that the switch (29) for the short-circuit winding (28) is closed during the time periods In which, when switching from one control voltage to another control voltage, there is temporarily no control voltage at another winding (11) that the switch (29) for the short-circuit winding (28) is closed only at such phase angles of the magnetic flux through the first winding (9) is where this Closing leads to a change in this magnetic flux which is as small as possible, and that this switch (29) is only opened at the zero crossing of the current flowing through the short-circuit winding (28). 22. A transformer circuit according to claim 18, characterized in that the two second ends of the two further windings (35, 36) can be connected to one another in a directly electrically conductive manner with the aid of the switches (180, 181) such that the two further windings (35 , 36) lie one behind the other in a current path which is electrically parallel to the first winding (9). 23. Transformer circuit according to claim 22, characterized in that the two switches (180, 181) through which the second ends of the two further windings (35, 36) can be connected to the connection connecting conductor (10) by another electrical conductors (185) are directly electrically conductively connected to one another and that between this conductor (185) and the connecting connecting conductor (10) a circuit arrangement (157) is provided which connects the two conductors (185, 10) to one another in an electrically conductive manner and that Flow of an impermissibly large current prevented. 24. Transformer circuit according to one of claims 7 or 23, characterized in that the circuit arrangement (157) is a current limiting circuit which opposes the current flowing through it a small, constant resistance, as long as this current is less than a variably predeterminable limit value and that The limit value is selected to be somewhat greater than the current which flows in the first or in the second switching state through the further winding (11; 35, 36) which is in each case connected to a control voltage. 25. Transformer circuit according to claim 24, characterized in that the current limiting circuit for periods in which the actuating unit is in the third switching state for a longer period of time can be switched over to a second limit value which is substantially smaller than the first limit value, in particular equal to zero. 26. Transformer circuit according to one of claims 6 or 24 or 25, characterized in that the current limiting circuit regulates the current flowing through it when approaching the limit value with a continuous transition to this limit value. 27. Transformer circuit according to claim 6 or one of claims 24 to 26, characterized in that the current limiting circuit (157) comprises the following components: two V-MOS transistors (190, 191) whose source / drain paths are connected in series with opposite polarity, two resistors (192, 193) which are connected to one another and to the source / drain paths of the two transistors (190, 191) in series between the two transistors (190, 191), the gate voltage for the two transistors ( 190, 191) between the connection point (195) of the two resistors (192, 193) and the respective gate connection, and two diodes (198, 199) 1 which are connected with opposite polarity in series between the two current connections (187, 188) of the current limiting circuit (157) and whose connection point (196) is electrically directly conductive with the connection point (195) of the two resistors ( 192, 193), the forward direction of each diode (198, 199) being equal to the permanent through direction of the V-MOS transistor (190, 191) located in the respective parallel branch. ₂₈ Transformer circuit according to one of the preceding claims, characterized in that the turns ratio of each further winding (11; 35, 36, 35 ', 36') of the transformer (8) to the first winding (9) is in a range from 3: 1 to 200 : 1 lies. ₂₉ . Transformer circuit according to one of the preceding claims, characterized in that the transformer circuit comprises at least two stages (55, 56, 57), each of which consists of at least one actuating unit (4; 34; 54, 54 ';144; 174) and so are connected together in series that the output ac voltage (U _A) of the front step (55, 56) ingangswechselspannung the _e (U _e) of the rear stage (56, 57), and in that the at least two first windings (9) of the Transformers (8) of the at least two stages (55, 56, 57) are directly in series with one another. _30th Transformer circuit according to Claim 29, characterized in that each stage (55, 56, 57) comprises at least two actuating units (54, 54 '; 174, 174') which form a pair of actuating units, the turns ratios of the respective first winding (9, 9 ') for the associated further windings {35, 36, 35', 36 ') are matched to one another in such a way that the output voltage (U _AP ) of the pair of actuating units (54, 54'; 174, 174 ') is the same of the input voltage (U _EP ) of the actuating unit pair (54, 54 '; 174, 174') when one (54; 174) of the actuating units is additive to its input voltage (U _EP ) and an induced voltage (ΔU ₁ ) another actuator (54 ';174') subtractively impresses an induced voltage (Δ _U2 ) on its input voltage (U _E ). 31. Transformer circuit according to claim 30, characterized in that the absolute values of the amplitude differences which can be generated by at least some of the stages (55, 56, 57) are in relation to one another in the ratio of integer powers of three 1: 3: 9: etc. 32. Circuit arrangement with a transformer circuit according to one or more of claims 29 to 31, characterized in that an AC voltage sensor arrangement (64, 67; 81), one comparing the output signals of the sensor arrangement with reference _values (U _ref1 , U _ref2 ; U _ref ) Comparator arrangement (63, 66; 82) and a switch control (23; 83) are provided, by means of which the switches of the stages (55, 56, 57) can be actuated selectively so that the load (7) has a load voltage (U _L ) amplitude is supplied as constant as possible. 33. Circuit arrangement according to claim 32, characterized in that the sensor arrangement comprises a sensor (67; 81) which measures the supply voltage (UV) emitted by the voltage source (1; 80) and / or comprises a sensor (64), which measures the load voltage ( ^U _L ). 34. Circuit arrangement according to one of claims 32 or 33, characterized in that for each of the phase conductors (R, S, T) of a multi-phase system, a transformer circuit (75, 76, 77) with one or more stages (55, 56, 57), a sensor arrangement (81) measuring the voltage on each of the phase conductors (R, S, T or R _K , S _K , T _K ), a comparator arrangement (82) comparing the output signals of the sensor arrangement (81) with at least one reference value (U _ref ) and a switch control (83) are provided, which are due to the differential signals emitted by the comparator arrangement (82) controls the switches of the stages (55, 56, 57) of all transformer circuits (75, 76, 77). 35. transformer circuit for a multi-phase system with neutral conductor, according to one of the preceding claims, characterized in that it comprises at least one actuator (4; 34; 54; 144; 174) for each phase, the first winding (9) in each of which The phase conductor concerned is located and its connecting connecting conductor (10) is connected to the neutral conductor of the multiphase system. 36. Transformer circuit for a multi-phase system without a neutral conductor according to one of claims 1 to 34, characterized in that it comprises at least one actuating unit (4; 34; 54; 144; 174) for each phase, the first winding (9) each lies in the phase conductor in question, and that the connection connecting conductors (10) of all actuating units are connected to one another to form an artificial neutral conductor. 37. Transformer circuit for a multi-phase system without a neutral conductor according to one of claims 1 to 34, characterized in that it comprises at least one actuating unit (4; 34; 54; 144; 174) for each phase and that those belonging to different phases Actuating units are arranged in a chained circuit, the first winding for each actuating unit being located in the associated phase conductor and the connecting connecting conductor (10) being formed by one of the other phase conductors. 38. Method for regulating the amplitude of an AC voltage using a circuit arrangement according to one of claims 32 to 34, characterized in that that the absolute value of the smallest possible change in amplitude (A) is between 1.0 times and 2.0 times the absolute value of the permissible deviation (δ) of the load voltage (U _L ) from the target value (S _L ) and that the switching thresholds at which with increasing deviation of the supply voltage (U _V ) emitted by the voltage source from the nominal alternating voltage, the impressed amplitude difference of n times the smallest possible change in amplitude (A) to (n + 1) times, and with decreasing deviation from (n + 1) -fold switching to n-fold, are selected so that the amplitude values of the load voltage (U _L ) are symmetrical to the setpoint CS _L ) during and continuously through the supply voltage (U _V ) through the respective switching threshold. 39. The method according to claim 38, characterized in that the load voltage (U _L ) is adjusted to a target value (S _L ) which is different from the nominal value (U _Vnom ) of the supply voltage (U _V ). 40. A method for switching an actuating unit of a transformer circuit according to one of claims 6 or 23 to 27, characterized in that the transition from the first to the second or from the second to the first switching state takes place with brief interposition of the third switching state. 41. The method according to claim 40 for a transformer circuit according to claim 6 or one of claims 24 to 27, characterized in that during the transition from the first switching state in which the first switch (150) and the fourth switch (153) are closed and the second switch (151) and the third switch (152) are open in the second switching state in which the second switch (151) and the third switch (152) are closed and the first switch (150) and the fourth switch (153) are open, first the second switch (151) and the third switch (152) are closed and then the first switch (150 ) and the fourth switch (153) are opened so that when the transition from the second to the first switching state occurs, the first switch (150) and the fourth switch (153) are closed and then the second switch (151) and the third switch (152 ) can be opened. 42. The method according to claim 40 for a transformer circuit according to claim 7 and one of claims 23 to 27, characterized in that during the transition from the first switching state to the second switching state, first the second switch (151) is closed, then the fourth switch (153) is opened , then the third switch (152) is closed and then the first switch (150) is opened and that when the transition from the second to the first switching state first the first switch (150) is closed, then the third switch (152) is opened and then the fourth Switch (153) is closed and then the second switch (151) is opened. 43. The method according to claim 40 for a transformer circuit according to claim 23 and one of claims 24 to 27, characterized in that during the transition from the first switching state, in which the switch (180), with the second end of the additive further winding (35) is connected, closed and the switch (181) connected to the second end of the subtracting further winding (36) is open, first the switch (181) for the subtracting winding (36) is closed and then the switch (180) for the adding winding (35) is opened, and that in the transition from the second to the In the first switching state, the switch (180) for the adding winding (35) is closed and then the switch (181) for the subtracting winding (36) is opened. 44. The method according to any one of claims 40 to 43, characterized in that electronic switches are used as switches (150, 151, 152, 153; 180, 181), which can be closed and opened at any time, and in that the switches, which have to be opened for the transition from the third switching state to the first or second switching state, are opened as precisely as possible at the ideal switching times in which the current flowing in the third switching state through the further winding (11; 35, 36) flows after the Transition to the first or second switching state is connected to its corresponding control voltage, has the same value as the current that flows in this further winding (11; 35, 36) immediately after the switching process. 45. The method according to claim 44, characterized in that the times for opening the switches are used as an approximation for the ideal switching times, in which the current which in the first or second switching state through the further winding (11; 35, 36) flows, which in this switching state is connected to its corresponding control voltage, has a zero crossing. 46. The method according to claim 45, characterized in that the time interval that a zero crossing of the current in the first or second switching state is due to the further winding (11; 35, 36) connected to its respective control voltage in this switching state. flows from the previous or subsequent zero crossing of this control voltage and the measured value is stored, and that in later transitions from the third to the first or to the second switching state this stored measured value is used to start the time from a zero crossing of the control voltage to open the to determine the relevant switch.

Images