EP0169488B1 - Transformer circuit - Google Patents

Description

The invention relates to a transformer circuit of the type mentioned in the preamble of claim 1.

Such a transformer circuit, as can be found in DE-A 2 233 020, is used, if necessary, to change the amplitude of an alternating supply voltage supplied by a voltage source with the aid of an actuating unit, which can be brought into different switching states, before it is used as a load. AC voltage is applied to a consumer.

For this purpose, the transformer of the known control unit comprises, in addition to a first winding, which is seen in series with the load from the voltage source, two further windings, one of which is used only as an adding and the other only as a subtracting winding in that it can be connected alternately to corresponding control voltages with the aid of switches.

Thus, the control unit can be brought into several switching states, a control voltage being applied to one of the two further windings in a first switching state such that the voltage thereby induced in the first winding of the transformer is added to the input voltage, while in a second switching state the second of the two further windings a control voltage is applied such that the voltage thereby induced in the first winding of the transformer is subtracted from the input voltage. As control voltages the input voltage of the actuating unit is used in the first switching state and the output voltage of the actuating unit is used in the second switching state.

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, neutral switching state in which no voltage is induced in the first winding of the transformer. So that the first winding in the neutral switching state does not develop a choke effect with a correspondingly high voltage drop, care must be taken that the magnetization of the transformer core is not essentially caused in it by the flooding of the first winding alone. For this purpose, the transformer of the known actuating unit has a short-circuit winding which is short-circuited with the aid of a switch in the third, neutral switching state, while the two further windings are simultaneously disconnected from all control voltages. In this third switching state, only an extremely low voltage drops across the first winding of the transformer, so that the output voltage of the actuating unit is, with good approximation, equal to the input voltage. Because of the small voltage drop across the first winding, only a small voltage is induced in the short-circuit winding, so that the short-circuit current flowing in its circuit remains small and causes very little power loss.

In order not to overload the transformer in the known circuit arrangement, it must be ensured that the switch of the short-circuit winding is only closed when the switches serving to apply the control voltages are open. It must also be ensured that the one to apply a control voltage serving switches are only closed when the switches are open, which are used to apply the other control voltage, and vice versa. For this purpose, it is necessary to monitor the switching status of each switch and to suppress a closing command for a previously open switch if it is indicated that a switch that is actually to be opened is still closed.

It is also desirable that when switching from one switching state to another, the output voltage of the actuating unit changes from its old to the new amplitude value without large fluctuations in the output AC voltage. This can not be achieved in the known circuit arrangement, in which the neutral switching state is established with the aid of a short-circuit winding, since criteria must be observed for the closing and opening of the switches, which make it impossible to switch so quickly that after less than a full oscillation period of the load AC voltage, the new amplitude value has been reached in a stable manner.

Thus, the invention has for its object to provide an improved circuit arrangement in which the neutral switching state can be achieved with less technical effort and in which it is possible to change the amplitude of the output voltage so quickly that the new amplitude value at the latest at the second half-wave of the AC output voltage following the switching process is available in a stable manner.

To achieve this object, the invention provides the features set out in claims 1 and 26, respectively.

By these measures, the third, neutral switching state is produced in a transformer which has only a single further winding in that this only further winding is electrically connected in parallel with the first winding. In the case of a transformer which has two further windings which are connected in each case with one of their two ends to the front or rear end of the first winding as seen from the voltage source, a series circuit consisting of these two further windings is connected in parallel with the first winding; In this case, these two further windings lying in series with one another can be regarded as a single winding with a continuous winding sense for the subsequent consideration.

In both cases, in this third switching state, a short-circuited transformer is obtained with two windings wound antiparallel to the core of the transformer, which are electrically parallel to one another at 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 it applies with good approximation

${\text{U}}_{\text{E}}{\text{= U}}_{\text{A}}\text{.}$

The current flowing through the further winding or the two further windings lying in series with one another is also correspondingly small, since these further Windings have 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 further winding, and three switches are sufficient for a transformer which has two further windings in the manner 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 be taken in these cases to ensure that the input voltage of the actuating unit is not either short-circuited or applied to one of the short-circuited further windings, in which an impermissibly high short-circuit current would then flow, by simultaneously closing corresponding 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 the reaching of the new amplitude value when changing from one switching state to another.

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.

If the transformer comprises only a single further winding, 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 the control unit can be connected, for example, 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 only provide a very small, constant resistance to the current flowing through them as long as this current is below a predetermined limit value remains, but prevent the current from rising above this limit.

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 connection connecting conductor of the actuating unit, are not directly connected to this connection. Lead the connecting conductor. Instead, the third and fourth switches are directly connected to each other in a galvanically conductive manner by a further conductor and is a circuit arrangement between this further conductor and the connecting connecting conductor provided that on the one hand connects the two conductors in an electrically conductive manner and on the other hand prevents the flow of an impermissibly large current from one of these two conductors to 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 suddenly limits the current flowing through it to zero when opened, this continuous limiting process has the advantage that there are no voltage peaks in the output voltage of the actuating unit. 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 end of the first winding on the output side. 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.

In the case of an actuating unit in which the transformer comprises two further windings, the two switches with which the two free ends of the two further windings can be connected to the connecting connecting conductor are also preferably connected directly to one another in a galvanically conductive manner by a further conductor, and is A circuit arrangement of the type described above is provided between the further conductor and the connecting connecting conductor, which circuit configuration is preferably again in the form of 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 then opened, as a result of which the control unit changes to the new 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 such that it switches over to at least one second current limiting value can be significantly lower than the first current limit value, preferably zero. In this way, the further winding or series connection of two further windings lying in parallel with 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 can not only be switched back and forth between two values 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 the currents which flow through the relevant further winding in the first or second switching state, if necessary.

If triacs are used as switches, which are known to be closed at any time, but can only be opened when the current flowing through them is zero, then those described above must be used Switching operations no special other criteria regarding the switching times are observed.

The following time sequences result for the different embodiments of actuating units according to the invention:

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 open switch at the start of switching, ie the second (first) and third (fourth) switches 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 the short-circuit current flowing through it and the further 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 actuating 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 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 left: After opening the switch flows in the first or second switching state, through the further winding which is then connected to its control voltage, a current which is driven by a completely different voltage source than the short-circuit current, namely 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 switches are opened, 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, in the transition from the first (second) switching state to the second (first) switching state, the two may until the start of the switching process open switch, namely the second (first) and the third (fourth) switch cannot be closed simultaneously. 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 in the transition from the first to the second or the second in the first switching state are even longer.

In the third embodiment, in which the transformer has two further windings, each of which can be connected to the further conductor by means of a switch and via this and a current limiting circuit to the connecting connecting conductor, in the worst case one must also use triacs as a switch Wait half a period 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 if 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 from the short-circuit current previously flowing through this winding, so that the same disturbing voltage peak occurs results as in the two previously described embodiments.

If you want to make the switching processes even faster in all three 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, two of which must be connected in series with their source-drain paths with opposite polarity in order to create one To build AC voltage switch. With these switches, there are no waiting times until the next zero current crossing when opening. 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, you use the time at which the current that flows through the further winding due to its control voltage after the switchover has its zero crossing, it can be achieved that already at the first half-wave that follows this switching process Output voltage of the actuator without voltage peaks or dips has exactly the new amplitude value.

Since in the interim period in which the actuating unit is in the third switching state, a different current flows through the one or the two further windings than when the corresponding further winding is connected to its control voltage in the new switching state, the time interval of the zero crossing becomes according to the invention of the last-mentioned current from the zero crossing of the input AC voltage measured and stored at an earlier point in time 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, in all three embodiments, 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 in the 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 be changed to any number Immediately carry out the instant 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 rapid successive steps is extremely advantageous, because in spite of the great 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 of the maximum possible change, this half must be managed in a single step.

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 other Winding has a high resistance value, which provides a high resistance value even after transformation down on the side of the first winding. In this switching state, the entire magnetization of the transformer core is caused by the flooding of the first winding. A voltage drop depends on the size of this flow and thus on the size of the load current 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.

Particularly favorable switching options result when two actuating units according to the invention are combined to form a pair of actuating units.

wenn U_EP die Eingangsspannung des Stelleinheiten-Paares ist.These are two actuating units connected in series, the transformers of which are dimensioned so that each of the two actuating units, both in an adding and in a subtracting manner, is capable of effecting approximately half of the total voltage change that is to be applied by the actuating unit pair. For example, if the pair of actuating units should be able to change the input voltage by ± ΔU _P , each of the two actuating units alone can change the input voltage supplied to them by approximately ± ΔU _P / 2. 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

${\text{U}}_{\text{AP1}}{\text{= U}}_{\text{EP}}{\text{+ ΔU}}_{\text{P}}$

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

${\text{U}}_{\text{AP2}}{\text{= U}}_{\text{EP}}{\text{- ΔU}}_{\text{P}}\text{.}$

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, ie 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. Such a pair of actuating units has the advantage that only half of that for each individual actuating unit is for the respective one The intended 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 when it comes to manufacturing, transport and spare parts storage.

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. This can be summarized in the following Table 1:

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

Preferably, however, in the case of a pair of actuating units, each of the two actuating units is designed in accordance with one of the above-described embodiments such that it can be brought into the third switching state on its own; you can see the above in every control unit mentioned current limiting circuit or current limiting circuits before, with the help of V-MOS transistor switches an extremely fast, in several steps switching from each switching state combination of the actuator pair in any other switching state combination can be carried out.

in die dritte Schaltzustands-Kombination ${\text{(U}}_{\text{AP3}}{\text{= U}}_{\text{EP}}\text{)}$

gebracht werden, so kann dies bei einem erfindungsgemäßen Stelleinheiten-Paar ohne Verzögerung dadurch geschehen, daß in beiden Stelleinheiten der Schalter geschlossen wird, durch dessen Schließen die Stelleinheit für sich allein in ihren dritten Schaltzustand gebracht wird, wie diesoben beschrieben wurde. Dadurch ergibt sich eine weitere Schaltzustands-Kombination, die hinsichtlich der Ausgangsspannung U_AP des Stelleinheiten-Paares mit der oben beschriebenen dritten Schaltzustands-Kombination äquivalent ist. Es gilt also auch hier ${\text{U}}_{\text{AP3}}{\text{' = U}}_{\text{EP}}$

. Diese Änderung der Ausgangsspannung um ΔU_P kann zu beliebigen Zeitpunkten erfolgen und die Ausgangsspannung geht praktisch unverzögert vom alten Spannungswert U_AP2 auf den neuen Spannungswert U_AP3' über.For example, if the pair of actuators from the second switching state combination is to be used ${\text{(U}}_{\text{AP2}}{\text{= U}}_{\text{EP}}{\text{- ΔU}}_{\text{P}}\text{)}$

into the third switching state combination ${\text{(U}}_{\text{AP3}}{\text{= U}}_{\text{EP}}\text{)}$

in a pair of actuating units according to the invention, this can be done without delay by closing the switch in both actuating units, the closing of which brings the actuating unit 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 it also applies here ${\text{U}}_{\text{AP3}}{\text{'= U}}_{\text{EP}}$

. 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.

in die weitere Schaltzustands-Kombination.The same applies to a transition of the pair of actuators from the first switching state combination ${\text{(U}}_{\text{AP1}}{\text{= U}}_{\text{EP}}{\text{+ ΔU}}_{\text{P}}\text{)}$

into the further switching state combination.

auf ${\text{U}}_{\text{AP3}}{\text{= U}}_{\text{EP}}$

über, ändert sich also praktisch nicht.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 favorable times in that the first switch is opened by opening the corresponding switch Actuating unit is brought into its first switching state and the second actuating unit into its second switching state. The output voltage of the pair of actuators goes from ${\text{U}}_{\text{AP3}}{\text{'= U}}_{\text{EP}}$

on ${\text{U}}_{\text{AP3}}{\text{= U}}_{\text{EP}}$

about, so practically does not change.

auf ${\text{U}}_{\text{E}}{\text{+ ΔU}}_{\text{P}}\text{/2}$

oder ${\text{U}}_{\text{P}}{\text{- ΔU}}_{\text{P}}\text{/2}$

über. Zum nächsten günstigen Zeitpunkt, der spätestens innerhalb der nächsten Halbperiode der Wechselspannung eintritt, wird dann die zweite oder die erste Stelleinheit aus dem dritten in den ersten oder den zweiten Schaltzustand gebracht, wodurch das Stelleinheiten-Paar in die erste bzw. zweite Schaltzustands-Kombination übergeht, in der ${\text{U}}_{\text{AP1}}{\text{= U}}_{\text{E}}\text{+}$

${\text{ΔU}}_{\text{P}}{\text{/2 + ΔU}}_{\text{P}}{\text{/2 bzw. U}}_{\text{AP2}}{\text{= U}}_{\text{E}}{\text{- ΔU}}_{\text{P}}{\text{/2 - ΔU}}_{\text{P}}\text{/2}$

gilt.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 pair of actuators changes instantaneously ${\text{U}}_{\text{AP3}}{\text{= U}}_{\text{E}}$

on ${\text{U}}_{\text{E}}{\text{+ ΔU}}_{\text{P}}\text{/ 2nd}$

or ${\text{U}}_{\text{P}}{\text{- ΔU}}_{\text{P}}\text{/ 2nd}$

about. 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 the ${\text{U}}_{\text{AP1}}{\text{= U}}_{\text{E}}\text{+}$

${\text{ΔU}}_{\text{P}}{\text{/ 2 + ΔU}}_{\text{P}}{\text{/ 2 or U}}_{\text{AP2}}{\text{= U}}_{\text{E}}{\text{- ΔU}}_{\text{P}}{\text{/ 2 - ΔU}}_{\text{P}}\text{/ 2nd}$

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 two actuating units are each converted into their second or their 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.

so werden die Spannungsdifferenzen der anderen Stufen so gewählt, daß sie in etwa gleich ± 3A%, ± 9A% usw. der Versorgungsspannung U_V sind.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 (in one arrangement also both types can be mixed), to connect in series and to select the voltage differences ± ΔU₁, ..., ± ΔU _n , which can generate n such stages, from each other. 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 with almost the supply voltage supplied 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 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 which form a pair, then, as an alternative to the arrangement just explained, only two switching state combinations can be used for each pair of actuating units Use is made, for example, of 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 lower than the input voltage by n · A%, where n is different for each pair of actuating units takes an 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 either results in a voltage change O or - n · A%. 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 U _V 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 one direction if there are deviations from the set value S _L 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 controller 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 ± δ%.

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)} - ie a fixed amplitude value of the supply voltage. If the positive deviation continues to decrease, the transition from the (n + 1) ⁻th combination to the n⁻th combination of switching states takes place in the opposite direction at approximately the same switching threshold. 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 additive impressions of (n + 1) times from A% must be achieved in order to achieve the desired constancy of the amplitude of the load voltage.

weiterhin gilt

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. U _{Lvor is} the amplitude of the load voltage before the switching process and U _{Lnach is} the amplitude of the load voltage after the switching process. The following should therefore apply with the best possible approximation:

${\text{| P}}_{\text{L}}{\text{- U}}_{\text{Lvor}}{\text{| = | S}}_{\text{L}}{\text{- U}}_{\text{Lnach}}\text{|}$

still applies

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 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 selection 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 target value S _L = 100%.

When determining the value of A, it must 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 δ will not can be observed. According to the invention, A is preferably chosen so that it is between 1.6 · δ and 1.8 · δ.

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 is therefore undertaken got to.

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 U _V 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-chained circuit.

Fig. 1

eine Transformatorschaltung, bei der zwischen Spannungsquelle und Last eine Stelleinheit angeordnet ist, die gemäß einer ersten Ausführungsform einen Transformator mit einer einzigen weiteren Wicklung besitzt, die zur ersten Wicklung parallelgeschaltet werden kann,

Fig. 2

eine Transformatorschaltung, bei der zwischen Spannungsquelle und Last eine Stelleinheit angeordnet ist, die gemäß einer zweiten Ausführungsform einen Transformator mit zwei weiteren Wicklungen besitzt, die miteinander in Reihe zur ersten Wicklung parallelgeschaltet werden können,

Fig. 3

den Aufbau einer Strombegrenzungsschaltung, wie sie bei den in den Fig. 1 und 2 wiedergegebenen Stelleinheiten Verwendung findet,

Fig. 4

ein Diagramm zur Erläuterung der Wahl der günstigsten Schaltzeitpunkte beim Übergang von einem Schaltzustand in einen anderen,

Fig. 5

eine als einphasiger Spannungskonstanter aufgebaute Transformatorschaltung mit drei in Reihe geschalteten Stufen, und

Fig. 6

eine weitere Ausführungsform eines Spannungskonstanters für ein 3-Phasen-System.

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

Fig. 1

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 further winding which can be connected in parallel with the first winding,

Fig. 2

a transformer circuit in which a control unit is arranged between the voltage source and the load, which according to a second embodiment has a transformer with two further windings which can be connected in parallel with one another in series with the first winding,

Fig. 3

the construction of a current limiting circuit, as used in the control units shown in FIGS. 1 and 2,

Fig. 4

1 shows a diagram to explain the selection of the cheapest switching times when changing from one switching state to another,

Fig. 5

a transformer circuit constructed as a single-phase voltage constant with three stages connected in series, and

Fig. 6

a further embodiment of a voltage constant for a 3-phase system.

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 control unit 4, 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 terminal 2 and the output terminal 5, while the input terminal 3 is directly electrically connected to the output terminal 6 by means of the connecting 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. 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. 3 .

With the help of the switches 150 to 153, the actuating unit 4 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 sense of the windings 9, 11 defined by the points 19, 20 is selected so that the voltage ΔU 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

${\text{U}}_{\text{A1}}{\text{= U}}_{\text{E}}\text{+ ΔU₁.}$

festgelegt.The absolute amplitude of the induced voltage ΔU₁ is the winding ratio w₁ / w _{w of} the first winding 9 to the further winding 11 according to the equation ${\text{ΔU₁ = w₁U}}_{\text{E}}{\text{/ w}}_{\text{w}}$

fixed.

Für die induzierte Spannung gilt in diesem Fall ${\text{ΔU₂ = w₁U}}_{\text{E}}{\text{/(w}}_{\text{w}}\text{+w₁)}$

. Es ist also die im zweiten Schaltzustand induzierte Spannung ΔU₂ etwas kleiner als die im ersten Schaltzustand induzierte Spannung ΔU₁.In the second switching state, which is shown in FIG. 1, 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 4 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 ΔU₂, which is induced in the first winding 9 of the transformer 8 in this second switching state, is subtracted from the input voltage U _E , so that the following are obtained at the output 5, 6:

${\text{U}}_{\text{A2}}{\text{= U}}_{\text{E}}\text{- ΔU₂}$

In this case applies to the induced voltage ${\text{ΔU₂ = w₁U}}_{\text{E}}{\text{/ (w}}_{\text{w}}\text{+ w₁)}$

. It is therefore the voltage ΔU₂ induced in the second switching state somewhat smaller than the voltage ΔU₁ induced in the first switching state.

In a third switching state of the actuating unit 4, 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 switching 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

${\text{U}}_{\text{A}}{\text{= U}}_{\text{E}}\text{.}$

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, for example from the second switching state shown in FIG. 1 to the first switching state, the switches 151, 152 must first be opened, and that 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 one uses triacs as a switch, would only be possible at zero crossing of the current flowing through them, and then 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. It enables the setting unit 4 to be brought into the third switching state first, in a switching process by which the setting unit is to be switched from the second switching state shown in FIG. 1, for example, 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 that the actuating unit 4 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 4 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 4 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. 1) which compares the load voltage U _L and / or the supply voltage U _V with setpoints and outputs corresponding difference signals in the event of deviations. Furthermore, the transformer 8 of the actuating unit 4 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 4 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. 3.

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 aid of triacs, this opening process must be used 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.

2 shows a transformer circuit with an actuating unit 34, the structure of which differs from that of the actuating unit 4, but which in principle has the same functions.

The actuating unit 34 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 connection connecting conductor 10 is directly electrically connected to the other output terminal 6.

In contrast to the actuating unit 4 in FIG. 1, the transformer 8 here has two further windings 35, 36, one 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 with the Input terminal 2 is directly electrically conductively connected, 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 34, 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 chosen so that the voltage ΔU₁, which is induced by the further winding 35 when the switch 180 is closed in the first winding 9, is added to the input voltage U _E (first switching state), and that the voltage ΔU₂, when the switch is closed 181 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. 2 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 with the same winding sense are connected in series with one another and with an anti-parallel winding sense first winding 9 are connected in parallel. Since in this switching state the two further windings 35, 36 can be regarded as a single winding, the same switching state is obtained as that described above as the third switching state of the actuating unit 4 from FIG. 1, and the input voltage U _E is also shown 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 is absolutely certain that switches 180 and 181 are closed at the same time 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 34 can also be brought into a fourth switching state, as shown in FIG. 2. 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.

nicht mehr notwendigerweise symmetrisch zur Eingangsspannung U_E liegen müssen.In addition, the embodiment shown in Fig. 2 offers the possibility to choose ΔU₁ independently within certain limits of ΔU₂, so that here the two output voltages ${\text{U}}_{\text{A1}}{\text{= U}}_{\text{E}}{\text{+ ΔU₁ and U}}_{\text{A2}}{\text{= U}}_{\text{E}}\text{- ΔU₂}$

no longer necessarily have to be symmetrical to the input voltage U _E.

Switching from the first to the second or from the second to the first switching state takes place 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 34 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 like 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 34 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 34 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 34 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 34 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 34 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 that are used overall as voltage constants, at least the other control units remain functional and the entire transformer circuit can maintain its control 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 according to the invention, it would remain in the first or second switching state at all times. Assuming that, for example, switch 180 is permanently closed, the current limiting circuit may be present 157 in all cases in which no additive impressing 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 34 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 34 is kept permanently in the third switching state which results in this way.
• 5. Line interruption in one of the switches 180 or 181
  If one of the two switches 180, 181 can no longer be closed, then whenever the other switch has to be opened, the strong throttling effect of the winding 9 formed above would occur. 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 34 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 setting unit 4 shown in FIG. 1 and, due to their construction according to the invention, can be partially overcome in a similar manner to that just described. Of course, a fuse 167 can also be provided in the setting unit 4 shown in FIG. 1, which is connected in series with the current limiting circuit 157.

3 shows a current limiting circuit 157, as can be used in the actuating units 4, 34 in FIGS. 1 and 2.

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 such that their forward directions are parallel to the forward direction of the diodes 198 and 199 lying in the parallel branch and thus opposed to one another. 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 4 and the actuating unit 34 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.

In Fig. 4 are shown in a diagram 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 I 1 flowing in the first switching state and the current I 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 4 or 34 can only ever be in one of the three switching states.

For the following considerations, it is now assumed that the control unit 4 or 34 is in the third switching state, from which during the first half period of the input voltage U _E shown in FIG. 4, ie between the times t 1 and t 1, the transition is made into the first switching state should.

For this purpose, switch 151 must be opened in the embodiment according to FIG. 1 and switch 181 in the embodiment according to FIG. 2. Since these switches are traversed by the short-circuit current I _K , they can, if they are implemented with the help of triacs, only be opened at the time t₄ in which the short-circuit current I _K passes through a zero crossing. 4 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 switches, has a value which is equal to the zero crossing value of the short-circuit current I _K which has 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 _E through the further winding 11 or 35. Since the transformer 8 is dimensioned so that the current that 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 _A 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 Figure 4, the optimal switching times would be the times t₂ or t₃, because in them the short-circuit current I _K , which flows in the other windings in question before switching, is equal to the current after the switching process in the respective other Winding should flow.

Since these ideal times t₂ and t₃ are very difficult to measure technically, they can be replaced approximately by the times t₂ 'or t₃', in which the current that flows through the further winding in the first or in the second switching state, one Has zero crossing. These replacement times t₂ 'and t₃' are not too far away from the ideal times t₂ and t₃. Since, as already mentioned, the Amplitude of I _K in Fig. 4 is shown greatly exaggerated, the current change required when using the replacement times t₂ 'or t₃' is not particularly large.

Since the time intervals τ₁ and τ₂, which have the replacement times t₂ 'and t₃' 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 actuating unit 4 or 34 is in the first or second switching state, and the measured values are stored. If the next switch from the third switching state to the first or second switching state is to be made, the switching time t₂ 'or the switching time t₂' or, starting from the time which has elapsed since the zero crossing t 1 of the input voltage U _E and which the switching process is to follow. the switching time t₃ '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.

Should an actuator, which is equipped with V-MOS transistor switches and a current limiting circuit 157 and which impresses a voltage change + ΔU on 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 voltage change 2 ΔU occurring in total 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 t₂ 'or t₃' 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 fast and precise switchover occurs when two of the actuating units 34 described above are connected in series to form a pair of actuating units.

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%. Furthermore, it is assumed that the supply voltage U _V supplied by the AC voltage source 1 can deviate in amplitude by ± Δ% from the nominal value U _Vnom . In principle, the setpoint S _L the load voltage U _{L is} equal to the nominal value U _{Vnom 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, between the voltage source 1 and the load 7, a transformer circuit according to the invention is provided, which consists of three stages 55, 56, 57 connected in series with one another, each of which either from an actuating unit 4 or 34, according to FIG. 1 or from can be formed a pair of actuators, which is composed of two actuators 34, 34 'according to FIG. 2. 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 or an actuating unit pair 34, 34 ', these line pairs symbolize the lines 158, 159, 160, 161 and 30 (see FIG. 1), lines 163, 164, 165 and 30 (see FIG. 2), or twice lines 163, 164, 165 and 30 (see FIG. 2).

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. Via the 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 from the target value S _L from the original. Before this deviation runs out of the permissible range ± δ%, the switch control 23 changes the switching states of the 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%. In addition, a second comparator 66 is provided which _{compares a} reference _voltage U _ref2 corresponding to the nominal value U _{Vnom of} the supply voltage U _V with the output signal of a second sensor 67 which measures this supply voltage U _V. 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 when U _L = 0, the switch control can recognize the fault from the fact that U _{V 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.

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 approximately ± 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 approximately ± 9A% or pass it on almost unchanged.

For an embodiment in which each stage 55, 56, 57 is formed by a pair of actuators 34, 34 ', this is shown in more detail in Table 3 for the case that ± A% ≈ ± 1% is selected so that there is a possible amplitude change of approximately ± 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 approximately ± 9% for the actuator unit pair of the foremost stage 55.

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 34 can effect a change of + 4.5%, while the subtracting winding can bring about a change of - 4.9%, and the additive or subtracting one Winding the actuator 34 'can apply a change of + 4.4% or - 4.2% to the input voltage of this rear actuator 34' of level 55.

These percentages are selected by a corresponding choice of the turns 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 throttling effect on the relevant first turns of these two actuating units 34, 34 '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.

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 actuator 34, 34 'of the three actuator pairs whether the additive or the subtracting winding is connected to the associated input or output voltage. A "1" means that the further winding in question is connected to the associated voltage, while a "0" indicates that the winding by opening the relevant switch 180, 181 or 180, 181 'from the connection connecting conductor 10 (see. Fig. 2) 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 = 0, all three pairs of actuating units are in the state just described and one can see from the right-hand column in 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 here} .

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.Assuming that the deviation ± δ% 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 lowered supply voltage U _V 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.

die obere Grenze 100,5% des zulässigen Bereichs übersteigt.For the switching state combination n = 13⁻ 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, preferably one always switches from one switching state combination to the next 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. 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%.

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 of A, 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 subtractively, the required fluctuation range ± Δ 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. Each of these therefore exists 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 34, 34 '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, 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 and 2. 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 multi-phase systems which comprise fewer or more than three phases.

Claims (36)

1. A transformer circuit for producing an adjustable load voltage at a load from a supply voltage which is delivered by a voltage source, comprising at least one adjusting unit which includes the following components:

   - a transformer having a first winding which is disposed in series with the load, and at least one further winding, the turns ratio of which with respect to the first winding is greater than 1,

   - a terminal connecting conductor which is arranged downstream of the load as viewed from the first winding of the transformer and is in series with the load, and

   - switches by means of which the adjusting unit can be switched over between different switching states, wherein in at least one of said switching states applied to a further winding is a control ac voltage which induces in the first winding a voltage which is impressed on the input ac voltage in such a way that the amplitude of the output ac voltage differs from the amplitude of the input ac voltage by the amplitude of the induced voltage, and in a neutral switching state a further winding is switched into circuit in such a way that the output voltage of the adjusting unit is equal to the input voltage,
   characterised in that in the neutral switching state by means of the switches (150, 151; 180, 181) the at least one further winding (11; 35, 36) is connected into a current path (150, 11, 151; 35, 180, 185, 181, 36) which is disposed electrically in parallel with the first winding (9) of the transformer (8).
2. A transformer circuit according to claim 1 wherein the transformer (8) includes a single further winding (11), characterised in that the adjusting unit (4) can be put into the two following switching states by means of the switches (150, 151, 152, 153):

   - an adding (first) switching state in which the further winding (11) is applied to the input voltage (U_E) of the adjusting unit (4) with a sense of winding such that the voltage (ΔU₁) induced thereby in the first winding (9) is additively impressed on the input voltage (U_E), and

   - a subtracting (second) switching state in which the further winding (11) is applied to the output voltage (U_A) of the adjusting unit (4) with a sense of winding such that the voltage (ΔU₂) induced thereby in the first winding (9) is subtractively impressed on the input voltage (U_E),
   and that to produce the neutral (third) switching state the two ends (13, 14) of the further winding (11) can be connected by means of first and second switches (150, 151) to the two ends of the first winding (9).
3. A transformer circuit according to claim 2 characterised in that the two ends (13, 14) of the further winding (11) can be connected to the terminal connecting line (10) by way of a third switch (152) and a fourth switch (153) respectively and that the third and fourth switches (152, 153) are each in the form of a current limiting circuit in such a manner that in the closed condition they oppose only a low constant resistance to the current flowing through them as long as that current is less than a predetermined limit value and that said limit value is selected to be somewhat greater than the current which flows through the further winding (11) in the first or second switching state.
4. A transformer circuit according to claim 2 characterised in that the two ends (13, 14) of the further winding (11) can be directly galvanically conductively connected to a further conductor (155) by way of a third switch (152) and a fourth switch (153) respectively and that provided between the further electric conductor (155) and the terminal connecting conductor (10) is a current limiting circuit arrangement (157) which electrically conductively connects together the two conductors (155, 10).
5. A transformer circuit according to claim 4 characterised in that the current path (152, 155, 153) which connects together the two ends (13, 14) of the further winding (11) when the third and fourth switches (152, 153) are closed at the same time has an electrical resistance which is greater than the ohmic resistance of the further winding (11).
6. A transformer circuit according to claim 1 characterised in that the transformer (8) includes two further windings (35, 36) of which the one is constantly connected as an adding winding (35) by its first end to the input terminal (2) of the adjusting unit (34), to which terminal the first winding (9) is connected, while the other of said two further windings is constantly connected as a subtracting winding (36) by its first end to the output terminal (5) of the adjusting unit (34), to which terminal the first winding (9) is connected, wherein the adjusting unit can be put into the following switching states by means of the switches (180, 181):

   - an adding (first) switching state in which only the adding further winding (35) is connected by its second end to the terminal connecting conductor (10) whereby induced in the first winding (9) is a voltage (ΔU₁) which is added to the input voltage (U_E), and

   - a subtracting (second) switching state in which only the subtracting further winding (36) is connected by its second end to the terminal connecting conductor (10) whereby induced in the first winding (9) is a voltage (ΔU₂) which is subtracted from the input voltage (U_E), and that in the neutral (third) switching state the two second ends of the two further windings (35, 36) are directly galvanically conductively connected to each other.
7. A transformer circuit according to claim 6 characterised in that the two switches (180, 181) by which the two ends of the two further windings (35, 36) can be connected to the terminal connecting conductor (10) are directly galvanically conductively connected together by a further electric conductor (185) and that provided between said conductor (185) and the terminal connecting conductor (10) is a current limiting circuit arrangement (157) which electrically conductively connects the two conductors (185, 10) together.
8. A transformer circuit according to one of claims 4, 5 and 7 characterised in that the circuit arrangement (157) is a switch which is closed in the first and second switching states of the adjusting unit (4, 34) and which is opened in the third switching state.
9. A transformer circuit according to one of claims 4, 5 and 7 characterised in that the circuit arrangement (157) is a current limiting circuit which opposes a low constant resistance to the current flowing through it as long as said current is less than a predetermined limit value and that the limit value is selected to be somewhat greater than the current which flows in the first or second switching state through the respective further winding (11; 35, 36) connected to the control voltage.
10. A transformer circuit according to claim 3 or claim 9 characterised in that the limit value of the current limiting circuit is variable.
11. A transformer circuit according to claim 10 characterised in that for periods of time in which the adjusting unit is disposed for a longer period in the third switching state the current limiting circuit can be switched over to a second limit value which is substantially lower than the first limit value.
12. A transformer circuit according to claim 11 characterised in that the second limit value is equal to zero.
13. A transformer circuit according to claim 3 or one of claims 9 to 12 characterised in that the current limiting circuit regulates the current flowing therethrough, as it approaches the limit value, with a steady transition to said limit value.
14. A transformer circuit according to claim 3 or one of claims 9 to 13 characterised in that the current limiting circuit (157) comprises two V-MOS-transistors (190, 191) whose source/drain paths are connected in series with mutually opposite polarities, and two resistors (192, 193) which are connected to each other and to the source/drain paths of the two transistors (190, 191) in series between the two transistors (190, 191), and that the gate voltage for the two transistors (190, 191) is applied to the connection point (195) of the two resistors (192, 193) and the respective gate terminal.
15. A transformer circuit according to claim 14 characterised in that the current limiting circuit (157) comprises two diodes (198, 199) which are connected with mutually opposite polarities in series between the two current terminals (187, 188) of the current limiting circuit (157) and whose connection point (196) is electrically conductively connected to the connection point (195) of the two resistors (192, 193), wherein the forward direction of each diode (198, 199) is the same as the permanent forward direction of the V-MOS-transistor (190, 191) disposed in the respective parallel branch.
16. A transformer circuit according to one of the preceding claims characterised in that the turns ratio of each further winding (11; 35, 36, 35', 36') of the transformer (8) relative to the first winding (9) is in a range of from 3:1 to 200:1.
17. A transformer circuit according to one of the preceding claims characterised in that the transformer circuit comprises at least two stages (55, 56, 57)each of which comprises at least one adjusting unit (4; 34; 34, 34') and which are so connected together in series that the output ac voltage (U_A) of the upstream stage (55, 56) is the input ac voltage (U_E) of the downstream stage (56, 57) and that the at least two first windings (9) of the transformers (8) of the at least two stages (55, 56, 57) are directly disposed in series with each other.
18. A transformer circuit according to claim 17 characterised in that each stage (55, 56, 57) includes at least two adjusting units (34, 34') which form an adjusting unit pair, wherein the turns ratios of the respective first windings (9, 9') with respect to the associated further windings (35, 36, 35', 36') are so matched to each other that the output voltage (U_AP) of the adjusting unit pair (34, 34') is equal to the input voltage (U_EP) of the adjusting unit pair (34, 34') when one (34) of the adjusting units additively impresses an induced voltage (ΔU₁) on its input voltage (U_EP) and the other adjusting unit (34') subtractively impresses an induced voltage (ΔU₂) on its input voltage (U_E).
19. A transformer circuit according to claim 18 characterised in that the absolute values of the amplitude differences which can be produced at least by some of the stages (55, 56, 57) are related to each other in a relationship of integral powers of three 1:3:9: etc.
20. A circuit arrangement comprising a transformer circuit according to one or more of claims 17 to 19 characterised in that there are provided an ac measuring sensor arrangement (64, 67; 81), a comparator arrangement (63, 66; 82) for comparing the output signals of the measuring sensor arrangement to reference values U_ref1, U_ref2, U_ref), and a switch control means (23; 83) by which the switches of the stages (55, 56, 57) can be selectively actuated so that the load (7) is supplied with a load voltge (U_L) at an amplitude which is as constant as possible.
21. A circuit arrangement according to claim 20 characterised in that the measuring sensor arrangement comprises a measuring sensor (67; 81) which measures the supply voltage (U_V) outputted by the voltage source (1; 80), and/or a measuring sensor (64) which measures the load voltage (U_L).
22. A circuit arrangement according to one of claims 20 and 21 characterised in that for each of the phase conductors (R, S, T) of a multi-phase system there are provided a transformer circuit (75, 76, 77) with one or more stages (55, 56, 57), a measuring sensor arrangement (81) for measuring the voltage on each of the phase conductors (R, S, T or R_K, S_K, T_K), a comparator arrangement (82) for comparing the output signals of the measuring sensor arrangement (81) to at least one reference value (U_ref), and a switch control means (83) which controls the switches of the stages (55, 56, 57) of all transformer circuits (75, 76, 77) on the basis of the difference signals outputted by the comparator arrangement (82).
23. A transformer circuit for a multi-phase system with neutral conductor according to one of the preceding claims characterised in that for each phase it includes at least one adjusting unit (4; 34) whose first winding (9) is disposed in the respective phase conductor and whose terminal connecting conductor (10) is connected to the neutral conductor of the multi-phase system.
24. A transformer circuit for a multi-phase system without neutral conductor according to one of Claims 1 to 22 characterised in that for each phase it includes at least one adjusting unit (4; 34) whose first winding (9) is disposed in the respective phase conductor and that the terminal connecting conductors (10) of all adjusting units are connected together to form an artificial neutral conductor.
25. A transformer circuit for a multi-phase system without neutral conductor according to one of claims 1 to 22 characterised in that for each phase it includes at least one adjusting unit (4; 34) and that the adjusting units belonging to different phases are arranged in a linked circuit, wherein for each adjusting unit the first winding is in the associated phase conductor and the terminal connecting conductor (10) is formed by one of the other phase conductors.
26. A method of switching over a transformer circuit which, for producing an adjusting load voltage at a load from a supply voltage delivered by a voltage source, has at least one adjusting unit which comprises the following components:

    - a transformer with a first winding disposed in series with the load and with at least one further winding, the turns ratio of which is greater than 1 relative to the first winding,

    - a terminal connecting conductor which is arranged downstream of the load as viewed from the first winding of the transformer and which is in series with the load, and

    - switches by means of which the adjusting unit can be switched over between different switching states, wherein in at least one of said switching states applied to a further winding is a control ac voltage which induces in the first winding a voltage which is impressed on the input ac voltage in such a way that the amplitude of the output ac voltage differs from the amplitude of the input ac voltage by the amplitude of the induced voltage, and in a neutral switching state a further winding can be switched into circuit so that the output voltage of the adjusting unit is equal to the input voltage, characterised in that in the neutral switching state by means of the switches (150, 151; 180, 181) the at least one further winding (11; 35, 36) is connected into a current path (150, 11, 151; 35, 180, 185, 181, 36) which is disposed electrically in parallel with the first winding (9) of the transformer (8).
27. A method according to claim 26 for a transformer circuit having an adjusting unit (4) in which the transformer (8) includes a single further winding (11), characterised in that the adjusting unit (4) can be put into the two following switching states by means of the switches (150, 151, 152, 153):

    - an adding (first) switching state in which the further winding (11) is applied to the input voltage (U_E) of the adjusting unit (4) with a sense of winding such that the voltage (ΔU₁) induced thereby in the first winding (9) is additively impressed on the input voltage (U_E), and

    - a subtracting (second) switching state in which the further winding (11) is applied to the output voltage (U_A ) of the adjusting unit (4) with a sense of winding such that the voltage (ΔU₂) induced thereby in the first winding (9) is subtractively impressed on the input voltage (U_E),
    and that to produce the neutral (third) switching state the two ends (13, 14) of the further winding (11) are connected by means of first and second switches (150, 151) to the two ends of the first winding (9).
28. A method according to claim 27 characterised in that the two ends (13, 14) of the further winding (11) can be connected to the terminal connecting conductor (10) by way of a third switch (152) and a fourth switch (153) respectively and that the third and fourth switches (152, 153) are each in the form of a current limiting circuit in such a manner that in the closed condition they oppose only a low constant resistance to the current flowing through them as long as that current is less than a predetermined limit value, that said limit value is selected to be somewhat greater than the current which flows through the further winding (11), in the first or second switching state, that the transition from the first to the second or from the second to the first switching state is effected, in each case with the temporary interposition of the third switching state, in that in 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 opened, into 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 opened, firstly the second switch (151) and the third switch (152) are closed and then the first switch (150) and the fourth switch (153) are opened, and that in the transition from the second to the first switching state, firstly the first switch (150) and the fourth switch (153) are closed and then the second switch (151) and the third switch (152) are opened.
29. A method according to claim 27 characterised in that the third and fourth switches (152, 153) are directly galvanically conductively connected together by a further electric conductor (155), that provided between the further electric conductor (155) and the terminal connecting conductor (10) is a current limiting circuit arrangement (157) which electrically conductively connects the two conductors (155, 10) together and that the transition from the first to the second or from the second to the first switching state is effected, in each case with the temporary interposition of the third switching state, in that in the transition from the first switching state into the second switching state firstly 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 in the transition from the second to the first switching state firstly the first switch (150) is closed, then the third switch (152) is opened, then the fourth switch (153) is closed and then the second switch (151) is opened, so that the third and fourth switches (152, 153) are never simultaneously closed.
30. A method according to claim 26 for a transformer circuit comprising an adjusting unit (34) in which the transformer (8) includes two further windings (35, 36) of which the one is constantly connected as an adding winding (35) by its first end to the input terminal (2) of the adjusting unit (34), to which terminal the first winding (9) is connected, while the other of said two further windings is constantly connected as a subtracting winding (36) by its first end to the output terminal (5) of the adjusting unit (34), to which terminal the first winding (9) is connected, characterised in that the adjusting unit can be put into the following switching states by means of the switches (180, 181):

    - an adding (first) switching state in which only the adding further winding (35) is connected by its second end to the terminal connecting conductor (10) whereby induced in the first winding (9) is a voltage (ΔU₁) which is added to the input voltage (U_E), and

    - a subtracting (second) switching state in which only the subtracting further winding (36) is connected by its second end to the terminal connecting conductor (10) whereby induced in the first winding (9) is a voltage (ΔU₂) which is subtracted from the input voltage (U_E), and that in the neutral (third) switching state the two second ends of the two further windings (35, 36) are directly galvanically conductively connected to each other.
31. A method according to claim 30 characterised in that the two switches (180, 181) by which the two ends of the two further windings (35, 36) can be connected to the terminal connecting conductor (10) are directly galvanically conductively connected together by a further electric conductor (185), that provided between said conductor (185) and the terminal connecting conductor (10) is a current limiting circuit arrangement (157) which electrically conductively connects the two conductors (185, 10) together, that in the transition from the first switching state in which the switch (180) which is connected to the second end of the adding further winding (35) is closed and the switch (181) which is connected to the second end of the subtracting further winding (36) is opened into the second switching state in which the switch (180) which is connected to the second end of the adding further winding (35) is opened and the switch (181) which is connected to the second end of the subtracting further winding (36) is closed, firstly the switch (181) for the subtracting winding (36) is closed and thereafter the switch (180) for the adding winding (35) is opened, and that in the transition from the second to the first switching state firstly the switch (180) for the adding winding (35) is closed and thereafter the switch (181) for the subtracting winding (36) is opened.
32. A method according to one of claims 26 to 31 characterised in that the switches (150, 151, 152, 153; 180, 181) used are electronic switches which can be closed and opened at any times and that the switches which must 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 at which the current which flows in the third switching state through the further winding (11; 35, 36) which is connected to its corresponding control voltage after the transition into the first or second switching state respectively is of the same value as the current which flows in said further winding (11; 35, 36) immediately after the switching operation.
33. A method according to claim 32 characterised in that used as an approximation for the ideal switching times are the times for opening of the switches at which the current which flows in the first or second switching state through the further winding (11; 35, 36) which in that switching state is connected to its corresponding control voltage has a passage through zero.
34. A method according to claim 33 characterised in that the time interval of a passage through zero of the current which in the first or second switching state flows through the further winding (11; 35, 36) which in that switching state is connected to its respective control voltage, from the preceding or in relation to the subsequent passage through zero of said control voltage is measured and the measurement value is stored, and that in later transitions from the third to the first or the second switching state said stored measurement value is used in order to determine the time for opening of the respective switches, beginning with a passage through zero of the control voltage.
35. A method according to one of claims 26 to 34 for a transformer circuit which includes at least two stages of which each comprises at least one adjusting unit and which are so connected together in series that the output ac voltage of the upstream stage is the input ac voltage of the downstream stage, wherein the at least two first windings of the transformers of the at least two stages are disposed directly in series with each other, and wherein there are provided an ac voltage measuring sensor arrangement, a comparator arrangement for comparing the output signals of the measuring sensor arrangement with reference values, and a switch control means by which the switches of the stages can be selectively actuated so that the load receives a load voltage at an amplitude which is as constant as possible, characterised in that the absolute value of the smallest possible variation (A) in amplitude is between 1.0 times and 2.0 times the absolute value of the admissible deviation (δ) of the load voltage (U_L) from the desired value (S_L), and that the switching thresholds at which, with an increasing deviation in respect of the supply voltage (U_V) which is outputted by the voltage source from the nominal ac voltage, the impressed amplitude difference is switched over from n-times the smallest possible change (A) in amplitude to (n+1)-times, and with a decreasing deviation it is switched over from (n-1)-times to n-times, are so selected that the amplitude values of the load voltage (U_L) with a steady passage of the supply voltage (U_V) through the respective switching threshold, lie symmetrically relative to the desired value (S_L) before and after the switching-over operation.
36. A method according to claim 35 characterised in that the load voltage (U_L) is regulated to a desired value (S_L) which is different from the nominal value (U_Vnenn) of the supply voltage (U_V).

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