WO2015086416A1

WO2015086416A1 - Cycloconverter having reactive-power reduction by using zero-voltage components

Info

Publication number: WO2015086416A1
Application number: PCT/EP2014/076481
Authority: WO
Inventors: Peter Stark; Oliver Reimann
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-12-11
Filing date: 2014-12-04
Publication date: 2015-06-18
Also published as: DE102013225598A1; AR098683A1

Abstract

The invention relates to a cycloconverter (4) having a number of first converter groups (6), which in turn each have a number of line-commutated first power converters (7). The first power converters (7) are designed at least as bipolar B6 groups and are connected to a first winding group (2) of a three-phase machine (1). The number of first power converters (7) per first converter group (6) corresponds to the number of phases of the first winding group (2). The first power converters (7) of at least one of the first converter groups (6) have a common first star point (8). The cycloconverter (4) has a common control device (10) that controls the first converter groups (6). The control device (1) receives a target control (S*) and determines respective first commutation signals (K1) for the first power converters (7) on the basis of the target control (S*). The control device (10) statically or dynamically determines a first zero-voltage component (N1) at least for some target controls (S*) on the basis of an optimization criterion (OK), which first zero-voltage component is taken into account in the determination of the first commutation signals (K1). The control device (10) transmits the first commutation signals (K1) to the first power converters (7).

Description

description

Direct converter with reactive power reduction using zero voltage components

The present invention relates to a cycloconverter,

wherein the direct converter has a number of first converter groups,

wherein the first converter groups each have a number of line-commutated first power converters,

wherein the first power converters are each formed at least as bipolar B6 groups and are connected to a first winding group of a three-phase machine,

wherein the number of first power converters per first converter group corresponds to the number of phases of the first winding group,

wherein the first power converters of at least one of the first converter groups have a common first neutral point,

wherein the direct converter has a common control device controlling the first converter groups,

- Wherein the control device accepts a setpoint drive and determined based on the setpoint drive for the first power converter respective first commutation signals and transmitted to the first power converter.

Direct drives are well known. They convert an input-side multiphase AC voltage directly into an output-side multiphase AC voltage. By way of example, reference is made to DE 44 39 760 A1. The number of

Phases of the input side and the output side AC voltage may be the same or different from each other. At least, however, there are three phases each. This embodiment also represents the rule that is far more prevalent in practice.

Mains-controlled converters have a high reactive power requirement and a high current. This leads to correspondingly high network repercussions and, correspondingly, to increased losses in energy transmission. Although this is not only true, but also applies to direct converters that are constructed with line-commutated power converters. For example, the reactive power demand is particularly high in the following operating states:

- when starting up ore mills under full load,

during jogging and positioning of ore mills under load,

- when trimming cables in conveyors,

during acceleration of the load in carriers,

- when emptying conveyor belts at reduced speed in the event of failure of one of several drives,

- for scaffold drives in rolling mills, such as cold rolling mills,

- For reel drives in rolling mills, especially in the case that a large train is to be applied at a high winding diameter at a standstill.

In DC drives it is known to operate the drive with a converter group having two series-connected line-commutated converters. To reduce the reactive power requirement, the two power converters are in supply and

Operated counter-modulation. Depending on the design and operating point, this can significantly reduce the reactive power requirement - in extreme cases by up to 50%. In today's usual control method for power converters, the ignition commands for the individual thyristors of the relevant power converter are generated by a respective tax rate associated with the respective power converter. The specification of the ignition commands by the respective headset causes a proper commutation within the thyristors of the respective power converter. With such control methods, the input and output modulation is only used for direct conversion. ruled with 12pulsiger series circuit in a loop current-carrying circuit with suction throttles.

The advantages of a reduction in reactive power by means of supply and counter control with the current control methods for line-commutated current converters are thereby offset by the disadvantages. For example, increased network harmonics occur. Furthermore, there are additional non-linearities in the converter due to the change between 12-pulse and 6-pulse system feedback, which depends on the modulation factor. Furthermore, an increased effort to avoid or to control saturation effects in the suction throttles is required. Due to these disadvantages, the input and output modulation for the reduction of reactive power consumption is hardly mastered in practice and hardly used.

In the prior art, the reactive power demand is usually compensated by means of compensation systems. The compensation systems, however, result in increased costs and increased costs.

The object of the present invention is to provide possibilities by means of which the reactive power requirement of a cyclo-converter can be reduced without having to accept the above-mentioned disadvantages of the prior art.

The object is achieved by a direct converter with the features of claim 1. Advantageous embodiments of the cycloconverter according to the invention are the subject of the dependent claims 2 to 10.

According to the invention, a direct converter of the type mentioned in the introduction is configured in that the control device determines, at least for some setpoint drives, statically or dynamically a first zero voltage component based on an optimization criterion, and the first commutation signals determined taking into account the first zero voltage component.

Various embodiments are possible for implementing the principle according to the invention. For example, it is possible for the control device to determine the first zero-voltage component such that within the first converter group having the common first star point, that first power converter in which the magnitude of the current delivered to the three-phase machine is greatest is as close as possible to the rectifier limit is operated. The term "rectifier limit" is a fixed term with clear meaning for a specialist in the field of converters and power converters and therefore does not need to be explained in more detail.

Alternatively, it is possible for the control device to determine the first zero voltage component in such a way that within the first converter group having the common first neutral point that first power converter in which the current delivered to the three-phase machine and / or the voltage applied to the three-phase machine is the most positive , is operated as close to the rectifier limit. Alternatively again, it is possible for the control device to determine the first zero voltage component in such a way that within the first converter group having the common first star point the first power converter in which the current delivered to the three-phase machine and / or the voltage applied to the three-phase machine is the most negative, is operated as close to the rectifier limit.

In order to realize the abovementioned possible embodiments of the principle according to the invention, only a single converter group-hitherto and also referred to below as the first converter group-is required. However, there are also cycloconverters which have more than one converter group, ie in addition to the first converter group. at least one second converter group. In this case, the cycloconverter according to the invention can additionally be configured by

- that the cyclo-converter has a number of second converter groups,

- That the second converter groups each have a number of network-controlled second power converters,

- That the second power converters are each formed at least as a bipolar B6 group and are connected to a winding group of the three-phase machine,

that the number of second power converters per second converter group corresponds to the number of phases of the first winding group,

in that the second power converters of at least one of the second converter groups have a common second neutral point,

- That the control device determined based on the target drive for the second converter respective second commutation signals and transmitted to the second power converter and

- That the control device for those Sollansteuerungen where it determines the first zero voltage component, based on the optimization criterion statically or dynamically also determines a second zero voltage component and determines the second Kommutierungssignale taking into account the second zero voltage component.

The winding group of the three-phase machine to which the second power converters are connected may be identical to the first winding group. Alternatively, it is possible that the winding group of the three-phase machine to which the second power converters are connected is a second winding group of the three-phase machine different from the first winding group. In this latter case, the number of phases of the second winding group corresponds to the number of phases of the first winding group. In the case of the presence of the at least one second converter group, an embodiment of the cyclo-converter is possible in particular because the control device

the first zero voltage component is determined such that, within the first converter group having the common first star point, the first power converter in which the current delivered to the three-phase machine and / or the voltage applied to the three-phase machine is most positive is operated as close as possible to the rectifier limit, and

- Determines the second zero voltage component such that within the common second star point having the second converter group that second power converter, in which the output to the three-phase machine current and / or the voltage applied to the three-phase machine voltage are the most negative, is operated as close to the rectifier limit.

There are various possibilities for determining the first zero voltage component. At present, it is preferred that the control device determines the first zero voltage component such that a ripple of a reactive power consumption of the direct converter from a three-phase network supplying the direct converter is minimized or assumes a predetermined value. This embodiment can be implemented as an alternative or in addition to the embodiments already mentioned above.

The optimization criterion can be determined as needed. For example, it may be determined such that network harmonics are reduced, reactive power is reduced, and / or flicker is reduced.

It is possible that the optimization criterion of the control device is fixed. Preferably, however, the control device accepts the optimization criterion from the outside. As a result, a particularly flexible operation of the cycloconverter according to the invention is possible. As a rule, the control device is designed as a programmable device. The object is therefore further achieved according to claim 11 by a control program for a programmable controller of a direct converter according to the invention, wherein the control program comprises machine code, wherein the execution of the machine code causes the cycloconverter is designed according to the invention. In particular, the control program can be stored on a data medium-for example a USB memory stick, an SD memory card or an internal memory of the control device-in machine-readable form.

The term "programmable device" may be understood to mean a processor-controlled device whose processor executes the control program sequentially. However, the term "programmable device" is not limited to this embodiment. It also comprises a device which, in addition to a processor or alternatively to a processor, more comprises programmable logic devices such as, for example, FPGAs, PLAs and the like. Likewise, the term "control program" is to be understood not only in terms of a sequentially processed program, but rather the term "control program" may comprise, in addition to or as an alternative to a sequentially executable program code, corresponding codes for programmable logic devices.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which will be described in more detail in conjunction with the drawings. These show in a schematic representation: FIG 1 to 3 different possible embodiments of a

Direct drive and a three-phase electrical machine, 4 to 6 different possible embodiments of

Power converters and

FIGS. 7 and 8 are flowcharts. According to FIG. 1, a three-phase machine 1 has a first winding group 2. The first winding group 2 has - according to the number of phases of the three-phase machine 1 - a number of first windings 3. In general, the three-phase machine 1 is formed in three phases. In this case, according to the illustration in FIG. 1, three first windings 3 are present. The first windings 3 of the first winding group 2 are interconnected according to FIG. 1 in a star connection. So they have a common first star point 15. Alternatively, the first windings 3 could be interconnected in a delta connection.

The three-phase machine 1 is connected via a direct converter 4 to a three-phase network 5. As a rule, the three-phase machine 1 acts by motor. In principle, however, a reverse flow of energy from the three-phase machine 1 in the three-phase network 5 is possible. In this case, the three-phase machine 1 acts as a generator.

In the embodiment according to FIG. 1, the direct converter 4 has a single converter group 6, hereinafter referred to as the first converter group 6. The first converter group 6 has a number of first power converters 7. The number of first power converters 7 corresponds to the number of phases of the first winding group 2. As a rule - i. in a three-phase three-phase machine 1 - so three first converter 7 are present. Each first power converter 7 is formed at least as a bipolar B6 group. The term "bipolar B6 group" will be explained in more detail later in conjunction with Figures 4 to 6. Each of the first power converters 7 of the first converter group 6 is one of the first according to FIG

Windings 3 of the first winding group 2 connected. Furthermore, the first power converters 7 have a common first star point 8. The first power converters 7 are above each a separate three-phase transformer 9 connected to the three-phase network 5. The three-phase transformers 9, in the embodiment according to FIG. 1, have a mutually identical phase position.

The first power converters 7 are network-guided. The term "network-guided" has a clearly defined meaning for the person skilled in the art: it means that switching valves of the respective power converter 7 (not shown in FIG. 1) can be actively ignited, but can not be actively extinguished, instead being erased automatically at zero crossing This is in contrast to power converters, which can not only be ignited but also actively extinguished, examples of which are GTOs and IGBTs.

The direct converter 4 also has a control device 10. The control device 10 controls the first power converters 7 of the first converter group 6 together. The control device 10 may be constructed in hardware. Often, however, the control device 10 is designed as a programmable control device. If the control device 10 is designed as a programmable control device, the control device 10 is programmed with a control program 11. The control program 11 includes machine code 12. The

Execution of the machine code 12 causes and determines the operation of the cyclo-converter 4. The control program 11 is stored at least within the control device 10 on a data carrier 13. It may additionally be stored outside the control device 10 on a (further) data carrier 14. The operation and operation of the controller 10 will be explained later in connection with FIG. 7. The embodiment according to FIG. 2 is based on the embodiment of FIG. The essential difference is that, in the embodiment according to FIG. 2, the three-phase machine 1 has, in addition to the first winding group 2, a second winding group 16 having second windings 17. The number of second windings 17 is equal to the number of first windings 3. The second windings 17 of the second winding group 16 are connected to one another in the same way as the first windings 3 of the first winding group 2. The second winding group 16 can be used relative to the first winding group 2 have a phase angle cpl of 0 °, + 30 °, -30 ° or 180 °. In the embodiment according to FIG. 2, the direct converter 4 furthermore has a second converter group 18 in addition to the first converter group 6. The second converter group 18 has a number of second power converters 19. The second power converters 19 are network-guided analogously to the first power converters 7. The number of second power converters 19 corresponds to the number of phases of the second winding group 16. Each second power converter 19 is analogous to the first

Power converters 7 - designed at least as a bipolar B6 group. Each of the second power converters 19 of the second converter group 18 is connected to one of the second windings 17 of the second winding group 16, as shown in FIG. Furthermore, the second power converters 19 have a common second star point 20. The second power converters 19 are - analogous to the first power converters 7 - connected via their own three-phase transformer 21 to the three-phase network 5. The three-phase transformers 21 have, in the embodiment according to FIG. 2, a mutually identical phase position. Their phase position can be equal to the phase position of the three-phase transformers 9. Alternatively, the phase position of the three-phase transformers 21 can deviate from the phase position of the three-phase transformers 9. In particular, a phase offset φ2 of 30 ° can exist electrically.

The embodiment of FIG 3 is based on the embodiment of FIG. The main difference is that in the embodiment according to FIG. 2, the first winding group 2 is operated in the form of a so-called open circuit. It is therefore also in the embodiment of FIG 3, the first converter group 6 and the second converter group 18 with their respective power converters 7, 19 present. Each first winding 3 of the first winding group 2 has two ends. One of the ends of each first winding 3 is connected to one of the first power converters 7 or one of the second power converters 19.

The converter groups 6, 18 of the embodiment according to FIG. 3 are constructed identically to one another. Their respective construction corresponds to that of the first converter group 6 explained above in connection with FIG. 1. The three-phase transformers 9 have the same phase position within the respective first converter group 6. Between the first converter group 6 and the second converter group 18, alternatively, the same phase position or a phase offset φ2 of 30 ° may exist.

The embodiment according to FIG. 3 can in principle also be realized in a three-phase machine 1, which has a second winding group 16 in addition to the first winding group 2. In this case, the arrangement shown in FIG. 3 would have to be doubled at first and second converter groups 6, 18.

The essential difference between the embodiments according to FIG. 2 and FIG. 3 therefore lies in the fact that, in the embodiment according to FIG. 2, the winding group 16 of the three-phase machine 1, to which the second power converters 19 are connected, has a further one different from the first winding group 2 Winding group 16 of the three-phase machine 1 is. In contrast, in the embodiment according to FIG. 3, the winding group 2 of the three-phase machine 1, to which the second power converters 19 are connected, is identical to the first winding group 2. In the embodiment according to FIG. 2, too, however, the number of phases of the second winding group 16 corresponds to the number of phases of the first winding group 2.

4 shows a possible construction of a power converter 7, 19. According to FIG. 4, the power converter 7, 19 is designed as a bipolar B6 group 22. The bipolar B6 group 22 has two unipolar re B6 groups 23, which are connected via the respective transformer 9, 21 with the (at least three-phase) three-phase network 5. Each of the two unipolar B6 groups 23 has two thyristors 24 per phase of the three-phase network 5. Each of the two unipolar B6 groups 23 can be in the

Rectifier operation, that is to say in the removal of energy from the three-phase network 5 via one of the two unipolar B6 groups 23 with simultaneous inactivity of the other unipolar B6 group 23, a rectification of the voltage of the three-phase network 5 with 6pulsiger network feedback effect. The two unipolar B6 groups 23 are connected in anti-parallel to each other and together form the bipolar B6 group 22. The structure of FIG. 4 is well known to those skilled in the art.

5 shows a possible alternative construction of a power converter 7, 19, which is designed as a bipolar B6 group 22. The operation of the power converter 7, 19 of FIG 5 is functionally completely equivalent to the bipolar B6 group 22 of FIG 4. As shown in FIG 5, the bipolar B6 group 22 per phase of the three-phase network 5 each have two switching elements 25. Each switching element 25 consists of two antiparallel arranged thyristors 23. Also, the structure of FIG 5 is well known to those skilled in the art.

The two embodiments of a bipolar B6 group 22 explained above in connection with FIGS. 4 and 5 represent by far the most common implementations. In principle, however, other embodiments are also possible and conceivable. Decisive is the functionality explained above in connection with FIG.

The design of the power converters 7, 19 as bipolar B6 groups 22 represents a minimum configuration. Alternatively, the power converters 7, 19 may have a plurality of bipolar B6 groups 22 of this type, with the bipolar B6 groups 22 of the respective power converter 7, 19 connected in series are. 6 shows purely by way of example a series connection of two bipolar B6 groups 22. Analogous configurations are also possible with a series connection of more than two bipolar B6 groups 22, for example with a series connection of three or four bipolar B6 groups 22.

According to FIG. 6, the bipolar B6 groups 22 are each connected to the three-phase network 5 via their own three-phase transformer 9, 21. Within the respective power converter 7, 19, the three-phase transformers 9, 21 may have the same phase position. Alternatively, three-phase transformers 9, 21 may have a phase offset φ3 of, for example, 30 ° electrical in the case of two bipolar B6 groups 22, or generally a phase offset φ3 of 60 ° / n, where n is the number of B6 bipolar groups 22 connected in series of the respective power converter 7, 19. Such embodiments are known to those skilled in the art, depending on the number of bipolar B6 groups 22, as 12-pulse, 18-pulse, 24-pulse and so on.

The operation of the control device 10 and thus also the operation of the cyclo-converter 4 will be explained below in conjunction with FIG. 7 and later also FIG. 8. The operation of the control device 10 explained in conjunction with FIG. 7 applies to an embodiment of the cycloconverter 4 according to FIG. 1. The explanations regarding FIG. 8 apply to the embodiments of the cycloconverter according to FIGS. 2 and 3. However, the explanations regarding FIGS. 7 and 8 apply regardless of whether the power converters 7, 19 according to FIG 4, according to FIG 5 or FIG 6 are formed. According to FIG. 7, the control device 10 accepts a setpoint control S * in a step S1. Furthermore, the control device 10 according to FIG. 2 ascertains a first zero-voltage component N1 in a step S2 for at least some target drives S * on the basis of an optimization criterion OK. The first zero-voltage component N1 can alternatively be determined statically or dynamically by the control device 10. In a step S3, the control device 10 uses the setpoint control S * to determine respective first commutation signals Kl for the first power converter 7. The controller 10 takes into account in determining the first Kommutierungs- signals Kl the first zero-voltage component Nl. The im

Step S3 detected first commutation signals Kl transmits the controller 10 in a step S4 (timely correct) to the first power converter. 7

In the case where the first windings 3 of the first winding group 2 are arranged in a star connection as shown in FIG. 1, the first zero-voltage component N1 can relate to an (actual) first neutral point 15 of the first winding group 2. In the event that the first windings 3 of the first winding group 2 are arranged in a delta connection, the first zero-voltage component N 1 can be related to a virtual first neutral point of the first winding group 2. The first zero-voltage component N1 can in this case be determined, for example, by averaging the voltages present at the corners of the delta connection between the first windings 3 of the first winding group 2. In any case, and thus in particular also in the case of an open circuit (see FIG. 3), the first zero voltage component N1 can be determined by the mean value of the voltages U, which switch the first power converters 7 to the first windings 3 of the first winding group 2.

The manner in which the controller 10 determines the first zero voltage component N1 may be determined as needed. Preferably, the control device 10 determines the first zero-voltage component N1 such that one of the first power converter 7 is operated as close as possible to the rectifier limit within the first converter group 6 having the common first star point 8. The first power converter 7 which is operated as close as possible to the rectifier limit can alternatively either the first power converter 7, in which the amount of the current I output to the three-phase machine 1 is greatest,

or the first power converter 7 in which the current I delivered to the three-phase machine 1 and / or the voltage U applied to the three-phase machine 1 is the most positive,

or the first power converter 7 in which the current I delivered to the three-phase machine 1 and / or the voltage U applied to the three-phase machine 1 is the most negative.

Furthermore, the control device 10 can determine the first zero-voltage component N1 in such a way that a ripple of a reactive power consumption of the cyclo-converter 4 from the

3-phase network 5 is minimized or assumes a predetermined value. This optimization can be used alternatively or in addition to the above criteria. It is also possible to determine the optimization criterion OK as needed. For example, the optimization criterion OK may be determined such that network harmonics are reduced, that reactive power is reduced, and / or that

Flicker is reduced. Optionally, a (weighted or unweighted) averaging can take place.

If the second converter group 18 is present with its second power converters 19, the procedure of FIG. 7 according to FIG. 8 is modified. In this case, steps S6 and S7 are present in addition to the steps S1 to S4. The steps S6 and S7 are arranged downstream of the steps S1 to S4 according to FIG. However, this is of secondary importance. In step S6, the control device 10 uses the setpoint control S * to determine the respective second commutation signals K2 for the second power converters 19. The second commutation signals K2 determined in step S6 are transmitted to the second power converters 19 in step S7 (with correct timing). In the context of the procedure of FIG. 8, a step S8 is preferably still present. If step S8 exists, it precedes step S6. In step S8, the control device 10 determines for those Sollansteue- ments S *, where it determines the first zero voltage component Nl, based on the optimization criterion OK, a second zero-voltage component N2. The second zero-voltage component N2 is determined in an analogous manner as the first zero-voltage component N1. In this case, the control device 10 takes into account the second zero voltage component N2 when determining the second commutation signals K2.

Analogously to the manner in which the control device 10 determines the first zero voltage component N1, the second zero voltage component N2 can also be determined by the control device 10 as required. Preferably, the control device 10 determines the second zero voltage component N2 such that within the second converter group 18 having the common second neutral point 20, one of the second power converters 19 is operated as close as possible to the rectifier limit. This second power converter 19 can - analogously to the first inverter group 6 - alternatively

either the second power converter 19, in which the amount of the current I output to the three-phase machine 1 is greatest,

or the second power converter 19, in which the current I delivered to the three-phase machine 1 and / or the voltage U applied to the three-phase machine 1 is the most positive,

or the second power converter 19 in which the current I delivered to the three-phase machine 1 and / or the voltage U applied to the three-phase machine 1 is the most negative.

Here as well, alternatively or additionally, the optimization can be carried out such that a ripple of a reactive power consumption of the direct converter 4 from the three-phase network 5 min. or assumes a predetermined value. This optimization can be used as before alternatively or in addition to the criteria mentioned above. In principle, the first and the second zero-voltage components N1, N2 can be determined independently of one another by the control device 10. However, the control device 10 often determines the second zero-voltage component N2 as a function of the first zero-sequence voltage component N1. In particular, it is possible that the control device 10 coordinates the determination of the first zero voltage component N1 and the determination of the second zero voltage component N2 as follows: The first zero voltage component N1 is determined in such a way that within the first converter group 6 having the common first star point 8 that first power converter 7, in which the current I output to the three-phase machine 1 and / or the voltage U applied to the three-phase machine 1 is most positive, is operated as close as possible to the rectifier limit.

The second zero voltage component N2 is determined in such a way that, within the second converter group 18 having the common second neutral point 20, that second power converter 19 in which the current I delivered to the three-phase machine 1 and / or the voltage U applied to the three-phase machine 1 is the most negative , is operated as close to the rectifier limit. In particular, it is often possible for the second zero-voltage component N2 to have the same magnitude as the first zero-voltage component N1. Often, therefore, either the relationship N2 = Nl or the relationship N2 = -Nl applies. It is possible that the optimization criterion OK of the control device 10 is fixed. Preferably, however, the optimization criterion OK is as shown in FIG 1 to 3 of the control device 10 specified from the outside, for example, by an operator, not shown.

In summary, the present invention thus relates to the following facts:

A direct converter 4 has a number of first converter groups 6, which in turn each have a number of line-commutated first power converters 7. The first power converters 7 are each formed at least as bipolar B6 groups and connected to a first winding group 2 of a three-phase machine 1. The number of first power converters 7 per first converter group 6 corresponds to the number of phases of the first winding group 2. The first power converters 7 of at least one of the first converter groups 6 have a common first star point 8. The direct converter 4 has a common control device 10 controlling the first converter groups 6. The control device 10 accepts a setpoint control S * and uses the setpoint control S * for the first power converters 7 to determine respective first commutation signals K1. The control device 10 statically or dynamically determines a first zero-sequence voltage component N1 for some setpoint drives S * based on an optimization criterion OK considered in the determination of the first commutation signals Kl. The first commutation signals Kl are transmitted to the first power converters 7 by the control device 10.

The present invention has many advantages. In particular, by the procedure according to the invention the

Reactive power demand can be significantly reduced. In extreme cases, a reduction of up to 75% can be achieved. Depending on the operating point of the three-phase machine 1 and the topology of the cyclo-converter 4, it is still possible to reduce network harmonics by up to 75%. Nevertheless, the usual advantages of the cyclo-converter 4 can be maintained. Although the invention has been further illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

claims

1. direct converter,

wherein the direct converter has a number of first converter groups (6),

- wherein the first converter groups (6) each have a number of line-commutated first power converters (7),

- Wherein the first power converters (7) are each formed at least as bipolar B6 groups and are connected to a first winding group (2) of a three-phase machine (1),

wherein the number of first power converters (7) per first converter group (6) corresponds to the number of phases of the first winding group (2),

wherein the first power converters (7) of at least one of the first converter groups (6) have a common first star point (8),

wherein the direct converter has a common control device (10) controlling the first converter groups (6), wherein the control device (10) accepts a setpoint drive (S *) and uses the setpoint drive (S *) for the first power converters (7) Commutation signals (Kl) determined and transmitted to the first power converter (7),

- The controller (10) for at least some Sollansteuerungen (S *) based on an optimization criterion (OK) statically or dynamically determined a first zero voltage component (Nl) and determines the first Kommutierungssignale (Kl) taking into account the first zero voltage component (Nl).

2. Direct converter according to claim 1, characterized in that the control device (10) the first zero voltage component (Nl) determined such that within the common first star point (8) having the first inverter group (6) that first power converter (7), wherein the Amount of charge to the three-phase machine (1) delivered current (I) is greatest, as close to the rectifier limit is operated.

3. direct converter according to claim 1, characterized 9 e - indicates that the control device (10) determines the first zero voltage component (Nl) such that within the common first star point (8) having first inverter group (6) that first power converter (7) in which the current (I) delivered to the three-phase machine (1) and / or the voltage (U) applied to the three-phase machine (1) is the most positive, as close as possible to the

Rectifier limit is operated.

4. direct converter according to claim 1, characterized 9 e - indicates that the control device (10) determines the first zero voltage component (Nl) such that within the common first star point (8) having the first inverter group (6) that first power converter (7) in which the current (I) delivered to the three-phase machine (1) and / or the voltage (U) applied to the three-phase machine (1) is the most negative, as close as possible to the

Rectifier limit is operated.

5. Direct-current converter according to claim 1, d a d e r c h 9 e k e n e c e n e,

in that the direct converter has a number of second converter groups (18),

- That the second converter groups (18) each have a number of network-controlled second power converters (19), - that the second power converters (19) are each formed at least as a bipolar B6 group and with a winding group (2,16) of the three-phase machine (1 ) are connected,

- That the number of second power converters (19) per second converter group (18) corresponds to the number of phases of the first winding group (2), - That the second power converter (19) at least one of the second converter groups (18) have a common second neutral point (20),

- That the control device (10) using the setpoint control (S *) for the second power converter (19) respective second commutation signals (K2) determined and transmitted to the second power converters (19) and

- That the control device (10) for those Sollansteuerungen (S *), where it determines the first Nullspannungskomponen- te (Nl), based on the optimization criterion (OK) statically or dynamically also a second Nullspannungskom- component (N2) determined and the second Commutation signals (K2) under consideration of the second zero voltage component (N2) determined.

6. direct converter according to claim 5, characterized in that the winding group (2,16) of the three-phase machine (1) to which the second power converters (19) are connected to the first winding group (2) is identical or that the winding group ( 2, 16) of the three-phase machine (1) to which the second power converters (19) are connected is a second winding group (16) of the three-phase machine (1) different from the first winding group (2) and the number of phases of the second winding group (16) corresponds to the number of phases of the first winding group (2).

7. Direct-current converter according to claim 5 or 6, characterized in that the control device (10)

the first zero voltage component (N1) is determined in such a way that within the first converter group (6) having the common first star point (8) that first power converter (7), in which the current (I) and / or output to the three-phase machine (1) the to the three-phase machine

(1) applied voltage (U) is the most positive, is operated as close to the rectifier limit, and the second zero voltage component (N2) is determined in such a way that, within the second converter group (18) having the common second star point (20), that second power converter (19) in which the current (I) and / or output to the three-phase machine (1) the voltage (U) applied to the three-phase machine (1) is the most negative, operated as close to the rectifier limit.

8. direct converter according to one of the above claims, characerized in that the control device (10) the first zero voltage component (Nl) determined such that a ripple of a reactive power consumption of the cycloconverter is minimized from a direct current feeding three-phase network (5) or a pre-determined voted value.

9. Direct converter according to one of the above claims, characterized in that the optimization criterion (OK) is determined such that network harmonics are reduced, reactive power is reduced and / or

Flicker is reduced.

10. Direct converter according to one of the above claims, characterized in that the control device (10) receives the optimization criterion (OK) from the outside.

11. Direct converter according to one of the above claims, characterized in that the control device (10) is designed as a programmable device.

A control program for a programmable controller (10) of a cycloconverter (4) according to claim 11, wherein the control program comprises machine code (12), the execution of the machine code (12) causing the cycloconverter (4) to be in accordance with claim 11.

13. Control program according to claim 12, characterized in that it is stored on a data carrier (13, 14) in machine-readable form.