EP2810291A1

EP2810291A1 - Device for switching direct currents

Info

Publication number: EP2810291A1
Application number: EP12711812.3A
Authority: EP
Inventors: Dominik ERGIN; Hans-Joachim Knaak
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2012-03-09
Filing date: 2012-03-09
Publication date: 2014-12-10
Anticipated expiration: 2032-03-09
Also published as: PL2810291T3; EP2810291B1; WO2013131582A1; ES2714426T3

Abstract

The invention relates to a device (1) for switching direct currents in a pole of a DC voltage network, comprising two connection terminals (21, 22), between which extends an operating current path (2) having a mechanical switch (4) that can be bridged by a shut-off branch (3); a power switching unit (5) which is disposed in the shut-off branch (3) and has a series circuit of two-pole submodules (10) having at least one power semiconductor switch (11) that can be switched on or off; and commutation means (6) for commutating the current from the operating current path (2) to the turn-off branch (3). The aim of the device is to reliably control fault currents in a DC voltage network, wherein at the same time low on-state losses are produced. In order to achieve said aim, the commutation means (6) are arranged in the shut-off branch (3) and are designed to produce a circuit current that flows through the bridged section of the operating current path (2) and the turn-off branch (3), said circuit current being opposite the current to be switched.

Description

description

The invention relates to a device for switching direct currents

DC currents in one pole of a DC network encompass ^¬ send two terminals, between which extends an operating current path with a mechanical switch which can be bridged by a Abschaltzweig, wherein in the Abschaltzweig a power switching unit is arranged, which is a series circuit of two-pole submodules with at least one power semiconductor switch which can be switched on and off, and wherein commutation means are provided for commutating the current from the operating current path to the turn-off branch.

The invention further relates to a method for switching direct currents with such a device. A device of the type mentioned at the outset is known from the publication by J. Häfner and B. Jacobson "Proactive Hybrid HVDC Breakers - A Key Innovation for Reliable HVDC Grids", symposium "The Electric Power System of the Future - Integrating Super-Grids and Micro-Grids International Symposium ", Bologna, Italy, 13.-15. September 2011, page 264 ff. And WO 2011/057675 AI known. The described therein ^¬ DC voltage switch has an operating current path with a me chanical ^¬ switch and a Abschaltzweig which is connected to the operating current path parallel. In the Abschalt branch a series circuit of power semiconductor scarf ^¬ tern is arranged, each of which a freewheeling diode is connected in parallel in opposite directions. The consisting of power semiconductor switch and freewheeling diode switching units are antise ^¬ riell arranged, the turn-off Leistungshalblei- terschalter are arranged in series and for each power semiconductor switch ^¬ a corresponding power semiconductor switch is provided with opposite passage direction. In this way, the current in both streams can be interrupted in the turn-off branch. In the operating current path, an electronic auxiliary switch is arranged in series with the mechanical switch in addition to the mechanical switch. In normal operation the current through the Be ^¬ operating current path and hence on the auxiliary electronic scarf ^¬ ter and via the closed mechanical switch flows, since the power semiconductor switches of the Abschaltzweiges represent an increased resistance for the direct current. To interrupt, for example, a short-circuit current of the electronic auxiliary switch is transferred to its disconnected position. As a result, the resistance increases in the operating current path, so that the direct current commutes in the Abschaltzweig. The fast mechanical isolation switch can therefore be de-energized geöff ^¬ net. The guided over the Abschaltzweig short ^¬ stream can be interrupted by the power semiconductor switches. For receiving the energy stored in the DC voltage network and to be reduced during switching Abieiter are provided, which are each connected in parallel to the power semiconductor switches of Abschaltzweiges.

Rising global energy demand and simultaneously ge ^¬ wished reduction in C0 ₂ emissions make so-called renewable energy more attractive. Sources of renewable energy, for example, lakeside erected wind turbines ^¬ or photovoltaic power plants in sunny desert areas. In order to be able to use the energy generated in this way economically, the connection of renewable energy sources to a shore supply network is becoming increasingly important. Against this background, the construction and operation of a meshed DC voltage network is becoming increasingly discussed. The prerequisite for this, however, is that short-circuit currents which can occur in such a meshed DC voltage network can be switched off quickly and reliably. However, this requires DC ^¬ switches are required which are not available on the market currently. From the prior art, different Konzep ^¬ te for such a DC voltage switches are known. In DE 694 08 811 T2, a DC voltage switch is described, ge ^¬ switches for the two mechanical switches in series. The series circuit consisting of the two mechanical switches is protected against high overvoltages by a Abieiter and a capacitor. Only one of the mechanical switches is a switched on and off power semiconductor switch connected in parallel. When opening the mechanical switch creates an arc. The voltage dropping across the arc ignites the power semiconductor switch, whereby the parallel open mechanical

Switch is shorted. The arc goes out. The run on the power semiconductor switch current can be by appropriate control of the power semiconductor un ^¬ interrupted.

In US 5,999,388 a DC voltage circuit breaker is described, which can be integrated serially in a DC voltage line. It consists of a series connection of power semiconductor switches which can be switched on and off, to each of which an opposite freewheeling diode is connected in parallel. Wei ^¬ terhin is parallel to each power semiconductor switch a Abieiter, for example, a varistor, connected to the voltage limit. The previously known DC voltage switch is designed purely electronic and thus switches considerably faster compared to commercially available mechanical switches. Within a few microseconds, a short-circuit current flowing via the DC voltage switch can be interrupted. The disadvantage, however, is that the operating current must also be conducted via the power semiconductor switches. This results in high transmission losses.

WO 2011/141055 discloses a DC voltage switch which can be serially connected in one pole of a high voltage direct current network. The DC-DC switch comprises a mechanical switch in series with a power semiconductor switch to which an opposite Freilaufdio ^¬ de is connected in parallel again. Parallel to the series circuit of power semiconductor switch and mechanical switch are a series circuit of coil and capacitor, ie an LC branch and a Abieiter, connected, which limits the voltage drop across the LC branch voltage. Also, the power semi-conductor switches ^¬ a Abieiter is connected in parallel. After opening the mechanical switch of Leistungshalblei ^¬ terschalter is switched with the natural frequency of the LC branch and off. As a result, a vibration and finally a current zero crossing is generated in the mechanical switch, so that the resulting arc can be deleted.

The object of the invention is to provide a device and a method of the type mentioned, with which fault currents can be safely interrupted in a DC voltage network, at the same time low passage losses are generated.

The invention solves this problem with regard to the device in that the commutation means is arranged in the turn-off branch and for generating a current flowing over the bridged section of the operating current ^path and the turn-off branch

Circular currents are set, the switching to the

DC is opposite.

The invention also achieves this object with a method in which a current sensor detects the current flow in the operating current path to obtain current measured values, a control unit connected to the current sensor monitors the current measured values for the presence of an intervention criterion and, when the intervention criterion is present, controls the commutation means, that such a large circulating current is generated that the current flow is limited via the mechanical switch to a maximum current.

According to the invention, the commutation means are no longer arranged in the operating current path, in contrast to the above-mentioned closest prior art. Therefore, the commu ^¬ tierungsmittel not act as passive commutator, which interrupt the operating current path. According to the invention, which actively generates a reverse voltage in a mesh formed by the turn-off branch and the portion of the operating current path bridged thereby. The the be ^¬ said mesh imposed reverse voltage drives one over the mechanical switch lead circuit current, which is opposite to the switching current. The two opposite currents cancel each other out in the ideal case. With equal currents in the operating path, the current in the mechanical switch is almost zero. In other words, the current is conducted almost completely across the turn-off branch by the active commutation means. Subsequently, the mecha ^¬ African switch open almost normally. If the mechanical switch is opened in the operating current path, the power switching unit can limit ^¬ Abschaltzweig in the current and / or completely broken.

The configuration of the power switching unit is fundamentally arbitrary within the scope of the invention. This also applies to the commutation means. However, it is essential that the ex ^¬ switching branch forms a higher electrical resistance than the bridged from him part of the operating current path. In addition, the sub-modules of the power switching unit able to switch off the high short-circuit currents safely and beyond kontrol ^¬ profiled reduce this energy released. By contrast, the commutation means are designed in such a way that they generate such a high ^circulating current in the time window that the current flow is suppressed via the mechanical switch and that current can then be opened without current. For detecting the current flow in Be ^¬ drive current path, a current sensor is provided. Of course, the voltage in the operating current path with respect to the ground potential and / or the voltage drop across the switch can be monitored. This applies expediently also for the turn-off branch. The commutation ^¬ medium include not only the current sensor is advantageously a control and / or regulation unit which is connected to the current measuring sensor ^¬ the operating current path. The current readings produced by the current ^¬ measuring sensor are transmitted to the regulation unit, which evaluates the received current measurement values to determine whether a previously defined intervention criterion exists. Such intervention criterion is for example an excessive increase in current (di / dt) or if the measured current values exceed a current threshold a pre ^¬ specified time window long. In principle, however, any linkages with further measured values of protective devices or the like or further criteria are possible within the scope of the invention. If such an intervention criterion exists, the said circulating current is generated so that the rising short-circuit current commutates into the turn-off branch. If the mechanical switch is opened, the current can be limited by the sub-modules, or if necessary also abge ^¬ on. In the context of the invention, it is also possible borrowed that the mechanical switch is opened only over a limited period of time, for example, if a Be ^¬ influence of the current flowing over the entire device current is desired. Advantageously, the submodules of the power ^{switching ¬} unit at least partially each on and off ^¬ baren power semiconductor switch and a reverse direction parallel thereto connected freewheeling diode on. Alternatively, each submodule may also include a single reverse conducting power semiconductor switch. As power semiconductor switches are for example IGBTs, GTOs or derglei ^¬ chen into consideration. As a rule, a power semiconductor switch has a plurality of power semiconductor switch chips arranged in a housing. To connect the load terminals of the power semiconductor switch chips serve as bonding wires. Deviating from this, however, pressure-contacted power semiconductor switches can also be used in the context of the invention, in which the power semiconductor switch chips are connected to each other on the load terminal side via a pressure contact. However, such power semiconductor switches are known to those skilled in the art, so that their Ausges ^¬ taltung here need not be discussed in more detail. According to a preferred development, the submodules of the power switching unit form two groups, each having identically oriented transmission directions of its power semiconductor switches, wherein the power semiconductor switches of one group are oriented opposite to the power semiconductor switches of the other group. According to this advantageous ^embodiment , the current can flow not only in both current directions via the turn-off branch, but also currents can be switched off safely in both directions.

When the current flows in the first direction, the power ^¬ semiconductor switch of the first group are driven to interrupt the current in said first direction. If the current flows in the opposite second direction, the power semiconductor switches of the second group are used. For example, the submodules can also be divided into groups with regard to their effect. Thus, a first group of submodules is provided for generating a reverse voltage in the operating current path and thus for commutation. The other group of submodules, on the other hand, serves to interrupt the current flow. Submodules can foiled ^¬ nen both functions. Such submodules are realized, for example, as full bridges.

In a preferred embodiment of the invention, the sub-modules of the power switching unit at least partially depending Weil an energy storage and parallel to the power ^¬ memory connected series circuit of two switched on and off power semiconductor switches, each with an oppositely arranged in parallel thereto freewheeling diode, wherein a submodule connection terminal with a potential point between tern incoming and turn-off power semiconductor saddle and the other terminal connected to one pole of the Ener ^¬ giespeichers. Such a submodule topology is also called a half bridge.

Of course, instead of a single power semiconductor ^switch and a synchronously driven series ^{scarf ¬} tion of power semiconductor switches are used. The synchronously controlled power semiconductor switches of the then behave exactly like a single power semiconductor switch. Incidentally, this also applies to the submodules described in more detail below, that is also to the full bridge circuit or the brake controller circuit.

To reduce an energy released during switching, which is stored in the DC voltage network, at least one drain and / or one varistor are provided for each submodule of the power switching unit.

Submodules of the power switching unit, which are designed as half-bridges, can interrupt the current in only one direction un. If the current flow in two directions are unterbro ^¬ chen, the formation of two groups of sub-modules is also necessary here, wherein the sub-modules of the one group for the interruption of the current in a first direction and the sub-modules of the other group for the interruption of the current in serve a direction opposite to the first direction translated second direction.

According to a preferred embodiment of the invention, however, the submodules of the power switching unit are at least partially ^{¬ formed} as a full bridge circuit and therefore have an energy storage and two parallel to the energy storage series circuits, each with two switched on and off power semiconductor switches with oppositely parallel freewheeling diode, with a first An ^¬ final terminal with the potential point between the two power semiconductor switches of the first series circuit and a second submodule connection terminal is connected to the potential point between the two power semiconductor switches of the second series circuit. Such a full bridge ^circuit is capable of interrupting currents in both directions, that is to say switching off in other words.

As already stated, each submodule of the Leis ^¬ tung switching unit advantageously a Abieiter and / or a varistor connected in parallel to either the single switched on and off power semiconductor switch or in parallel to the energy storage of the submodule on.

Notwithstanding this, the submodules of Leistungsschaltein unit are at least partially designed as a brake actuator modules. Such brake actuator modules have an energy store, to which a first series circuit is connected in parallel. The first series circuit also consists of a switched on and off power semiconductor switch with oppositely parallel freewheeling diode and an ode in the same direction to Freilaufdi oriented diode. In addition, a second Rei ^¬ henschaltung is provided, which is also connected in parallel to the energy storage. The second series circuit consists of a switched on and off power semiconductor switch with opposite parallel freewheeling diode and another oriented in the same direction to the freewheeling diode. The diode of the second series circuit bridges an ohmic resistance. The first Submodulanschlussklemme is connected to one pole of the energy store and the second Submodulanschlussklemme with the potential point between the turn-off power ^¬ semiconductor switch and the diode of the first series circuit. Such brake actuator modules can ge in the network ^¬ stored and controlled in switching degraded energy converted into thermal energy and lead to the outside atmosphere from ^¬.

According to a preferred embodiment of the invention, the commutation form a series connection of two-pole submodules, each submodule has a Energiespei ^¬ cher and a power semiconductor ^switch in parallel with the energy storage. With the help of the power semiconductor circuit ^¬ the falling of the voltage of the two-pole Submodulanschlussklemmen submodule is adjustable. Either the voltage dropping across the energy store is applied to the submodule connection terminals or a zero voltage, ie no voltage. Due to the series connection, therefore, the voltage dropping across the entire series connection of the submodules of the commutation means can be stepped in gradually. be, wherein the height of the stages corresponding to the energy ^¬ memory of a submodule voltage drops.

The design of the power semiconductor circuit of the commutation can, as already described in connection with the submodules of the power switching unit, either a half-bridge or a full bridge circuit. If the power semiconductor circuit is a half-bridge circuit, only one series connection of two turn-off power semiconductor switches is provided, each with a parallel freewheeling diode, a first submodule terminal is connected to the potential point between the abschaltba ^¬ Ren power semiconductor switches and another Submodulan- circuit terminal with a pole of the energy storage. The submodules of the commutation means designed as a half-bridge circuit must be oriented so that a Ge ^¬ gene voltage with the desired polarity in the operating current path can be generated. This is usually the case when the half-bridge circuits of the commutation are oriented opposite to the half-bridge circuits of the submodules of the power switching unit.

Deviating from this, the power semiconductor circuit of the submodules of the commutation is formed together with the energy ^¬ memory as a full bridge circuit, wherein, as already described above, two series circuits are provided. The two series circuits are connected in parallel to the energy store and each have two switched on and off power semiconductor switches, each with ge ^¬ gensinnig parallel freewheeling diode. Instead of power semi ^¬ conductor switch with freewheeling diode and reverse leit ^¬ enabled power semiconductor switches can be used. The potential point between the two power semiconductor switches is in each case connected to a submodule connection terminal, so that either the voltage dropping across the energy store, a zero voltage or the inverse energy storage voltage can be generated at the submodule connection terminals. The full-bridge circuit can thus generate voltages which have different polarities. These are particularly advantageous when reverse voltages for currents in both directions to be generated. The submodules of the ^commutation means can also be used for cutting off or limiting the current to be switched. This is beispielswei ^¬ se useful when both the sub-modules of the power ^¬ switching unit and the sub-modules of the commutator are designed as full bridges, the commutation ^¬ agents are then also equipped with Abieitern, varistors or other non-linear resistors. Conveniently, the sub-modules of the power switching unit ^¬ not differ from the sub-modules of Kommutierungsmit ^¬ tel. This identity also includes the connection of Abieiter or varistors.

As energy storage of the submodules of both the commutation and the power switching unit, for example, a capacitor is provided.

Conveniently, a charging branch is provided which is connected either to the ground potential or to a counter pole. The opposite pole is polarized opposite to the pole with which the device according to the invention is connected to at least one of its terminals. The charging branch has a switch which is galvanically connected to one of its contacts with the potential point between the power ^{switching ¬} unit and the Kommutierungssmitteln. If the switch is actuated, the charging branch is connected to the turn-off branch, so that a charging current can flow to the earth or to the opposite pole both via the commutation means and via the power switching unit. Here, the energy storage of submodules are loaded. Furthermore, a voltage drops across the power semiconductor switches, which voltage can be used to supply power to the electronics of the submodules. Advantageously, the loading arm with the potential point between power switching unit and communications ^¬ tierungsmittel is connectable. In addition, several charging branches can be provided. Further expedient refinements and advantages of the inven ^¬ tion are the subject of the following description with reference to the figures of the drawings, wherein like Bezugszei ^¬ chen refer to the same components acting and wherein

Figure 1 shows an embodiment of a DC voltage switch ^¬ and

Figures 2

to 5 possible embodiments of submodules for the

DC voltage switch according to Figure 1 show.

Figure 1 shows schematically an embodiment of the inventions ^¬ inventive device 1, which can also be referred to as a DC voltage switch. The DC voltage switch 1 shown there has an operating current ^path 2 and ei ^¬ nen turn-off branch 3, wherein in the operating current ^path 2, a mechanical switch 4 is arranged, which is bridged by the Abschaltzweig 3. The operating current path 2 ER extends between a first terminal 21 and ei ^¬ ner second terminal 22. In Abschaltzweig 3, a power switching unit 5 and commutator 6 are mutually arranged in series. Furthermore, a charge branch 7 is provided which has a mechanical switch 8 and an ohmic resistor 9 and which connects the switch-off branch 3 to a ground potential when the switch 8 is closed. Is the

Switch 8 closed, the charging branch 7 is connected to the potential point between the power switching unit 5 and the commu ^¬ tierungsmitteln 6.

The power switching unit 5 and the commutation means 6 each have a series connection of two-pole submodules 10. The number of submodules 10 in the power ^¬ switching unit 5 is dependent on the voltage to be switched. The number of submodules 10 in the commutation means 6 determines the counter voltage which can be generated in a mesh, which consists of the turn-off branch 3 and the section of the operating current path 2 bridged by the turn-off branch 3. The opposing voltage drives a circulating current in the said mesh, which is opposite to the current to be switched in the operating current path. In the mechanical switch 4, these currents expire mutually beneficial.

Examples of possible sub-modules 10 for the DC ^¬ switch according to Figure 1 are shown in Figures 2, 3, 4 and 5. FIG. In the simplest case according to FIG. 2, a submodule 10 is a power semiconductor switch 11 which can be switched on and off, to which a freewheeling diode 12 is connected in parallel in opposite directions. Each power semiconductor switch 11, a Abieiter 13 is also connected in parallel. Submodules 10 according to FIG 2, however, are not eligible for the ^commutation means 6 into consideration, since these can not produce counter-voltage in said mesh. However, submodules 10, each having an energy store 14, for example in the form of a capacitor, are suitable for this purpose. The capacitor or energy storage 14 is connected in a submodule according to Figure 3, a series circuit 15 of two power semiconductor switches 11 each with parallel opposite freewheeling diode 12 paral ^¬ lel. A first submodule connection terminal 16 is connected to the potential point between the power semiconductor switches 11 of the series circuit 15. The other submodule connection terminal 17, however, is applied to one pole of the unipolar capacitor 14. Depending on the control of the switched on and off power semiconductor switch 11 is therefore between the terminals 16 and 17, either the capacitor 14 dropping on the capacitor voltage U _c or a zero ^¬ voltage generated. In order not to have to be ^¬ sue the failure of the entire direct voltage switch 1 on failure of a single submodule, each submodule 10 is bridged by a fast mechanical or electronic switch 18th Furthermore, a diode 19 or a thyristor between the connection terminals 16 and 17 serves to carry high short-circuit currents. If the submodule 10 is to be part of the power switching unit 5, it is expedient to connect a capacitor 13 in parallel to the capacitor 14, as shown in FIG. 1 in a figurative manner. Such a Abieiter 12 is for the submodules 10th the commutation 6 not mandatory. These then serve only to generate a current flowing through the mechanical switch 4 circulating current and thus to generate a current zero crossing in the mechanical switch 4. From a construction of electromagnetic energy that is stored in the network, by the commutation is not required. However, the submodules of commutation can also be used to switch or limit a current. In this case, these also have a Abieiter or other the submodule connected in parallel non-linear resistance.

Half bridges according to FIG. 3 can interrupt the current flow in only one direction. A current flow from the second submodule connection terminal 17 shown in FIG. 3 to the first submode connection terminal 16 would lead via the uncontrolled freewheeling diode 12 arranged between these terminals. A Steue tion of the stream is therefore not possible.

However, an influence of the two current directions can be achieved with egg ner full bridge circuit according to Figure 4. In Fi gur 4, a submodule 10 is illustrated, which represents a full bridge circuit. The capacitor 14, two series circuits 15 and 20 are connected in parallel. Each row scarf ^¬ tung 15, 20 has two on and turn-off power semiconductor ^¬ state switch 11 with oppositely directed free-wheeling diode 12. Submodule connection terminals 16, 17 are each connected to a potential point between the power semiconductor switches 11. If the full bridges of the commutation means have a drain, these can also be considered part of the power switching unit.

For connecting a direct-voltage network is the on ^¬ connecting terminal 3 of the DC circuit breaker 1 is first connected to the zuzuschaltenden direct voltage network section. The switch 4 in the operating current path 4 is open. Anschlie ßend the DC voltage switch 1 is made ready for operation via the charging branch 7 by the switch 8 is closed and the Abschaltzweig 3 is thus connected via the resistor 9 to a ground potential. In the case of submodules 10 according to FIG. 3 or 4, the capacitors 14 of the submodules 10 can now be charged after the application of a DC voltage to the connection terminal 22, which is connected to a pole of a DC voltage source. Also, the control electronics of the power semiconductor switch 11, which is fed from the voltage dropping to the turn-off power semiconductor switches 11, is now ready for operation.

If the power switching unit 5 is ready for operation, the switch 8 of the charge branch 7 can be opened and controlled with a zweckmäßi ^¬ gene control of the power semiconductor switch 11 of the power switching unit 5, connected to the second terminal 22 DC power supply section ^¬ switched, the voltage is ramped up. However, this is only possible without further ado when the submodules 10 of the commutation means 6 form half-bridge circuits according to FIG. In the case of full bridge circuits according to FIG. 4, these must either be bridged or else the submodules 10 have to be made ready for operation in order to convert the power semiconductor ^switches 11 into their open position at closing. For this purpose, the charging branch would, for example, be connected to the potential point between the commutation means 6 and the terminal 22. For this purpose, appropriate switches could be used. Notwithstanding this, a second charge branch is provided at this point.

FIG. 5 shows a further exemplary embodiment of a submodule 10 for the power switching unit 5, which is also referred to here as a brake actuator module. The submodule 10 has as ^¬ the two series circuits 15, 20. The first series ^{scarf ¬} tion 15 consists of a switched on and off power semiconductors, IGBT, with oppositely parallel freewheeling diode 12. In series with the IGBT, a diode 23 is connected. The diode 23 is opposite to the said IGBT and therefore oriented in the same direction to the free-wheeling diode. Furthermore, a second series circuit 20 is provided, which is the energy store 14 also connected in parallel. The second series ^¬ circuit has an IGBT 11 with opposite parallel freewheeling diode 12 and a series thereto a diode 24. IGBT 11 and diode 24 are oriented in opposite directions to each other, wherein the diode 24, an ohmic resistor 25 is connected in parallel. The first submodule connection terminal 16 is connected to the potential point between the diode 23 and the IGBT 11. The second submodule connection terminal 17 is connected to a pole of the energy accumulator 14.

The DC voltage switch 1 is now ready for operation. During operation of the DC voltage switch, the switch 8 can be opened or remain closed. This depends on the height of the ohmic resistor 9 and the resulting losses. In any case, the mechanical switch 9 may be a slow mechanical switch.

In the description of a switch-off process, it is now assumed that the power switching unit 5 consists of a series connection of submodules 10 according to FIG. 4, ie full-bridge circuits. This applies correspondingly to the submodules 10 of the commutation means 6. In the operating position, the mechanical switch 4 in the operating ^{current path} 2 is closed. The power semiconductor switch 11 of the submodules 10 of the power switching unit 5 and the commutation ^¬ medium 6 are in their passage position. In this switching state of the submodules 10, a current flow via the turn-off branch 3 is basically possible. However, due to the higher compared to the working path 2 electrical resistance of the Abschaltzweigs 3 the operating current flows na ^¬ hezu exclusively and without loss disposed on the operating current path 2. A during operation current path 2 current measuring sensor 26 detects the current flowing through the operating current path 2 operating current to give power measurements. Said current measuring sensor 26 is connected to a control unit 27 of the DC voltage switch 1, with which a control or regulation of the power semiconductor switches 11 of the submodule le 10 is possible. The control unit 27 monitors the current measured values transmitted by the current measuring value sensor 26 in the presence of an error criterion. Such error ^¬ criterion is, for example, an extraordinary rapid rise of the current is then present or when the current exceeds a predetermined current threshold value over a specified ^differently also surrounded period of time. If such a Feh ^¬ lerkriterium before, 6 induce the commutator in the mesh from Abschaltzweig 3 and bridged operating current path portion of a reverse voltage. Depending on the nature of the error criterion Festge ^¬ set the counter voltage is turned ^¬ assumed that a commutation by the topology of the medium ^¬ predetermined period of time a counter-directed short-circuit current circulating current in said loop sets. The short-circuit current and the opposite circular current add up to almost zero. In this case, the mechanical switch 4 can open almost without power, without that when disconnecting its contacts an undesirable arc is pulled. This arc could lead to destruction of the DC switch 1. In particular, after opening the mechanical switch 4, the current through the arranged parallel to the switch Abschaltzweig flows 3. Only when the switch is open the submodules 10 of the power switching unit 5 and the commutator means are transferred into their disconnected ^¬ position, so that the current flow through the Vorrich ^¬ tung 1 is completely interrupted. The switching energy released in this process is dissipated by the Abieiter 13, which behave like an ohmic resistance after exceeding a threshold voltage and heat up due to the current flowing through them and thus thermally release the energy stored in the network to the outside environment. Finally, it should be pointed out that still further current measuring sensors 26 or voltage sensors can be provided with which the regulation of the device is supported. Moreover, the commutating Abieiter aufwei ^¬ sen, which are connected to the sub-modules in parallel. Also, it should be noted once again that with open switch 4 only parts of the submodules can be converted into their blocking position. In the case of blocked submodules, the current flows from a certain limit voltage across the arrester connected in parallel. In the case of full bridges of the arrester, for example, the energy storage and thus the capacitor connected in parallel. If the voltage dropping across the capacitor ^{exceeds the} threshold voltage of the arrester, it behaves like an ohmic resistor, so that a limitation of the current is brought about. The more submodules are transferred to their blocking position, the higher the resistance and the higher the limit.

Claims

claims

1. Device (1) for switching DC currents in a pole of a DC network comprising

two terminals (21, 22) between which an operating current path (2) with a mechanical switch (4) extends,

- Which can be bridged by a Abschaltzweig (3),

- Wherein in the Abschaltzweig (3) a power switching unit (5) is arranged, which is a series circuit of two-pole

Submodules (10) with at least one on and off switchable power semiconductor switch (11), and

- wherein commutation means (6) are provided for commutating the current from the operating current path (2) to the turn-off branch (3),

d a d u r c h e c e n c i n e s that

the commutation means (6) are arranged in the turn-off branch (3) and are set up to generate a circulating current which flows over the bridged section of the operating current path (2) and the turn-off branch (3) and which is to be switched

DC is opposite.

2. Device (1) according to claim 1,

d a d u r c h e c e n c i n e s that

the submodules (10) of the power switching unit at least in part, in each case a mono- ^¬ and disconnectable Leistungshalblei ^¬ terschalter (11) and a counter-parallel to this ge ^¬ switched freewheeling diode (12).

3. Device (1) according to claim 1 or 2,

d a d u r c h e c e n c i n e s that

the submodules (10) of the power switching unit (5) two Grup ^¬ pen with similarly oriented each passage directions of the power semiconductor switch (11) form, wherein the power semiconductor switch (11) of one group opposed to the power semiconductor switches (11) of the other group are oriented.

4. Device (1) according to one of claims 1 to 3,

d a d u r c h e c e n c i n e s that

the submodules (10) of the power switching unit (5) at least partially in each case an energy store (14) and a parallel to the energy storage (14) connected series circuit (15) of two switched on and off power semiconductor switches (11) with oppositely arranged parallel thereto Freilaufdi ^¬ oden (12), wherein a submodule connection terminal (16) having a potential point between the switched on and off power semiconductor switches (11) and the other terminal ^¬ terminal (17) are connected to a pole of the energy store (14).

5. Device (1) according to one of claims 1 to 4,

d a d u r c h e c e n c i n e s that

the submodules (10) of the power switching unit (5) at least partially an energy store (14) and two parallel to the energy storage (14) connected series circuits (15,20) each with two switched on and off power semiconductor switches (11) with oppositely parallel freewheeling diode ( 12), wherein a first terminal (16) with the Po ^¬ tenzialpunkt between the two power semiconductor switches (11) of the first series circuit (15) and a second Submodulanschlussklemme (17) ((with the potential point between the two power semiconductor switches 11) of the second series circuit 20) is connected.

6. Device (1) according to one of the preceding claims, characterized in that a

the power switching unit (5) varistors and / or Abieiter (13) in parallel with at least one submodule (10).

7. The device according to claim 1, wherein:

the varistors and / or Abieiter (13) are at least partially connected in parallel to an energy store (14).

8. Device (1) according to one of the preceding claims, characterized in that a

the submodules (10) of the power switching unit (5) are at least partially designed as a brake actuator module and an energy storage (14) having a first series circuit (15) of a turn-off power semiconductor switch (11) with opposite parallel freewheeling diode and a diode oriented in the same direction to the freewheeling diode and a second series circuit comprising a turn-off power semiconductor switch with a parallel freewheeling diode and a further in the same direction to the freewheeling diode oriented diode is connected in parallel, wherein the diode of the second series circuit bridges an ohmic resistance, the first submodule connection terminal with a pole of the energy storage and the second submodule connection terminal is connected to the Potenzi ^¬ alpunkt between the turn-off Leistungshalbleiterschal ^¬ ter and the diode of the first series circuit.

9. Device (1) according to one of the preceding claims, characterized in that a

the commutation means (6) form a series circuit of zweipo ^¬ ligen submodules (10), each submodule (10) via an energy store (14) and a power semiconductor circuit in parallel to the energy storage (14) has.

10. Device (1) according to claim 9,

d a d u r c h e c e n c i n e s that

the power semiconductor circuit, a series circuit (15) of two power semiconductor switches forms (11) each in opposite directions parallel freewheeling diode (12), wherein a first Submodulanschlussklemme (16) with the poten ^¬ potential point between the turn-off power semiconductor switches (11) and a further Submodulanschlussklemme (17) is connected to a pole of the energy store (14).

11. Device (1) according to claim 9,

characterized in that the power semiconductor circuit two series circuits

(15,20) of each two switched on and off power semiconductor switches (11) each with oppositely parallel freewheeling diode (12), wherein the potential point between see the on and off power semiconductor switches (11) of the first series circuit (15) with the first Submodule connection terminal (16) and the potential point between the switched on and off power semiconductor switches (11) of the second series circuit (20) with the second submodule connection terminal (17) is connected.

12. Device (1) according to one of the preceding claims, e e c e n e c e n e d d e r c h

a charge branch (7) connected to a ground potential or to an opposite pole polarized opposite pole.

13. Device (1) according to one of the preceding claims, characterized in that a

in the charging branch (7) an ohmic resistor (9) is arranged.

14. A method for switching DC currents in a pole of a DC network comprising two terminals (21,22), between which an operating current path (2) with a mechanical switch (4), which can be bridged by a Abschaltzweig (3), wherein the Turn-off branch (3) has a series connection of two-pole submodules (10) with at least one switched on and off power semiconductor switch (11) and wherein in Abschaltzweig (3) arranged commutation means (6) for generating a bridged over section of the operating current path (2) and the turn-off branch (3) are arranged circulating current, in which

a current sensor detecting the current flow in the operating current path to obtain current measurements,

a control unit connected to the current sensor monitors the current measured values for the presence of an intervention criterion and - In the presence of the intervention riteriums Kommutierungsmit ^¬ tel (6) controls so that a large circuit current is generated so that the current flow through the mechanical switch (4) is limited to a maximum current.

15. The method according to claim 14,

d a d u r c h e c e n c i n e s that

the current flow is limited to a maximum current of about zero and the mechanical switch (4) is then opened.

16. The method according to claim 14 or 15,

d a d u r c h e c e n c i n e s that

the mechanical switch (4) is opened and the current flowing through the ex ^¬ switching branch (3) current over a predetermined period of time ^¬ duration is limited to a predetermined maximum fault current.