CN104205281B - Equipment for an extremely middle switching DC current in direct current network - Google Patents

Abstract

In order to reliably and cost-effectively disconnect fault currents in a DC grid, wherein at the same time small losses occur during normal operation, a device (1) for switching DC currents in one pole of a DC grid is proposed, the The device has: two terminals (2,3) for series connection with said poles; a main current branch (4) extending between said terminals (2,3), at said main current branch Two mechanical switches (6, 7) are arranged in the circuit; a bypass current branch (5) extending between the terminals (2, 3) and connected in parallel with the main current branch (4), in the Two mechanical switches (8, 9) and/or two power semiconductors (20, 21) are also arranged in the bypass current branch; an intermediate branch (11), which arranges the main current path (4) in The potential point (10) of the intermediate branch between the mechanical switches (6, 7) and the potential point (12) of the intermediate branch of the bypass current branch (5) arranged between the mechanical switches (8, 9) are mutually connected, and it has a power switch unit (13) with a series circuit consisting of bipolar sub-modules (14), each with at least one power semiconductor switch (22) and a means (24) for reducing the energy released when switching; and commutating means (34) for commutating direct current into the intermediate branch (11) so that the total direct current is conducted through the intermediate branch (11) , wherein the commutation component (34) has at least one controllable power semiconductor (22, 36).

Description

Equipment for switching direct current in one pole of a direct current network

technical field

The invention relates to a device for switching a direct current in one pole of a branch of a direct current network.

Background technique

The worldwide increasing energy demand and the simultaneously expected reduction in carbon dioxide emissions make so-called renewable energy sources increasingly attractive. Renewable energy sources are, for example, wind power plants built by the sea or photovoltaic power plants in sunny desert regions. In order to be able to use the energy generated in this way economically, the connection of renewable energy sources to the continental power grid is becoming increasingly important. Against this background, the construction and operation of networked direct current grids are increasingly being discussed. A prerequisite for this, however, is that short-circuit currents that may occur in such an interconnected DC network can be disconnected quickly and reliably. However, DC voltage switches, which have not been available on the market until now, are required for this purpose. Various concepts for such DC voltage switches are known from the prior art.

WO 2011/057675 A1 describes a DC voltage switch having an operating current path with a mechanical switch and an opening branch connected in parallel to the operating current path. A series circuit of power semiconductor switches, which are each connected in antiparallel to a freewheeling diode, is arranged in the disconnection branch. The switching units consisting of power semiconductor switches and freewheeling diodes are arranged in anti-series, wherein the disconnectable power semiconductor switches are arranged in series, and for each power semiconductor switch a corresponding power semiconductor switch with opposite direction of conduction is provided. In this way, the current flow in both directions in the disconnected branch can be interrupted. In addition to the mechanical switch, an electronic auxiliary switch is arranged in series with the mechanical switch in the operating current path. During normal operation, the current flows via the operating current path and thus via the electronic auxiliary switch and via the closed mechanical switch, since the open branch power semiconductor switch has an increased resistance to the direct current. To interrupt, for example, a short-circuit current, the electronic auxiliary switch is switched into its disengaged position. As a result, the resistance in the operating current path increases, so that the direct current in the disconnection branch commutates. The fast mechanical disconnection switch can thus be disconnected without current. The short-circuit current conducted via the open branch can be interrupted by the power semiconductor switch. In order to absorb the energy stored in the direct current network which is to be reduced during switching, arresters are provided which are connected in parallel with the power semiconductor switches which disconnect the branches.

In DE69408811T2 a DC voltage switch is described in which two mechanical switches are connected in series. The series circuit formed by the two mechanical switches is protected against high overvoltages by arresters and capacitors. The ON/OFF power semiconductor switches are connected in parallel with only one mechanical switch. Arcing occurs when a mechanical switch opens. The voltage falling across the arc triggers the power semiconductor switches, whereby the open mechanical switches connected in parallel are short-circuited. The arc is extinguished. The current conducted via the power semiconductor switches can now be interrupted by correspondingly actuating the power semiconductors.

US Pat. No. 5,999,388 describes a DC voltage power switch which can be integrated in series in a DC voltage line. It consists of a series circuit of power semiconductor switches that can be turned on and off, and the power semiconductor switches that can be turned on and off are respectively connected in parallel with a reverse freewheeling diode. Furthermore, a voltage limiting arrester, for example a varistor, is connected in parallel to each power semiconductor switch. Known DC voltage switches are implemented purely electronically and thus switch significantly faster than conventional mechanical switches on the market. The short-circuit current flowing through the DC voltage switch can be interrupted within a few microseconds. However, the disadvantage is that the operating current also has to be conducted via the power semiconductor switches. This results in high transmission losses.

WO 2011/141055 discloses a DC voltage switch which can be connected in series in one pole of a high voltage DC grid. The DC voltage switch is composed of a mechanical switch connected in series with a power semiconductor switch, and the power semiconductor switch is connected in parallel with a reverse freewheeling diode. The series circuit of coil and capacitor, ie the LC branch, and the arrester, which limits the voltage drop across the LC branch, are connected in parallel to the series circuit of power semiconductor switches and mechanical switches. The power semiconductor switches are also connected in parallel to the arrester. After the mechanical switch is turned off, the power semiconductor switch is turned on and off at the natural frequency of the LC branch. This produces oscillations in the mechanical switch and finally a current zero crossing, so that the resulting arc can be extinguished.

Contents of the invention

The technical problem addressed by the invention is to provide a device of the type mentioned at the outset, with which fault currents in a direct-current network can be disconnected reliably and cost-effectively, with simultaneous low losses occurring during normal operation.

The invention solves the above-mentioned technical problems by means of a device for switching a direct current in one pole of a direct current network, said device having: two terminals for series connection with said pole; extending between the terminals a main current branch in which two mechanical switches are arranged; a bypass current branch connected in parallel with the main current branch extending between the terminals, in which Two mechanical switches and/or two power semiconductors are also arranged in the middle; the intermediate branch, which connects the intermediate branch potential point of the main current path arranged between the mechanical switches, and the bypass current branch between the mechanical switches The potential points of intermediate branches arranged occasionally or between the power semiconductors are interconnected and have power switching units with a series connection of bipolar submodules each with at least one power semiconductor switch and means for reducing the energy released during switching; commutation means for commutating direct current into the intermediate branch so that the total direct current is conducted through the intermediate branch, wherein the commutation means has at least one control power semiconductors.

According to the invention, a so-called H-circuit is provided which has two branches running parallel to one another, namely a main current branch and a bypass current branch. Two parallel branches each run between two terminals, wherein each branch has two mechanical switches. The potential point between the mechanical switches of the main current branch is connected to the potential point between two mechanical switches of the bypass current branch or between the power semiconductor switches via the intermediate branch. Arranged in the middle branch is a power switching unit, which in its own right comprises a series circuit of bipolar submodules. Each sub-module has at least one power semiconductor switch that can be turned on and off, that is, IGBT, IGCT, TGO, etc., and the power semiconductor switches have anti-parallel freewheeling diodes according to requirements. Instead, however, it is also possible to use power semiconductor switches with reverse conduction capability. The number of submodules depends on the respective requirements. In each case, the submodules of the power switching unit must be able to absorb the applied voltage and also be able to disconnect high short-circuit currents safely and sufficiently quickly. The energy stored in the DC grid and released during disconnection is reduced by suitable components for reducing the switching energy. These are, for example, non-linear resistors such as dischargers, varistors or the like. If the voltage dropped across it exceeds the threshold voltage, the component behaves like an ohmic resistor, in which it converts the energy released during switching into heat and dissipates it into the external environment. It is expedient to integrate components for reducing switching energy into submodules. In contrast to this, the varistors are each connected in parallel to one or more submodules. Furthermore, within the scope of the invention, the submodule can also have an energy store. Within the scope of the invention, the direct current to be switched can be conducted separately via the main current branch during normal operation. Alternatively, a direct current is conducted both through the main current branch and through the bypass current branch during normal operation. In each case the H-circuit allows the direct current to be commutated into the intermediate branch such that it is always conducted in one direction only through the intermediate branch independently of the direction of the direct current. The power semiconductors of the power switching unit must therefore basically be designed for switching current in one direction only. However, reverse currents in intermediate branches may have to be taken into account in the event of possible grid fluctuations.

Furthermore, according to the invention, a commutation element is provided which has at least one controllable power semiconductor. Within the scope of the invention, the commutation element enables an active commutation of the direct current to be switched at least from a section of the main current branch into an intermediate branch. For this purpose, the power semiconductors of the commutation components are controlled by means of a control signal, so that the resistance in said sections of the main current branch and possibly in the bypass current branch increases or a loop current conducted through said sections is generated, which is compatible with the section to be operated. The switched DC currents add up to approximately zero. The commutation element supports the mechanical switch when the direct current is commutated into the intermediate branch.

Advantageously, a charging branch is provided which is connected on the one hand to ground potential or to the opposite pole of the opposite polarity of the direct current network and on the other hand is or can be connected to an intermediate branch, wherein the charging branch has an ohmic resistance. The charging branch is used both for start-up operation and for operation of the device in normal operation. If the charging branch is connected, for example, to an intermediate branch potential point of the bypass current branch, the main current branch is connected via the intermediate branch and the charging branch to ground potential or to the opposite pole of the DC network. As a result, a voltage at which the electronics, for example power semiconductor switches of the power switching unit can be operated, is applied to the power switching unit. If the submodule has an energy store in the intermediate branch, it can be charged via the charging branch, the height of the charging current being determined by the configuration of the ohmic resistance of the charging branch. Within the scope of the invention, the charging branch is either continuously connected to the intermediate branch, or it has a mechanical switch with which the connection between the charging branch and the intermediate branch can be established and also interrupted. The connection between the charging branch and the intermediate branch can only be provided uninterruptedly in fault-free network operation due to the ohmic resistance. Within the scope of the invention, it is also not necessary to separate the charging branch from the intermediate branch before breaking the short-circuit current. Within the scope of the invention, the current flow is at any time limited by the ohmic resistance of the charging branch.

If a power switching unit is provided, the short-circuit current can be interrupted, for example, by means of the device according to the invention. In normal operation, the direct current flows almost losslessly through the main current branch with its two mechanical switches. This also holds true for the bypass current branch in the case of a symmetrical design of the device according to the invention. In the event of a fault, the switch of the main current branch arranged behind the potential point of the intermediate branch in the direction of current flow and the mechanical switch of the bypass current branch, which may be arranged in front of the potential point of the intermediate branch, are opened. When no further measures are taken, an arc occurs due to the separation of the contacts of the switch. Ideally, the commutation components completely suppress the generation of arcs. By opening the switch, the current is commutated from the main current branch into the intermediate branch and the lower part of the bypass current branch. The power semiconductor switches of the power switching unit can then break the short-circuit current. The energy released here is reduced by means for reducing the energy released during switching. Finally, the remaining mechanical switches of the device according to the invention are also opened. The short-circuit current is broken, and the intermediate branch is electrically separated from the conductor.

The resistors of the charging branch are designed high-resistance so that they can be operated at least temporarily at the full DC voltage present and at the same time low-resistance so that the required flow for precharging the energy store and maintaining the charge permanently can flow through. the charging current. To charge the energy store of the power switching unit, a voltage drop of several thousand volts is sufficient. The resistance of the charging branch can thus be designed to be very high-resistance. The maximum power loss and the component size of the ohmic resistor are thus relatively small.

Expediently, the charging branch is or can be connected to an intermediate branch potential point of the bypass current branch. According to this advantageous embodiment of the invention, the charging current flows from the main current branch through the entire intermediate branch. When the first mechanical switch of the main current branch in the direction of current flow is in its closed position, all energy stores arranged in the intermediate branch can thus be charged.

Expediently, the charging branch has a mechanical switch connected in series with the ohmic resistor, which is designed to connect the charging branch to the intermediate branch. As already explained, the mechanical switch may be a relatively slow mechanical switch due to ohmic resistance. The switch is, for example, a simple circuit breaker, which opens almost without current flow. A resistor of the charging branch, which can also be referred to as a precharging resistor, is thermally unloaded via the switch.

Advantageously, the submodules of the power switching unit each have at least partially a power semiconductor switch that can be switched on and off and a freewheeling diode connected antiparallel thereto. Alternatively, each submodule can also have a single reverse-conducting power semiconductor switch. As power semiconductor switches, for example, IGBTs, IGCTs, GTOs and the like are conceivable. Usually, a power semiconductor switch has a plurality of power semiconductor switch chips arranged in a housing. Bonding wires are used, for example, to connect the load terminals of the power semiconductor switching chips. In contrast to this, however, pressure-contact power semiconductor switches can also be used within the scope of the invention, in which the power semiconductor switch chips are connected to one another via pressure contacts on the load connection side. However, such power semiconductor switches are known to those skilled in the art, so that a detailed discussion of their construction is not required here.

The switchable and switchable power semiconductor switches of the submodules are preferably designed for breaking the current flow in one direction.

According to a development different from this, however, the submodules of the power switching unit are formed by two groups of their power semiconductor switches each having the same direction of conduction, wherein the power semiconductor switches of one group are connected to the power semiconductor switches of the other group. The semiconductor switches are oriented oppositely. According to this advantageous development, current can not only flow in both current directions via the disconnection branch, but also the current in both directions can be disconnected safely. If a current flows in a first direction, for example due to grid fluctuations, the power semiconductor switches of the first group are controlled in order to interrupt the current flow in said first direction. If the current flows in a second, opposite direction, a second set of power semiconductor switches is used.

In a preferred configuration of the invention, the submodules of the power switching unit each have at least partially an energy store and a series circuit consisting of two switchable power semiconductor switches connected in parallel to the energy store, the power The semiconductor switches each have a freewheeling diode arranged in antiparallel to them, one submodule terminal being connected to a potential point between the switchable and deactivatable power semiconductor switches, and the other terminal being connected to the energy store. A pole is connected. Such a submodule topology is also known as a half-bridge.

Of course, instead of individual power semiconductor switches in a submodule, a series circuit of synchronously controlled power semiconductor switches can also be used. The synchronously controlled power semiconductor switches of the series circuit then behave like individual power semiconductor switches. Furthermore, this also holds true for the submodules described in detail below, that is to say for the full bridge circuit or the brake regulator circuit.

In order to reduce the energy stored in the DC network which is released during switching, at least one non-linear resistor, for example in the form of a discharger and/or a varistor, is provided for each submodule of the power switching unit. The varistor is connected in parallel with the entire submodule, for example.

As a submodule of a power switching unit designed as a half-bridge, the current can only be interrupted in one direction. If the current flow in both directions is to be interrupted, it is also necessary to form two groups of submodules, one of which is used for the disconnection of the current in the first direction, and the other group of submodules The submodule is used for disconnection of the current in a second direction opposite to the first direction.

According to a preferred embodiment of the invention, however, the submodules of the power switching unit are designed at least partially as a full-bridge circuit and thus have an energy store and two series circuits connected in parallel to the energy store, the series circuits respectively Two power semiconductor switches that can be switched on and off, each with a freewheeling diode connected in antiparallel, wherein the first terminal is connected to a potential point between the two power semiconductor switches of the first series circuit, and the second The second submodule terminal is connected to a potential point between the two power semiconductor switches of the second series circuit. Such a full-bridge circuit is capable of interrupting, in other words breaking, current flow in both directions.

As already explained, each submodule of the power switching unit expediently has a discharger and/or a varistor connected in parallel with the individual switchable power semiconductor switches or with the energy store of the submodule.

Advantageously, the sub-module of the power switch unit has a series circuit composed of a power semiconductor switch that can be turned on and can be disconnected with a reverse freewheeling diode and a diode with the same conduction direction as the freewheeling diode, wherein the series circuit is connected to the energy storage connected in parallel, and the terminal of the first submodule is connected to the potential point between the power semiconductor switch and the diode which can be turned on and off, and the terminal of the other submodule is connected to one pole of the energy storage and can be connected to On-off power semiconductor switches are arranged between sub-module terminals. Such a submodule can be referred to as a half-bridge with only one controllable power semiconductor. A corresponding configuration of the full bridge circuit can likewise be advantageous within the scope of the invention. Such a full bridge circuit then has two controllable power semiconductor switches.

In contrast to this, the submodules of the power switching unit are at least partially designed as brake regulator modules. Such a brake regulator module has an energy store which is connected in parallel to the first series circuit. The first series circuit consists of a switchable power semiconductor switch with a freewheeling diode connected in antiparallel and a diode aligned in the same manner as the freewheeling diode. Furthermore, a second series circuit is provided, which is likewise connected in parallel to the energy store. The second series circuit consists of a switchable power semiconductor switch with an anti-parallel freewheeling diode and a further diode aligned in the same manner as the freewheeling diode. The diode of the second series circuit shunts the ohmic resistor. The first submodule terminal is connected to one pole of the energy store, and the second submodule terminal is connected to a potential point between the disconnectable power semiconductor switch and the diode of the first series circuit. Such a brake regulator module can convert energy stored in the grid, which is to be reduced during switching, into thermal energy particularly well and conduct it into the external environment.

According to a preferred configuration, the commutation element in the intermediate branch is arranged in series with the power switching unit and is designed to generate a loop current flowing through at least one mechanical switch of the main current branch, which is opposite to the direct current to be switched . Such loop currents can be generated in two cells to the left and right of the middle branch, each mesh being formed from the middle branch, a section of the main current path and a section of the bypass current path. In a mesh it is opposite to the direct current to be switched in the main current branch. Ideally, the two currents add to zero, so that the mechanical switch in this section of the main current branch can then be opened without current flow. In the other mesh, however, the loop current and the direct current to be disconnected in the main current branch flow in the same direction and are thus amplified. In the case of a symmetrical configuration of the device according to the invention, the corresponding situation also holds for the bypass current branch, so that the mechanical switch is also open without current flow in the bypass current branch. The two current-free open switches are thus arranged in the bypass current branch and the main current branch in the direction of the direct current behind the respective intermediate branch potential point. When at least one mechanical switch of the main current branch is open and the flow of the direct current to be switched via the bypass current branch is blocked by a mechanical switch or diode which is also open, the external current, that is to say in the direct current according to the invention The current flowing outside the voltage switch is only affected. The commutation element is designed so that it generates a high reverse voltage in the mesh in the required time window, thereby suppressing the current flow in the main current branch, and is arranged in the direction of flow of the direct current at A mechanical switch after the potential point of the intermediate branch of the main current branch can be opened without current flow.

Expediently, the commutation component has a current sensor which is arranged in the main current branch. The current sensor is connected to the control or regulation unit of the device according to the invention. The current sensor detects the current flowing through the main current branch and provides a current measurement value for the regulating unit. The control unit checks the received measured current values for the occurrence of violations. Such violations are, for example, too large a current increase, di/dt, or a violation occurs when the measured current value exceeds a current threshold within a predetermined time window. In principle, however, any combination with other measured values etc. of the protective device or other criteria are possible within the scope of the present invention. If such a violation occurs, the current is commutated into the intermediate branch and the mechanical switch opens. As soon as the mechanical switch is able to absorb the voltage, the current flowing through the intermediate branch is now limited or interrupted. If the current is only limited but not disconnected in the intermediate branch, only a few submodules of the power switching unit are disconnected. If a varistor, such as a discharger, is connected in parallel to the disconnected submodule, the varistor plays its role in this, ie increases the resistance of the intermediate branch. The current flowing through the intermediate branch is thus limited. If this limitation becomes redundant, for example after the fault has been eliminated quickly, the mechanical switch of the main current branch can be closed again, so that the current flows again almost without losses via the main current branch and optionally via the bypass current branch.

In a development suitable for this purpose, the charging branch is connected to a potential point between the power switching unit and the commutation element. Such a connection of the charging branch between the commutation component and the power switching unit makes it possible to also use components of the bypass current branch for the charging current for charging the energy store of the commutation component. This is then particularly advantageous if the commutation component has submodules in the form of a so-called half-bridge.

According to a preferred embodiment of the invention, the commutation element consists of a series circuit of bipolar submodules, each submodule having an energy store and a power semiconductor switch connected in parallel to the energy store. The voltage dropped at the submodule terminal of the bipolar submodule can be adjusted by means of the power semiconductor circuit. The voltage dropped on the energy store or zero voltage, ie no voltage, is applied to the terminal of the submodule. Due to the series circuit, the voltage dropped across the entire series circuit of the submodules of the commutation components can thus be adjusted step-by-step, with the height of the stages corresponding to the voltage dropped across the energy stores of the submodules. The higher the voltage generated across the commutation element in the mesh, the higher the loop current driven by this voltage.

As already described in connection with the submodules of the power switching unit, the power semiconductor circuits of the commutation components can be configured as half-bridge or full-bridge circuits. If the power semiconductor circuit is a half-bridge circuit, only a series circuit of two disconnectable power semiconductor switches each with anti-parallel freewheeling diodes is provided, wherein the first submodule terminal is connected to the switchable and disconnectable power The potential points between the semiconductor switches are connected, and the other submodule terminal is connected to one pole of the energy storage. The submodules of the commutation components configured as half-bridge circuits must be oriented in such a way that a reverse voltage with the desired polarity can be generated in the operating current path. The half-bridge circuits of the commutation components are then generally oriented opposite to the half-bridge circuits of the submodules of the power switching unit.

In contrast to this, the power semiconductor circuits of the submodules of the commutation component are designed together with the energy store 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 switchable power semiconductor switches each with an antiparallel freewheeling diode. Instead of power semiconductor switches with freewheeling diodes, power semiconductor switches capable of reverse conduction can also be used. The potential points between the two power semiconductor switches are each connected to a submodule terminal, so that a voltage drop across the energy store, a zero voltage or an inverted energy store voltage can be generated at the submodule terminal. The full bridge circuit can thus generate voltages with different polarities. This is particularly advantageous when opposite voltages are to be generated for current flow in both directions.

For example, capacitors are provided as energy stores for the commutation components and submodules of the power switching unit.

According to a different embodiment of the invention, the commutation element is designed as a commutation semiconductor switch which is arranged in the main current branch. The commutation semiconductor switches are switched on and off like other power semiconductor switches and if required have antiparallel freewheeling diodes. Instead of the parallel connection of the power semiconductor circuit and the freewheeling diode, it is also possible to use a power semiconductor switch capable of reverse conduction. To reduce the energy released during switching, power semiconductor switches can be connected in parallel with arresters, varistors or other non-linear resistors. Energy storage such as capacitors etc. may also be used to reduce energy. In this case, the commutation semiconductor switch is arranged between the potential point of the intermediate branch, that is to say the intermediate branch potential point of the main current branch, and a mechanical switch of the main current branch. This provides two commutation semiconductor switches with anti-parallel freewheeling diodes and, if necessary, an arrester as means for reducing the energy released during switching. However, the non-linear circuit is not always mandatory and can be omitted if necessary within the scope of the present invention. In order to commutate the current flowing through the main current branch into the intermediate branch, the reversing switch arranged after the potential point of the intermediate branch in the direction of direct current flow is switched into its open position, in which position, the current flow through the reversing switch is interrupted. If the resistance in the main current branch is too great, the direct current is commutated into the intermediate branch and can be disconnected there in a targeted manner after opening the mechanical switch. Simultaneously with the actuation of the commutation semiconductor switch, a mechanical switch arranged downstream of the commutation semiconductor switch in the direction of current flow is also opened. The conduction direction of the commutation semiconductor switches is selected such that the current flowing from the intermediate branch potential point to the respective associated mechanical switch can be interrupted by the commutation semiconductor switches. In order to be able to switch off both current directions, according to this exemplary embodiment the two commutation semiconductor switches are oriented opposite to each other.

If the bypass current branch does not have a commutation semiconductor switch, the mechanical switch is open during normal operation, since otherwise the current flow would flow through the bypass current branch due to the increased resistance in the main current branch. The bypass current branch must therefore have a fast-closing mechanical switch to ensure commutation in the intermediate branch.

According to a preferred embodiment of the invention, the bypass current branch thus also has two commutation semiconductor switches, which are arranged and aligned in the same manner as the commutation switches of the main current branch. During normal operation, current can thus flow both via the main current branch and via the bypass current branch. For the commutation of the current in the intermediate branch, the reversing switch in the main current branch which is arranged after the potential point of the intermediate branch of the main current branch and the switch which is arranged in the current direction in the bypass current branch The reversing switches before the potential point of the intermediate branch switch to their respective disengaged positions.

Instead of two mechanical switches, the bypass current branch can also have power semiconductors, wherein the intermediate branch potential point is arranged between the power semiconductors. The power semiconductors have oppositely oriented conduction directions and are designed, for example, as diodes or thyristors. It prevents current flow through the bypass current branch during normal operation.

Expediently, the mechanical switch of the main current branch is designed as a fast switch and is designed to open within 1 ms to 10 ms. However, the mechanical switch of the bypass current branch is, for example, a relatively slow mechanical switch which opens within a time range of 10 ms to 60 ms. Such fast switches have a small switching mass that must be moved during switching. Furthermore, fast-response drives, such as electrokinetic drives, are required. Common power semiconductor switches currently on the market are usually turned off within an order of magnitude of 10 ms to 50 ms. Such a commercially available switch is arranged, for example, in a bypass current branch. It is disconnected before a fault occurs, where the direction of the direct current to be switched is known. Of course mechanical switches are also known which open within a few milliseconds.

According to a further variant of the invention, it is expedient if the device according to the invention is likewise used in a modular manner and is thus used as a two-pole or two-pole assembly in a series circuit.

Finally, it should be pointed out that although the switchable power semiconductor switches which can be turned on and off are always disclosed here in combination with an anti-parallel freewheeling diode or as power semiconductors capable of reverse conduction, this is above all due to the fact that the power semiconductors which can be turned off such as IGBTs, IGCTs, GTOs, etc. are usually always sold in the market with anti-parallel freewheeling diodes. Such freewheeling diodes are used for the protection of power semiconductor switches which are extremely sensitive to voltages opposite their conduction direction. However, the freewheeling diode is not mandatory in all cases shown here. These situations are obvious to those skilled in the art, so that they will not be specified in detail. However, implementations of the invention in which the freewheeling diode arranged in antiparallel to the power semiconductor switch can be dispensed with due to functional limitations are intended to be included within the scope of protection.

Description of drawings

Further suitable configurations and advantages of the invention are the subject of the following description of exemplary embodiments of the invention with reference to the drawings, in which identical reference numbers designate identically acting parts and in which:

Figure 1 shows a first embodiment of the device according to the invention,

Figures 2 and 3 show the embodiment according to Figure 1 in different states to explain step by step the charging of the device according to Figure 1,

Figure 4 shows another embodiment of the device according to the invention,

Figures 5 to 8 show an embodiment of a submodule employed in a device according to the invention, and

9 to 14 show further embodiments of the device according to the invention.

detailed description

FIG. 1 shows an exemplary embodiment of a device 1 according to the invention, which has two terminals 2 and 3 , with which the device 1 can be connected in series in one pole, ie, one line, of a DC network. The device 1 is used to interrupt the current flow in the poles of the direct current network and can therefore be referred to as a direct voltage switch.

The device 1 has a main current branch 4 and a bypass current branch 5 . In the exemplary embodiment shown in FIG. 1 the two current paths are equal, in other words have approximately the same resistance. The direct current flowing between the terminals 2 and 3 thus flows both via the main current branch 4 and via the bypass current branch 5 . The main current branch 4 and the bypass current branch 5 each have two mechanical switches 6 , 7 , 8 and 9 . An intermediate branch potential point 10 is formed between the mechanical switches 6 and 7 of the main current branch 4 . The intermediate branch potential point 10 is connected to the intermediate branch potential point 12 of the bypass current branch 5 via the intermediate branch 11 . The intermediate branch 11 has a power switching unit 13 with a series connection of submodules 14 , the construction of which will be discussed in more detail below. It has already been mentioned here that each submodule 14 has at least one switchable power semiconductor switch whose conduction direction is from the middle branch potential point 10 of the main current branch 4 to the side of the bypass current branch 5 The middle branch potential point 12 is oriented. As a result, the current flowing in this direction via the power switching unit 13 can be switched off in a targeted manner by the switchable and deactivable power semiconductor switches of the power switching unit 13 . Components for absorbing the energy released during switching, that is to say for example nonlinear resistors such as arresters or varistors, are used to absorb the switching energy released here. These arresters are either part of the submodules as shown or connected in parallel with one or more submodules.

Furthermore, a reversing element 34 can also be seen in FIG. 1 , the construction of which will likewise be discussed in more detail below. The commutation element 34 has in each case at least one switchable power semiconductor switch which is not shown in FIG. 1 . With corresponding control of the power semiconductor switches, the commutation element 34 carries out the commutation of the direct current to be disconnected into the intermediate branch 11 .

For switching on the electronics and also for charging the energy storage of the power switching unit 13 and possibly of the commutation components, a charging branch 15 is provided which has an ohmic resistor 16 as a precharging resistor and a mechanical switch 17, The mechanical switch is designed here as a disconnect switch. In the exemplary embodiment shown in FIG. 1, the charging branch 15 is connected to ground potential. In contrast to this, however, the charging branch 15 is connected to the opposite pole of the DC network, ie, for example the negative pole, while the terminals 2 and 3 are connected to the positive pole of the DC network. In both variants, after the pole voltage has been applied to the terminal 2 and the mechanical switch 6 is closed after the switch 17 has been closed, there is the possibility of intercepting the The voltage is used for the energy supply of the electronics of the power semiconductor switches and thus makes the power switching unit 13 ready. Furthermore, it is possible to charge the energy store arranged in the submodule 14 in a controlled manner, the magnitude of the charging current being determined by the magnitude of the ohmic resistor 16 . The ohmic resistor is designed such that it can be operated at least temporarily with the full voltage drop between said pole and ground potential or the opposite pole. In principle, switch 17 can remain permanently closed with a correspondingly high configuration of resistor 16 . In contrast to this, it can be used for unloading the ohmic resistor 16 that occurs when the switch 17 is opened.

2 and 3 show the charging of the energy stores of the submodules 14 of the power switching unit 13 and optionally of the not shown submodules of the commutation element 34 . To do this, initially only the mechanical switches 6 and 17 are closed. The charging current I now flows from terminal 2 via switch 6 via intermediate branch 11 and charging branch 15 to ground. First the energy buffers of the electronics of the power semiconductor switches are charged, and then the high-voltage energy stores of the submodules 14 are charged. If the power switching unit 13 is ready, the switch 7 is closed. The main current now flows to terminal 3 via mechanical switches 6 and 7 . However, the charging current flowing via the intermediate branch 11 remains as long as the switches 8 and 9 of the bypass current branch 5 are open.

FIG. 4 shows another embodiment of the device 1 according to the invention, which corresponds as far as possible to the embodiment according to FIG. Between the branch points 18 between the roads 5, the switch 9 is arranged between the branch points 19 and the terminals. Power semiconductors 20 and 21 in the form of diodes are arranged in their place in the bypass current branch, which prevent current from flowing directly from the terminal 2 or 3 via the bypass current branch 5 into the charging branch 15 , whereas It does not conduct through the intermediate branch 11. The switches 8 and 9 between the terminals 2 and 3 and the branch point 18 or 19 can in principle be omitted. However, it enables a controlled connection of a DC grid segment and an electrical separation of the unit from the DC grid.

Examples of possible submodules 14 for the device 1 according to the invention are shown in FIGS. 5 , 6 , 7 and 8 . The submodule 14 shown in FIG. 5 has only a single switchable power semiconductor switch 22 with an antiparallel-connected freewheeling diode 23 . In the embodiment of the invention according to FIGS. 1 to 4, such a submodule 14 can only be used as a component of the power switching unit 13, but not as a component of the commutation element 34, since it is arranged in the intermediate branch 11. The case must have an accumulator to generate the loop current. A discharger 24 is connected in parallel to the parallel circuit of the power semiconductor switch 23 and the freewheeling diode, which discharger absorbs the switching energy released during switching. The arrester 24 is thus a component for absorbing the energy released during switching. Instead of individual switchable power semiconductors, it is also possible within the scope of the invention to use controllable switchable power semiconductors at the same time for the series circuit, with individual dischargers being connected in parallel to the entire series circuit.

The number of submodules 14 in the power switching unit 13 depends on the blocking capability of the power semiconductor switches 22 , in this case the blocking capability of the IGBTs. It is currently in the range up to 6.5 kV. The voltages in high-voltage direct current grids, which are currently constructed almost exclusively as point-to-point connections, typically lie between 300 and 500 kV. 800 kV transmission lines are also known. The arrester 24 is dimensioned such that it is generally blocked, ie does not conduct, when an operating voltage is applied. However, if the voltage dropped across it exceeds the maximum voltage, it is switched on so that a controlled current flow is possible, wherein the arrester 24 heats up and electrical energy is output as thermal energy to the external environment. The number of arresters 24 connected in series corresponds to the number of non-conductive, ie disconnected, submodules. That is, if the submodule 14 is not switched into its off position, a current flow of a controlled magnitude can be established through the arrester. This is used, for example, for the controlled connection of grid segments.

FIG. 6 shows a submodule 14 which forms a so-called half bridge. The half-bridge consists of an energy store 25 , here a high-voltage capacitor, and a series circuit 26 connected in parallel to the energy store 25 . The series circuit 26 has two switchable power semiconductor switches 22 in the form of IGBTs connected in series to one another, each of which is connected in antiparallel to a freewheeling diode 23 . The first terminal 27 is connected to a potential point between the two power semiconductor switches 22 of the series circuit 26 . The second terminal 28 is at the potential of one pole of the energy store 25 . A bypass switch 29 is provided between the terminals 27 and 28 , with which the submodule 14 can be bypassed in the event of a fault. In the event of a failure of an individual submodule, the entire power switching unit 13 remains operable. In order to absorb high short-circuit currents, a diode 30 is arranged between submodule terminals 27 and 28 . It supports freewheeling diode 23 , which is likewise arranged between submodule terminals 27 and 28 , in the case of high currents flowing through submodule 14 . Instead of diodes 30 , thyristors can also be used. However, bypass switches 29 and diodes 30 or thyristors 30 between the terminals are not always mandatory. If the submodule 14 is used, for example, in the power switching unit 13 to interrupt the current flowing via the intermediate branch 11 , the diode 30 or the thyristor used in place of the diode can be omitted without replacement. Furthermore, within the scope of the invention it is also possible to use pressure-contact power semiconductors with the so-called “conduct on fail” characteristic, ie they conduct in the event of a fault. This generally makes diode 30 unnecessary. Finally, it is pointed out that one, that is to say overall two series circuits of power semiconductor switches can be used in each case in place of two individual power semiconductor switches. The half bridge also has a discharger 24 which is connected in parallel to an energy store 25 . Furthermore, the arrester 24 also serves to absorb the energy released during switching. In a different embodiment from FIG. 6 , arrester 24 is arranged between submodule terminals 27 and 28 . However, the half-bridge circuit according to FIG. 6 can only interrupt the current flow in the direction from the first submodule terminal 27 to the second submodule terminal 28 . In the opposite direction, the current flows unimpeded and uncontrolled via freewheeling diode 23 and optionally via short-circuit diode 30 . However, the current to be switched off flows in principle only in one direction via the intermediate branch 11 via the half-bridge circuit selected within the scope of the invention, so that the half-bridge switching the current as a submodule 14 in the intermediate branch 11 is particularly preferred. It should be noted here that the power semiconductor switch 22 at the top of FIG. 6 , ie not the power semiconductor switch 22 arranged between the submodule terminals 28 , 29 , can also be dispensed with for switching or limiting the current. The series circuit 26 according to FIG. 6 then corresponds to the series circuit 26 according to FIG. 8 . However, such half-bridge submodules 14 are not suitable for generating loop currents and are therefore not suitable for use as a component of a commutation element 34 in the intermediate branch 11 , which will be discussed in more detail below.

FIG. 7 shows the submodule 14 implemented as a full bridge circuit. The full bridge circuit according to FIG. 7 also has an energy store 25 and a first series connection 26 of two IGBTs 22 with antiparallel freewheeling diodes 23 . In addition, however, a second series circuit 31 is provided, which likewise connects the energy store 25 in parallel and likewise has two IGBTs 22 connected in series with each other with antiparallel freewheeling diodes 23 . The first submodule terminal 27 is connected to a potential point between the IGBTs 22 of the first series circuit, and the second submodule terminal 28 is connected to a potential point between the IGBTs 22 of the second series circuit 31 . The half-bridge circuit according to FIG. 6 is able to generate a capacitor voltage Uc or a voltage zero, ie zero voltage, which drops across the capacitor 25 at the submodule terminals 27 and 28 depending on the actuation of the IGBT 22 . Furthermore, not only the capacitor voltage Uc and the zero voltage dropped at the energy store 25 but also the reverse capacitor voltage −Uc can be generated at the submodule terminals 27 and 28 . The submodule terminals 27 , 28 of the full bridge circuit can thus have different polarities. It should also be pointed out here that in each series circuit 26 and/or 31 one of the IGBTs 22 , for example the IGBT 22 respectively shown above in FIG. 7 , can be omitted without replacement. That is to say that such a full-bridge submodule 14 with a total of two or three switchable and switchable power semiconductors 22 as part of the power switching unit 13 is suitable for switching or limiting the current in the intermediate branch 11 . However, no loop current can be generated with such a submodule 14 . A full-bridge submodule 14 with two or three switchable power semiconductor switches 22 is therefore not suitable as part of a commutation element 34 in the intermediate branch 11 , the construction of which will be discussed in more detail below.

FIG. 8 shows a submodule 14 referred to here as a brake regulator module. The brake regulator module 14 also has an energy store 25 and a first series connection 26 connected in parallel to the energy store 25 . However, the series circuit 26 has only one power semiconductor switch 22 with an antiparallel freewheeling diode 23 . A further diode 32 is connected in series with the power semiconductor switch 22 , in this case an IGBT, which diode is oriented in the same way as the freewheeling diode 23 of the first series circuit 26 . Furthermore, a second series circuit 31 is provided, which is likewise connected in parallel to the energy store 25 and likewise has only one IGBT 22 with a freewheeling diode 23 and a further diode 32 connected in series thereto. An ohmic resistor 33 is arranged in parallel with the diode 32 of the second series circuit 31 . The second series circuit 31 serves to limit the voltage drop across the energy store 25 . If this voltage is too high, IGBT 22 is switched on, so that current flows through ohmic resistor 33 and energy store 25 is discharged. The first submodule terminal 27 is connected to the potential point between the diode 32 of the first series circuit 26 and the IGBT 22 , while the second submodule terminal 28 is at the potential of the pole of the energy store 25 . Due to this connection, the application of the energy storage voltage between the submodule terminals 27 and 28 is not possible. Only the current flow from the submodule terminal 27 to the submodule terminal 28 can be switched on. The energy store 25 is mainly used for the energy supply of the electronics of the IGBT. The capacitor also ensures that no voltage spikes occur during switching, which could damage the semiconductors. It should be noted here that, instead of the second series circuit 31 , a discharger can also be used, which is connected in parallel to the energy store 25 . In other words, the brake regulator module then corresponds to the half-bridge circuit shown in FIG. 6 , the IGBT 22 not being arranged between the two submodule terminals 27 and 28 being omitted.

Within the scope of the invention, both submodules 14 according to FIG. 7 as well as according to FIG. 8 can be advantageous if a power semiconductor switch or a mechanical switch 29, such as a thyristor, is arranged between the submodule terminals 27 and 28, as in connection with FIG. 6 shown in the half bridge. A mechanical switch 29 is used to bypass the submodule 14 when required.

FIG. 9 shows another embodiment of the device 1 according to the invention, which corresponds as far as possible to the embodiment shown in FIG. 13 Commutation elements 34 arranged in series. The commutation element 34 likewise consists of a series circuit of submodules 14, only one of which is shown in FIG. . According to the exemplary embodiment shown in FIG. 9 , submodule 14 of commutation element 34 is designed as a full bridge circuit with arrester 24 according to FIG. 7 . The submodule 14 of the commutation element 34 is designed to drive two mutually opposite return currents into the mesh formed by the main current branch, the bypass current branch and the intermediate branch. The device shown in FIG. 9 is symmetrically constructed. In other words, the direct current to be disconnected during normal operation flows both via the main current branch 4 and via the bypass current branch 5 , for example from terminal 2 to terminal 3 . Each of the two loop currents generated by the reversing element 34 is in the mechanical switch, here one of 7 and 8 , opposite to the direct current to be switched on, so that in the respective mechanical switch 7 and 8 current is approximately zero. The mechanical switches 7 and 8 are thus open without current. The total current is commutated to the intermediate branch 11 and flows to the terminal post 3 via the power switching unit 13 and the mechanical switches 6 and 9 . The submodule 14 of the power switching unit 13 can now break or limit the direct current. The remaining mechanical switches 6 and 9 can then be opened.

As already described above, via the submodule 14 of the commutation element 34, the two return currents are driven through the two meshes formed by the intermediate, bypass and main current branches. One of the loop currents flows in a clockwise direction, while the other loop current flows in a counterclockwise direction through the respective meshes. In this way it is ensured that independent of the direction of the direct current to be switched off, one of the direct current to be switched on and the loop current is always bypassed in one of the mechanical switches 6, 7 of the main current branch The superposition in a mechanical switch 8 or 9 of the current branch is approximately zero. In this case, the switches in which the resulting current is adjusted to approximately zero are arranged on different sides of the intermediate branch, that is to say in the direction of the direct current to be switched on before or at the intermediate branch potential point of their respective branch. after. The mechanical switches, eg 7 and 8 , can now be opened so that current flows through the power switching unit 13 , whose submodule 14 can then open or limit the current flow. The submodule 14 of the commutation element 34 shown in FIG. 9 likewise has an arrester 24 so that it can also be operated as a submodule of the power switching unit 13 . If the submodule 14 of the power switching unit 13 is likewise formed as a full bridge circuit according to FIG. 7 , it can also be said that there is only a single series circuit, wherein only the submodule is actuated via a control and regulation unit not shown, to distinguish the submodule 14 Whether it works as part of the commutation element 34 or as part of the power switching unit 13 . Of course, the full-bridge sub-module 14 can also play two roles in a time-shifted manner. Of course, the submodule 14 of the commutation element 34 configured according to FIG. 7 as a full bridge circuit with the arrester 24 can also be used for breaking or limiting the current.

It is pointed out here that within the scope of the present invention, the submodules 14 of the power switching unit 13 do not always have to be constructed identically. Thus, for example, one part of the submodule 14 can be configured according to FIG. 5 , another part according to FIG. 6 , another part according to FIG. 7 , and the last part according to FIG. 8 . However, the submodule 14 of the commutation element 34 must have an energy store 25 with which the circuit current in the mesh can be generated. Furthermore, the submodule 14 must be able to generate the voltage dropped across the energy store 25 at the submodule terminals 27 , 28 .

FIG. 10 shows the configuration according to FIG. 9 , but in which the commutation element 34 is designed as a half-bridge circuit according to FIG. 6 , but in which no diode 30 and no bypass switch are provided. In FIG. 10 , a plurality of submodules 14 of the commutation element 34 are also connected in series, wherein the series circuit is also shown here by dashed lines. In contrast to the full bridge circuit according to FIG. 9 , the half bridge circuit according to FIG. 10 can generate only one voltage polarity at submodule terminals 27 and 28 . However, since the current through the intermediate branch 11 always flows in one direction only, this one voltage polarity is quite sufficient to switch or limit the direct current in both directions. Furthermore, the current flowing from the main current branch 4 via the intermediate branch 11 to the bypass current branch 5 cannot be disconnected by the submodule 14 of the commutation part 34 because it passes through the connection between the submodule terminals 27 and 28 Freewheeling diode 23 flows. After commutation of the current into the intermediate branch 11 , it may thus be expedient to close a switch 29 , which is not shown in FIGS. 9 and 10 , bypassing the submodule 14 of the commutation element 34 . If the submodules 14 of the power switching unit 13 likewise have a half-bridge circuit, the submodules 13 of the IGBTs or of the commutation part 34 opposite the IGBTs have the opposite orientation. In the configuration of the device 1 shown in FIG. 10 , the reversing element 34 generates loop currents that flow oppositely, that is, clockwise and counterclockwise, so that two of the mechanical switches can be disconnected without current, And the current is commutated into the intermediate branch 11 . Due to the different polarity of the power semiconductor switches 22 of the submodule 14 of the commutation part 34 compared to the submodule 14 of the power switching unit 13, the charging branch 15 is no longer connected to the middle branch of the bypass current branch 5 Instead, it is connected to a potential point between the power switching unit 13 and the commutation element 34 . The charging current for charging the energy store 25 of the submodule 14 of the commutation part 34 then flows from the terminal 3 via the switch 9 , via the commutation part 34 and finally via the charging branch 15 to ground or the opposite pole.

FIG. 11 shows another configuration of the invention, in which instead of a single device, a plurality of bipolar devices 1 are connected in series with each other. The mode of operation of the individual devices corresponds to that explained in conjunction with the preceding figures. The device 1 can also be constructed according to the configurations shown otherwise or described above of the invention. The number of devices 1 connected in series is completely arbitrary. A series circuit has the advantage that the entire DC voltage switch composed of it for breaking the current can be better scaled and configured for different voltage levels. Relatively smaller devices can be produced and used at low cost. The voltage dropped across the individual switches is lower, so that the switching speed of the mechanical switches is accelerated. The downside, however, is that the devices need to be synchronized. It is also possible, as already shown in FIG. 1 , to equip device 1 with an inductor in the form of a coil or choke. Such coils or chokes are also possible in the configuration according to FIG. 11 , in which the chokes are distributed to the individual devices. As a result, the choke can also be scaled more easily.

FIG. 12 shows a further exemplary embodiment of the device 1 according to the invention, in which the reversing element 34 is no longer arranged in the intermediate branch 11 . Instead, commutation semiconductor switches 36 and 37 each having an antiparallel freewheeling diode 23 are arranged between the intermediate branch potential point of the main current branch 4 and each mechanical switch 6 and 7 of the main current branch 4 . An arrester 24 is connected in parallel to each commutation semiconductor switch 36 and thus also to each freewheeling diode 23 , serving as a means for reducing the energy released during switching. The commutation component 34 thus comprises the commutation semiconductor switches 36 , 37 , the respective freewheeling diode 23 and the respective varistor 24 . The commutation semiconductor switches 36 and 37 are oriented opposite to each other so that the current flow in both directions can be interrupted or limited. Compared to FIG. 1 , the commutation semiconductor switch 36 or 37 supports the mechanical switches 6 and 7 to commutate the current into the intermediate branch 11 . For example, if a current flows from terminal 2 via main current branch 4 to terminal 3 when mechanical switch 8 is open, commutation semiconductor switch 37 is actuated and mechanical switch 7 is simultaneously actuated in order to break the current. Due to such a rapidly increasing resistance, the current flow is reversed into the intermediate branch 11 so that the power switching unit 13 can interrupt this current flow. Then turn off all mechanical switches.

FIG. 13 shows a further embodiment of the device 1 according to the invention, which corresponds as much as possible to the embodiment shown in FIG. The reversing semiconductor switches 38 and 39. According to this advantageous development, all mechanical switches 6 , 7 , 8 and 9 are closed during normal operation. Reversing semiconductor switches 36 , 37 , 38 and 39 are switched into their conductive positions, so that current can flow from terminal 2 to terminal 3 via both main current branch 4 and bypass current branch 5 . To break the current, the reversing semiconductor switches 37 and 38 and the mechanical switches 7 and 8 are simultaneously switched into their disengaged positions or opened. The current then flows from terminal 2 only via main current branch 4 , mechanical switch 6 , freewheeling diode 23 into intermediate branch 11 and then via freewheeling diode 23 , closed mechanical switch 9 to terminal 3 . The power switching unit 13 can now break the current.

FIG. 14 shows a further configuration of the switch according to the invention, in which, compared to the embodiment according to FIG. 13 , the commutation semiconductor switches 38 and 39 of the bypass current branch 5 are omitted. Instead, as in the exemplary embodiment according to FIG. 4 , two diodes 20 and 21 are arranged in bypass current branch 5 . Diodes 20 and 21 prevent current flow through bypass current branch 5 without first conducting the circuit flow through intermediate branch 11 . The switches 8 and 9 support the diodes 20 and 21 , but can also be omitted with a corresponding design of the diodes 20 and 21 .

Claims (22)

1. A device (1) for switching direct current in one pole of a direct current network, having - two terminals (2, 3) for series connection with said poles, - a main current branch (4) extending between said terminals (2, 3), in which two mechanical switches (6, 7) are arranged, - a bypass current branch (5) extending between said terminals (2, 3) connected in parallel with the main current branch (4), in which two mechanical a switch (8, 9) and/or two power semiconductors (20, 21), - intermediate branch (11) which connects the arrangement of the main current branch (4) with the arrangement of the intermediate branch potential point (10) between the mechanical switches (6, 7), and the bypass current branch (5) The intermediate branch potential points (12) between the mechanical switches (8, 9) or between the power semiconductors (20, 21) are interconnected and have a power switching unit (13) with a bipolar a series circuit of submodules (14) each with at least one power semiconductor switch (22) and with means (24) for reducing the energy released during switching, and - a commutation element (34) for commutating direct current into the intermediate branch (11) so that the total direct current is conducted through the intermediate branch (11), wherein the commutation element (34) has at least one commutation A semiconductor switch, wherein the commutation semiconductor switch is a controllable power semiconductor. 2. The device (1) according to claim 1, It is characterized in that, A charging branch (15) is provided which is connected on the one hand to ground potential or to the opposite pole of the polarity of the direct current network opposite to said pole and on the other hand is connected or can be connected to said intermediate branch (11), wherein , the charging branch (15) has an ohmic resistor (16). 3. The device (1) according to claim 2, It is characterized in that, The charging branch (15) is connected or can be connected to the intermediate branch potential point (12) of the bypass current branch (5). 4. The device (1 ) according to claim 2 or 3, It is characterized in that, The charging branch (15) has a mechanical switch (17) connected in series with an ohmic resistor (16), which is designed to connect the charging branch (15) to the intermediate branch (11). 5. The device (1) according to claim 1, It is characterized in that, The submodules (14) of the power switching unit (13) at least partially each have a power semiconductor switch (22) and a freewheeling diode (23) connected in antiparallel to the power semiconductor switch (22), wherein the power semiconductor The switch (22) is a power semiconductor switch that can be turned on and turned off. 6. The device (1) according to claim 1, It is characterized in that, The power switching unit (13) is designed to break the current in only one direction. 7. The device (1) according to claim 1, It is characterized in that, The submodules (14) of the power switching unit (13) at least partially have an energy storage (25) and two power semiconductor switches ( 22) the series circuit (26) that forms, and described can switch on and off power semiconductor switch has the freewheeling diode (23) of antiparallel connection respectively, wherein, a submodule binding post (27) and can switch on and off The potential points between the disconnected power semiconductor switches (22) are connected and the other submodule terminal (28) is connected to one pole of the energy storage (25). 8. The device (1) according to claim 1, It is characterized in that, The submodule (14) of the power switch unit (13) at least partially has an energy store (25) and a first series circuit (26) and a second series circuit (31) connected in parallel to the energy store (25) ), the first series circuit and the second series circuit respectively have two power semiconductor switches that can be switched on and off with antiparallel freewheeling diodes, wherein a submodule terminal (27) is connected to The potential point between the two switchable and disconnectable power semiconductor switches (22) of the first series circuit (26) is connected, and another submodule terminal (28) is connected with the second series circuit (31) The potential points between the two turn-on and turn-off power semiconductor switches (22) are connected. 9. The device (1 ) according to claim 7 or 8, It is characterized in that, Said means for reducing the energy released upon switching are varistors and/or arresters (24). 10. Apparatus (1) according to claim 9, It is characterized in that, The varistor and/or discharger are at least partially connected in parallel with the energy store (25). 11. Apparatus (1) according to claim 1, It is characterized in that, The submodule (14) of the power switching unit (13) is at least partially designed as a brake regulator module and has an energy store (25), which is connected to a first series circuit (26) and a second The series circuit (31) is connected in parallel, and the first series circuit is composed of an on-off power semiconductor switch (22) with an anti-parallel freewheeling diode (23) and the same as the freewheeling diode (23) oriented diode (32), and the second series circuit is made up of a power semiconductor switch (22) that can be turned on and off with a freewheeling diode (23) connected in antiparallel and another with the freewheeling diode (23) ) identically oriented diodes (32), wherein the diode (32) of the second series circuit (31) bypasses the ohmic resistor (33), a submodule terminal (27) with one of the energy storage (25) and another submodule terminal (28) is connected to a potential point between the switchable and disconnectable power semiconductor switch (22) of the first series circuit (26) and the diode (32). 12. Apparatus (1) according to claim 2, It is characterized in that, The commutation element (34) in the intermediate branch (11) is arranged in series with the power switching unit (13) and is designed to generate a circuit current opposite to the direct current to be switched. 13. Apparatus (1) according to claim 12, It is characterized in that, The charging branch (15) is or can be connected to a potential point between the power switching unit (13) and the commutation element (34). 14. Apparatus (1 ) according to claim 12 or 13, It is characterized in that, The commutation element (34) consists of a series circuit of bipolar submodules (14), wherein each bipolar submodule (14) has an energy store (25) and a power semiconductor connected in parallel to the energy store (25) circuit (26, 31). 15. Apparatus (1) according to claim 14, It is characterized in that, Described power semiconductor circuit is made up of series circuit (26), and described series circuit is made up of two power semiconductor switches (22) that have antiparallel freewheeling diode (23) respectively, wherein a submodule terminal (27) is connected with The potential points between the power semiconductor switches ( 22 ), which are disconnectable power semiconductor switches, are connected and a further submodule terminal ( 28 ) is connected to one pole of the energy store ( 25 ). 16. Apparatus (1) according to claim 14, It is characterized in that, The power semiconductor circuit is composed of a first series circuit (26) and a second series circuit (31), and the first series circuit and the second series circuit are respectively composed of anti-parallel freewheeling diodes (23). Two switchable and disconnectable power semiconductor switches (22) are composed, wherein the potential point between the switchable and disconnectable power semiconductor switches (22) of the first series circuit (26) is connected to a submodule terminal ( 27) is connected, and the potential point between the switchable and disconnectable power semiconductor switches (22) of the second series circuit (31) is connected with another submodule terminal (28). 17. The device (1) according to claim 1, It is characterized in that, The commutation element (34) is arranged in the main current branch (4) and has commutation semiconductor switches (36, 37) which are connected with means for reducing the energy released during switching ( 24) Parallel connection, wherein each reversing semiconductor switch (36, 37) is arranged at the intermediate branch potential point (10) of the main current branch (4) and the mechanical switch (6, 7) of the main current branch (4) ) between one of them. 18. Apparatus (1) according to claim 17, It is characterized in that, Arrange commutation semiconductor switches between each mechanical switch (6, 7) of the main current branch (4) and the potential point (10) of the intermediate branch, wherein two commutation semiconductor switches of the main current branch (4) (36, 37) are oriented opposite to each other. 19. Apparatus (1 ) according to claim 17 or 18, It is characterized in that, The bypass current branch (5) has a commutation semiconductor switch (38, 39) and is arranged in parallel with the commutation semiconductor switch (38, 39) for reducing the energy released during switching (24) . 20. Apparatus (1) according to claim 19, It is characterized in that, Between each mechanical switch (8, 9) of the bypass current branch (5) and the intermediate branch potential point (12) of the bypass current branch (5), or in the bypass current branch (5) Between each power semiconductor (20, 21) of each power semiconductor (20, 21) and the intermediate branch potential point (12) of the bypass current branch (5), respectively arrange commutation semiconductor switches (38, 39), wherein two commutation semiconductor switches (38, 39) are oriented opposite to each other. 21. Apparatus (1) according to claim 1, It is characterized in that, The mechanical switches (6, 7) of the main current branch (4) are fast switches and are configured to open within 1 ms to 10 ms, wherein the mechanical switches (8, 9) of the bypass current branch (5) are relatively slow A mechanical switch that opens in the time range of 10ms to 50ms. 22. A device for switching a direct current in one pole of a direct current network, comprising a series connection of devices (1) according to any one of the preceding claims.