EP2810289B1 - Method for connecting a direct current network section by means of dc current switch - Google Patents

Description

The invention relates to a method for connecting a DC voltage section by means of a DC voltage switch.

The world's rising energy demand and the simultaneous desired reduction of CO ₂ emissions make so-called renewable energy increasingly attractive. Sources of renewable energies are, for example, wind power plants set up at sea 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. For this purpose, however, DC switches are required, which are currently not available on the market. Different concepts for such a DC voltage switch are known from the prior art.

In the DE 694 08 811 T2 a DC voltage switch is described in which two mechanical switches are connected in series. The series circuit consisting of the two mechanical switches is protected against high overvoltages by a surge arrester 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 drop across the arc ignites the power semiconductor switch, thereby shorting the parallel open mechanical switch. The arc goes out. Of the Power conducted via the power semiconductor switch can now be interrupted by appropriate control of the power semiconductor.

In the 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. Furthermore, an arrester, for example a varistor, is connected in parallel with each power semiconductor switch for limiting the voltage. 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.

The WO 2011/141055 discloses a DC voltage switch that can be serially connected to one pole of a high voltage DC network. The DC voltage switch consists of a mechanical switch in series with a power semiconductor switch, which is again connected in parallel with a counter-rotating freewheeling diode. Parallel to the series circuit of power semiconductor switch and mechanical switch, a series circuit of coil and capacitor, ie an LC branch and an arrester, connected, which limits the voltage drop across the LC branch voltage. The power semiconductor switch, a trap is connected in parallel. After opening the mechanical switch, the power semiconductor switch is turned on and off at the natural frequency of the LC branch. 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.

In the publication of J. Heffner and B. Jacobssen "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. Also a DC voltage switch is disclosed. The DC voltage switch described therein has an operating current path with a mechanical switch and a Abschaltstrompfad, which is connected in parallel to the operating current path. In the Abschaltstrompfad a series circuit of power semiconductor switches 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 arranged anti-serial, the turn-off power semiconductor switches 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 can be interrupted in both directions in Abschaltstrompfad. In the operating current path, an electronic auxiliary switch is arranged in series with the mechanical switch in addition to the mechanical switch. During normal operation, the current flows through the operating current path and thus via the electronic auxiliary switch and via the closed mechanical switch, since the power semiconductor switches of the Abschaltstrompfades represent an increased resistance to 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 commutated into the Abschaltstrompfad. The fast mechanical disconnector can therefore be opened normally. The short circuit current conducted via the switch-off current path can be interrupted by the power semiconductor switches. For receiving the energy stored in the DC power network and to be reduced during switching, arresters are provided which are connected in parallel to the power semiconductor switches of the disconnecting current path.

If a faulty DC voltage section connected by means of one of the previously known DC voltage switch, a high DC voltage, it may result in unwanted damage to the components in the faulty DC voltage section due to the then occurring extremely high inrush currents.

document DE 10 2008 057 874 A also discloses such a method.
The object of the invention is therefore to provide a method with which an error in the network section, for example a short circuit, can already be detected during the connection of a network section so that countermeasures can be initiated at an early stage.
The invention solves this problem by a method for connecting a DC voltage section by means of a two-terminal DC switch having an operating current path with a mechanical switch and a mechanical switch bridging Abschaltstrompfad, in which at least one switchable on and off power semiconductor switch is arranged, the Abschaltstrompfad has a greater electrical resistance than the bridged section of the operating current path, wherein the mechanical switch is opened and a current flow in the Abschaltstrompfad is blocked by suitable control of the power semiconductor switch or, then the first terminal with a pole of a DC voltage source and the second terminal with a pole of the DC power supply section, finally the DC power supply section by driving the power semiconductor switch controlled voltage is applied and the mechanical switch is then closed.
According to the invention, the DC voltage section is switched on in a controlled manner with the aid of a DC voltage switch, which has a shutdown current path with power semiconductor switches which can be switched on and off, whereas a mechanical switch is arranged in the operating current path.

This known as such embodiment of the DC voltage switch allows to transfer the mechanical switch before switching the network section in its disconnected position and to avoid a hard switching, so a connection by closing the mechanical switch. According to the invention, the current during connection via the Abschaltstrompfad and thus out on the switched on and off power semiconductor switch. These can now be controlled so that the current or voltage is gradually increased, for example, ramp-shaped. If a protective device arranged in the DC power supply section to be connected detects the presence of a short-circuit current, the switching on of the network section can be interrupted early so that damage during connection, for example in the DC voltage switch or in the direct current network section itself, can be avoided. For this purpose, the protective device communicates expediently directly or indirectly with a control or regulation unit of the DC voltage switch.

The design of the mechanical switch is fundamentally arbitrary within the scope of the invention. However, it is important that the mechanical switch can absorb the required voltage. In addition, the mechanical switch should be able to open as quickly as possible, for example within a time window of 5 ms from the error message. The DC voltage switch according to the invention is connected in series in one pole of the DC voltage network, wherein a first terminal of the DC voltage switch is connected to one pole of the DC voltage source and the other terminal of the DC voltage switch with a pole of the DC power supply section. During normal operation of the DC switch, its terminals have approximately the same potential. The voltage dropping across the mechanical switch in the event of an earth fault in the DC voltage section therefore corresponds to the voltage of one pole with respect to the earth potential.

The configuration of the Abschaltstrompfades, in particular the interconnection and arrangement of the power semiconductor switches, in the invention is basically arbitrary. For example, the power semiconductor switches can form a series connection of power semiconductor switches which can be switched on and off, with each power semiconductor switch having an opposite freewheeling diode connected in parallel with it. In this case, it is expedient for each power semiconductor switch to connect an arrester for power consumption in parallel. The power semiconductor switches may be arranged antiseries, with the on-state of some power semiconductor switches being opposite to that of other of the series-connected power semiconductor switches. In this way two groups of power semiconductor switches are formed, one group responsible for switching off the current in one direction and the other group for switching off the current in the opposite direction. Such antiserial arrangement is described for example in the publication by Heffner and Jacobssen mentioned above.

Deviating from this, however, the Abschaltstrompfad also submodules with energy storage, such as capacitors, have. On this configuration of the Abschaltstrompfads will be discussed in more detail later.

Conveniently, the Abschaltstrompfad after connecting the DC voltage source and before the controlled connection of the DC power supply section by means of a charging branch, which advantageously has an ohmic resistance, connected to the ground potential. According to this advantageous further development of the invention, a current flows via the turn-off power semiconductor switches of the Abschaltstrompfads to earth, which is determined by the design of the ohmic resistance. In addition, a voltage drop is generated at the power semiconductor switches. This voltage drop allows, for example, a power supply to the electronics of the power semiconductor switches.

If submodules with their own separate energy stores, such as capacitors and the like, are also provided in the turn-off current path, these capacitors can first be charged before the DC voltage switch is put into operation and before the switched-on DC power grid section is switched on. The charging current flows down the said charge branch to earth. Advantageously, the charging branch is connectable via a switch with the Abschaltstrompfad. The switch is for example an electronic switch. However, cost-effective mechanical switches are preferably used, but their use is only possible due to the ohmic resistance.

Conveniently, before the controlled connection of the DC voltage section of the Abschaltstrompfad means of a charging branch, which advantageously has an ohmic resistance, connected to a Gegenpol the DC voltage source. According to this advantageous development of the Abschaltstrompfad is not connected as in the previous embodiments with the ground potential, but with the opposite pole of the DC voltage source. The term "opposite pole of the DC voltage source" is to be understood as the pole of the DC network that is polarized opposite to the pole to which the terminal of the DC voltage switch is connected. If, for example, the DC voltage switch is serially connected in series in the positive pole of a two-pole DC voltage network, the switch-off current path is connected to the negative pole according to this expedient further development of the invention. This connection takes place for example by means of a mechanical switch. If the terminal with positive pole and the Abschaltstrompfad connected via the charging branch to the negative pole, falls on the turn-off power semiconductor switches from a voltage that drives a charging current. If energy stores are arranged in the shutdown current path, they can be loaded. It is essential that before the connection of the DC voltage section of the Abschaltstrompfad is operable in the sense that the DC voltage section controlled by the functional power semiconductor switch can be switched with optionally charged energy storage or capacitors.

According to a preferred embodiment of the invention, a series arrangement of two-pole submodules is arranged in the Abschaltstrompfad, each having an energy storage and a power semiconductor circuit parallel to the energy storage, which is connected to the two submodule connection terminals of the submodule, that with appropriate control of the power semiconductor switch of the power semiconductor circuit either the voltage dropping across the energy store or a zero voltage at the submodule connection terminals can be generated. Such a modular design of the Abschaltstrompfads is already known from the inverter technology. Inverters with such a topology are referred to as "modular multilevel inverters" (MMC). Due to the series connection of the submodules, it is possible to generate in the Abschaltstrompfad stepwise a voltage, wherein the height of the stages is determined by the voltage drop across the energy storage.

The submodules can be designed as a half-bridge circuit or else as a full-bridge circuit. In a half-bridge circuit, the respective energy store of the submodule is connected in series with two switched on and off power semiconductor switches each with parallel opposing freewheeling diodes, wherein a first submodule connection terminal is connected to the potential point between the power semiconductor switches and a second submodule connection terminal to a pole of the energy store. The energy store is expediently a capacitor. Instead of parallel connection of power semiconductor switches and free-wheeling diodes, reverse-conducting power semiconductor switches can also be used. It is also possible to use two series circuits of power semiconductor switches in the series circuit instead of the two individual power semiconductor switches. The power semiconductors of a series circuit are then controlled synchronously. A series circuit of simultaneously or synchronously controlled power semiconductor switches then acts as a single power semiconductor switch. Of course, then larger voltages can be switched. This also applies in principle to the full bridge circuit described below.

In the case of the full-bridge circuit, two series circuits each consisting of two power semiconductor switches which can be switched on and off with freewheeling diodes in parallel are provided. Both series circuits are again connected in parallel to the energy store, wherein, however, a first submodule connection terminal is connected to 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. In a full-bridge circuit, not only the voltage dropping across the energy store or a zero voltage at the submodule connection terminals can be generated, but also the inverse energy storage voltage. Furthermore, the current flowing across the full bridge current can be interrupted in both directions.

Both in the half-bridge circuit and in the full-bridge circuit, it is essential that the submodules have varistors or arresters. The arresters or varistors, for example, each connected in parallel to an energy store. In addition, however, ohmic resistors may also be installed in the submodule. The arresters absorb a power to be removed during switching, stored in the DC voltage network.

It is also possible within the scope of the invention that both full-bridge and half-bridge circuits are formed in the turn-off current path. In addition, the Abschaltstrompfad may also have other deviating submodules. In the Abschaltpfad and commutation can be provided, which serve in the operating current path to induce or impress a counter tension. Such commutation means are, for example, series-arranged half-bridge circuits or else series-connected full-bridge circuits. The commutation means do not require varistors or arresters.

Figur 1

einen möglichen Gleichspannungsschalter zur Durchführung des erfindungsgemäßen Verfahrens,

Figur 2

einen weiteren beispielhaften Gleichspannungsschalter zur Durchführung des erfindungsgemäßen Verfahrens,

Figuren 3, 4 und 5

mögliche Ausgestaltungen der Submodule für den Gleichspannungsschalter gemäß Figur 2,

Figur 6

einen weiteren beispielhaften Gleichspannungsschalter zur Durchführung des erfindungsgemäßen Verfahrens,

Figur 7

eine Abwandlung des Gleichspannungsschalters gemäß Figur 6,

Figuren 8 bis 11

ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens durchgeführt mit einem Gleichspannungsschalter gemäß Figur 6 und

Figuren 12 bis 15

ein weiteres Ausführungsbeispiel des erfindungsgemäßen Verfahrens zeigen, das mit einem Gleichspannungsschalter gemäß Figur 7 durchgeführt wurde.

Further expedient embodiments and advantages of the invention are the subject of the following description of embodiments of the invention with reference to the figures of the drawing, wherein like reference numerals refer to like-acting components and wherein

FIG. 1

a possible DC voltage switch for carrying out the method according to the invention,

FIG. 2

a further exemplary DC voltage switch for carrying out the method according to the invention,

FIGS. 3, 4 and 5

possible embodiments of the submodules for the DC voltage switch according to FIG. 2 .

FIG. 6

a further exemplary DC voltage switch for carrying out the method according to the invention,

FIG. 7

a modification of the DC switch according to FIG. 6 .

FIGS. 8 to 11

an embodiment of the method according to the invention carried out with a DC voltage switch according to FIG. 6 and

FIGS. 12 to 15

show a further embodiment of the method according to the invention, with a DC switch according to FIG. 7 was carried out.

FIG. 1 shows an example of a first DC voltage switch 1, with the method of the invention can be performed. The DC voltage switch 1 has a first connection terminal 2 and a second connection terminal 3, between which an operating current path 4 extends. In the operating current path 4, an inductance 5 for limiting a current flow, a mechanical switch 6, a comparatively fast mechanical switch 7 and an electronic commutation switch 8 are arranged. The electronic commutation switch 8 has a series connection of power semiconductor switches 10 which can be switched on and off. In this case, each freewheeling diode 11 is connected in parallel with each power semiconductor switch 10 in opposite directions.

The DC voltage switch 1 further has a Abschaltstrompfad 9, which bridges the mechanical switch 7 and the electronic Kommutierungsschalter 8 and in which also switched on and off power semiconductor switch 10 are arranged. Each power semiconductor switch 10 which can be switched on and off is in turn connected in parallel with a freewheeling diode 11 in opposite directions. It can be seen that the two first power semiconductor switches which can be switched on and off, for example IGBTs, IGCTs or the like, have the same forward direction. This applies correspondingly to the associated freewheeling diodes 11. The subsequent power semiconductor switches 10, however, are oriented opposite thereto. Thus flows a current from the terminal 2 to the terminal 3, this can only be interrupted by the first two power semiconductor switches 10. An opposite current, that flows from the terminal 3 to the terminal 2, but can only be interrupted by the third and fourth power semiconductor switches 10. In other words, the power semiconductor switches 10 are arranged antiserially. They form two groups, wherein the transmission directions of the power semiconductor switch a Group are the same orientation, the forward directions of the power semiconductor switch of a group, however, is opposite to the forward directions of the power semiconductor switch 10 of the other group aligned. In this way the switching of direct currents in both directions is possible.

In order to be able to absorb the energy stored in the DC voltage network when switching off the current through the power semiconductor switch 10, the power semiconductor switches 10, an arrester 12 is connected in parallel. In the in FIG. 1 Shown embodiment, the Abschaltstrompfad 9 is modular and forms two-pole modules 13, which are connected in series. In FIG. 1 For reasons of clarity, only two modules 13 can be seen. However, their number depends on the height of the respective voltage.

In one embodiment of the method according to the invention the zuzuschaltende network section is first connected to the terminal 3. Here, the fast mechanical switch 7 is open and the previously made ready for use switched off and power semiconductor switches 10 are in their disconnected position. Subsequently, the switch 6 is closed. By appropriate control of the switched on and off power semiconductor switch, for example, by a pulse width modulation, the output side of the terminal 3 and thus provided in the connected DC voltage section voltage is slowly, for example, ramped up. If the DC voltage provided at the connection terminal 3 corresponds approximately to the DC voltage present on the input side of the connection terminal 2, the mechanical switch 7 is closed. Subsequently, the switched on and off power semiconductor switches are converted into their conductive state. The DC voltage switch 1 is now ready for operation. The DC voltage section is switched on. Of the DC voltage switch is arranged in series in one pole of a DC voltage network.

Another DC voltage switch 1 is in FIG. 2 shown. The in FIG. 2 shown DC voltage switch again has an operating current path 4 and a Abschaltstrompfad 9, wherein in the operating current path 4, a mechanical switch 7 is arranged, which is bridged by the Abschaltstrompfad 9. In Abschaltstrompfad 9 a power switching unit 14 and commutation 15 are arranged in series. Furthermore, a charge branch 16 is provided, which has a mechanical switch 17 and an ohmic resistor 18 and connects the switch-off current path 9 with a ground potential when the switch 17 is closed.

The power switching unit 14 and the commutation means 15 each have a series connection of two-pole submodules 19. The number of submodules 19 in the power switching unit 14 depends on the voltage to be switched. The number of submodules 19 in the commutation means determines the maximum countervoltage that can be generated.

Examples of possible submodules 19 for the DC voltage switch according to FIG. 2 are in the FIGS. 3, 4 and 5 shown. In the simplest case, a submodule 19 is a power semiconductor switch which can be switched on and off, to which a freewheeling diode is connected in parallel in opposite directions. Each power semiconductor switch 10, an arrester 12 is connected in parallel. Submodules 19 according to FIG. 3 However, they are not considered for the commutation 15, since they can not generate a reverse voltage. However, submodules 19, each having an energy store 20 in the form of a capacitor, are suitable for this purpose. The capacitor or energy storage 20 is in accordance with a submodule FIG. 4 a series circuit 21 of two power semiconductor switches 10 with oppositely parallel freewheeling diodes 11 connected in parallel. A first submodule connection terminal 22 is connected to the potential point between the power semiconductor switches 10 the series circuit 21 connected. The other submodule connection terminal 23, however, is applied to one pole of the unipolar capacitor 20. Depending on the control of the power semiconductor switch 10 which can be switched on and off, therefore, either the capacitor voltage dropping across the capacitor 20 or else a zero voltage can be generated between the connection terminals 22 and 23. In order not to have to complain about the failure of the entire DC voltage switch 1 in case of failure of a single submodule, each submodule 19 can be bridged by a fast mechanical or electronic switch 24. Further, a diode 25 between the terminals 22 and 23 serves to carry high short-circuit currents. If the submodule 19 is to be part of the power switching unit 14, it is expedient to connect the capacitor 20 to an arrestor in parallel. Such arrester 12 is not required for the submodules 19 of the commutation means 15. They serve only to generate a reverse voltage in the operating current path 4 and thus to generate a current zero crossing in the mechanical switch. 7

Half bridges according to FIG. 4 can interrupt the flow of electricity in one direction only. A current flow from the in FIG. 4 shown second submodule connection terminal 23 to the first submodule connection terminal 22 would lead over the arranged between these terminals uncontrolled freewheeling diode 11. A control of the current is therefore not possible.

However, an influence of the two current directions can with a full bridge circuits according to FIG. 5 be achieved. In FIG. 5 is a submodule 19 illustrates that represents a full bridge circuit. The capacitor 20 has two series circuits 21a and 21b connected in parallel. Each series circuit 21a, 21b has two switched on and off power semiconductor switch 10 with opposite freewheeling diode. Submodule connection terminals 22, 23 are each connected to a potential point between the power semiconductor switches 10.

To connect the DC voltage network 1, the terminal 3 of the DC voltage switch 1 is first connected to the zuzuschaltenden DC voltage section. The switch 7 in the operating current path 4 is open. Subsequently, the DC voltage switch 1 is made ready for operation via the charge branch 16 by the switch 17 is closed and the Abschaltstrompfad 9 is thus connected via the resistor 18 to a ground potential. In the case of submodules 19 according to FIG. 4 or 5 Now, after applying a DC voltage to the terminal 2, which is connected to a pole of a DC voltage source, the capacitors 20 of the submodules 19 are charged. Also, the control electronics of the power semiconductor switch, which is fed from the voltage dropping to the turn-off power semiconductor switches 10, is now ready for operation.

If the power switching unit 14 is ready for operation, the switch 17 of the charging branch 16 can be opened and switched on with a suitable control of the power semiconductor switch 10 of the power switching unit 14, the connected to the terminal 3 DC power supply section, wherein the voltage is ramped up. However, this is only readily possible if the submodules 19 of the commutation means 15 are half-bridge circuits according to FIG FIG. 4 form. In the case of full bridge circuits, these must either be bridged or the submodules 19 have to be made ready for operation in order to then convert the power semiconductor switches 10 into their open position. For this purpose, the charging branch would be connected, for example, to the potential point between the commutation means 15 and the terminal 3. For this purpose, appropriate switches could be used. Notwithstanding this, a second charge branch is provided at this point.

FIG. 6 shows a further DC voltage switch 1 for carrying out the method according to the invention. The DC voltage switch 1 again has a first terminal 2 and a second terminal 3. Between the terminals 2 and 3, an operating current path 4 extends in which two mechanical switches 26 and 27 are arranged in series. Furthermore, a Abschaltstrompfad 9 can be seen, with which the mechanical switch 26 can be bridged. In Abschaltstrompfad 9 is a power switching unit 14 is arranged, which consists of a series circuit of submodules 19 according to one of FIGS. 3, 4 or 5 consists. Furthermore, a third mechanical switch 29 is provided in Abschaltstrompfad 9. The potential point between the power switching unit 14 and the third mechanical switch 29 is connectable to the charging branch 16 and thus to earth potential. Via a fourth mechanical switch 28, the current path between the terminal 2 and the connected charging branch 16 can be interrupted, so that the current from the terminal 2 to earth can flow only through the power switching unit 14 and the optionally arranged there energy storage 20 loads.

To limit the current again two inductors 5 are provided in the form of coils or the like. In the Abschaltstrompfad 9 again figuratively not shown commutation can now be arranged, which are essential for the subsequent operation of the DC voltage switch 1.

FIG. 7 shows one of FIG. 6 slightly different embodiment of a DC voltage switch 1, wherein the mechanical switches 28 and 29 are arranged in the immediate vicinity of the terminals 2 and 3 respectively. The fourth mechanical switch 28 is now in the operating current path 4, the same applies to the third switch 29. The diodes 30 and 31 prevent current flow from the terminals 2 or 3 directly to the connected charging branch 16, without the current flowing through the power switching unit 14. Thus, a charge of the energy storage of the power switching unit 14 by means of the charging branch 16 is possible.

The inventive method will now be described by way of example with reference to FIG FIGS. 8, 9 . 10 and 11 for a switch according to FIG. 6 clarified. First, all mechanical switches 26, 27, 28 and 29 are in their open position. The connection terminal 2 is connected to a DC voltage source, for example the positive pole of a DC voltage network, and the connection terminal 3 is connected to the DC voltage network section to be connected. In the initial state, the DC network to be connected is approximately at ground potential. For simplicity, assume that the power switching unit 14 is made up of a series circuit of submodules according to FIG FIG. 5 - that is, from full bridges - exists. To charge the capacitors 20, the mechanical switch 17, the charging part 16 and the mechanical switch 27 in the operating current path 4 are closed. Thus, a charging current whose size is determined before the resistor 18 of the charging branch 16 flows through the power switching unit 14. At the power semiconductor switches 10 also drops from a voltage, with the aid of which the electronics of the switched on and off power semiconductor switch 10 is supplied with the necessary energy.

The charging of the capacitors 20 is in FIG. 9 illustrates, wherein the current path of the charging current I is figuratively clarified.

If capacitors 20 are charged and the electronics are ready for operation, the switch 17 of the charge branch 16 is opened and the third mechanical switch 29 is closed so that a controlled connection of the DC voltage network section connected to the connection terminal 3 can take place. Here, the power semiconductor switch 10 of the power switching unit 14 are selectively controlled, so that a slow startup of the voltage takes place. If the DC voltage dropping at the connection terminal 3 corresponds approximately to the voltage applied to the connection terminal 2, the first switch 26 in the operating current path 4 is closed. The current is thus passed through the operating current path 4.

FIGS. 12 to 15 illustrate an embodiment of the method according to the invention by means of a DC voltage switch 1 according to FIG. 7 , First, the switches 17, 27 and 28 are closed to charge the energy storage 20 of the power semiconductor switch 14 and to operate the electronics of the switched on and off power semiconductor switch. In FIG. 13 the charging current flow I for charging the energy storage 20 is illustrated.

Subsequently, the switch 17 of the charge branch 16 is opened and the switch 29 is closed at the terminal 3. In this switch position can now be a controlled charging of the connected to the terminal 3 DC power supply section. For this purpose, the switched on and off power semiconductor switch 10 of the power switching unit 14 are selectively and controlled controlled. By closing the switch 17, charging of the energy store 20 is possible even in the normal operating state. The built-in diodes 30, 31 force the charging current via the power switching unit 14 to flow to the ground.

Claims (8)

1. Method for connecting a DC voltage power supply system section by means of a DC voltage switch (1), having two connection terminals (2, 3), that has an operating current path (4), having a mechanical switch (7), and a disconnection current path (9), bypassing the mechanical switch (7), in which power semiconductor switches (10) that can be switched on and off are arranged, wherein the disconnection current path (9) has a greater electrical resistance than the section of the operating current path (9) that is bypassed by it,
   characterized in that

   - the mechanical switch (7) is opened and a flow of current via the disconnection current path (9) is blocked,

   - the first connection terminal (2) is then connected to a pole of a DC voltage source and the second connection terminal (3) is connected to a pole of the DC voltage power supply system section,

   - finally, the DC voltage power supply system section undergoes controlled application of a voltage by virtue of actuation of the power semiconductor switches (10), and

   - the mechanical switch (7) is then closed.
2. Method according to Claim 1,
   characterized in that
   the disconnection current path (9) is connected to earth potential, following the connection of a pole of the DC voltage source and prior to the controlled connection of the DC voltage power supply system section, by means of a charging branch (16) that has a nonreactive resistance (18).
3. Method according to Claim 1,
   characterized in that
   prior to the controlled connection of the DC voltage power supply system section, the disconnection current path (9) is connected to an opposite pole of a DC voltage source by means of a charging branch (16) that has a nonreactive resistance (18) .
4. Method according to Claim 3,
   characterized in that
   the disconnection current path (9) is connected, prior to the connection of the first connection terminal (2) to a pole of the DC voltage source, to the opposite pole of the DC voltage source.
5. Method according to one of the preceding claims,
   characterized in that
   the disconnection current path (9) contains a series circuit comprising two-pole submodules (19) that each have an energy store (20) and a power semiconductor circuit (21) in parallel with the energy store (20), which power semiconductor circuit is connected up to submodule connection terminals (22, 23) of the submodule (19) such that appropriate actuation of the power semiconductor switches (10) of the power semiconductor circuit (21) prompts either the voltage drop across the energy store (20) or else a zero voltage to be able to be produced on the submodule connection terminals (22, 23).
6. Method according to Claim 5,
   characterized in that
   at least some of the submodules (9) form a half-bridge circuit, wherein the respective energy store (20) has a series circuit (21), comprising two power semiconductor switches (10) that can be switched on and off, with parallel freewheeling diodes (11) in the opposite sense, connected in parallel with it, wherein a first submodule connection terminal (22) is connected to the potential point between the power semiconductor switches (10) and the second submodule connection terminal (23) is connected to a pole of the energy store (20).
7. Method according to Claim 5 or 6,
   characterized in that
   at least some of the submodules (19) form a full-bridge circuit, wherein the respective energy store (20) has two series circuits (21a, 21b), each comprising two power semiconductor switches (10) that can be switched on and off, with parallel freewheeling diodes (11) in the opposite sense, connected in parallel with it and the first submodule connection terminal (22) is connected to the potential point between the power semiconductor switches (10) of the first series circuit (21a) and the second submodule connection terminal (23) is connected to the potential point between the power semiconductor switches (10) of the second series circuit (21b) .
8. Method according to one of Claims 5 to 7,
   characterized in that
   the submodules (19) have varistors or arrestors (12) connected in parallel with them.

Images