Switching device for DC voltage circuits

Abstract

This invention relates to a switching device for coupling a DC voltage branch to a DC voltage bus, wherein the switching device has a series circuit of first and second switching modules. The first switching module has a controllable first semiconductor switching element for a first current direction, and the second switching module has a controllable second semiconductor switching element for the opposite current direction. The first semiconductor switching element is connected in parallel with a first diode, which conducts in the opposite current direction, and the second semiconductor switching element is connected in parallel with a second diode, which conducts in the first current direction. The series circuit of the two switching modules is connected in parallel with a third semiconductor switching element. A current sensor is provided, capable of determining the magnitude and direction of the current in the DC voltage branch. A voltage sensor is provided, capable of determining the magnitude of the voltage on the DC voltage bus side. A control device is provided, which is connected to a control connector of a first semiconductor switching element, a second semiconductor switching element, and a bridging semiconductor switching element, a voltage sensor, and a current sensor. The control device is designed to switch the bridging semiconductor switching element to conduct when the voltage is below a first threshold and during current flow in special circumstances, in order to support current flow from the DC voltage branch to the DC voltage bus, where the voltage on the DC voltage branch is higher than the voltage on the DC voltage bus in special circumstances.

Description

Technical Field

[0001] The present invention relates to a switching device for coupling a DC voltage branch to a DC voltage bus. Background Technology

[0002] DC voltage refers to a voltage with a maximum of 1500 volts. DC voltages up to this level are also called low voltage. More specifically, DC voltage specifically refers to voltages greater than the low voltage of 120 volts. DC voltage specifically refers to voltages between 400 and 800 volts.

[0003] A DC voltage circuit or DC circuit refers to a circuit used for currents from 2 to 1000 or 5000 amperes, especially the nominal current or maximum current; more specifically, a circuit used for currents from 2 amperes to 400 amperes or 200 amperes.

[0004] A DC voltage bus is a two-wire system with a positive and a negative conductor, supplied with DC voltage by at least one energy source. DC voltage devices, such as DC voltage electrical equipment, loads, inverters, combined energy sinks or sources, or individual (other) energy sources, are connected to the DC voltage bus via DC voltage branches. Multiple DC voltage devices can also be connected to a single DC voltage branch.

[0005] DC voltage equipment specifically refers to equipment with a power of 1 kilowatt to 500 kilowatts.

[0006] At the same time, more and more DC voltage circuits, also known as DC voltage networks or low-voltage DC networks, are being developed and constructed, which typically have a DC voltage bus with DC voltage branches.

[0007] The DC voltage branch, also known as the electrical equipment branch, is typically protected by a DC voltage switch (DC switch), which is referred to herein as a switching device. This switching device has at least one switching module, usually two switching modules, each having at least one controllable semiconductor switching element, also known as a power electronic switching element, which may be connected in parallel with a diode.

[0008] European patent application EP 3 057 232 A1 discloses a circuit breaker device for interrupting current flow in a circuit and a method for interrupting current flow using such a circuit breaker device. The circuit breaker device includes a first switching device having a silicon-based first semiconductor switch and a silicon-based second semiconductor switch, which are connected to each other in an anti-symmetrical manner. The circuit breaker device also includes a second switching device comprising a first semiconductor switch with a large bandgap and a second semiconductor switch with a large bandgap, which are connected in series in a back-to-back arrangement. The first and second switching devices are arranged in parallel.

[0009] Chinese public document CN 108 418 192A relates to the field of energy transmission and distribution technology, and in particular to a DC current limiter and its coordinated control method, as well as a DC protection switch. The DC current limiter is characterized by comprising the following components: a first current flow branch for guiding the steady-state current of the DC line during normal operation and for identifying faults in the DC line during fault occurrence; current transmission to a first transmission branch; the first transmission branch for transmitting fault current from the first flow branch to a current-limiting branch; and the current-limiting branch for guiding the fault current and connected to the current-limiting function of the DC line.

[0010] The functions of a controllable semiconductor switching element and a diode connected in parallel can also be physically realized within a single semiconductor structural element. This type of structural element is called a reverse-conducting element.

[0011] In addition, a fusible link device may be present.

[0012] exist Figure 1 The diagram illustrates a switching device according to the prior art for coupling a DC voltage branch to a DC voltage bus.

[0013] Figure 1 A DC voltage bus DCB is shown, which has a positive conductor DCP and a negative conductor DCN, and is connected to a DC voltage energy source, for example, having a DC voltage of 600 volts (not shown).

[0014] The DC voltage bus DCB has a first DC voltage branch DCA1, a second DC voltage branch DCA2, and a third DC voltage branch DCA3; additional DC voltage branches can be configured.

[0015] The first DC voltage branch DCA1 is connected to the first device G1 through the first switching device SCH1, and the second DC voltage branch DCA2 is also connected to the second device G2 through the second switching device SCH2.

[0016] The first switching device SCH1 has a series circuit of first and second switching modules SM1 and SM2. The first switching module SM1 has a controllable first semiconductor switching element Q1 for a first current direction, and the second switching module SM2 has a controllable second semiconductor switching element Q2 for the opposite current direction.

[0017] A first semiconductor switching element Q1 is connected in parallel with a first diode D1, which conducts in the opposite current direction to the first semiconductor switching element Q1. A second semiconductor switching element Q2 is connected in parallel with a second diode D2, which conducts in the first current direction of the first semiconductor switching element Q1.

[0018] The first switching device SCH1 is implemented with bipolar terminals (for the positive and negative conductors). In this example, the first and second switching modules SM1 and SM2 are located in one conductor, specifically in the positive conductor of the first DC voltage branch DCA1; the negative conductor is continuous and does not contain any switching modules. Alternatively, the switching modules SM1 and SM2 may also be arranged in the negative conductor, or both conductors may contain switching modules.

[0019] The series circuit of the two switch modules SM1 and SM2 is followed by the separation contacts on the equipment side or DC voltage branch side. The first separation contact TK1 is set for the positive conductor, and the second separation contact TK2 is set for the negative conductor. They are generally called separation contacts and are used for the separation of current (galvanischen) of the equipment or electrical appliances.

[0020] The second switching device SCH2 is constructed in a similar manner. Other switching devices can be constructed in a similar manner.

[0021] Devices G1 and G2 are typically DC voltage devices with capacitors. In this example, the first device G1 has a first capacitor C1, and the second device G2 has a second capacitor C2. A significant amount of energy is often stored in the capacitors of (DC voltage) devices.

[0022] If based on Figure 1 A fault occurs in the DC voltage circuit / DC voltage network or DC network, such as a short circuit at fault location F1 between the second switching device SCH2 and the second device G2. This short circuit is fed from surrounding DC voltage branches or DC branches and the energy sources or capacitors located within them. This results in a large current in the associated switching device, in this example, the second switching device SCH2, triggering the switching device to shut down.

[0023] Importantly, other switching devices or switches do not trigger, thus enabling selective shutdown in the event of a fault.

[0024] Furthermore, other switching devices should, as far as possible, impede the current flow from the corresponding DC voltage branch or the equipment branch to the short circuit, so that the switching device, in this example, the second switching device SCH2, can be reliably triggered. Therefore, in the switching device, the turn-off semiconductor, such as a bipolar transistor with an insulated gate electrode (IGBT), is more of a barrier because it typically has desaturation characteristics and serves to limit current. Moreover, these semiconductor switches will turn off very quickly, typically in the single-digit μs range.

[0025] If a short circuit occurs at fault location F1, the energy of the second capacitor C2 (or second capacitor C2) of the associated second device G2 will discharge to that fault location. Additionally, the energy of the first capacitor C1 of the unrelated first and third DC voltage branches DCA1 and DCA3, and possibly the third capacitor C3 (not shown), will also discharge to that fault location F1.

[0026] The first and third capacitors C1 and C3 may provide large (fault) currents. For example, if the first device G1 has a small nominal current, the size of the first switching device SCH1 is designed to be correspondingly small, and the first switching device SCH1 can interrupt current flow even if a fault occurs in another branch, or not further feed power to that other branch before it is turned off.

[0027] The goal is to be able to carry the reverse current of the switching device for as long as possible (without saturation).

[0028] To date, the problem has been solved by designing the size of the switchgear to be significantly too large, which is either expensive or uneconomical. Summary of the Invention

[0029] The technical problem to be solved by the present invention is to provide a solution to the aforementioned problem, in particular to enable selective triggering of switching devices in DC voltage branches.

[0030] This problem is solved by a switching device having the features of the present invention.

[0031] According to the invention, this is achieved by connecting a series or parallel circuit of two (electronic or semiconductor-based) switching modules in parallel with a bridging semiconductor switching element. Here, the bridging semiconductor switching element is used to guide current in a specific situation where the voltage on the DC voltage branch is higher than the voltage on the DC voltage bus, particularly when the voltage difference exceeds a voltage threshold.

[0032] Under normal circumstances, in a positive conductor, current flows from the DC voltage bus to the device through a switching device or a DC voltage branch.

[0033] In special cases, on the positive conductor, current flows from the device to the DC voltage bus through a switching device; this is also known as the reverse direction.

[0034] Similarly, under normal circumstances, current flows from the device through the DC voltage branch and switching device to the DC voltage bus on the negative conductor. In special circumstances, current flows from the DC voltage bus through the negative conductor, via the switching device or DC voltage branch to the device, i.e., it flows to the device in the reverse direction. Here, "special circumstances" refers to the reverse current flow, which can also be a permissible operating condition.

[0035] The bridging semiconductor switching element is designed to carry a larger current in one direction and to carry current in the reverse direction of the switching device for as long as possible, thereby enabling the triggering of a switching device in another DC voltage branch. In this case, the bridging semiconductor switching element is activated.

[0036] Advantageous designs of the invention are given in the following description.

[0037] In an advantageous embodiment of the invention, the bridging semiconductor switching element is a thyristor, which is arranged to be switched on, for example, to allow current in the positive conductor to flow from the device to the DC voltage bus. Similarly, if the switching module is arranged in the negative conductor, the thyristor is also arranged in the negative conductor.

[0038] When current flows from the anode side connector of the thyristor through the switching module to the cathode side connector of the thyristor, the thyristor can be switched to conduction; and the thyristors are arranged accordingly.

[0039] This has the particular advantage of providing a particularly simple and cost-effective solution for bridging semiconductor switching elements, especially since it can easily guide large currents in one direction.

[0040] In an advantageous embodiment of the invention, the first and / or second or third and / or fourth semiconductor switching element is a bipolar transistor with an insulated gate electrode, a metal-oxide-semiconductor field-effect transistor, a gallium nitride transistor, or a silicon carbide transistor (SiC transistor).

[0041] This has the particular advantage of providing a simple solution for the semiconductor switching elements of the switching module.

[0042] In an advantageous embodiment of the invention, a current sensor is provided, which can determine the magnitude and direction of the current. Furthermore, a voltage sensor is provided, which in particular can determine the magnitude of the voltage on the DC voltage bus side.

[0043] This has the particular advantage of providing an integrated and compact solution for switching devices that does not require external sensors.

[0044] In an advantageous embodiment of the invention, a control device is provided, which is connected to the control terminals of the first and second or third and fourth semiconductor switching elements and the bridging semiconductor switching elements, particularly the corresponding gate terminals, voltage sensors and current sensors. The control device is designed to switch the bridging semiconductor switching elements or thyristors to conduct when the voltage is below a first threshold, and in special cases of current flow, i.e., in the case of thyristors, when current flows from the anode side terminal of the thyristor through the switching module to the cathode side terminal of the thyristor.

[0045] This has the particular advantage of providing a compact solution with integrated control for switching devices.

[0046] In an advantageous design of the invention, the series or parallel circuit of the two switching modules is connected in series with the separation contact on the DC voltage branch side.

[0047] This has the particular advantage of enabling current (galvanische) separation in DC voltage branches.

[0048] In an advantageous embodiment of the invention, the parallel circuit of the bridging semiconductor switching elements has an interruption device, particularly a relay contact, particularly a normally open contact.

[0049] This has the particular advantage that, in the case of thyristors or similar semiconductor switching elements, the current flow can be reset or reset.

[0050] In an advantageous embodiment of the invention, the disconnecting contact or interrupting device can be operated by a control device such that the current flow through the bridging semiconductor switching element, particularly the thyristor, is resettable or reversible.

[0051] This has the particular advantage that, especially when it is necessary to prevent further power supply to the DC voltage bus through the DC voltage branch, it enables controlled reset of the current flow, particularly through the thyristors, via a control device.

[0052] In an advantageous embodiment of the invention, the first threshold voltage is between 10% and 50% of the nominal voltage of the DC voltage bus, particularly 30% of the nominal voltage of the DC voltage bus.

[0053] Alternatively, a second voltage sensor can be used to determine the difference between the voltage of the DC voltage bus and the voltage of the DC voltage branch, and compare it with a voltage threshold or a voltage threshold.

[0054] This has the particular advantage of having a simple standard for voltage thresholds.

[0055] In an advantageous embodiment of the invention, the current sensor is a sensor based on the Hall effect.

[0056] This has the particular advantage of providing a simple solution for determining the magnitude and direction of the current.

[0057] In an advantageous embodiment of the invention, in the series circuit of the first and second switching modules, the emitters or collectors or sources or drains of the first and second semiconductor switching elements in the form of transistors are interconnected. The anodes of the diodes connected in parallel are connected to the emitters or sources, and the cathodes of the diodes connected in parallel are connected to the collectors or drains.

[0058] This has the following particular advantage: a simple implementation of the switching module is provided for this invention.

[0059] In an advantageous embodiment of the invention, the control device is designed to interrupt the current flow, particularly under normal conditions, by means of at least one switching module, and particularly two switching modules, when a first threshold current is exceeded.

[0060] This has the particular advantage that the control device not only provides overcurrent protection but also provides the functions according to the present invention.

[0061] All design schemes incorporating the various features or combinations thereof of the present invention improve the switching device, thereby enhancing selectivity in DC voltage networks. Consequently, devices of different power levels can operate on a common DC voltage bus. Attached Figure Description

[0062] The features, characteristics, and advantages of the present invention, as well as the ways in which they are implemented, will become clearer and more readily understood in conjunction with the following detailed description of embodiments taken in conjunction with the accompanying drawings.

[0063] In the relevant accompanying figures:

[0064] Figure 1A schematic diagram of a DC voltage branch with switching devices on a DC voltage bus according to the prior art is shown;

[0065] Figure 2 A schematic diagram of a DC voltage branch with a switching device on a DC voltage bus according to the present invention is shown;

[0066] Figure 3 A first schematic diagram of the present invention is shown;

[0067] Figure 4 A second schematic diagram of the present invention is shown;

[0068] Figure 5 A portion of another switching device is shown;

[0069] Figure 6 Another switching device according to the invention is shown. Detailed Implementation

[0070] Figure 1 A schematic diagram of a DC voltage branch with switching devices on a DC voltage bus according to the prior art, as described at the beginning, is shown.

[0071] Figure 2 It shows that according to Figure 1 The schematic diagram differs from the previous one in that, according to the present invention, the series circuit of the first and second switch modules SM1 and SM2 is bridged with a semiconductor switching element QU (in accordance with...). Figure 2 In the example, thyristors are connected in parallel. Here, the series circuit of the two switching modules is arranged in the positive conductor of the first DC voltage branch DCA1. The thyristor is connected to the DC voltage bus side of the series circuit of the switching module via its cathode, which also forms the DC voltage bus side of the switching device, and is connected to the device side of the series circuit of the switching module via its anode.

[0072] In this example, the first and / or second semiconductor switching elements Q1, Q2 are bipolar transistors (IGBTs) with insulated gate electrodes. However, they can also be metal-oxide-semiconductor field-effect transistors or gallium nitride transistors.

[0073] In addition, at least one current sensor (not shown) is provided, which can determine the magnitude and direction of the current in the DC voltage branch. Furthermore, at least one voltage sensor (not shown) is provided, which in particular can determine the magnitude of the voltage in the DC voltage branch on the DC voltage bus side.

[0074] A control device SE1 is provided, which is connected to the control terminals, particularly the gate terminals, of the first, second, and bridged semiconductor switching elements Q1, Q2, and QU. Furthermore, the control device SE1 is connected to a voltage sensor (not shown) and a current sensor (not shown).

[0075] The control device SE1 is designed to switch the thyristor to conduct when the voltage is below a first threshold and when current flows from the anode side terminal of the thyristor through the switching module to the cathode side terminal of the thyristor.

[0076] The series circuit of the two switching modules SM1 and SM2 is connected in series with the separation contacts on the DC voltage branch side, i.e., on the first device G1 side. In this example, the two conductors of the DC voltage branch, i.e., the positive and negative conductors, have separation contacts TK1 and TK2. The separation contacts, in particular, have a separation function according to standards, i.e., providing reliable current separation with standard-compliant spacing and / or creepage distance or air distance.

[0077] The separate contacts TK1 and TK2 can be implemented as relay contacts operated by the control device SE1.

[0078] The bridging semiconductor switching element QU, in this example a parallel circuit of thyristors, has an interruption device RK1, specifically a relay contact, which in this example is designed as a normally open contact.

[0079]

[0080] Parallel circuits of bridging semiconductor switching elements QU are particularly connected in parallel only with switching modules. For example... Figure 2 As shown, the first and / or second separate contacts TK1, TK2 are not included in the parallel circuit.

[0081] The first and second disconnect contacts TK1, TK2 or the interrupt device RK1 can be operated by the control device SE1 so that the current flowing through the bridging semiconductor switching element, in particular the thyristor QU, can be reset.

[0082] The first and second switch modules SM1 and SM2 connected in series can be designed such that, depending on the semiconductor switching elements used, the emitters or collectors or sources or drains of the first and second semiconductor switching elements Q1 and Q2 are interconnected. Figure 2 In the example, the collectors of the IGBTs are connected to each other. The emitters form corresponding external connectors for the series circuit of the switching modules SM1 and SM2, wherein the first external connector is connected to the DC voltage bus via a fuse if necessary, and the second external connector is connected to the device via separate contacts TK1 and TK2 if necessary.

[0083] As shown in the figure, the anode of the parallel diodes is connected to the emitter or source, and the cathode of the parallel diodes is connected to the collector or drain.

[0084] The control device is also designed to interrupt the flow of current by at least one switching module, particularly two switching modules, when the current exceeds a first threshold, especially when the current flows under normal conditions (contrary to special conditions).

[0085] Figure 3 A schematic diagram of the present invention is shown, comprising a first semiconductor switching element Q1, a second semiconductor switching element Q2, and a first device or electrical appliance load1.

[0086] A thyristor-type bridging semiconductor switching element QU is connected in parallel with the series circuit of the first and second semiconductor switching elements Q1 and Q2.

[0087] Figure 4 It shows that according to Figure 3 The schematic diagram differs in that the first series circuit of the first and second semiconductor switching elements Q1 and Q2 is connected to the DC voltage bus DCB through the first fuse Si1, and the second series circuit of the fifth and sixth semiconductor switching elements Q5 and Q6 is connected to the DC voltage bus DCB through the second fuse Si2 in a similar manner. The second semiconductor switching element QU in the form of a thyristor is connected in parallel with the fifth and sixth semiconductor switching elements Q5 and Q6, and the second device or electrical equipment load2 is connected to the second semiconductor switching element QU that is bridged.

[0088] Figure 5 It shows that according to Figure 1 or Figure 2 The third switching device SCH3 used to couple a DC voltage branch to a DC voltage bus differs in that the third switching device SCH3 has a parallel circuit of a third switching module SM3 and a fourth switching module SM4. The third switching module SM3 has a series circuit of a controllable third semiconductor switching element Q3 and a third diode D3 for the first current direction, and the fourth switching module SM4 has a series circuit of a controllable fourth semiconductor switching element Q4 and a fourth diode D4 for the opposite current direction. The third diode D3 is cut off in the opposite current direction, and the fourth diode D4 is cut off in the first current direction.

[0089] The functions of controllable semiconductor switching elements (Q3, Q4) and series-connected diodes (D3, D4) can also be physically realized within a single semiconductor structural element. This type of structural element is called a reverse-blocking element.

[0090] In this example, the parallel circuit is arranged in the positive conductor. The parallel circuit has a third disconnecting contact TK3 in the positive conductor and a fourth disconnecting contact TK4 in the negative conductor.

[0091] Figure 6 It shows that according to Figure 5 The difference lies in the arrangement, where the parallel circuits of the third and fourth switch modules SM3 and SM4 are connected in parallel with a bridging semiconductor switch element QU.

[0092] Furthermore, a current sensor SI is provided, for example, in the positive conductor. Additionally, a voltage sensor SU is provided, connected to both the positive and negative conductors, and is particularly positioned on the DC voltage bus DCB side to determine the magnitude of the voltage on the DC voltage bus DCB side.

[0093] Current and voltage sensors SI, SU and according to Figure 2 The control device is connected to the third and fourth switch modules SM3 and SM4, especially their control connectors, and particularly the gate connectors of the third and fourth semiconductor switch elements Q3 and Q4 (preferably bipolar transistors with insulated gate electrodes).

[0094] The control device SE1 is connected to the control connector of the bridging semiconductor switching element QU, particularly the gate connector of the thyristor.

[0095] The bridging semiconductor switching element QU, especially the parallel circuit of thyristors, has an interruption device RK1, which is connected in particular to the switching device SE1.

[0096] In one design scheme, the third and fourth separation contacts TK3 and TK4 can be connected to the control device SE1, such as... Figure 6 As shown.

[0097] On the DC voltage branch side, i.e., on the equipment side, another DC voltage sensor can be installed to determine the magnitude of the voltage on the equipment side, i.e., on the DC voltage branch side. This other DC voltage sensor can be connected to the control device SE1.

[0098] It can be used according to Figure 6 The first and second switching devices SCH1 and SCH2 can be replaced by a switching device. Alternatively, a DC voltage branch with a first, second, or third switching device SCH1, SCH2, or SCH3 can be provided.

[0099] The present invention will now be briefly described again.

[0100] An electronic bidirectional switch device with a semiconductor switch and a freewheeling diode was designed for the operating current. Under short-circuit conditions, the electronic bidirectional switch device can only carry saturation current for a short time in the μs range.

[0101] Selective disconnection of the faulty branch becomes difficult when the feedback current from other branches is interrupted. The goal is to carry the current in the reverse direction from the branch for as long as possible without saturation.

[0102] This necessitates designing the switching device to be excessively large. This is an expensive solution.

[0103] According to the invention, additional semiconductor switching elements, particularly advantageously thyristors, are provided so that the branch can be rapidly discharged to the faulty DC voltage branch via the DC voltage bus.

[0104] The thyristor QU used for bridging, "in the reverse direction," is connected in parallel with a series or parallel circuit of a switching module, semiconductor switching element, or semiconductor switch, and is used as a bypass. When the voltage is below the DC voltage bus limit (e.g., 30% of the nominal DC voltage bus voltage) and a (large) current flows from the device into the DC voltage bus through the positive conductor of the DC voltage branch (i.e., in the reverse direction), the thyristor QU is switched to conduction or ignition.

[0105] Therefore, the switching modules SM1, SM2 or SM3, SM4, or the semiconductor switching elements Q1, Q2 / Q3, Q4, do not need to guide the full (short-circuit) current in the reverse direction; this is handled by the bridging (bypass) thyristor QU. This thyristor guides a (large) (short-circuit) current, thus providing sufficient energy for disconnecting the faulty DC voltage branch.

[0106] After the fault (short circuit) is cleared, the switching device is reset. In particular, the thyristor QU that is bridging is turned off. This is mandatory if, after the short circuit is cleared, the voltage on the DC voltage bus side is greater than the voltage on the DC voltage branch side, or it can be done by disconnecting the interrupt device / relay contact RK1 in the thyristor's line branch or by disconnecting the disconnect contacts TK1, TK2 or TK3, TK4.

[0107] Therefore, the switching devices SCH1 and SCH3 are ready to be switched on again.

[0108] This invention enables improved selectivity in DC voltage distributions or networks with multiple branches and distributed capacitance. Therefore, the switching mechanism for faulty branches is strengthened for disconnection.

[0109] In applications where the return (short-circuit) current is generated by the connected device or its capacitor, the (additional) thyristor QU that is used for bridging is switched.

[0110] Using this invention, the switching modules SM1, SM2, SM3, SM4 or the semiconductor switching elements Q1, Q2, Q3, Q4 can be designed to have a smaller size, and a robust overall structure can be achieved using thyristors.

Claims

1. A switching device (SCH1, SCH2) for coupling DC voltage branches (DCA1, DCA2, DCA3) to a DC voltage bus (DCB), in, The switching devices (SCH1, SCH2) have a series circuit of a first switching module (SM1) and a second switching module (SM2). The first switching module (SM1) has a controllable first semiconductor switching element (Q1) for a first current direction, and the second switching module (SM2) has a controllable second semiconductor switching element (Q2) for the opposite current direction. In this configuration, the first semiconductor switching element (Q1) is connected in parallel with the first diode (D1), which conducts in opposite current directions. Similarly, the second semiconductor switching element (Q2) is connected in parallel with the second diode (D2), which conducts in the first current direction. The series circuit of the two switching modules (SM1, SM2) is connected in parallel with the bridging semiconductor switching element (QU). Its features are, The bridging semiconductor switching element (QU) is a thyristor, which is arranged to switch on when, under special circumstances, the voltage on the DC voltage branch is higher than the voltage on the DC voltage bus, to support current flow from the DC voltage branch to the DC voltage bus. A current sensor is provided to determine the magnitude and direction of the current. A voltage sensor is also provided to determine the magnitude of the voltage on the DC voltage bus (DCB) side. A control device (SE1) is provided, connected to the control terminals, gate terminals, voltage sensor, and current sensor of the first semiconductor switching element (Q1), the second semiconductor switching element (Q2), and the bridging semiconductor switching element (QU). The control device is designed to… The thyristor is switched on when the voltage is below a first threshold and when current flows under special conditions.

2. The switching device (SCH1, SCH2, SCH3) according to claim 1, Its features are, The first and / or second semiconductor switching elements (Q1, Q2) are bipolar transistors, metal-oxide-semiconductor field-effect transistors, gallium nitride transistors, or silicon carbide transistors with insulated gate electrodes.

3. The switching device (SCH1, SCH2, SCH3) according to claim 1, Its features are, The series circuit of the first switch module (SM1) and the second switch module (SM2) is connected in series with the separate contacts (TK1, TK3).

4. The switching device (SCH1, SCH2, SCH3) according to claim 1, Its features are, The series circuit of the first switch module (SM1) and the second switch module (SM2) is connected in series with the separation contacts (TK1, TK3) on the DC voltage branch side.

5. The switching device (SCH1, SH2, SCH3) according to claim 3 or 4, Its features are, The separation contacts (TK1, TK3) can be manipulated by the control device (SE1) to reset the current flow through the bridging semiconductor switching element (QU) or thyristor.

6. The switching device (SCH1, SCH2, SCH3) according to any one of claims 1 to 4, Its features are, The first threshold of the voltage is between 10% and 50% of the nominal voltage of the DC voltage bus (DCB).

7. The switching device (SCH1, SCH2, SCH3) according to any one of claims 1 to 4, Its features are, The first threshold of the voltage is 30% of the nominal voltage of the DC voltage bus (DCB).

8. The switching device (SCH1, SCH2, SCH3) according to any one of claims 1 to 4, Its features are, The current sensor is a sensor based on the Hall effect.

9. The switching device (SCH1, SCH2, SCH3) according to any one of claims 1 to 4, Its features are, In the series circuit of the first and second switching modules (SM1, SM2), the emitters or collectors or sources or drains of the first and second semiconductor switching elements in the form of transistors (Q1, Q2) are connected to each other. In parallel diodes, the anode is connected to the emitter or source, and the cathode is connected to the collector or drain.

10. The switching device (SCH1, SCH2, SCH3) according to any one of claims 1 to 4, Its features are, The control device (SE1) is designed to interrupt the current flow by at least one or two switching modules when a first threshold current is exceeded.

11. The switching device (SCH1, SCH2, SCH3) according to any one of claims 1 to 4, Its features are, The control device (SE1) is designed to interrupt the current flow by at least one or two switching modules when the current flow is opposite to that in special cases.

12. A switching device (SCH3) for coupling DC voltage branches (DCA1, DCA2, DCA3) to a DC voltage bus (DCB), in, The switching device (SCH3) has a parallel circuit of a third switching module (SM3) and a fourth switching module (SM4). The third switching module (SM3) has a series circuit of a controllable third semiconductor switching element (Q3) and a third diode (D3) for the first current direction, and the fourth switching module (SM4) has a series circuit of a controllable fourth semiconductor switching element (Q4) and a fourth diode (D4) for the opposite current direction. The third diode (D3) is cut off in the opposite current direction, and the fourth diode (D4) is cut off in the first current direction. The parallel circuits of the third and fourth switch modules (SM3, MS4) are connected in parallel with the bridging semiconductor switch element (QU). Its features are, The bridging semiconductor switching element (QU) is a thyristor, which is arranged to switch on when, under special circumstances, the voltage on the DC voltage branch is higher than the voltage on the DC voltage bus, to support current flow from the DC voltage branch to the DC voltage bus. A current sensor is provided to determine the magnitude and direction of the current. A voltage sensor is also provided to determine the magnitude of the voltage on the DC voltage bus (DCB) side. A control device (SE1) is provided, connected to the control terminals, gate terminals, voltage sensors, and current sensors of the third semiconductor switching element (Q3), the fourth semiconductor switching element (Q4), and the bridging semiconductor switching element (QU). The control device is designed to… The thyristor is switched on when the voltage is below a first threshold and when current flows under special conditions.

13. The switching device (SCH1, SCH2, SCH3) according to claim 12, Its features are, The third and / or fourth semiconductor switching elements (Q3, Q4) are bipolar transistors with insulated gate electrodes, metal-oxide-semiconductor field-effect transistors, gallium nitride transistors, or silicon carbide transistors.

14. The switching device (SCH1, SCH2, SCH3) according to claim 12, Its features are, The parallel circuits of the third switch module (SM3) and the fourth switch module (SM4) are connected in series with the separate contacts (TK1, TK3).

15. The switching device (SCH1, SCH2, SCH3) according to claim 12, Its features are, The parallel circuits of the third switch module (SM3) and the fourth switch module (SM4) are connected in series with the separation contacts (TK1, TK3) on the DC voltage branch side.

16. The switching device (SCH1, SCH2, SCH3) according to claim 12, Its features are, The parallel circuit of the bridging semiconductor switching elements (QU) has an interruption device (RK1).

17. The switching device (SCH1, SCH2, SCH3) according to claim 12, Its features are, The parallel circuit of the bridging semiconductor switching elements (QU) has relay contacts.

18. The switching device (SCH1, SCH2, SCH3) according to claim 12, Its features are, The parallel circuit of the bridging semiconductor switching elements (QU) has normally open contacts.

19. The switching device (SCH1, SH2, SCH3) according to claim 14 or 15, Its features are, The separation contacts (TK1, TK3) can be manipulated by the control device (SE1) to reset the current flow through the bridging semiconductor switching element (QU) or thyristor.

20. The switching device (SCH1, SH2, SCH3) according to claim 16, Its features are, The interrupt device (RK1) can be operated by the control device (SE1) to reset the current flow through the bridging semiconductor switching element (QU) or thyristor.

21. The switching device (SCH1, SCH2, SCH3) according to any one of claims 12 to 18, Its features are, The first threshold of the voltage is between 10% and 50% of the nominal voltage of the DC voltage bus (DCB).

22. The switching device (SCH1, SCH2, SCH3) according to any one of claims 12 to 18, Its features are, The first threshold of the voltage is 30% of the nominal voltage of the DC voltage bus (DCB).

23. The switching device (SCH1, SCH2, SCH3) according to any one of claims 12 to 18, Its features are, The current sensor is a sensor based on the Hall effect.

24. The switching device (SCH1, SCH2, SCH3) according to any one of claims 12 to 18, Its features are, The control device (SE1) is designed to interrupt the current flow by at least one or two switching modules when a first threshold current is exceeded.

25. The switching device (SCH1, SCH2, SCH3) according to any one of claims 12 to 18, Its features are, The control device (SE1) is designed to interrupt the current flow by at least one or two switching modules when the current flow is opposite to that in special cases.

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