FAST ELECTRONIC SWITCH

Description

[0001] The invention relates to an electronic switch with at least one turn-off semiconductor switch and a series circuit arranged parallel to the semiconductor switch, which comprises a capacitor for absorbing energy during the turn-off process.

[0002] Today, electrical energy is primarily supplied via alternating current networks. These have the advantage that different voltage levels can be created using transformers. Semiconductors, which are becoming increasingly affordable on the market, also make it easy to generate different voltage levels for DC networks, making energy supply via DC networks particularly economical, especially within industrial networks.

[0003] DC grids in future industrial plants are intended to reduce losses, ensure the direct exchange of energy between converters, energy storage systems, and loads, and achieve increased robustness. For example, small DC grids can be operated with different cable lengths between the various load outgoers and infeeds. The short cable lengths lead to very small series inductances in the supply lines, so that fault currents can exhibit very steep current increases. Likewise, DC grids lack the reactance present in AC grids, which limits the maximum current of a short circuit. This necessitates very fast fault detection and shutdown in the event of a fault. Mechanical switches often cannot meet these requirements. Therefore, so-called electronic switches with semiconductor switches are being introduced. These are also known as solid-state breakers.In contrast to mechanical switches, these switches are characterized by particularly fast switching, typically in the order of 100ns.

[0004] EP 3 367 567 A1 discloses a switching device for interrupting a current path. This document relates to a switching device for interrupting a current path of a DC voltage network comprising source-side and load-side inductance. The switching device comprises at least two switching modules connected in series, each of the switching modules comprising at least one controllable semiconductor switching element with which a series circuit comprising a resistor and a capacitor is connected in parallel.

[0005] The invention is based on the object of improving an electronic switch, particularly with regard to its switching behavior. This object is achieved by an electronic switch having the features of claim 1.

[0006] The electronic switch according to the invention comprises a turn-off semiconductor switch and a series circuit arranged in parallel with the turn-off semiconductor switch and comprising a first resistor, a capacitor, and a second resistor. The first and second resistors are constructed together as a bifilar resistor.

[0007] A turn-off power semiconductor switch can be a switch that can only switch off current in one direction. This is particularly suitable for loads that are not capable of regenerative power and therefore only conduct current in one direction. It can also be a turn-off power semiconductor switch that can switch off current in both directions.

[0008] The turn-off semiconductor switch is sensitive to voltage spikes that occur during switching, especially when turning off, the current. Due to the inductances present in the DC network, for example, due to parasitic inductance in the cables, current fluctuations and especially power interruptions lead to high voltages, some of which then drop across the turn-off semiconductor switch, potentially damaging it or reducing its service life. The parallel series circuit of a capacitor and a bifilar resistor reliably protects the turn-off semiconductor switch from resulting overvoltages and voltage spikes.

[0009] A transition from the blocking to the conducting state of a switch is referred to as switching on and a transition from the conducting to the blocking state of a switch is referred to as switching off or switching off.

[0010] Depending on its current-voltage characteristic, part of the voltage generated when the turn-off semiconductor switch is turned off drops across the resistor, the other part across the capacitor. This builds up a voltage in the capacitor, which is added to the voltage across the resistor. The load current drops due to the applied countervoltage of the capacitor according to the equation u(t) = L*di / dt, and due to the behavior of the capacitor with i(t) = C*du / dt, a countervoltage builds up more and more across the capacitor. In any case, this generates a countervoltage that is greater than the driving DC voltage, since the current flow through the capacitor builds up a countervoltage that inevitably and reliably stops the current flow after a certain time.

[0011] The inventive design advantageously creates an electronic switch, particularly for DC connections, in which the resistor arranged in series with the parallel capacitor has a particularly low inductance. This creates an electronic switch that can quickly commutate even high short-circuit currents into the capacitor and thus switch off these short-circuit currents particularly quickly.

[0012] The use of the electronic switch is particularly advantageous in medium-voltage DC networks, i.e., in the range of several kV and with currents that are in the range of several kA, at least in the case of a short circuit. However, the switch can also be used in low-voltage DC networks, i.e., less than 1500 V DC. Therefore, an electronic DC switch is preferred.

[0013] For the low-inductance design, it is important that the first and second resistors, which together form the bifilar resistor, are electrically arranged on either side of the capacitor. In other words, the sequence of first resistor, capacitor, second resistor is maintained, as this is the only way to achieve the low-inductance design. In this case, the first and second resistors are physically arranged next to each other so that the direction of the electrical current in both resistors is opposite to each other. This largely cancels out the resulting magnetic fields, and the overall component, i.e., the bifilar resistor, achieves a very low inductance.

[0014] According to the invention, the first and second resistors have a meandering section. In other words, the resistor in question has a section in which the material is shaped such that the current path is meandering. The shaping of the material can be achieved, for example, by suitable punching. This or other means can be used to introduce gaps into the resistor material, forcing the current path into a meandering shape. If a meandering shape is introduced into a rectangular area that carries the current, along which the current must flow, the current path is lengthened and its cross-section is reduced.

[0015] This significantly increases the electrical resistance compared to the free current flow in the rectangular area. This, in turn, allows for a resistance within the range required for the electronic switch, given the physical size of the resistor and a minimum thickness required by mechanical strength. The meander shape is conveniently arranged so that the currents through the meanders cancel each other out. The currents from the two plates thus flow in exactly opposite directions, virtually canceling out the total magnetic field. The size of the total magnetic field, in turn, is responsible for the remaining inductance.

[0016] Advantageous embodiments of the device according to the invention emerge from the claims dependent on claim 1. The embodiment according to claim 1 can be combined with the features of one of the subclaims or, preferably, with those of several subclaims. Accordingly, the following additional features can be provided for the electronic switch: The bifilar resistor can be made of an iron alloy, particularly V4A steel. V4A steel stands for CrNiMo steel. These iron alloys are non-magnetic and have a significantly higher resistivity than copper or aluminum, which makes the construction of the bifilar resistor much easier. Alternatively, the bifilar resistor can be made of other resistance alloys, such as constantan, or in particular, of this material.

[0017] Particularly advantageously, the bifilar resistor can have a thickness in the millimeter range without resulting in an excessively low electrical resistance. This allows for a sufficiently stable connection between the semiconductor switch and the capacitor. A bifilar resistor made of copper, on the other hand, would be as thin as a foil, since its width cannot be made very small without again increasing the inductance. The two resistors that together form the bifilar resistor can be manufactured by punching. Punching is advantageously a simple, cost-effective and flexible manufacturing method that can also be used when the resistors are used as busbars and have to bear the mechanical load of the capacitor connection, i.e. the material thickness is in the range of mm. The first and second resistors can each have the shape of a rectangle, with two opposite edges bent at 90° to one side. This results in the cross-section of a square C or a square bracket [ for each of the resistors. The two resistors are preferably arranged with their backs to each other, resulting in a cross-section of the shape ][. The bent end pieces serve for attachment to the semiconductor switch and the capacitor, while the backs facing each other make up the actual resistor.If the material is thick enough, and therefore has sufficient mechanical load-bearing capacity, the bifilar resistor can, in addition to the electrical connection, also represent the only mechanical connection between the semiconductor switch and the capacitor. In an alternative design, the bifilar resistor still has a cross-section of the shape ][, but no longer a rectangular shape when viewed from above. Rather, the resistors taper towards the capacitor, so that the two resistors have the shape of a trapezoid or a rectangle with an attached trapezoid when viewed from above. In another alternative design, the resistors have an L-shaped cross-section. The two resistors are placed inside each other to form the bifilar resistor, thus forming a double-walled L-shape.One arm of this L-shaped resistor rests on the terminals of the semiconductor switch, while the other arm protrudes from the surface of the semiconductor switch and serves to connect the capacitor. If the capacitor has an elongated cylindrical shape, its cylinder axis lies parallel to the surface of the semiconductor switch, rather than extending perpendicularly from it as in the case of the previous alternatives with a cross-section of the shape ][. This makes this alternative space-saving.

[0018] All mechanical arrangements have the bifilar structure of the resistance surface in common. Since all line connections introduce their own inductances into the circuit, the electronic switch preferably comprises a single turn-off semiconductor switch in parallel with the bifilar resistor. If the resistor also represents the direct electrical connection between the semiconductor switch and the capacitor, virtually all electrical lines in the commutation circuit consisting of the semiconductor switch, resistor, and capacitor that still possess inductance and could cause high voltages during the turn-off process and delay current commutation are eliminated. This advantageously creates a low-inductance commutation circuit, which is very difficult to achieve with just two semiconductor switches in parallel with the bifilar resistor and capacitor. Even if the electronic switch contains only exactly one semiconductor switch, several electronic switches can be combined to form a complete switch.For example, several electronic switches can be connected in series. Alternatively, the switch can comprise exactly one power semiconductor module. The power semiconductor module is the most common design for power semiconductors today and comprises one or more individual semiconductor switches in a common housing. In such a module, for example, two series, two parallel, two anti-serial, or two anti-parallel semiconductor switches can be arranged. Since the line connections within such a module are short and therefore low-inductance, a very low-inductance switch can be created, even if the module itself contains more than one semiconductor switch. For example, a low-inductance bidirectional switch can also be created in this way.In another alternative, the switch comprises a plurality of power semiconductors in a plurality of power semiconductor modules, wherein the power semiconductor modules are connected in series or anti-serial. Commercially available turn-off semiconductor switches can usually only turn off a current in one direction. Typical examples of such turn-off semiconductor switches are IGBTs or MOSFETs. If one wants to be able to turn off currents in both directions through the switch when using such turn-off semiconductor switches, two of these turn-off semiconductor switches are used. This allows both polarities of the current to be turned off by the electronic switch.The switches are arranged in such a way that a current can be conducted from a first terminal of the electronic switch to a second terminal of the electronic switch through a first of the two turn-off semiconductor switches and switched off, and a current can be conducted from the second terminal of the electronic switch to the first terminal of the electronic switch through a second of the two turn-off semiconductor switches and switched off. If a diode is arranged in parallel with the switching element of the semiconductor switch, which enables the turn-off semiconductor switch to be conductive backwards, the two semiconductor switches are arranged in a series circuit. Since the switching elements of the two semiconductor switches can each conduct and switch off a current with different polarity, this series circuit is also referred to as anti-serial.The two semiconductor switches are rotated relative to each other with respect to their collector and emitter, or drain and source, terminals. For bidirectional operation, two or more electronic switches can be connected in series. Typically, an even number of electronic switches is used, with half assigned to one current direction and the other half assigned to the other. The first and second resistors can be separated by an insulating plate or insulating foil and pressed together using screwed plates. This requires that the resistors have flat areas that can be pressed together. These are advantageous because they allow the resistors to be arranged close to one another, resulting in low inductance.When the semiconductor switch is turned off and a significant current, such as a short-circuit current in the kA range, commutates, a significant mechanical force occurs between the two resistors, forcing them apart. However, an increased distance between the resistors increases the inductance. Therefore, it is advantageous if the resistors are pressed together to maintain a small distance. The first and second resistors can be screwed directly onto terminals of the turn-off semiconductor switch. The capacitor, in turn, can be screwed directly onto the first and second resistors. This results in a very low-inductance connection. The electronic switch can be a medium-voltage DC switch or a low-voltage DC switch. As a low-voltage DC switch, it can be used, for example, in ship systems at voltages of around 500 V to 1500 V.As a medium-voltage DC switch, it can be used for voltages from 1500 V DC to greater than 10 kV DC. Its low inductance and thus high switching speed are particularly advantageous for isolating sub-grids, such as those used on ships, when these must be disconnected quickly in the event of a fault. The switch can also be used in HVDC (high-voltage direct current) applications in a "multiple" series circuit, i.e., a series connection of a large number of electronic switches. In this case, DC voltages of up to 1000 kV DC can be achieved.

[0019] The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures. They show: Figure 1 shows a DC network with an electronic switch, Figure 2 shows an embodiment of an electronic switch with low inductive resistance, Figure 3 shows a cross-section of the electronic switch, Figure 4 shows a spatial view of a partial resistance of the low inductive resistance, Figure 5 shows a spatial view of the electronic switch, Figures 6 and 7 show spatial views of alternative shapes for the partial resistances, Figure 8 shows an electronic switch with a plurality of switching blocks, Figure 9 shows a bidirectional electronic switch.

[0020] The Figure 1 shows a DC network 33, also referred to as a direct voltage network. This network supplies a load 31 from a DC source 30, also referred to as a direct voltage source. This load can be, for example, a drive with a power converter, with the power converter and its intermediate circuit connected to the DC source 30 via an electronic switch 1.

[0021] An electronic switch 1 with a first terminal 12 and a second terminal 13 is connected to the line of the DC network 33. The electronic switch 1 can switch off the current flowing in the line. Depending on the type of electronic switch 1, it can switch off a current in only one direction or in both directions between the first and second terminals 12, 13.

[0022] The lines between DC source 30 and load 31 can exhibit very different properties regarding their inductive behavior. This inductive behavior is illustrated in the diagram using inductances 32. These can assume very small values, since there is no transformer present to limit the current with its inductance. On the other hand, the inductances can also assume very large values ​​due to long cable lengths.

[0023] This results in the requirements for electronic switch 1: Due to its low inductance and the associated large current changes, especially during a short circuit, it must exhibit very fast switching behavior so that excessively high currents, such as those generated during a short circuit, can be safely controlled. Furthermore, electronic switch 1 must also be capable of functioning reliably at high inductances. Large inductances store significantly more energy for the same currents. This energy must be stored or dissipated when switching off a short circuit, otherwise overvoltages will occur at the circuit breaker.

[0024] The Figure 2shows an embodiment of an electronic switch 1 with overvoltage limitation. A first series circuit 10 is arranged in parallel with a turn-off semiconductor switch 21. This first series circuit 10 has a capacitor 3 and two partial resistors 4a, b arranged in a series circuit. If the turn-off semiconductor switch 21 turns off the current between the terminals 12, 13 of the electronic switch 1, the current driven by the inductors is commutated to the first series circuit 10. The capacitor 3 and the resistors absorb the energy from the inductors. This reduces the voltages generated at the switch 1, which result from the large current draw during the turn-off, and prevents damage to the switch.

[0025] The two partial resistors 4a, b are as in Figure 2 indicated and in Figure 3shown even more clearly. The arrangement is such that a current flowing through the partial resistors 4a, b as shown in Figure 2 indicated by arrows, is in opposite directions. As a result, the magnetic fields caused by the flowing current largely cancel each other out. The partial resistors 4a, b together form a resistor 4 which is bifilar in design. The resistor 4 is therefore very low inductance and the commutation of the current into the series circuit 10 and thus to the capacitor 3 can therefore take place very quickly. Since the currents in the two resistors 4a, b must be in opposite directions in order to achieve a low-inductance resistor 4, one of the two resistors 4a, 4b must be arranged before and the other after the capacitor 3 in the series circuit 10. In other words, the sequence resistor, capacitor, resistor, i.e. RCR, must be maintained in the series circuit 10.

[0026] One possibility for the construction of the bifilar resistor 4 is shown in the cross-section of the Figure 3 The two partial resistors 4a, b are shown in cross-section and each have the shape of a square C or a square bracket [. Both partial resistors 4a, b are arranged with the backs of this shape to each other, so that in the Figure 3 shown cross-section takes the form of two square brackets pointing apart. At one end region 41a, 41b, each of the partial resistors 4a, b is attached to a contact surface of the semiconductor switch 21 by means of a screw connection 5. The other end region 42a, 42b is connected to the capacitor 3 by means of a screw connection 5. In conjunction with V4A steel as the material for the resistor 4, a mechanically stable structure is obtained in which the capacitor 3 is carried by the resistor 4. The thickness d of the resistor 4 is in the millimeter range, ideally between 0.5 mm and 3 mm.

[0027] In other embodiments, other materials can be used for the partial resistors 4a, b, for example, the resistance material constantan. Non-metallic materials such as carbon can also be used. The thickness d of the partial resistors 4a, b can be greater or smaller than the above-mentioned values.

[0028] Figure 4 shows a spatial view of one of the partial resistors 4a, b .The resistor 4a, b, manufactured by stamping, comprises a meander structure 6 in a central region. In this meander structure 6, the electrical current is forced onto a meandering path, thereby significantly increasing the conductor length while simultaneously reducing the conductor width. The meander structure 6 thus increases the overall electrical resistance of the resistor 4a, b. This is advantageous for setting the desired electrical resistance of between 0.1 ohms and 0.5 ohms. Without the meander structure 6, this would require such a thin material that mechanical stability would be more difficult to achieve. Figure 4 further shows holes 7, which serve for screwing to the semiconductor switch 21 and holes 8 for the connection to the capacitor 3. The size of the back of the resistor 4a, 4b is preferably between 10 cm x 10 cm and 20 cm x 20 cm.

[0029] Figure 5shows a complete structure of an electronic switch 1 in a three-dimensional view. The electronic switch 1 comprises a semiconductor switch module 51, which is arranged on a cooler 52. The resistor 4 is arranged on top of the semiconductor switch module 51, and on top of this, in turn, the capacitor 3. When a current is switched off through the electronic switch 1, a high current flow is commutated into the resistor 4 in a short time. This generates a considerable mechanical force on the partial resistors 4a, b, the direction of which is such that the partial resistors 4a, b are forced apart. In order to maintain the low-inductance structure, however, the distance between the partial resistors 4a, b must remain small. Therefore, the two partial resistors 4a, b are pressed together by screwed plastic plates 53, with an insulating film 9 arranged between the resistors 4a, 4b.This ensures that the mechanical structure is retained even when the device is switched off.

[0030] Figure 6 shows an alternative design of resistor 4. The shape of the partial resistors 4a, 4b is changed. As in the Fig.5In the form shown, the partial resistors have a first end region 41a, 41b, which is shaped to be suitable for attachment to the semiconductor switch module 51 and has bores 7. This end region 41a, 41b is followed by a rectangular region 61, which borders on a trapezoidal region 62. In this trapezoidal region, the partial resistors 4a, 4b taper towards the second end region 42a, 42b, which thereby has a reduced width and only one bore 8 for connecting the capacitor 3 in each of the partial resistors 4a, 4b. As with all of these resistors 4, the partial resistors 4a, 4b are separated by the insulating film 9, which is shaped analogously to the partial resistors 4a, 4b, i.e., also tapers.

[0031] The tapered shape of the partial resistors 4a, 4b of Fig. 6increases the electrical resistance of the partial resistors 4a, 4b. Nevertheless, it is advantageous to provide a meandering shape for these partial resistors 4a, 4b as well, in order to bring the electrical resistance into the range of between 0.1 ohms and 0.5 ohms, which is appropriate for the function of the electronic switch.

[0032] Figure 7 shows another alternative construction of the resistor 4. The shape of the partial resistors 4a, 4b is changed. While the previously described shapes of the partial resistors 4a, 4b had the shape of two square brackets ][ aligned with their backs to each other, the shape according to Figure 7an LL shape, i.e. the cross-section corresponds to two nested L-shapes, with one of the partial resistors 4a, 4b forming the outer L and the other of the partial resistors 4a, 4b forming the inner L. A first leg of the L-shape serves for the connection to the semiconductor switch module 51 and in turn has holes 7a, b. Since the partial resistors 4a, 4b must lie on top of one another, the holes 7a, b differ in order to allow the connection of the outer partial resistor 4a to the holes 7b on one side and the connection of the inner partial resistor 4b to the holes 7a on the other side.

[0033] The second leg forms the busbar to the capacitor 3 and has holes 8a, b at the end for screwing the capacitor 3. The holes 8a, b are again designed differently to contact the inner partial resistor 4b and the outer partial resistor 4a. The resistor 4 of the Figure 7 has an insulating film 9 arranged between the partial resistors 4a, 4b for electrically insulating the partial resistors 4a, 4b.

[0034] In order to meet different requirements of the DC network 33, it is possible to connect two or more of the semiconductor switches 21 in series with their associated series circuit of the partial resistors 4a, 4b and the capacitor 3. Such an electronic switch 1 is shown in Figure 8shown. Therefore, multiple semiconductor switches 21 are not connected in series with a capacitor 3 connected in parallel. Rather, the entire block consisting of semiconductor switch 21 and the series circuit of partial resistors 4a, 4b and capacitor 3 is multiplied and connected in series. This maintains the very low-inductance connection of resistor 4 to the respective semiconductor switch 21. If multiple semiconductor switches 21 were connected in parallel with capacitor 3, additional electrical conductors or busbars would be required in the commutation circuit, which would increase the inductance.

[0035] The connection between one block formed by a semiconductor switch 21 and the associated series circuit of the partial resistors 4a, 4b and the capacitor 3, and the next such block, can, however, be highly inductive without any particular disadvantages for the electronic switch 1.

[0036] In order to create a bidirectional electronic switch 1 and thus be able to switch off current in both directions, the Figure 8 The electronic switch 1 shown in the drawing is supplemented by a number of further blocks of semiconductor switches 21 with their associated series circuit of the partial resistors 4a, 4b and the capacitor 3, wherein the semiconductor switches 21 are arranged anti-serially to the already existing semiconductor switches 21. Preferably, the same number of blocks is used for both current directions. Such an electronic switch 1 is shown in Figure 9 shown.

[0037] For example, an electronic switch 1 formed in this way can have eight blocks for a first current direction and eight further blocks for the other current direction. Reference symbol

[0038] 1 Electronic switch 12, 13 Connections 31 Load 33 DC network 32 Line inductance 30 DC voltage source 3 Capacitor 4 Resistor 4a, 4b Partial resistors 21 Semiconductor switch 5 Screw connection 41a, b End area 42a, b End area d Thickness 6 Meandering area 7, 8 Holes 52 Cooling 51 Semiconductor switch module 53 Plastic plates 61 Rectangular area 62 Trapezoidal area 63a, b End area 7a, 7b Holes 8a, 8b Holes 9 Insulating film

Claims

1. Electronic switch (1), having - a semiconductor switch (21) that can be switched off, - a series circuit, which is arranged parallel to the semiconductor switch (21) that can be switched off and comprises a first resistor (4a), a capacitor (3) and a second resistor (4b), which are arranged in the order resistor-capacitor-resistor, wherein the first and second resistor (4a, b) are jointly constructed as a bifilar resistor (4), wherein the first and second resistors (4a, b) each have a meandering portion (6), wherein the meandering portions (6) are arranged relative to each other such that these meanders in turn form a bifilar arrangement.

2. Electronic switch (1) according to claim 1, in which the bifilar resistor (4) comprises at least one of the following materials: an iron alloy, in particular V4A steel; constantan; carbon.

3. Electronic switch (1) according to claim 1 or 2, in which the first and second resistors (4a, b) are produced by means of punching or laser beam cutting.

4. Electronic switch (1) according to one of the preceding claims, in which the bifilar resistor (4) is designed as a mechanical carrier for the capacitor (3).

5. Electronic switch (1) according to one of the preceding claims, in which the first and second resistors (4a, b) each have the shape of a quadrilateral, in particular of a rectangle, wherein two mutually opposing edges are bent by 90° to one side, in particular with a cross-section with the shape of a square bracket.

6. Electronic switch (1) according to claim 5, in which the first and second resistors (4a, b) are placed together so as to be isolated by way of an insulation panel or insulation film (9) and are pressed together by means of screwed panels (53).

7. Electronic switch (1) according to claim 5 or 6, in which the first and second resistors (4a, b) jointly have a cross-section with the shape of two square brackets arranged with their backs to each other.

8. Electronic switch (1) according to one of the preceding claims, in which the first and second resistors (4a, b) are each L-shaped, wherein the two L-shapes are placed one inside the other in order to form the bifilar resistor (4).

9. Electronic switch (1) according to one of the preceding claims, in which the first and second resistors (4a, b) can be screwed directly onto connectors of the semiconductor switch (21, 51) that can be switched off.

10. Electronic switch (1) according to one of the preceding claims, in which the capacitor (3) is screwed directly onto the first and second resistors (4a, b).

11. Switching facility with a first number of electronic switches (1) according to one of the preceding claims, which are connected in series with each other.

12. Switching facility according to claim 11 with one or more further electronic switch(es) (1) according to one of claims 1 to 10, which are connected antiserially to the first number of electronic switches (1), wherein in particular the number of electronic switches (1), which is assigned to a first current direction, is equal to the number of electronic switches (1), which is assigned to the other current direction.

13. Ship's network with one or more electronic switches (1) according to one of claims 1 to 10 and / or one or more switching facilities according to claim 11 or 12.

14. High-voltage direct current transfer network with at least one switching facility according to claim 11 or 12.