DC Switch

Abstract

The invention relates to a DC switch for coupling two DC grids, wherein the DC grid on the load side in particular comprises a load-side capacitor, the DC switch comprising one or more power semiconductors, a preload resistor for limiting the current during the switch-on process, and a heat sink for dissipating heat for the power semiconductor and the preload resistor, characterized in that, in the heat sink, the preload resistor is arranged inside the heat sink in a recess in the heat sink.

Description

Technical Field

[0001] The invention relates to a device for coupling two DC power grids including capacitors on the power supply side and the load side by means of a DC switch. Background Art

[0002] Direct current grids, also known as DC grids, usually include large capacitors, such as the intermediate circuit capacitors of converters. If two DC grids, including capacitors on the supply side and the load side, are connected to one another, one of the capacitors already being at operating voltage while the capacitors in the other DC grid are still being discharged, very high balancing currents will occur when the two DC grids are directly connected, which can significantly exceed the rated current.

[0003] In order to limit the magnitude of this current, two DC grids including capacitors on the power supply side and the load side are connected through appropriate switching devices, such as Figure 1 The electrical equivalent circuit diagram is shown in Figure 1. This switching device can also be called a DC switch or a "DC circuit breaker".

[0004] Figure 1 The electrical equivalent circuit of a switching device 1 is shown, which is connected to a DC voltage source 2 via an inductance 3 on the supply side. A capacitor 7 on the supply side is arranged in parallel with the series circuit comprising the DC voltage source 2 and the inductance 3 on the supply side. On the output side, the switching device 1 is connected to a capacitor 8 on the load side via an inductance 5 on the load side. The inductances 3, 5 on the supply side and the load side are not necessarily physical components of two DC networks connected via the switching device 1. The inductances 3, 5 on the supply side and the load side can also be line inductances. The capacitors 7, 8 on the supply side and the load side are, for example, intermediate circuit capacitors of a converter (not shown).

[0005] exist Figure 1 In the variant of the known switchgear 1 shown in , the connection between the two DC voltage networks is first established via a loading resistor 20. The loading resistor 20 is connected in series with a switching element 21 and serves to limit the current I and avoid damage to the components. Only when the voltage between the two lines of the DC network is close enough to allow a low-impedance connection, the loading resistor 20 is bridged by the main switch 22. This switch 21 is also called a preload switch.

[0006] A disadvantage of the known switchgear is that the preload resistor generates a large amount of heat. However, for a single switching process, the heat is predictable, so the preload resistor can be arranged in a manner that matches other components of the switchgear, such as power semiconductors, so as not to damage the other components of the switchgear. However, due to external circumstances, the switchgear may be disconnected and connected several times in succession, that is, large balancing currents may occur several times in succession. In this case, which may also occur due to human intervention, the heat generated can no longer be predicted, and damage to the switchgear components around the preload resistor cannot be ruled out. Summary of the invention

[0007] Therefore, the technical problem to be solved by the present invention is to provide a DC switch for coupling two DC grids, which is improved in structure and / or function.

[0008] The above technical problem is solved by a DC switch for coupling two DC grids.

[0009] According to the present invention, a DC switch for coupling two DC grids comprises one or more power semiconductors, a preload resistor for limiting current during a switch-on process, and a heat sink for dissipating heat for the power semiconductor and the preload resistor. Here, the preload resistor is arranged inside the heat sink in a recess in the heat sink.

[0010] Here, the heat sink comprises a cooling channel formed by internally located cooling fins, which extend between a first outer surface and a second outer surface of the heat sink, wherein one or more power semiconductors are arranged on a third outer surface of the heat sink. Finally, a recess extends from an outer surface of the heat sink facing away from the third outer surface into the heat sink.

[0011] In particular, a DC grid includes capacitance on the load side, but may also include capacitance on the source side and even inductance on both sides, such as line inductance.

[0012] In the invention, it has been recognized that the best placement of the preload resistor is provided if the preload resistor is arranged in a heat sink that is already present for the device. In this case, a recess is provided in the heat sink, in which the preload resistor is arranged. In this case, a recess is a cavity in which cooling fins or cooling channels that are usually present in other cases have been removed or are absent. Preferably, the recess opens into the surface of the heat sink. However, it is also possible for the recess to be located only in the heat sink. In this case, the installation of the preload resistor is possible, for example, by assembling the heat sink from two elements.

[0013] Due to the arrangement in the heat sink, all heat generated in the preload resistor is not dissipated to the surrounding electronics, such as power semiconductors, but directly to the heat sink. As a result, even if the preload resistor generates a lot of heat, that is, even in the case of multiple switching, there is always good heat dissipation and the possibility of other components of the DC switch being adversely affected is minimized.

[0014] Particularly advantageously, the preloading resistor is used only for preloading and is not used in normal operation, so that, although the cooling power of the heat sink is also used, the cooling power is not reduced in normal operation.

[0015] This application also provides advantageous embodiments of the DC switch according to the invention. Therefore, the DC switch can also be provided with the following features in addition.

[0016] In a manner known per se, the DC switch can include a fan for actively ventilating the heat sink. The forced air flow significantly improves the heat removal from the DC switch.

[0017] The heat sink advantageously surrounds the preload resistor. In other words, the recess is designed so that the preload resistor can be inserted into the heat sink so that the outer dimensions of the heat sink completely surround the preload resistor. Advantageously, almost all heat dissipation is thereby transferred directly to the heat sink in all directions in the form of radiation or heated air and can be discharged. Other components, such as the housing of the DC switch, are, however, only slightly affected by the heating of the preload resistor.

[0018] - The recess can be designed so that the preload resistor can be inserted into the heat sink in the direction of the air flow in the heat sink. In other words, in a tubular heat sink, the recess can extend from one end of the tube into the tube. For example, if the preload resistor is arranged on a circuit board, a part of the cooling fins can be designed so that these cooling fins serve as guides for the insertion of the circuit board.

[0019] The DC switch can include one or more temperature measuring devices for determining the temperature of the heat sink, wherein the device is designed to enable active ventilation when a threshold temperature is exceeded. In other words, the fan is switched on when the threshold temperature is exceeded. As is known, as an alternative, the fan speed can also be adjusted continuously or a combination of the two possibilities can be provided. Advantageously, the heating of the preload resistor can also be counteracted directly by increasing the heat dissipation.

[0020] -The electrical wiring of the DC switch can include a first current path with at least one power semiconductor and a second current path connected in parallel with the first current path, the second current path having a series circuit consisting of a preload switch and a preload resistor. In particular, the first current path can include power semiconductors arranged in series in the form of an anti-series connection. In this case, the power semiconductors are preferably operated with reverse diodes respectively so that current flow in both directions can be achieved. As an alternative, anti-parallel connected reverse-cut-off insulated gate bipolar transistors, also called IGBTs, can also be used. Here, two reverse-cut-off IGBTs are arranged in a parallel circuit and oriented so that the disconnectable first semiconductor switch can conduct a current with a first polarity and the disconnectable second semiconductor switch can conduct a current with an opposite polarity. In addition to the reverse-cut-off IGBT, any other reverse-cut-off disconnectable semiconductor switch can also be arranged in the anti-parallel circuit. One or more power semiconductors cause the actual disconnection or connection of the DC grid, while the preload resistor is connected with the help of the preload switch for the connection process.

[0021] In the case of an antiparallel arrangement, it is advantageous to integrate the antiparallel diode into the transistor chip. Such a switch is also referred to as a reverse-conducting switch. In addition, in the case of a metal-semiconductor field-effect transistor, also known as a MOSFET, or a junction field-effect transistor, also known as a JFET, the channel can be operated in both current directions (antiparallel arrangement).

[0022] The DC switch can include a component for overvoltage protection, in particular a varistor. The component for overvoltage protection can be expediently arranged in a third current path which is connected in parallel to the first and second current paths.

[0023] Furthermore, the cooling capacity of the heat sink must be adequately designed for the DC switch. The reduced cooling capacity due to the recess in the heat sink can therefore be compensated by the increased outer dimensions of the heat sink compared to known DC switches.

[0024] As an alternative to air cooling, the DC switch can also include water cooling.

[0025] - Preferably, the power semiconductor is a Si-IGBT, a SiC-MOSFET or a GaN-FET.

[0026] The described switchgear is designed in particular for use in DC voltage networks with voltages between 100 V and 1500 V. The provided rated currents are in the range of 8 A to 2000 A. Further embodiments provide that a DC switch of the type described here is used as a short-circuit-proof circuit breaker. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further advantages and features are obtained from the following description of the embodiments with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same components and functions. In the drawings:

[0028] Figure 1 shows the electrical equivalent circuit of the switching device 1,

[0029] Figure 2 shows the electrical equivalent circuit of a DC switch with a preload resistor,

[0030] Figure 3 A cross-sectional view showing a heat sink of a DC switch with a preload resistor in side view,

[0031] Figure 4 shows a front view of the heat sink,

[0032] Figure 5 A perspective view of a heat sink with a preload resistor is shown. DETAILED DESCRIPTION

[0033] Figure 2 An electrical equivalent circuit diagram of an exemplary DC switch 100 is shown, which is integrated into the surrounding DC grid. Towards the output end on the power supply side, the DC switch 100 is connected to the DC grid 32 through a fuse 30. The DC grid 32 can be, for example, an industrial DC grid, such as a DC grid in a factory. The DC grid 32 can include a generator, a photovoltaic device, an energy supply grid or an energy storage device. The fuse 30 ensures that the electrical appliance is protected independently of the DC switch 100 under high current load conditions. On the load side, the DC switch 100 is connected to a load 33 having a capacitive portion, for example, a converter having an intermediate circuit capacitor, through a load isolation switch 31. The DC switch 100 is used to separate the electrical load 33 from the DC grid 32 and disconnect the current.

[0034] The DC switch 100 itself comprises a first current path with two IGBTs 24, 25 connected in anti-series. This means that the current flowing through the first IGBT 24 also flows through the diode connected in anti-parallel to the second IGBT 25. When the polarity is reversed, i.e. when the current direction is reversed, the current flows through the second IGBT 25 and through the diode connected in anti-parallel to the first IGBT 24. An alternative anti-parallel circuit of the two IGBTs 24, 25 is not shown here. In this case, the diode can be omitted, but the semiconductor switch must be capable of reverse blocking. In normal operation, the first current path is used in the switched-on state of the DC switch 10, i.e. in the switched-on state, the two IGBTs 24, 25 are switched on. If the DC switch 100 is to perform a disconnection of the DC connection, the two IGBTs 24, 25 are disconnected.

[0035] In parallel with the first current path, there is a second current path, which includes a series circuit of a preload switch 21 and a preload resistor 20. The preload resistor is used only for the switch-on process and is therefore connected only when the DC switch 100 is to switch on the intermediate circuit by means of the preload switch 21. When the voltage across the capacitor in the load 33 is already largely balanced with the voltage of the DC grid 32, i.e. when the flowing balancing current is no longer too high, the IGBTs 24, 25 are switched on.

[0036] In parallel with the first and second current paths, there is also a third current path, which includes an overvoltage limiter, in this example a varistor 28. A current measuring device, not shown, is used to measure the current through the DC switch 100, and the current measuring device can be arranged inside the DC switch 100 or outside the DC switch 100. A control device, not shown, is used to control the IGBTs 24, 25, and is connected to the control terminals of the IGBTs 24, 25.

[0037] exist Figures 3 to 5 1 shows how the preload resistor 20 is integrated into the DC switch 100 in a side view, a front view and a perspective view. The DC switch 100 comprises a cube-shaped heat sink 101, which has a plurality of cooling fins 102 of different designs. The heat sink 101 comprises two independent air channels, which are actively ventilated by two fans 103. For this purpose, the fans 103 are arranged at the ends of the heat sink 101. The electronic and electrical structure of the DC switch 100, i.e., in particular the IGBTs 24, 25 on the corresponding circuit boards, busbars and other electronic components, such as electronic components for control and for display elements, are arranged on a first side of the heat sink 101.

[0038] In one of the two cooling channels, a recess 105 is introduced over a portion of the length of the heat sink 101, in which the cooling fins 102 are partially removed. In this example, the cooling fins 102 have been removed by milling. However, the production of the corresponding recess 105 can also be realized in other ways.

[0039] The preload resistor 20 is arranged in the recess 105, which for its part is mounted on the carrier circuit board 111. In this example, the cooling channel comprises cooling fins extending along the side, which are also retained in the area of ​​the recess 105 and are used as insertion rails for the carrier circuit board 111. As a result, the preload resistor 20 is arranged in the middle of the heat sink 101 and is surrounded by metal material on multiple sides. Therefore, the heat emitted by the preload resistor 20 hits the material of the heat sink 101 to a large extent in the form of radiation or heated air and can be effectively spread and discharged. If other components of the DC switch, such as IGBTs 24, 25, are arranged in the area of ​​the electronic device instead of in the heat sink 101, direct heating or even overheating of other components of the DC switch, such as IGBTs 24, 25, caused by the preload resistor 20 will not occur.

[0040] It is particularly advantageous to use, for example, a signal from a temperature sensor to control the fan 103. The heat input caused by the preload resistor 20 or even a plurality of such heat inputs in a short time then leads to a corresponding reaction of the fan 103, so that an optimal heat dissipation adapted to the switching process is achieved. Advantageously, this eliminates the need for an over-designed preload resistor 20, which would only heat up slightly during the preload process but would also overheat during multiple preloads in a short time.

[0041] Reference numerals list

[0042] 1 Switchgear

[0043] 2 DC voltage source

[0044] 3 Inductance on the power supply side

[0045] 5 Inductance on the load side

[0046] 6 Line to disconnect

[0047] 7 Capacitor on the power supply side

[0048] 8 Capacitance on the load side

[0049] 20 Preload resistor

[0050] 21 Preload switch

[0051] 24, 25 IGBT

[0052] 28 Varistor

[0053] 30 Fuse

[0054] 31 Load isolation switch

[0055] 32 DC grid

[0056] 33 Capacitive load

[0057] 100 DC switch

[0058] 101 Radiator

[0059] 102 Cooling fins

[0060] 103 Fan

[0061] 105 recess

[0062] 111 Carrier circuit board

[0063] I Current

Claims

1. A DC switch (100) for coupling two DC grids (32), wherein the DC grid on the load side comprises a capacitor (33) on the load side, and the DC switch comprises - one or more power semiconductor switches, - a preload resistor (20) which is used to limit the current during the switch-on process, - a metal heat sink (101) for dissipating heat for a power semiconductor switch and the preload resistor (20), wherein the heat sink (101) comprises a cooling channel formed by cooling fins (102) located inside, the cooling channel extending between a first outer surface and a second outer surface of the heat sink (101), and wherein the power semiconductor switch is arranged on a third outer surface of the heat sink (101), It is characterized in that The preload resistor (20) is arranged in a recess (105) in the heat sink (101) in the middle of the heat sink (101) and is surrounded by metal material on multiple sides, wherein the recess (105) extends from an outer surface of the heat sink (101) facing away from the third outer surface into the heat sink (101).

2. The DC switch (100) according to claim 1, characterized in that: The heat sink (101) is substantially cubic in shape.

3. The DC switch (100) according to claim 1 or 2, characterized in that: The recess extends parallel to the cooling channel in the heat sink.

4. The DC switch (100) according to claim 1, characterized in that: The DC switch has one or more fans (103) for actively ventilating the heat sink.

5. The DC switch (100) according to claim 1, characterized in that: The heat sink (101) surrounds the preload resistor (20).

6. The DC switch (100) according to claim 1, characterized in that: The recess (105) is designed so that the preload resistor (20) can be inserted into the heat sink (101) along the direction of air flow in the heat sink (101).

7. The DC switch (100) according to claim 6, characterized in that: The preload resistor (20) is arranged on a carrier circuit board (111), and a part of the cooling fin (102) is designed so that the cooling fin serves as a guide rail for inserting the carrier circuit board (111).

8. The DC switch (100) according to claim 1, characterized in that: The DC switch has a temperature measuring device for determining the temperature of the heat sink, wherein the DC switch (100) is designed for active ventilation when a threshold temperature is exceeded.

9. The DC switch (100) according to claim 1, characterized in that: The electrical wiring comprises a first current path having at least one power semiconductor switch and a second current path connected in parallel with the first current path, the second current path having a series circuit consisting of a preload switch (21) and the preload resistor (20).

10. The DC switch (100) according to claim 9, characterized in that: The electrical arrangement comprises two power semiconductor switches arranged in opposite series.

11. The DC switch (100) according to claim 9, characterized in that: The electrical circuit comprises two reverse-blocking power semiconductors arranged in anti-parallel.

12. The DC switch (100) according to claim 11, characterized in that: The electrical wiring includes two reverse blocking insulated gate bipolar transistors arranged in anti-parallel.

13. The DC switch (100) according to claim 1, characterized in that: The DC switch has components for overvoltage protection.

14. The DC switch (100) according to claim 13, characterized in that: The DC switch has a varistor (28).

15. The DC switch (100) according to claim 1, characterized in that: The DC switch has a current measuring device and / or a voltage measuring device.

16. A DC voltage system, characterized in that: The DC voltage system includes - at least one energy source with a DC voltage, one or more capacitive loads having a DC voltage connection, - One or more DC switches (100) according to any of the preceding claims.

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