Switch-off assembly and method for switching-off a direct current in high-voltage direct current lines (HVDC lines)

Abstract

The invention relates to a switch-off assembly (9) for switching-off a direct current in a direct current line (1), in particular in an HVDC line, having at least one switching module (M, M1...Mn) with power semiconductor switching units (27). The at least one switching module (M, M1...Mn) is part of an intermediate circuit, at least in some portions, when the switching module is connected to the direct current line (1), and the at least one switching module (M, M1...Mn) has at least one energy storage device (17) and at least one power supply device (21) for supplying an electronics module (23) of the switching module (M, M1...Mn). In order to obtain a switch-off assembly which has a simple construction and can be operated safely, the at least one energy storage device (17) and the at least one power supply device (21) are connected to the intermediate circuit when the switching module (M, M1... Mn) is connected to the direct current line (1).

Description

[0001] Description

[0002] Disconnection arrangement and method for disconnecting direct current in high-voltage direct current (HVDC) transmission lines

[0003] The present invention relates to a disconnection arrangement for disconnecting a direct current in a direct current line, in particular in an HVDC line, comprising at least one switching module with power semiconductor switching units, wherein the at least one switching module, in a state connected to the direct current line, is at least partially part of an intermediate circuit, and wherein the at least one switching module comprises at least one energy storage device and at least one power supply device for supplying module electronics of the switching module. The invention further relates to a method for operating a disconnection arrangement according to the invention.

[0004] The switching off of direct currents, especially in HVDC lines where voltages of up to 500 kV and currents of up to 2000 A can occur, presents various challenges. In particular, the safe switching off of direct currents at high voltages and currents, as well as the efficient dissipation of the energy stored in the lines, pose technical problems. The energy stored in the inductances of the lines can cause an arc to ignite in a simple opener, which can persist for a very long time and lead to the destruction of the switch.

[0005] Disconnect devices for direct current lines are also known as "DC breakers." Known solutions for disconnecting direct currents in HVDC lines include mechanical switches with suitable reverse current imprinting, power electronic switches, and hybrid breakers, which represent a combination of mechanical and power electronic switches. Each of these concepts has its own advantages and disadvantages. The object of the invention is to provide a simple disconnect device for direct currents that enables the safe disconnection of direct currents, particularly in HVDC lines.

[0006] This problem is solved according to the invention by the shutdown arrangement defined in claim 1. Further advantageous embodiments are the subject of the dependent claims. The shutdown arrangement according to the invention is characterized in that the at least one energy storage device and the at least one power supply device are connected to the intermediate circuit in the state of the switching module being connected to the DC line.

[0007] The inventive method for operating an inventive shutdown arrangement is characterized by the following steps: charging the energy storage device by the direct current of the direct current line and subsequent supplying the power supply device to supply a module electronics of the switching module by the energy storage device.

[0008] Because the power supply unit draws the energy for the module electronics directly from the intermediate circuit, a complex and therefore expensive, galvanically isolated power supply for the power semiconductor switching units from earth potential can be dispensed with.

[0009] The switching module of the shutdown arrangement according to the invention falls into the group of power electronic switches. The power supply unit is connected in parallel to the energy storage device. The shutdown arrangement constitutes a switch for the DC line. The switch is closed when the DC line is in operation.

[0010] The solution according to the invention can be further improved by various embodiments, each advantageous in itself and arbitrarily combinable with one another. These embodiments and their associated advantages are discussed below.

[0011] The power semiconductor switching units preferably each comprise a semiconductor switch and a freewheeling diode connected in parallel to the semiconductor switch and facing in the opposite direction to the semiconductor switch. The semiconductor switches can, in particular, be formed by insulated-gate bipolar transistors (IGBTs).

[0012] The disconnection device is generally designed to be connected in series with the DC line. Preferably, the individual switching modules of the disconnection device are also connected in series with the DC line when the disconnection device is connected to the DC line.

[0013] According to an advantageous embodiment of the shutdown arrangement, the power semiconductor switching units of the at least one switching module are arranged in a full bridge circuit.

[0014] To obtain a simply constructed energy storage device, the at least one energy storage device includes or is formed by at least one capacitor. The at least one capacitor can also be referred to as an intermediate circuit capacitor. In addition to the simple construction, the use of a capacitor is advantageous because capacitors, as energy storage devices, enable efficient energy conversion and switching off of the direct current. Capacitors also offer a fast response time.

[0015] According to a further advantageous embodiment of the invention, at least one braking divider can be connected in parallel to the at least one energy storage device. The integration of braking dividers in parallel with the energy storage device enables a targeted limitation or reduction of the energy in the capacitor. The electrical energy can be converted into heat in the braking divider. Since the braking divider is part of the shutdown arrangement, its use allows the electrical energy to be dissipated within the shutdown arrangement itself.

[0016] In order to obtain a brake divider that is both simple in design and effective, it can have at least one resistor and at least one power conductor switching unit connected in series with the resistor.

[0017] To ensure reliable shutdown even at high voltages, the shutdown arrangement can comprise multiple switching modules connected in series. Furthermore, the arrangement of multiple switching modules connected in series enables a scalable and adaptable shutdown arrangement.

[0018] According to a further advantageous embodiment, the disconnection arrangement can include at least one surge arrester connected in parallel to at least a subset of the series-connected switching modules. The integration of surge arresters makes it possible to dissipate the energy stored in the line during disconnection and convert it into heat. Furthermore, the at least one surge arrester can provide additional protection against unwanted voltage spikes.

[0019] It is particularly preferred that at least one surge arrester be connected in parallel to all switching modules connected in series.

[0020] Another way to convert electrical energy into heat is to equip each switching device with its own surge arrester connected in parallel to the DC link. Such a surge arrester is therefore preferably connected in parallel to the energy storage device.

[0021] In operation of the shutdown arrangement, that is, when the switch formed by the shutdown arrangement is closed, it will be sufficient if only the energy storage of one of the switching modules is recharged at any given time.

[0022] Alternatively, the energy storage devices of several switching modules can be recharged simultaneously. For example, the energy storage device of the switching module whose energy storage is most discharged can be preferentially recharged. Subsequently, recharging of the energy storage device of another switching module can begin. Recharging the energy storage device of a switching module can be very fast, especially when using capacitors. The duration of a charging process can be in the range of 10 to 50 microseconds.

[0023] The effect of the short recharging process of a switching module on the transmitted power will usually be very small, since for large transmission voltages a very large number of switching modules can be present, typically more than 100 switching modules.

[0024] If the feedback effect should nevertheless be undesirable, it can possibly be eliminated via a superimposed feedforward control in a rectifier or inverter connected to the DC line.

[0025] The method according to the invention can include the following further steps: switching off the power semiconductor switching unit, in particular by switching off the semiconductor switches contained therein and diverting the current into the at least one braking divider and / or the at least one surge arrester in order to convert the electrical energy into heat.

[0026] For further explanation of the invention, reference is made in the following part of the description to figures from which further advantageous details and possible areas of application of the invention can be derived. The figures are to be understood as exemplary and are intended to illustrate the character of the invention, but in no way to restrict or even exhaustively represent it. The same reference symbols are always used for elements with the same structure and / or the same function.

[0027] They show:

[0028] Fig. 1 shows a schematic representation of a disconnection arrangement in a direct current line;

[0029] Fig. 2 shows a schematic representation of a disconnection arrangement with a surge arrester; and

[0030] Fig. 3 shows an advantageous embodiment of a switching module according to the invention.

[0031] Fig. 1 shows an example of a DC line 1 with a total resistance 3, an inductance 5 and a switch 7, which connects two DC voltages Ui and U2. The voltage across the switch 7 is denoted by U. s marked. In operation of the DC line 1, switch 7 is closed and the DC current I flows. DC in the DC line 1 .

[0032] If switch 7 is closed, then U s ~ 0 and the direct current I DC It can flow in both directions. If switch 7 is open, the current I DC ~ 0 and the voltage U is present at switch 7 s ~ Ui - U2an .

[0033] Switch 7 is provided as a shutdown arrangement 9, which is described below with reference to Figures 2 and 3.

[0034] The switching arrangement 9 can have a large number of identical switching modules M (M1...Mn), typically more than 100. The switching modules M are connected in series. The voltage across the switch 7, i.e., across the switching arrangement 9, is then U. s = U Mi + UM2 + ••• + U M n •

[0035] At least one surge arrester 11 can be connected in parallel to the series connection of the switching modules M1...Mn. If the sum of all voltages U Mi + U M 2 + - + U Mn If the current at the switching modules Ml...Mn exceeds a predefined level of the surge arrester 11, it takes over the current and converts the resulting energy into heat.

[0036] The switching modules M1...Mn are preferably identically constructed. The structure of a single switching module M is shown in Fig. 3 and is briefly described below.

[0037] The switching module M has two terminals, 13 and 15, which can be designated as either inputs or outputs, depending on the current direction. Switching modules M connected in series can be connected to each other at terminals 13 and 15, whereby terminal 13 of one switching module M can be connected to terminal 15 of an adjacent switching module M.

[0038] Furthermore, the switching module M comprises at least one energy storage device 17, which is preferably designed as a capacitor 19. The capacitor 19 is also referred to as a DC link capacitor.

[0039] Parallel to the energy storage device 17, a power supply unit 21 is connected to supply the module electronics 23 (shown only in dashed lines in Fig. 3).

[0040] For switching currents, the switching module M has four power semiconductor switching units 27 arranged in a full bridge circuit 25.

[0041] Each power semiconductor switching unit 27 comprises a semiconductor switch T (T1...T4) and a freewheeling diode D (D1...D4). Each freewheeling diode D (D1...D4) of a power semiconductor switching unit 27 is connected in parallel and oppositely oriented to the semiconductor switch T (T1...T4) of the same power semiconductor switching unit 27. The semiconductor switches T are in particular formed by IGBTs.

[0042] The power semiconductor switching units 27 can be counted as part of the module electronics 23 and are therefore supplied by the power supply unit 21 during operation.

[0043] A brake divider 29 can be connected in parallel to the energy storage device 17. The brake divider 29 preferably comprises at least one resistor Rb and at least one power semiconductor switching unit 31 connected in series with the resistor.

[0044] The power semiconductor switching unit 31 comprises a semiconductor switch Tb and a freewheeling diode Db connected in parallel to the semiconductor switch Tb and arranged in the opposite direction to it. With the aid of the braking controller 29, the energy in the energy storage device 17 can be limited or even selectively reduced.

[0045] The following is a brief description of the functionality of the above-described implementation form, whereby, for the sake of simplicity, the function is described using a single switching module M.

[0046] If the power supply unit 21 is not yet operating because the energy storage device 17 is not charged or not sufficiently charged, none of the four semiconductor switches T (T1...T4) can conduct. Therefore, every current I carries DC via the freewheeling diodes D to charge the energy storage device 17, i.e. the capacitor 19.

[0047] As soon as sufficient voltage is present in the energy storage device 17, the power supply unit 21 begins to supply all electronics in the switching module M with auxiliary energy. From this point on, all switching states of the semiconductor switches T (T1...T4) can also be controlled.

[0048] If terminal 13 is used as an input, opening one of the semiconductor switches T2 or T3 leads to the closing of switch 7, which is represented by the shutdown arrangement 9. The current is then given by I DC > 0 . The current I DC The current flows either via the freewheeling diode D1 and the semiconductor switch T2, or via the semiconductor switch T3 and the freewheeling diode D4, bypassing the energy storage device 17 in a kind of bypass. The forward voltage between terminal 13 and terminal 15 therefore consists of the sum of the forward voltages of a semiconductor switch T and a freewheeling diode D.

[0049] If the current flows in the opposite direction, i.e. from terminal 15 to terminal 13, then I DC < 0 . The current then flows through the freewheeling diode D2 and the semiconductor switch TI or through the semiconductor switch T4 and the freewheeling diode D3 .

[0050] During operation, the semiconductor switches T can be controlled such that in a first switching state, semiconductor switches TI and T2 are switched on, and semiconductor switches T3 and T4 are switched off. In a second switching state, semiconductor switches TI and T2 can be switched off, and T3 and T4 can be switched on.

[0051] By switching the two switches, flow losses can be distributed across two installation locations, which can facilitate cooling.

[0052] To open switch 7, all semiconductor switches T are switched off. The remaining current I DCThe freewheeling diodes D further charge capacitor 19. This draws energy from the DC line 1. The increasing back EMF of all capacitors 19 of the switching modules M1...Mn acts on the current I. DC increasingly contrary. There are several possibilities for converting the energy into heat. One possibility is to use the brake divider 29. In this case, the energy can be converted into heat locally in each switching module M via the resistor Rb and the semiconductor switch Tb in parallel with each capacitor 19.

[0053] Alternatively, electrical energy can be converted into heat externally. The sum of the voltages U across the series connection of all modules M1...Mn is... Mi + U M 2 + - + U Mn All capacitors 19 are effective. As soon as this total voltage exceeds a predefined discharge level of the surge arrester 11, the surge arrester takes over the current and dissipates the energy.

[0054] Another way to convert electrical energy into heat is to provide each switching arrangement 9 with its own surge arrester 33, which is connected in parallel to the intermediate circuit. The surge arrester 33 is therefore preferably connected in parallel to the energy storage device 17. Such a surge arrester 33 is indicated by dashed lines in Figure 3.

[0055] In the operation of the switching modules Ml...Mn, the capacitors 19 are discharged very slowly after the first charging, because the required auxiliary energy during bypass operation will be in the range of a few watts.

[0056] In order to keep the auxiliary energy permanently available, the slow discharge of the capacitors 17 may only proceed as far as the power supply unit 21 still operates safely.

[0057] Depending on the transmission current, the charging of the capacitors 19 can be carried out with several kilowatts if all transistors T in a switching module are blocked for a short time at appropriate times.

[0058] This reloading can already occur when the necessary

[0059] The locking time changes between the two switching states described above. For controlled recharging to a desired capacitor voltage, the locking time would have to be extended accordingly.

[0060] During operation, i.e., when switch 7 is closed, it may be sufficient to recharge only one switching module M, or a few switching modules M, at any given time. For example, the switching module M that is most discharged can always be recharged preferentially. Afterwards, recharging can proceed to another switching module M.

[0061] The effect of the short recharging process of a switching module M on the transmitted power can then be very small, since a very large number of switching modules M will be needed for large transmission voltages, typically more than 100 .

[0062] If the feedback is still disruptive, it can be eliminated by means of a superimposed feedforward control in a rectifier or inverter connected to the DC line 1, i.e. by influencing Ui or U2.

[0063] Reference sign

[0064] 1 DC line

[0065] 3 Total resistance

[0066] 5 Inductance

[0067] 7 switches

[0068] 9 Shutdown arrangement

[0069] 11 surge arresters

[0070] 13, 15 connections

[0071] 17 Energy storage

[0072] 19 Capacitor

[0073] 21 Power supply unit

[0074] 23 Module electronics

[0075] 25 full bridge circuit

[0076] 27 power conductor switch unit

[0077] 29 brake dividers

[0078] 31 Power semiconductor switching unit of the brake actuator

[0079] 33 surge arresters

[0080] Ui, Ui direct current

[0081] U s Switch voltage

[0082] I D c Current

[0083] D, D1...D4 freewheeling diodes

[0084] T, T1...T4 semiconductor switches

[0085] M, Ml...Mn switching modules

[0086] Rb resistance of the brake actuator

[0087] Tb semiconductor switch of the brake actuator

[0088] DB freewheel diode of the brake actuator

Claims

Patent claims 1. Switching arrangement (9) for switching off a direct current in a direct current line (1), in particular in an HVDC line, comprising at least one switching module (M, M1...Mn) with power semiconductor switching units (27), wherein the at least one switching module (M, M1...Mn) is at least sectionally part of an intermediate circuit in a state connected to the direct current line (1), and wherein the at least one switching module (M, M1...Mn) includes at least one energy storage device (17) and at least one power supply device (21) for supplying module electronics (23) of the switching module (M, Ml...Mn) has, characterized in that the at least one energy storage device (17) and the at least one power supply device (21) are connected to the intermediate circuit in the state of the switching module (M, Ml...Mn) connected to the DC line (1).

2. Switch-off arrangement (9) according to claim 1, characterized in that the power semiconductor switching units (27) of the switching module (M, Ml...Mn) are arranged in a full bridge circuit (25).

3. Switch-off arrangement (9) according to claim 1 or 2, characterized in that the energy storage device (17) comprises at least one capacitor (19).

4. Shutdown arrangement (9) according to one of claims 1 to 3, characterized in that at least one brake divider (29) is connected in parallel to the energy storage device (17).

5. Switch-off arrangement (9) according to claim 4, characterized in that the at least one brake divider (29) has at least one resistor (Rb) and at least one power semiconductor switching unit (31) connected in series with the resistor (Rb).

6. Switch-off arrangement (9) according to one of claims 1 to 5, characterized in that the switch-off arrangement (9) comprises a plurality of switching modules (M, Ml...Mn) connected in series according to one of the above claims.

7. Switch-off arrangement (9) according to one of claims 1 to 6, characterized in that the switch-off arrangement (9) has at least one surge arrester (11) which is connected in parallel to at least a subset of the series-connected switching modules (M, Ml...Mn).

8. Switch-off arrangement (9) according to claim 7, characterized in that the at least one surge arrester (11) is connected in parallel to all series-connected switching modules (M, Ml...Mn) of the shutdown arrangement (9) is switched.

9. Method for operating a shutdown arrangement (9) according to one of the preceding claims, characterized by the following steps: Charging the energy storage device (17) by the direct current of the direct current line (1) ; and supplying the power supply device (21) to supply the module electronics (23) of the switching module (M, Ml...Mn) by the charged energy storage device (17) .

10. Method for operating a shutdown arrangement (9) according to claim 9, further comprising the steps: Shutdown of the power semiconductor switching units (27) ; and Diverting the current into at least one brake divider (29) and / or at least one surge arrester (11) and converting the electrical energy into heat.

11. Method for operating a plurality of shutdown arrangements (9), each configured according to one of claims 1 to 8 and operated according to the method of claim 9 or 10, wherein the energy storage device (17) of a single shutdown arrangement (9) or the energy storage device is operated according to the method of claim 9 or 10, wherein the energy storage device (17) of a single shutdown arrangement (9) or the energy storage device (17) of a single shutdown arrangement (9) ... and the energy storage device (17) of a single shutdown arrangement (9) is operated according to the method of claim 9 or rather (17) a small number of shutdown arrangements (9) , are charged simultaneously, wherein the small number of shutdown arrangements (9) is less than 50%, preferably less than 25%, of a total number of shutdown arrangements (9) within a series connection of shutdown arrangements (9).

12. Method according to claim 11, wherein the most deeply discharged energy storage device (17) of the shutdown arrangements (9) the series connection of shutdown arrangements (9) is loaded first.

13. Method according to one of claims 9 to 12, wherein a duration of a charging process for charging an energy storage device (17) is in the range of 10 to 50 microseconds.

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