DE102021113205A1 - PROCEDURE FOR OPERATION OF A SHORT-CIRCUIT PROTECTED SUPPLY SYSTEM AND SHORT-CIRCUIT PROTECTED SUPPLY SYSTEM - Google Patents

Abstract

The application relates to a method for operating a short-circuit protected supply system (10) of a DC network (14) from an AC network (12), the supply system (10) having an active rectifier (20) with upstream sine filter chokes (20.1) on the AC side. , a pre-charging device and a short-circuit protection device, wherein the short-circuit protection device is set up to direct a short-circuit current occurring as a result of a fault in the DC network, bypassing the active rectifier (20) from the AC network (12) into the DC network (14). conduct. The method comprises the following steps for starting up the supply system (10): a) Pre-charging the DC network (14) via the pre-charging device (39, 41), with the active rectifier (20) being connected to the DC network (14 ) is connected, b) establishing an AC-side connection of the active rectifier (20) to the AC grid (12) at a first point in time during the pre-charging at which a voltage of the DC grid (14) exceeds a first threshold value, c) Establishing a connection between the AC network (12) and the DC network (14) via the short-circuit protection device (37, 41) at a second time during the pre-charging, at which the voltage of the DC network (14) has a second threshold exceeded. The application also relates to a short-circuit protected supply system (10).

Description

background

The application relates to a method for short-circuit protected operation of a DC network, and a short-circuit protected supply system of a DC network from an AC network.

Thyristor rectifiers or active rectifiers are used to supply a DC voltage network, also referred to below as a DC network. Active rectifiers, also referred to below as AFE (Active Front End), have a bridge circuit in which power semiconductor switches, in particular IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) with antiparallel freewheeling diodes, are used. In this case, the freewheeling diodes form a rectifier in relation to the AC voltage network, also referred to below as the AC network, so that uncontrolled current flows through the freewheeling diodes when the DC voltage on the output side of an active rectifier is below a rectified value of the AC mains voltage.

For this reason, with active rectifiers, in the event of a ground fault or short-circuit on the DC side, where the output-side DC voltage falls below the rectified value of the AC grid, there is a risk that an excessively high current will flow through the freewheeling diodes, causing them to damaged.

One possible measure would be to design the freewheeling diodes of the AFE in such a way that an expected short-circuit current could be accepted without damaging them. However, the freewheeling diodes cannot then be optimally designed for normal operation of the AFE, which has a disadvantageous effect on the costs, the required installation space and/or the efficiency in nominal operation and per AFE.

It is known to use fast-switching DC circuit breakers so that the fault location is separated more quickly than the freewheeling diodes are damaged by the overcurrent caused by the short circuit or ground fault. This requires hybrid DC disconnect switches that have both electromechanical switches and fast semiconductor switches. However, such hybrid circuit breakers are expensive and introduce additional complexity into a supply system for a DC network. Furthermore, the conduction losses of the semiconductor switches are higher than with fuses or circuit breakers, which is why additional cooling measures are necessary.

task

The object of the invention is to ensure that the network structure and operation of the DC network are protected against short circuits.

solution

The object is solved by a method having the features of independent patent claim 1 . The method can be carried out by a supply system with the features of claim 13. Advantageous embodiments of the method and the supply system are claimed in the dependent claims.

description

1. a) Vorladen des DC-Netzes über die Vorladevorrichtung, wobei das AFE DC-seitig mit dem DC-Netz verbunden ist.
2. b) Herstellen einer AC-seitigen Verbindung des AFE mit dem AC-Netz zu einem ersten Zeitpunkt während des Vorladens, zu dem eine Spannung des DC-Netzes einen ersten Schwellwert überschreitet.
3. c) Herstellen einer Verbindung zwischen dem AC-Netz und dem DC-Netz über die Kurzschlusssicherungsvorrichtung zu einem zweiten Zeitpunkt während des Vorladens, zu dem die Spannung des DC-Netzes einen zweiten Schwellwert überschreitet.

A short-circuit protected supply system of a DC network from an AC network has an active rectifier with upstream sine filter reactors on the AC side, a pre-charging device and a short-circuit protection device, the short-circuit protection device being set up to prevent a short-circuit current occurring as a result of a fault in the DC network, bypassing the active rectifier from the AC grid to the DC grid. A method for operating such a supply system includes the following steps for starting up the supply system:

1. a) Pre-charging of the DC network via the pre-charging device, with the AFE being connected to the DC network on the DC side.
2. b) Establishing an AC-side connection of the AFE to the AC grid at a first point in time during the pre-charging at which a voltage of the DC grid exceeds a first threshold value.
3. c) Establishing a connection between the AC grid and the DC grid via the short-circuit protection device at a second point in time during the pre-charging, at which the voltage of the DC grid exceeds a second threshold value.

In step a), the DC network is initially precharged via the precharging device to a first threshold value of the DC voltage. The pre-charging via the pre-charging device is preferably current-limited, for example via a pre-charging resistor of the pre-charging device. In step a), at least the AFE is already connected to the DC network on the DC side. If there is a short circuit or ground fault in the DC grid during this precharging process, the current limitation of the precharging device can prevent the first threshold value of the DC voltage from being reached. The subpoena can then be canceled in this case.

If the first threshold value of the DC voltage is exceeded, the AFE can be connected to the AC grid on the AC side in step b). The DC grid may be precharged to a second DC voltage threshold. If the second threshold value of the DC voltage is exceeded, in step c) the AC network is connected to the DC network via the short-circuit protection device. In one embodiment of the method, the second threshold is greater than the first threshold. If the DC voltage of the DC network is pre-charged in a continuously increasing manner, the first threshold value and then the second threshold value of the DC voltage are reached first. This therefore corresponds to an embodiment in which the first point in time is before the second point in time.

Also conceivable is an embodiment in which the second threshold value is selected to be smaller than the first threshold value. In this case, the second threshold value is first reached at the second point in time during the pre-charging and the short-circuit protection device is switched on on the AC side. If the first threshold value is then reached at the first point in time during the further course of the pre-charging, the AFE is also connected to the AC grid. If there is a short circuit or ground fault in the DC grid during this pre-charging process, the current limitation of the pre-charging device can prevent the second threshold value of the DC voltage from being reached. The subpoena can then be canceled in this case. Because the short-circuit protection device is connected to the AC grid in front of the AFE, the AFE is protected from the consequences of a short circuit or ground fault at all times.

Sinusoidal filter chokes are part of an AC-side mains filter of the AFE, which ensure a strongly delayed increase in current.

The supply system can be connected to the AC grid via a pre-transformer, which converts the voltage level to a value desired for the supply system. The AC network connected to the supply system can be a grounded network, for example in that the pre-transformer has a ground connection connected to PE on the secondary side. But an unearthed AC network is also conceivable, in which case one-sided earth faults do not lead to a short-circuit current and therefore remain unprotected.

The pre-charging device is a power electronic circuit that allows current-limited pre-charging of the DC network at least until the first threshold value is reached, preferably until the rated voltage of the DC network is reached. A precharging device can be implemented, for example, by an active rectifier—also an AFE—with a downstream DC/DC converter with step-down function or by a thyristor rectifier with a downstream DC/DC converter with step-up function. Other forms of circuitry are also known to those skilled in the art and can be used.

In one embodiment of the method, the pre-charging device and the short-circuit protection device can each be arranged in separate branches parallel to the active rectifier between the AC network and the DC network. In a further embodiment, the pre-charging of the DC side and the short-circuit protection can be taken over by a common, combined device. For example, it is possible to provide a bridgeable pre-charging resistor in series with the short-circuit protection device, in which case the pre-charging resistor can be bridged, for example, by a closed switch when operating as a short-circuit protection device. When operating as a pre-charging device, this switch can be open and the pre-charging resistor can thus limit the pre-charging current.

In one embodiment of the method, the DC grid is precharged after the AC-side connection of the AFE to the AC grid has been established, at least partially via the AFE. This means that the DC grid can be pre-charged up to the first threshold value of the DC voltage via the pre-charging device and thereafter via the pre-charging device and/or the AFE.

In one embodiment of the method, the first threshold value depends on a first AC input voltage at the AC input of the AFE and can in particular correspond to a rectified value of the first AC input voltage or be a predetermined first distance above the rectified value of the first AC input voltage. By selecting the first threshold value in this way, it can be achieved that the active rectifier is only connected to the AC grid on the AC side when the DC voltage in the DC grid is high enough and the active rectifier is switched on without current or largely without current can. This ensures that the freewheeling diodes in the active rectifier are not damaged.

In one embodiment of the method, the DC grid is precharged up to a rated voltage of the DC grid. The first and the second threshold are both below the nominal voltage of the DC network. The method can thus ensure safe pre-charging of the DC network up to its rated voltage. If a short circuit or earth fault occurs before the rated voltage is reached, the safety function is already active through the short-circuit protection device.

In one embodiment of the method, the short-circuit protection device has a rectifier, via which the connection between the AC grid and the DC grid is established. The rectifier can be a passive rectifier, for example, which is connected to the AC grid on the AC side and to the DC grid on the DC side. The rectifier is supplied with a second AC input voltage. Optionally, the short-circuit protection device can have a transformer, in particular a step-up transformer, the transformer supplying the rectifier with a second AC input voltage that is higher than the first AC input voltage at the AFE, so that the rectified value of the second AC input voltage can also be higher . In the absence of such a transformer, the second AC input voltage corresponds to the first AC input voltage.

In one embodiment of the method, the second threshold value depends on the second AC input voltage of the rectifier of the short-circuit protection device and can in particular correspond to a rectified value of the second AC input voltage or be a predetermined second distance above the rectified value of the second AC input voltage. The second threshold value can thus be selected in such a way that the diodes of the passive rectifier block at a DC voltage greater than the second threshold value, so that no current flows from the AC grid into the DC grid via the passive rectifier when it is switched on.

If a short circuit or ground fault occurs in the DC grid during operation, the DC voltage drops suddenly. If this falls below the rectified value of the second AC input voltage, the diodes of the rectifier of the short-circuit protection device become conductive and make at least a significant part of the short-circuit current from the AC network available. At the same time, the intermediate circuit capacitance of the active rectifier can be further discharged.

Even if the DC voltage falls below the rectified value of the first AC input voltage and the freewheeling diodes of the AFE become conductive, the sine-wave filter chokes ensure that the current flowing through the freewheeling diodes of the active rectifier increases with a considerable delay. As a result, the short-circuit current flowing in the event of a fault can be provided for a certain period of time largely by the rectifier of the short-circuit protection device and the intermediate circuit capacitance. A suitable dimensioning of the sine-wave filter chokes can ensure that the period of time is sufficient to trigger or actuate corresponding isolating devices on the DC side, for example fuses. As a result, the supply system can then also be designed without a step-up transformer on the AC side of the rectifier of the short-circuit protection device, which can save costs. By means of the sine-wave filter chokes, which are arranged, for example, as mains filters on the active rectifier, an increase in the current can be limited and the AFE can be kept supplied with subcritical current over a sufficiently long period of time in the event of a short circuit. The fuses can then be triggered, for example, by the short-circuit current supplied via the short-circuit protection device.

In the event that short-circuit currents could also occur for a period longer than that which can be achieved with the sine-wave filter chokes, for example with slow-acting fuses, it is possible to provide the transformer on the AC side of the rectifier of the short-circuit protection device. The transformation ratio of the transformer can now be selected in such a way that the rectifier of the short-circuit protection device changes to the conductive state in the event of a ground fault or short-circuit and if the DC voltage drops and provides the current required to trip the DC-side isolating devices before the Freewheeling diodes of the active rectifier would switch to the conductive state. As a result, the freewheeling diodes of the active rectifier can be protected even better.

In one embodiment, the supply system may have a plurality of AFE connected in parallel. Here, the AFE can be connected to the AC grid by connecting the plurality of AFEs in parallel. All AFEs connected in parallel in this way can be started up using the method described via the precharging device and the short-circuit protection device.

In one embodiment, the active rectifiers of the plurality of active rectifiers are connected in parallel one after the other when the supply system is started up. The active rectifiers are preferably connected in parallel individually according to the method described above.

• - Auftrennen der Verbindung zwischen dem AC-Netz und dem DC-Netz über die Kurzschlusssicherungsvorrichtung, und
• - Auftrennen der Verbindung des einen AFE oder der Mehrzahl der AFE mit dem AC-Netz.

In one embodiment, the method also has the following steps when decommissioning the supply system:

• - breaking the connection between the AC grid and the DC grid via the short-circuit protection device, and
• - Disconnecting one or more AFEs from the AC grid.

In one embodiment of the method, after a connection has been established between the AC grid and the DC grid, an enable signal is generated via the short-circuit protection device and transmitted to a DC load or to DC loads of the DC grid.

This makes it possible to inform the DC load or the DC loads of the DC network when the start-up is complete and safe normal operation of the DC network is possible. The release signal can also be transmitted to other DC units connected to the DC network, such as a battery or the like. The release signal can also be transmitted to the AFE and used, for example, to determine a power value or power limit value provided by the AFE or its operating mode.

• - ein AFE;
• - eine Vorladevorrichtung zum Vorladen des DC-Netzes aus dem AC-Netz;
• - eine Kurzschlusssicherungsvorrichtung;
• - eine Steuereinheit;

dadurch gekennzeichnet, dass
die Steuereinheit zur Durchführung des Verfahrens nach einem der vorhergehenden Ansprüche eingerichtet ist.A short-circuit protected supply system for a DC network from an AC network can have:

• - an AFE;
• - A pre-charging device for pre-charging the DC grid from the AC grid;
• - a short-circuit protection device;
• - a control unit;

characterized in that
the control unit is set up to carry out the method according to one of the preceding claims.

A mains filter, which can have sinusoidal filter chokes, can be connected upstream of the AFE on the AC side. The mains filter can then greatly delay the increase in current through the AFE in the event of a fault. The mains filter is preferably designed in such a way that it delays the rise in the current so much and for so long that fuses in the supply system trip in good time in the event of a fault before the AFE is damaged.

In one embodiment, the supply system has a plurality of AFEs connected in parallel, which are preferably connected in parallel individually one after the other when starting up using the method described above.

In one embodiment, the short-circuit protection device has a rectifier via which the connection between the AC grid and the DC grid is established, the rectifier being supplied with a second AC input voltage on which the second threshold value depends, the second threshold value corresponds in particular to a rectified value of the second AC input voltage of the rectifier. The rectifier is preferably a passive rectifier, via the diodes of which short-circuit currents can be diverted from the DC network to the AC network in the event of a fault.

In one embodiment, the short-circuit protection device and the pre-charging device have a common, preferably step-up transformer and a common rectifier, the short-circuit protection device also having a switch and the pre-charging device also having a pre-charging resistor connected in parallel with the switch. The pre-charging device and the short-circuit protection device are therefore in parts the same combined device, with the pre-charging resistor of the pre-charging device being bridged by the closed switch during operation as a short-circuit protection device. Such a system design enables a low-cost implementation with fewer components. The use of a step-up transformer as a common component of the short-circuit protection device and the pre-charging device enables improved short-circuit protection and faster pre-charging, as well as a currentless connection of the active rectifier to the AC grid.

Detailed description

• 1 schematisch Schritte eines Verfahrens zum Betrieb eines kurzschlussgesicherten Versorgungssystems zeigt,
• 2 eine Ausführungsform eines kurzschlussgesicherten Versorgungssystems zeigt und
• 3 eine weitere Ausführungsform eines kurzschlussgesicherten Versorgungssystems zeigt.

The invention is illustrated below with the aid of figures, of which

• 1 shows schematically the steps of a method for operating a short-circuit protected supply system,
• 2 shows an embodiment of a short-circuit protected supply system and
• 3 shows a further embodiment of a short-circuit protected supply system.

In the figures, identical or similar elements are denoted by the same reference symbols.

1 shows schematically steps a), b), c) of a method for operating a short-circuit protected supply system 10 ( 2 , 3 ). When the supply system 10 is started up, a DC network 14 is precharged via a precharging device 39, 41 in step a). An active rectifier 20 of the supply system 10 is connected to the DC network 14 on the DC side in step a). At a first point in time during the pre-charging, at which a voltage of the DC network 14 exceeds a first threshold value, the active rectifier 20 is connected to the AC network 12 by closing AC switches 22 in a step b). At a second point in time during the pre-charging, at which the voltage of the DC network 14 has a second threshold value is exceeded, a connection between the AC network 12 and the DC network 14 is established in a step c) via a short-circuit protection device 37, 41. The DC network 14 is then further precharged via the precharging device 39, 41 and/or the active rectifier 20 up to a rated voltage of the DC network. The preloader 39 off 2 can be separated from the AC grid by opening the AC switch 23. This can happen, for example, after the rated voltage of the DC network 14 has been reached.

In 2 an exemplary embodiment of a short-circuit-protected supply system 10 for supplying the DC network 14 from the AC network 12 is shown schematically. The AC network 12 is, for example, a three-phase AC network and can in particular be an AC supply network, which can be provided, for example, via a network transformer that provides a suitable voltage level for the supply system 10 via its transformation ratio. This can be grounded by connecting to potential earth PE. The supply system 10 has the active rectifier 20 with upstream sine filter chokes 20.1 on the AC side, a short-circuit protection device 37 and a pre-charging device 39.

As an equivalent equivalent circuit for a ground fault, the DC network 14 has a two-part insulation resistance 50 to ground potential PE. A battery 42 can be connected to the DC grid 14 via DC switches 46 . A load 44 can be connected to the DC grid via DC switches 48 . The load 44 may have an undesirable parasitic resistance 44.P to ground potential PE. A load 44 can in particular include one or more consumers, such as a machine, an industrial plant or an electrolyzer. The DC grid 14 may also include multiple loads 44 and multiple batteries 42 . Instead of parasitic resistances to ground potential PE, the DC network can also have parasitic resistances between the DC lines without a ground connection.

The pre-charging device 39 can be connected to the AC grid 12 via the AC switches 23 . The pre-charging device 39 has a current-limiting charging circuit 38, with the aid of which the current is limited when the DC network 14 is being pre-charged. The intermediate circuit 18 of the active rectifier 20 can be precharged via the precharging device 39 when the supply system 10 is started up before the AC side is connected to the AC network 12 . The pre-charging device 39 is set up to carry out such a pre-charging from the AC grid 12 . The intermediate circuit 18 of the active rectifier 20 can be precharged directly from the AC network 12 via the precharging device 39 .

The short-circuit protection device 37 can be connected to the AC grid 12 via AC switch 24 and has a passive rectifier 36, via which a short-circuit current occurring as a result of a fault in the DC grid 14 is removed from the AC grid 12, bypassing the active rectifier 20 the DC grid 14 can be routed. Such a fault in the DC network occurs, for example, if the two-part insulation resistance 50 or the parasitic resistance 44.P becomes too small and this causes a ground fault or short circuit in the DC network, i.e. a too low-resistance connection to the potential ground PE or between DC+ and DC-, arises. The passive rectifier is supplied with a second AC input voltage from the AC network 12 . A transformer 16 which supplies the rectifier 36 with the second AC input voltage can optionally be arranged between the AC switches 24 and the passive rectifier 36 . The second threshold value depends on the second AC input voltage and can be used to ensure that the connection between the AC network 12 and the DC network 14 via the short-circuit protection device 37 is only established when the intermediate circuit 18 and thus the DC network 14 is sufficiently preloaded. The connection via the short-circuit protection device 37 can be established, for example, via the switches 24 that are controlled by the control unit 30 .

The active rectifier 20 is designed to convert alternating current or alternating voltage on its AC side into direct current or direct voltage on its DC side. The active rectifier 20 is also designed to convert direct current or direct voltage on its DC side into alternating current or alternating voltage on its AC side. In the exemplary embodiment shown, the conversion takes place in that a control unit of the active rectifier 20 suitably controls the semiconductor switches. The control unit 30 of the supply system 10 is set up and designed to carry out the method for operating the short-circuit protected supply system 10 and to activate the switches 22, 23, 24 accordingly, for example. For example, it has suitable computing power and suitable memory. The control unit 30 can also include the control unit of the active rectifier 20 . However, each active rectifier can also have its own control unit. The sine filter chokes 20.1 can act as a mains filter of the active rectifier, with the mains filter being able to have further components, for example a filter capacitance. In addition, the sine wave chokes have the property of a sudden increase in current through the active rectifier ter to delay effectively. This delay can give DC fuses 32.1, 32.2 of the DC network time to blow before excessive current damages elements of the active rectifier 20, such as its freewheeling diodes. Such a case can occur, for example, if a ground fault or short circuit in the DC network 14 would cause a fault current from the AC network 12 into the DC network 14, which would damage the freewheeling diodes of the active rectifier 20 if it were to flow at full strength through the active rectifier 20 would be passed.

In 3 a further exemplary embodiment of a short-circuit-protected supply system 10 for supplying the DC network 14 from the AC network 12 is shown schematically. The AC network 12 is, for example, a three-phase AC network and can in particular be an AC supply network. The AC grid 12 can be provided via a grid transformer. This can be grounded by connecting to potential earth PE. The supply system 10 has the active rectifier 20 with the upstream sine filter chokes 20.1 on the AC side and a combined device 41, which can assume both the function of the precharging device and the function of the short-circuit protection device. The combined pre-charging and short-circuit protection device 41 can be connected to the AC grid via AC switches 24 . It has a transformer 16 which supplies a passive rectifier 36 with a second AC input voltage. This transformer 16 can also be connected to the ground potential PE; in particular, it is connected to the ground potential when the AC network 12 is also grounded.

As an equivalent circuit diagram for a ground fault, the DC network 14 has a two-part insulation resistance 50 to ground potential PE. A battery 42 can be connected to the DC grid 14 via DC switches 46 . A load 44 can be connected to the DC grid via DC switches 48 . The load 44 can also have an undesired parasitic resistance 44.P to ground potential PE. A load 44 can in particular include one or more consumers, such as a machine, an industrial plant or an electrolyzer. The DC grid 14 may also include multiple loads 44 and multiple batteries 42 .

The AC grid 12 can be connected to the supply system 10 via an upstream transformer. The voltage provided by the AC network 12 can be adjusted to a level suitable by the supply system 10 by the upstream transformer. For example, the active rectifier 20 can be supplied with a first AC input voltage via the pre-transformer, on which the first threshold value depends. In this way, it can be achieved that the active rectifier 20 is only connected to the AC network 12 by controlling the AC switch 22 by a control unit 30 when the DC network 14, including the intermediate circuit 18, is at a sufficiently high level DC voltage is preloaded, so that the switching on of the active rectifier 20 can be done gently, so completely or largely without current.

The active rectifier 20 is designed to convert alternating current or alternating voltage on its AC side into direct current or direct voltage on its DC side. The active rectifier 20 is also designed to convert direct current or direct voltage on its DC side into alternating current or alternating voltage on its AC side. In the exemplary embodiment shown, the conversion takes place in that the control unit 30 suitably controls the semiconductor switch of the active rectifier 20 . The control unit can also be set up and designed to carry out the method for operating the short-circuit-protected supply system 10 and to activate the switches 22, 24, 34 accordingly, for example. For example, it has suitable computing power and suitable memory. However, the semiconductor switches of the active rectifier 20 and the controller 30 for carrying out the method can also be driven by separate control units.

In addition to a passive rectifier 36, the device 41 has a pre-charging resistor 28 via which the current is limited when the DC network 14 is being pre-charged. If the device 41 is operated as a pre-charging device, the switch 34 is open. The intermediate circuit 18 of the active rectifier 20 can be precharged via the precharging device 41 when the supply system 10 is started up before the AC side is connected to the AC network 12 . For this purpose, the AC switch 24 is first closed with the switch 34 open and the DC network 14 is pre-charged. The pre-charging device 41 is set up to carry out such a pre-charging from the AC network 12 and has the passive rectifier 36 for this purpose. At least the intermediate circuit 18 of the active rectifier 20, preferably the entire DC network 14, can be precharged directly from the AC network 12 via the precharging device 41.

If the combined device 41 is operated as a short-circuit protection device, the switch 34 is closed and the precharging resistor is thus bridged. The pre-charging of the intermediate circuit 18 and the DC network 14 then only takes place via the active rectifier 20 or has already ended. The second threshold value, via which it can be ensured that the connection between AC network 12 and DC network 14 via the closed circuit, depends on the second AC input voltage NEN switch 34 is only produced at the second time during the pre-charging when the intermediate circuit 18 and thus the DC network 14 is sufficiently pre-charged. The switch 34 can be closed, for example, by activation by the control unit 30 .

A short-circuit current occurring as a result of a fault in the DC network 14 can be conducted via the passive rectifier 36 from the AC network 12 into the DC network 14 , bypassing the active rectifier 20 . Such a fault in the DC network occurs, for example, if the insulation resistance 50 or the parasitic resistance 44.P becomes too small and this results in a ground fault in the DC network, ie a connection to the potential ground PE that is too low.

reference list

10

supply system

12

AC grid

14

DC grid

16

transformer

18

intermediate circuit

20

active rectifier

20.1

sine filter chokes

22, 23, 24

AC switch

28

preload resistor

30

control unit

32.1, 32.2

DC fuses

34

Switch

36

rectifier

37

short-circuit protection device

38

current-limiting charging circuit

39

preloading device

41

combined device

42

battery

44

load

44th P

parasitic resistance

46

DC switch

48

DC switch

50

insulation resistance

PE

potential earth

a), b), c)

process steps

Claims (17)

Method for operating a short-circuit protected supply system (10) of a DC network (14) from an AC network (12), the supply system (10) having an active rectifier (20) with upstream sine filter chokes (20.1) on the AC side, a pre-charging device ( 39, 41) and a short-circuit protection device (37, 41), wherein the short-circuit protection device (37, 41) is set up to prevent a short-circuit current occurring as a result of a fault in the DC network (14), bypassing the active rectifier (20) from the AC - Conducting the network (12) in the DC network (14), comprising the steps for starting up the supply system (10): a) Pre-charging of the DC network (14) via the pre-charging device (39, 41), the active rectifier (20) being connected to the DC network (14) on the DC side, b) Establishing an AC-side connection of the active rectifier (20) to the AC grid (12) at a first point in time during the pre-charging at which a voltage of the DC grid (14) exceeds a first threshold value, c) Establishing a connection between the AC network (12) and the DC network (14) via the short-circuit protection device (37, 41) at a second time during the pre-charging, at which the voltage of the DC network (14) has a second threshold exceeded. procedure after claim 1 , wherein the pre-charging of the DC network (14) takes place at least partially via the active rectifier (20) after the AC-side connection of the active rectifier (20) to the AC network (12). procedure after claim 1 or 2 , wherein the second threshold is greater than the first threshold. A method according to any one of the preceding claims, wherein the first time is prior to the second time. Method according to one of the preceding claims, wherein the first threshold value depends on a first AC input voltage of the active rectifier (20) and in particular corresponds to a rectified value of the first AC input voltage or is a predetermined first distance above the rectified value of the first AC input voltage. Method according to one of the preceding claims, wherein the precharging of the DC network (14) takes place up to a rated voltage of the DC network (14) and the first and the second threshold value are below the rated voltage of the DC network (14). Method according to one of the preceding claims, in which the short-circuit protection device (37, 41) has a rectifier (36) via which the connection between the AC network (12) and the DC network (14) is established, the rectifier (36 ) is supplied with a second AC input voltage. procedure after claim 7 , The short-circuit protection device (41) having a transformer (16), in particular a step-up transformer (16), the transformer (16) supplying the rectifier (36) with the second AC input voltage. procedure after claim 7 or 8th , wherein the second threshold value depends on the second AC input voltage of the rectifier (36) and in particular corresponds to a rectified value of the second AC input voltage or is a predetermined second distance above the rectified value of the second AC input voltage. Method according to one of the preceding claims, wherein the supply system (10) comprises a plurality of active rectifiers (20) connected in parallel and wherein establishing a connection of the active rectifier (20) to the AC grid (12) by connecting the plurality of active rectifiers in parallel (20) takes place. procedure after claim 10 , the plurality of active rectifiers (20) being connected in parallel one after the other when the supply system (10) is started up. Method according to one of the preceding claims, further comprising the steps when decommissioning the supply system (10): - Separating the connection between the AC network (12) and the DC network (14) via the short-circuit protection device (37, 41), and - Separating the connection of the active rectifier (20) or the plurality of active rectifiers (20) to the AC grid (12). Method according to one of the preceding claims, wherein after establishing a connection between the AC network (12) and the DC network (14) via the short-circuit protection device (37, 41) an enable signal is generated and sent to a DC load (44) of the DC -Network (14) is transmitted. Short-circuit protected supply system (10) for a DC network (14) from an AC network (12), comprising: - an active rectifier (20); - A pre-charging device (39, 41) for pre-charging the DC network (14) from the AC network (12); - a short-circuit protection device (37, 41); - a control unit (30); characterized in that the control unit (30) is set up to carry out the method according to one of the preceding claims. supply system Claim 14 , comprising a plurality of active rectifiers (20) connected in parallel. Supply system according to one of the Claims 14 or 15 , wherein the short-circuit protection device (37, 41) has a rectifier (36) via which the connection between the AC network (12) and the DC network (14) is made, the rectifier (36) having a second AC Input voltage is supplied, on which the second threshold value depends, wherein the second threshold value corresponds in particular to a second DC output voltage of the rectifier (36). Supply system according to one of the Claims 14 until 16 , wherein the short-circuit protection device and the pre-charging device are designed as a combined device (41) and have a common transformer (16), in particular a common step-up transformer (16) and a common rectifier (36), the short-circuit protection device also having a switch (34) and the precharging device also has a precharging resistor (28) connected in parallel with the switch (34).

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