Method for producing a defined state of an electrochemical system, separating device, and power converter

Abstract

The invention relates to a method for producing a defined state of an electrochemical system (14) which can be connected to an AC / DC converter (12) via a switch disconnector (TS) of a disconnecting device (20) in order to exchange electric power, wherein at least one DC connection (DC+, DC-) of the electrochemical system (14) is connected to the AC / DC converter via the disconnector switch (TS) of the disconnecting device (20). The method has the following step: in a first operating state in which the at least one DC connection (DC+, DC-) is electrically disconnected from the AC / DC converter (12): a) a first switch (S1) of the disconnecting device (20) is closed in order to produce an electric connection between the DC connections (DC+, DC-) of the electrochemical system. The invention additionally relates to a disconnecting device, to a power converter comprising such a disconnecting device, and to an assembly comprising an electrochemical system (14) and such a power cconverter.

Description

[0001] Method for producing a defined state of an electrochemical system, separation device and power converter

[0002] TECHNICAL FIELD

[0003] The application relates to a method for establishing a defined state of an electrochemical system which can be connected to an AC / DC converter for exchanging electrical power via at least one isolating switch of a isolating device, as well as to an isolating device having at least one isolating switch for connecting an electrochemical system to an AC / DC converter for exchanging electrical power.

[0004] STATE OF THE ART

[0005] Electrolyzers and power converters for connecting an electrolyzer to an AC voltage network are known from the prior art. A disconnecting device can be arranged between an electrolyzer and an AC / DC converter of the power converter. This disconnecting device establishes or disconnects the connection between the electrolyzer and the AC / DC converter as needed via a disconnecting switch. The power converter can thus include the disconnecting device in addition to the AC / DC converter. In this application, AC (alternating current) refers to alternating current / alternating voltage, and DC (direct current) refers to direct current / direct voltage.

[0006] An electrolyzer is a device in which a chemical reaction, i.e., a material transformation, is induced using electrical current, for example, electrolysis. The electrolyzer can be used, in particular, for the electrolytic production of hydrogen and oxygen from water.

[0007] A fuel cell, as a galvanic cell, converts the chemical reaction energy of a supplied fuel and an oxidizer into electrical energy. A fuel cell often refers to a hydrogen-oxygen fuel cell. Some fuel cells can also use other fuels besides hydrogen, particularly methanol, butane, or natural gas. Furthermore, fuel cells are known that can be operated reversibly and thus serve as electrolyzers.

[0008] In an electrochemical system, energy conversion takes place between electrical and chemical energy. Fuel cells and electrolyzers are examples of electrochemical systems. The AC / DC converter connected to the electrochemical system can convert electrical power in both directions, depending on the desired direction of power exchange. For example, it can act as an inverter to convert the direct current generated by a fuel cell into alternating current, or it can act as a rectifier to generate the direct current required to operate an electrolyzer from alternating current.

[0009] The DC voltage of an electrolyzer can remain at a high value for an extended period after electrolysis has been stopped, especially after the production of hydrogen, for example, has been stopped. Since discharging these systems—i.e., reducing the voltage to a level considered safe, such as less than 50 volts—can take several hours or even several days, any maintenance on the electrolyzer can be very lengthy.

[0010] Load resistors can be used to discharge an electrolyzer or fuel cell. These are only used temporarily for discharging, and their installation on a charged electrolyzer or fuel cell is not without risk.

[0011] GB 903426 A describes a process for the electrolytic production of insoluble metal hydroxide from metal electrodes in a suitable electrolyte by passing a current between the electrodes. In this process, a gel film formed on the electrodes is elastically displaced from the surfaces of the electrodes before it hardens and forms a crust on the surfaces.

[0012] The document DE 102021 101440 A1 describes a method for precharging an electrochemical load via a precharging circuit arranged between a DC source and the electrochemical load. The precharging circuit comprises a series circuit comprising a precharging resistor and a disconnecting switch, with a further disconnecting switch arranged in parallel with the precharging resistor or in parallel with the series circuit comprising the precharging resistor and disconnecting switch. The method comprises several active time windows during which a power loss is generated at the precharging resistor that lies above a nominal power of the precharging resistor. The method also comprises one or more inactive time windows during which the current through the precharging resistor is suppressed.

[0013] TASK

[0014] The application is based on the object of improving the creation of a defined state of the electrochemical system.

[0015] SOLUTION The object is achieved by a method having the features of patent claim 1 or by a separating device having the features of independent patent claim 15, as well as a power converter according to claim 19 and an arrangement according to claim 20. Preferred embodiments are specified in the dependent patent claims.

[0016] DESCRIPTION

[0017] An electrochemical system can be connected to an AC / DC converter for exchanging electrical power via a disconnect switch of a disconnecting device. The disconnecting device has two DC inputs for connecting the AC / DC converter, two DC outputs for connecting the electrochemical system, and two current paths. Each of the two current paths connects a DC input to a corresponding DC output. A disconnect switch is arranged in at least one of the two current paths, optionally also in each of the two current paths, so that at least one of the DC connections, optionally also each of the two DC connections of the electrochemical system, is connected to the AC / DC converter via a disconnect switch. The disconnecting device further has a first switch, via which an electrical connection can be established between the DC outputs.

[0018] A method for producing a defined state of an electrochemical system comprises:

[0019] In a first operating state in which the at least one DC terminal is electrically separated from the AC / DC converter, for example by the open isolating switch: a) Closing a first switch of the isolating device to establish an electrical connection between the DC terminals of the electrochemical system.

[0020] A power converter comprises the AC / DC converter and the isolating device. The first operating state, in which at least one of the DC terminals of the electrochemical system is electrically isolated from the AC / DC converter, is, for example, the state when the at least one isolating switch of the isolating device is open. The first operating state can also exist when the electrochemical system is isolated from the AC / DC converter, e.g., when the electrochemical system is no longer connected to the isolating device or when the electrochemical system is still connected to the isolating device, but the isolating device is no longer connected to the AC / DC converter.

[0021] In this first operating state, the designated first switch of the isolating device is closed, establishing an electrical connection between the DC terminals and thus enabling or bringing about a discharge of the electrochemical system. This makes it possible to establish a defined state of the electrochemical system by discharging the electrochemical system via its now connected DC terminals. This makes it possible to establish a touch-safe state of the terminals of the electrochemical system, e.g. of the electrolyzer, even if the electrochemical system would otherwise generate a voltage at its DC terminals, e.g. due to internal electrochemical processes that are not related to the actual operation of the electrolyzer. The method thus also makes it possible to safeguard a maintenance process on the electrochemical system, e.g. the electrolyzer.

[0022] The method thus makes it possible to solve the following problem: An electrochemical system, in particular an electrolyzer or a fuel cell, can generate a significant DC voltage during certain process steps on its own and without a power supply via a power converter, even if there is no connection to an AC voltage grid, in particular if there is no power supply via the power converter or no power exchange with the AC / DC converter of the power converter. An example of such a process step is when an electrolyzer is rinsed with clean water. This can be done after each maintenance of the electrolyzer and / or before each hydrogen production, with the electrolyzer in its first operating state, i.e. disconnected from the AC / DC converter. The DC voltage at the terminals of the electrolyzer can rise to over 50V (i.e. above the protective extra-low voltage of 50V). This phenomenon was previously unknown.This (unexpected) voltage can also be present at the DC connections within the power converter, including within its housing, particularly at the DC lines that establish the electrical connection from the isolation device to the electrolyzer or fuel cell. The voltage generated at the electrolyzer during such a process can be high and thus pose a hazard, especially if, due to the disconnection between the electrolyzer and the AC grid, it is mistakenly assumed that the electrolyzer's DC connections are largely voltage-free.

[0023] The described method makes it possible to bring the electrochemical system into a defined state and, in particular, into a safe state in which, in particular, maintenance can be carried out safely and unexpectedly generated electrical charges at the DC terminals can be discharged via the closed first switch. In this way, a voltage at the DC terminals of the electrochemical system that would otherwise be caused by the electrical charges is prevented, or at least reduced to a value that excludes any danger to persons. This makes it possible to establish a safe operating state during maintenance work on an electrochemical system, e.g., on an electrolyzer or a fuel cell.

[0024] Sometimes it may be desirable to use the isolating device to isolate the electrochemical system from the AC / DC converter at only one pole. This may be the case, for example, if the electrochemical system has a ground connection at one of its DC terminals, either at the positive or the negative DC terminal. In these cases, it may be advantageous if the current path of the isolating device that is connected to the grounded DC terminal during normal operation of the electrochemical system does not have a isolating switch, and a isolating switch is only arranged in the other current path. Alternatively, it may also be desirable to isolate the electrochemical system from the AC / DC converter at all poles. For this purpose, a isolating switch can be arranged in each of the two current paths of the isolating device, which is designed to isolate the respective DC input from its associated DC output.This is the case, for example, if the electrochemical system has a grounding point located between both of its DC terminals. Such a point can be a voltage midpoint of the electrochemical system, so that the electrochemical system has a midpoint grounding.

[0025] In one embodiment of the method, step a) is divided as follows: a.1) Before closing the first switch: measuring a voltage between the DC terminals a.2) If the measured voltage falls below a predefinable first threshold value: closing the first switch.

[0026] This embodiment ensures that the voltage between the DC terminals is not too high when the first switch is closed. For example, the first threshold can be 50 V. This would mean that the first switch is only closed when the safety extra-low voltage of 50 V is undershot. This allows the first switch to be closed safely. At the same time, with the first switch then closed, safe maintenance of the electrochemical system can be carried out. The closed first switch prevents a voltage build-up between the two DC terminals of the electrochemical system, which can be dangerous, especially if it occurs unexpectedly. In one embodiment of the method, the DC terminals are short-circuited by closing the first switch.The provision of the first switch in the isolating device enables the first switch to serve as a short-circuit switch, by means of which a defined, safe operating state of the electrochemical system, e.g.

[0027] B. of the electrolyzer, can be achieved by short-circuiting the two DC terminals of the electrochemical system. The short circuit creates a defined state in which no voltage can build up between the two terminals.

[0028] The proposed solution thus offers the possibility of a safe short circuit of the electrochemical system with minimal circuit complexity, making it cost-effective. The additional effort required to perform a short circuit directly on the electrochemical system is avoided because the first switch is located within the disconnecting device. The additional connections otherwise required for a short circuit on the electrochemical system itself can be avoided. At the same time, such a short circuit can be performed in a way that is both gentle on the electrochemical system and safe for the entire system, including the power converter with AC / DC converter and disconnecting device.

[0029] The proposed solution establishes advantageous galvanic isolation between the electrochemical system and the AC / DC converter by first isolating the AC / DC converter and then short-circuiting the electrochemical system. Maintenance work on the electrochemical system can then be carried out safely. For maintenance work only on the AC / DC converter, it may be sufficient to ensure galvanic isolation of the AC / DC converter from the electrochemical system, as the AC / DC converter may already provide internal fuses.

[0030] In one embodiment of the method, the DC terminals are connected via an ohmic resistor by closing the first switch, and the electrochemical system is discharged via the ohmic resistor. This embodiment allows the DC terminals to be connected safely even at potentially higher voltages at the DC terminals, and allows the electrochemical system to be safely discharged via the first switch and the ohmic resistor. The flowing discharge current is limited by the ohmic resistor.

[0031] In one embodiment, the isolating device has a precharging circuit in at least one current path that connects a DC input to a corresponding DC output. The precharging circuit can have a series circuit comprising a precharging resistor and a precharging switch. The series circuit can be arranged in parallel with the isolating switch in the relevant current path, so that the precharging resistor can be bridged with low resistance by the closed isolating switch. To precharge the electrochemical system, the relevant DC connection of the electrochemical system can therefore be connected to the AC / DC converter via the precharging resistor and the precharging switch. This can be done with the isolating switch of the relevant current path open, so that the precharging resistor has a current-limiting effect when precharging the electrochemical system.Once the precharging of the electrochemical system has progressed sufficiently, the series circuit comprising the precharging resistor and the precharging switch can be bridged by closing the isolating switch in the relevant current path, and the relevant DC input can be connected to its associated DC output with low impedance. The ohmic resistor through which the electrochemical system is discharged can comprise at least one of the precharging resistors. For example, the ohmic resistor through which the electrochemical system is discharged can be designed as one of the precharging resistors.The provision of the first switch as a component of the isolating device and the provision of the ohmic resistor as a component of the isolating device's precharge circuit allows the first switch to serve as the switch through which the DC terminals of the electrochemical system are connected, and one of the precharge resistors to serve as the resistor through which the electrochemical system is discharged. This design offers a simple structure and reduces circuit complexity, since the precharge resistor already present in the precharge circuit can be used as a resistor for discharging the electrochemical system.The advantage of reduced circuit complexity is particularly evident when the isolating device has a precharging circuit in each of the two current paths, each with a precharging switch and a precharging resistor arranged in series therewith, so that each of the two DC terminals of the electrochemical system can be connected to the AC / DC converter via a precharging resistor and a precharging switch for precharging the electrochemical system. Specifically, the ohmic resistor through which the electrochemical system is discharged can comprise one or two of the two precharging resistors. This can be the case, for example, with an electrochemical system that has a center ground.

[0032] In one embodiment of the method, in which a precharging circuit with a precharging switch and a precharging resistor arranged in series with it is arranged in each of the two current paths, the two precharging resistors can also have different resistance values, in particular resistance values ​​different by one order of magnitude or by several orders of magnitude. Specifically, one of the precharging resistors can be low-resistance and the other high-resistance. In this way, the electrochemical system can be precharged via a low-resistance of the two precharging resistors, while the electrochemical system can be discharged via a high-resistance of the two precharging resistors.

[0033] In one embodiment of the method, step a) is followed by step b), in which a second switch is closed to short-circuit the DC terminals. In this embodiment, the first switch is closed and the electrochemical system is discharged via the ohmic resistor. The second switch is then closed and the electrochemical system is short-circuited via the second switch. This has the advantage that the electrochemical system can first be discharged and then short-circuited. As a result, the system is always in a defined state and, after the second switch is closed, in a safe state with short-circuited DC terminals.

[0034] In one embodiment of the method, step b) is divided as follows: b.1) Before closing the second switch: measuring the voltage between the DC terminals b.2) If the measured voltage falls below a predeterminable second threshold value: closing the second switch.

[0035] In this embodiment, in step b.1), by measuring the voltage between the DC terminals, it can be checked whether the electrochemical system has already discharged sufficiently via the ohmic resistance to safely close the second switch in b.2). This further increases the safety of the process.

[0036] In one embodiment of the method, the first operating state is established by opening the isolating switch and / or by disconnecting the isolating device from the AC / DC converter. This step of entering the first operating state advantageously precedes the previously described step a), so that the electrochemical system is electrically disconnected from the AC / DC converter when, in step a), the first switch of the isolating device is closed to establish an electrical connection between the DC terminals of the electrochemical system.

[0037] With the proposed solution, the isolation device can be used to establish the safe state. Additional galvanic isolation between the electrolyzer or fuel cell and the AC / DC converter, which would involve additional effort and expense, is thus eliminated. Furthermore, the AC / DC converter already has an all-pole isolation to the DC side, which can be used to establish the first operating state.

[0038] In a second operating state, the electrochemical system is connected to the separating device, which is connected to the AC / DC converter. When the separating device's isolating switches are closed, an electrolyzer, for example, can be supplied with electrical power from an AC source, in particular from an AC grid, via the AC / DC converter. Alternatively or additionally, a fuel cell, for example, can exchange electrical power with an AC sink, in particular with the AC grid, via the AC / DC converter when the separating device's isolating switches are closed.

[0039] In one embodiment, the method comprises:

[0040] In the second operating state, in which the DC terminals are electrically connected to the AC / DC converter via the closed isolating switch or switches: c) exchanging electrical power of the electrochemical system with the AC / DC converter d) establishing the first operating state by opening one or each of the isolating switches.

[0041] In this embodiment, it is thus possible to switch from the second operating state to the first operating state by opening one or each of the isolating switches of the isolating device. In the first operating state, the electrochemical system can then be discharged via the ohmic resistor, for example, by closing the first switch, and a short circuit can then be established between the DC terminals by closing the second switch. In this safe state, maintenance of the electrochemical system can then be performed, for example.

[0042] In one embodiment of the method, a precharging operating state precedes the second operating state. In the precharging operating state, the electrochemical system can be charged via one of the precharging resistors when the precharging switch is closed. If the separating device has a precharging circuit with a precharging switch and a precharging resistor in each of its two current paths, it is also possible for the electrochemical system to be charged via the precharging resistors in the precharging operating state when both precharging switches are closed. During precharging, the electrochemical system is supplied with electrical power for a period of time via the precharging resistors and thus precharged.

[0043] In this embodiment, a start can occur, for example, in such a way that the electrochemical system is connected to the AC / DC converter, for example, via the isolating device, and both the pre-charging switch(es) and the isolating switch(es) are open. The electrochemical system can then initially be pre-charged via the pre-charging circuit(s) by closing the existing pre-charging switches. Once pre-charging is complete, the second operating state can be entered by closing the isolating switch(es). In this case, the pre-charging switch(es) can be opened again, although this is not mandatory. The second operating state can, in particular, comprise normal operation of the electrochemical system and last for some time, for example, a few hours or days.

[0044] To terminate normal operation as needed, the device can be switched from the second operating state to the first operating state by opening the isolating switch(es). In the first operating state, the electrochemical system can then be discharged via the ohmic resistance by closing the first switch, for example, and then a short circuit can be established between the DC terminals by closing the second switch. In this safe state, maintenance of the electrochemical system can then be carried out, for example.

[0045] In one embodiment of the method, the first switch and / or the second switch, if present, can comprise a normally closed switch. A "normally closed switch," or also called an "opener," is a switch that assumes a closed state and / or remains in a closed state on its own and without a control signal applied to the switch. Furthermore, the open state of the switch is only brought about by a control signal applied to the switch. It must therefore be opened actively, usually with the expenditure of energy. Designing the first switch as a normally closed switch, and possibly also the second switch as a normally closed switch, is particularly advantageous when an arrangement comprising the electrochemical system and a power converter for supplying the electrochemical system has an emergency shutdown device.Such an emergency shutdown device is intended to ensure that, when activated, any power exchange on the input side between the system's power converter and the grid is reliably prevented and, in addition, that the system's electrochemical system assumes a safe state. Typically, actuation of the emergency shutdown device also intentionally prevents the control of components in the system. Thus, it is possible that, once the emergency shutdown is triggered, active control of switches in the isolation unit is also prevented and can no longer occur. However, since the first switch, and possibly also the second switch, are designed as normally closed switches, each of these switches assumes the closed state after the emergency shutdown device is activated.Specifically, in one embodiment of the method, the first switch and / or the second switch, if present, can each be coupled to an emergency shutdown device such that each of these switches assumes its normally closed state in response to actuation of the emergency shutdown device. The second switch can additionally have a voltage monitor or a time delay element. This ensures that the second switch only assumes its normally closed state with a time delay compared to the first switch, thus preventing premature hard short-circuiting of both DC connections, i.e., while a significant DC voltage is still present, and the associated high short-circuit current.In this way, the electrochemical system can be safely discharged and / or short-circuited even if the first switch and, if applicable, also the second switch of the isolating device are no longer activated.

[0046] In a disconnecting device with disconnecting switches for connecting an electrochemical system to an AC / DC converter for exchanging electrical power, a DC output of the disconnecting device can be connected to a DC connection of the electrochemical system. The disconnecting device further comprises a first switch, via which an electrical connection can be established between the DC outputs.

[0047] In one embodiment of the isolating device, the DC outputs can be connected via an ohmic resistor by closing the first switch. The isolating device is designed to discharge the electrochemical system connected to the DC outputs via the ohmic resistor when the first switch is closed.

[0048] The separating device has DC inputs that can be connected to the AC / DC converter. In one embodiment, the separating device has a precharging circuit via which the DC outputs can be connected to the DC inputs via a precharging resistor and a precharging switch for precharging the electrochemical system. The ohmic resistor through which the electrochemical system can be discharged comprises at least one of the precharging resistors. In one embodiment, the ohmic resistor through which the electrochemical system can be discharged is one of the precharging resistors.

[0049] An arrangement according to the invention comprises the power converter, the electrochemical system, and a system controller for controlling the arrangement. The system controller is an information processing system designed and configured to carry out the method described above. BRIEF DESCRIPTION OF THE FIGURES

[0050] In the following, the application is further explained and described using exemplary embodiments shown in the figures.

[0051] Figs. 1, 2a, 2b, 3a and 3b show different embodiments of a power converter with an electrochemical system.

[0052] The same reference numerals are used in the figures for the same or similar elements.

[0053] FIGURE DESCRIPTION

[0054] Fig. 1 schematically shows an electrochemical system 14, e.g., an electrolyzer or a fuel cell, which is connected to an AC grid 18 via a power converter 10 and a transformer 16. The AC grid 18 is, for example, an AC voltage grid of an energy supplier. The power converter 10 has an AC / DC converter 12 and a separation device 20. The AC / DC converter 12 has a switched-mode semiconductor circuit and can convert AC voltage into DC voltage or AC current into DC current and vice versa. The semiconductor circuit of the AC / DC converter 12 is controlled by a system controller 30. The system controller 30 can be part of the power converter 10 and has hardware such as a processor and memory and is configured and designed to execute computer program instructions of a software. The electrochemical system 14 is connected to the AC / DC converter 12 via the separation device 20.

[0055] The isolating device 20 has two current paths 41, 42, each connecting a DC input 26, 28 to a DC output assigned to the DC input 26, 28. The isolating device 20 illustrated in Fig. 1 is designed as an example with all poles, i.e. it has a isolating switch TS for each of the DC connections of the electrochemical system, i.e. in each of its two current paths 41, 42. In the example shown, both DC connections DC+, DC- of the electrochemical system 14 are each connected to one pole, i.e. a DC output 22, 24, of the isolating device 20. Each DC connection DC+, DC- of the electrochemical system 14 can be connected to or disconnected from the AC / DC converter 12 via the respective isolating switch TS. Each of the isolating switches TS is optionally protected by a fuse F1, F2. The respective DC inputs 26, 28 of the isolating device are each connected to a DC-side connection of the AC / DC converter.When the TS disconnect switches are open, the electrochemical system 14 is completely disconnected from the AC / DC converter 12. This corresponds to a first operating state of an arrangement comprising the electrochemical system 14 and the power converter 10.

[0056] In the first operating state, the voltage applied between the DC terminals DC+ and DC- can be measured via the voltmeter V and monitored by the system controller 30. In the first operating state, the electrochemical system 14 is discharged. Depending on the state of charge, this can take some time, e.g., a few hours or a few days. The voltmeter V can be used to detect the state of charge of the electrochemical system 14 and to determine whether a charge level has been reached in which a first switch S1 can be safely closed. This is the case, for example, when a protective extra-low voltage of 50 V is undershot. Such detection of the state of charge and such closing of the first switch S1 can be controlled, for example, by the system controller 30. After the first switch S1 has been closed, the electrochemical system 14 can be safely serviced.Even if the electrochemical system 14 should generate an unexpected DC voltage at its DC terminals DC+ and DC- and thus possibly also within the electrochemical system 14, this voltage is reduced by the safe (external) connection of the DC terminals DC+ and DC- via the closed first switch S1.

[0057] When the disconnect switches TS are closed, an exchange of electrical power can occur between the electrochemical system 14 via the power converter 10 and the transformer 16 with the AC network 18. This corresponds to a second operating state of the arrangement. In the second operating state, the current flowing during the exchange of electrical power can be measured via the ammeter A and evaluated by the system controller 30, for example, to prevent a maximum value from being exceeded.

[0058] In the embodiment shown in Fig. 2a, the isolating device 20 is equipped with an all-pole DC pre-charging unit. In each of the current paths 41, 42 of the isolating device 20, a pre-charging circuit with a series connection of a pre-charging switch VS and a pre-charging resistor R1, R2 is arranged parallel to the isolating switch TS and the optional fuse F1. Each of the two poles, i.e. each of the two DC connections DC+, DC- of the electrochemical system 14, is connected to one of the DC outputs 22, 24 of the isolating device 20. Each of the pre-charging circuits has one of the pre-charging resistors R1, R2, via which the electrochemical system 14 can be charged when the pre-charging switches VS are closed. Each of the pre-charging circuits is optionally protected by fuses F3, F4. The pre-charging circuits of the isolating device 20 can be used, for example, toto precharge an electrolyzer to an open circuit voltage of the AC / DC converter 12 before the isolating switches TS are closed and power is exchanged via the power converter, so that, for example, hydrogen production takes place.

[0059] In the example shown, the isolating device 20 has the first switch S1. In Fig. 2a, the first switch S1 is exemplarily connected by one of its contacts to a connection point between the precharging switch VS and the precharging resistor R1 of the precharging circuit assigned to the positive current path 41, while the second contact is connected to the negative DC output 24 of the isolating device. Alternatively, it is also possible for the first switch S1 to be connected by one of its contacts to the connection point between the precharging switch VS and the precharging resistor R2 of the precharging circuit assigned to the negative current path 42, while the second contact is connected to the positive DC output 22 of the isolating device 20 (not shown in Fig. 2a).Finally, it is also possible for the first switch S1 to be connected with one of its contacts to the connection point between the pre-charging switch VS and the pre-charging resistor R1 of the pre-charging circuit assigned to the positive current path 41, while its other contact is connected to the connection point between the pre-charging switch VS and the pre-charging resistor R2 of the pre-charging circuit assigned to the negative current path 42 (not shown in Fig. 2a). When the isolating switches TS and the pre-charging switches VS are open, a safe operating state of the electrochemical system 14 can be initiated, e.g., for maintenance purposes, by closing the first switch S1. The two DC outputs 22, 24 and the DC connections DC+, DC- connected thereto are connected to one another via the pre-charging resistor R1, via the pre-charging resistor R2, or via a series connection of the pre-charging resistors R1 and R2, depending on the arrangement of the first switch S1.The electrochemical system 14 can discharge via the respective pre-charging resistor R1, R2 or the pre-charging resistors R1 and R2 and in the event of unexpectedly occurring voltages at the DC terminals DC+, DC-, these can be reduced via the respective pre-charging resistor R1, R2 or the pre-charging resistors R1 and R2.

[0060] Optionally, an intermediate circuit of the AC / DC converter 12 can also be discharged via the precharging circuits shown in Fig. 2a. For this purpose, in addition to the first switch S1, the precharging switches VS can also be closed, so that the intermediate circuit of the AC / DC converter 12 is discharged via the precharging resistor R2. The switches TS, VS, and / or S1 can be controlled, for example, by the system controller 30.

[0061] An all-pole isolating isolating device 20, each with a isolating switch TS and a pre-charging circuit in each of the current paths 41, 42, is particularly advantageous when the electrochemical system 14, as symbolized in Fig. 2a, has a center point earthing. The arrangement can additionally have an optional emergency shutdown device 31, which is designed to isolate the AC / DC converter on the AC side and the DC side when actuated, i.e. to isolate it on the AC side from the AC network and on the DC side from the electrochemical system 14. In this case, it can be necessary for the electrochemical system 14 to also be safely discharged, even if control of the isolating device 20 by the system control unit 30 is prevented due to the actuation of the emergency shutdown device 31. In order to nevertheless achieve safe discharge of the electrochemical system 14, the first switch S1 can be designed as a normally closed switch, which is automatically, i.e.i.e., in the absence of a control signal, it assumes its closed state. The first switch S1 is coupled to the emergency shutdown device 31 in such a way that, upon actuation of the emergency shutdown device 31, it assumes its normally closed state and discharges the electrochemical system 14.

[0062] In the embodiment shown in Fig. 2b, the isolating device 20 has, in addition to the first switch S1, a second switch S2 and optionally the voltmeter V.

[0063] When the isolating switches TS and the pre-charging switches VS are open, a safe operating state of the electrochemical system 14 can be initiated by closing the first switch S1, e.g., for maintenance purposes. The two DC outputs 22, 24 and the associated DC terminals DC+, DC- are connected to each other via the pre-charging resistor R1. The electrochemical system 14 can discharge via the pre-charging resistor R1.

[0064] The voltmeter V can be used to measure the voltage between the DC outputs 22, 24 and thus determine whether and to what extent an electrochemical system 14 connected to the DC outputs 22, 24 is (still) charged. If the voltage measured by the voltmeter V is small enough, e.g., below a predefined threshold value of, for example, 50 V, the second switch S2 can be closed. The voltage at the electrochemical system 14 can optionally be reduced by discharging via the pre-charging resistor R1. Closing the second switch S2 short-circuits the DC outputs 22, 24, and any unexpected voltages at the DC terminals DC+, DC- connected to the DC outputs 22, 24 can be dissipated directly via the short circuit.

[0065] The control of the switches TS, VS, S1 and / or S2 as well as the measurement of the voltage using the voltmeter V and the determination of the charge state of the electrochemical system 14 connected to the DC outputs 22, 24 can be carried out, for example, by the system controller 30. The second switch S2 can also be designed as a normally closed switch S1, analogous to the first switch S1. It can also have an independently operating time delay element or an independently operating voltage monitor. This ensures that the second switch S2 only assumes its normally closed state after the first switch S1 or when the voltage falls below a predefined level.This is particularly advantageous if the arrangement has an emergency shutdown device 31, wherein the first switch S1 and the second switch S2 are coupled to the emergency shutdown device 31 in such a way that they assume their normally closed state upon actuation of the emergency shutdown device 31.

[0066] The addition of the described discharge function and the described short-circuit function to the pre-charging circuit offers the advantage that system costs and maintenance costs can be significantly reduced.

[0067] Figs. 3a and 3b illustrate further embodiments of an arrangement in which an electrochemical system 14 is connected to an AC network 18 via a power converter 10, comprising an AC / DC converter 12 and a separating device 20, and a transformer 16. The embodiments in Figs. 3a and 3b are similar in many features to the embodiment illustrated in Fig. 2b. Therefore, the following primarily explains the differences from the embodiment in Fig. 2b, while for identical features, reference is made to the figure description of Fig. 2b.

[0068] In contrast to Figs. 2a and 2b, the isolating device in Fig. 3a has only a single-pole disconnection with a disconnect switch TS in the positive current path 41. The negative current path 42 is free of a disconnect switch TS. In addition, a pre-charging circuit with a pre-charging switch VS and a pre-charging resistor R1 is arranged only between the positive DC input 26 and the positive DC output 22, which is therefore assigned to the positive current path 41. The isolating device 20 also has a first switch S1, which connects a connection point between the pre-charging switch VS and the pre-charging resistor R1 of the pre-charging circuit assigned to the positive current path 41 to the negative DC output 24. The isolating device 20 can optionally also have the second switch S2, which can short-circuit the two DC outputs 22, 24 of the isolating device 20, and thus the DC connections DC-, DC+ of the electrochemical system 14. In Fig.3a, the optional second switch S2 and its arrangement are symbolized by dashed lines. The second switch S2 can also be designed as a normally closed switch, analogous to the first switch S1, which assumes its closed state automatically, i.e. in the absence of a control signal. The second switch S2 can additionally have a (self-sufficiently operating) time delay element or a self-sufficiently operating voltage monitor (not shown in Fig. 3a). This ensures that the second switch S2 only assumes its normally closed state after the first switch S1, in particular after a preset period of time has elapsed, or when a preset voltage is undershot. Such a single-pole isolating disconnecting device 20 with a precharging circuit assigned to the positive current path 41 is particularly advantageous when the electrochemical system 14 has an earth connection at its negative DC connection.

[0069] The embodiment in Fig. 3b differs from that in Fig. 3a in that the isolating switch TS and the pre-charging circuit comprising the pre-charging switch VS and the pre-charging resistor R2 are arranged between the negative DC input 28 and the negative DC output 24 of the isolating device 20, and are therefore assigned to the negative current path 42 of the isolating device 20. The first switch S1 here connects a connection point between the pre-charging switch VS and the pre-charging resistor R2 of the pre-charging circuit to the positive DC output 22 of the isolating device 20 and thus to the positive DC terminal DC+ of the electrochemical system 14. Such a single-pole isolating isolating device 20 with a pre-charging circuit assigned to the negative current path 42 is particularly advantageous when the electrochemical system 14 has a ground connection at its positive DC terminal DC+.

[0070] LIST OF REFERENCE SYMBOLS

[0071] 10 power converters

[0072] 12 AC / DC converters

[0073] 14 electrochemical system

[0074] 16 T ransformer

[0075] 18 AC network

[0076] 20 Separator

[0077] 22, 24 DC output

[0078] 26, 28 DC input

[0079] 30 Control Panel

[0080] 31 Emergency shutdown device

[0081] 41 , 42 current path

[0082] DC+, DC- DC connection

[0083] S1 first switch

[0084] S2 second switch

[0085] TS disconnector

[0086] V voltmeter

[0087] A ammeter

[0088] F1, F2, F3, F4 fuse

[0089] R1, R2 precharge resistor

[0090] Pre-charge switch

Claims

PATENT CLAIMS Method for producing a defined state of an electrochemical system (14) which can be connected via a disconnecting device (20) to an AC / DC converter (12) for the exchange of electrical power, - wherein the isolating device (20) has two DC inputs (26, 28), two DC outputs (22, 24) and two current paths (41, 42), each current path (41, 42) connecting one DC input (26, 28) to a corresponding DC output (22, 24), and wherein a disconnect switch (TS) is arranged in at least one of the current paths (41, 42) such that at least one of the DC terminals (DC+, DC-) of the electrochemical system (14) is connected to the AC / DC converter (12) via the disconnect switch (TS) of the isolating device (20), the method comprising: In a first operating state, in which the at least one DC terminal (DC+, DC-) is electrically disconnected from the AC / DC converter (12) by the open disconnect switch (TS): a) Closing a first switch (S1) of the disconnecting device (20) to establish an electrical connection between the DC terminals (DC+, DC-). Method according to claim 1, wherein the disconnecting device (20) has two disconnect switches (TS), one disconnect switch (TS) being arranged in each of the two current paths (41, 42), so that each of the DC terminals (DC+, DC-) of the electrochemical system (14) can be connected to the AC / DC converter (12) via a disconnect switch (TS). - wherein, in the first operating state in which step a) is performed, each of the two DC terminals (DC+, DC-) is electrically disconnected from the AC / DC converter (12) by an open disconnect switch (TS). Method according to claim 1 or 2, wherein step a) is subdivided as follows: a.1) Before closing the first switch (S1): measuring a voltage between the DC terminals (DC+, DC-) a.2) If the measured voltage falls below a predefinable first threshold: closing the first switch (S1). Method according to claim 3, wherein the DC terminals (DC+, DC-) are short-circuited by closing the first switch (S1). Method according to any one of claims 1 to 3, wherein the DC terminals (DC+, DC-) are connected via an ohmic resistor by closing the first switch (S1) and the electrochemical system (14) is discharged via the ohmic resistor. Method according to claim 5, wherein the disconnecting device (20) has in at least one current path (41, 42) a pre-charging circuit with a pre-charging switch (VS) and a pre-charging resistor (R1, R2), such that at least one DC connection (DC+, DC-) of the electrochemical system (14) can be connected to the AC / DC converter (12) via the pre-charging resistor (R1, R2) and the pre-charging switch (VS) for pre-charging the electrochemical system (14), and wherein the ohmic resistance through which the electrochemical system (14) is discharged comprises the pre-charging resistor (R1, R2).A method according to claim 6, wherein the disconnecting device (20) in each of the two current paths (41, 42) has a pre-charge circuit with a pre-charge switch (VS) and a pre-charge resistor (R1, R2), such that each of the two DC terminals (DC+, DC-) of the electrochemical system (14) can be connected to the AC / DC converter (12) for pre-charging the electrochemical system (14) via a pre-charge resistor (R1, R2) and a pre-charge switch (VS), and wherein the ohmic resistance through which the electrochemical system (14) is discharged comprises one or two of the pre-charge resistors (R1, R2). A method according to any one of claims 5 to 7, comprising, after step a): b) closing a second switch (S2) for short-circuiting the DC terminals (DC+, DC-). Method according to claim 8, wherein step b) is subdivided as follows: b.1 ) Before closing the second switch (S2): measuring the voltage between the DC terminals (DC+, DC-) b.2) If the measured voltage falls below a predefinable second threshold: closing the second switch (S2). Method according to any one of the preceding claims, wherein the first operating state is established by opening the disconnect switches (TS) and / or by disconnecting the disconnecting device (20) from the AC / DC converter (12). Method according to claim 10, comprising: in a second operating state in which the DC terminals (DC+, DC-) are electrically connected to the AC / DC converter (12) via the closed disconnect switch(es) (TS): c) exchanging electrical power of the electrochemical system (14) with the AC / DC converter (12); d) establishing the first operating state by opening one or each of the disconnect switches (TS). A method according to claim 11, wherein the second operating state is preceded by a pre-charging operating state in which the electrochemical system (14) is charged via one of the pre-charging resistors (R1, R2) when one pre-charging switch (VS) is closed, or in which the electrochemical system (14) is charged via the pre-charging resistors (R1, R2) when both pre-charging switches (VS) are closed. A method according to any one of the preceding claims, wherein the first switch (S1) and / or the second switch (S2), if present, comprises a normally closed switch. A method according to claim 13, wherein the first switch (S1) and / or the second switch (S2), if present, is coupled to an emergency shutdown device.Disconnecting device (20) with one or two disconnect switches (TS) for connecting an electrochemical system (14) to an AC / DC converter (12) for exchanging electrical power, wherein the disconnecting device (20) has two DC inputs (26, 28), two DC outputs (22, 24) and two current paths (41, 42), wherein each current path (41, 42) connects one DC input (26, 28) to a corresponding DC output (22, 24), and wherein a disconnect switch (TS) is arranged in one or each of the current paths (41, 42), wherein each DC output (22, 24) of the disconnecting device (20) is connectable to each DC terminal (DC+, DC-) of the electrochemical system (14), and wherein the disconnecting device (20) further has a first switch (S1) via which an electrical connection between the DC outputs (22, 24) can be produced.Disconnecting device (20) according to claim 15, wherein the DC outputs (22, 24) can be connected via an ohmic resistor by closing the first switch (S1) and wherein the disconnecting device (20) is designed to discharge the electrochemical system (14) connected to the DC outputs (22, 24) via the ohmic resistor when the first switch (S1) is closed. Disconnecting device (20) according to claim 16, wherein the disconnecting device (20) has a pre-charge circuit in at least one of its current paths (41, 42) such that at least one of the DC outputs (22, 24) can be connected to the corresponding DC input (26, 28) via a pre-charge resistor (R1, R2) and a pre-charge switch (VS) for pre-charging the electrochemical system (14), and wherein the ohmic resistance through which the electrochemical system (14) can be discharged comprises the pre-charge resistor (R1, R2). Disconnecting device (20) according to claim 17, wherein the disconnecting device (20) has a pre-charge circuit in each of its two current paths (41, 42) such that each of the DC outputs (22, 24) can be connected to the corresponding DC input (26, 28) via a pre-charge resistor (R1, R2) and a pre-charge switch (VS) for pre-charging the electrochemical system (14), and wherein the ohmic resistance through which the electrochemical system (14) can be discharged comprises one or two of the pre-charge resistors (R1, R2). Power converter (10) with an AC / DC converter (12) and a disconnecting device (20) according to any one of claims 15 to 18. Arrangement with an electrochemical system (14) and a power converter (10) according to claim 19.

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