Electrolysis system and operation method therefor

Abstract

An electrolysis system includes an electrolyzer and a conversion device for power supply of the electrolyzer out of a grid is disclosed. The electrolyzer includes a plurality of electrolysis cells connected in series to each other. The series connection of electrolysis cells is connected through a positive DC-line and through a negative DC-line to a DC-output of the conversion device. A conscious grounding of the series connection is provided via a grounding line at a connection point of the positive DC-line, at a connection point of the negative DC-line or at a connection point of an intermediate power line between two adjacent electrolysis cells. The electrolysis system has at least one overcurrent protection circuit that is arranged between two adjacent electrolysis cells of the series connection of electrolysis cells and connected in series with an intermediate power line connecting the two adjacent electrolysis cells of the series connection of electrolysis cells, and/or arranged in series with the grounding line between the connection point and ground (PE). If a ground fault is occurring at the series connection of electrolysis cells, one or more of the at least one overcurrent protection circuit is configured to trip and prevents an application of a damaging overcurrent and/or a damaging overvoltage to the electrolysis cells.

Claims

1. An electrolysis system comprising: an electrolyzer; and a conversion device configured to supply power to the electrolyzer out of a grid, wherein the electrolyzer comprises a plurality of electrolysis cells connected in series to each other and wherein the series connection of electrolysis cells is connected through a positive DC-line and through a negative DC-line to a DC-output of the conversion device, wherein a conscious grounding of the series connection is provided via a grounding line at a connection point of the positive DC-line, at a connection point of the negative DC-line or at a connection point of an intermediate power line between two adjacent electrolysis cells, and at least one overcurrent protection circuit, wherein each of the at least one overcurrent protection circuit is: i.) arranged between two respective adjacent electrolysis cells of the series connection of electrolysis cells and connected in series with an intermediate power line connecting the two adjacent electrolysis cells of the series connection of electrolysis cells, and/or ii.) arranged in series with a respective grounding line between its respective connection point and ground (PE), wherein one or more of the at least one overcurrent protection circuit receives a ground fault trip signal from a control circuit or a current sensor, and is configured to trip when the ground fault trip signal indicates an overcurrent condition when a ground fault is occurring at the series connection of electrolysis cells, or wherein the at least one overcurrent protection circuit comprises a melt fuse and trips when a predetermined energy level associated with an overcurrent condition is achieved, thereby preventing an application of a damaging overcurrent and/or a damaging overvoltage to the electrolysis cells.

2. The electrolysis system according to claim 1, wherein the grid is a DC grid and the conversion device is configured as a DC/DC-converter.

3. The electrolysis system according to claim 1, wherein the grid is an AC grid and the conversion device is configured as an AC/DC-converter.

4. The electrolysis system according to claim 3, wherein the AC/DC-converter is configured as a multi-stage converter comprising an AC/DC-conversion circuit and a DC/DC-conversion circuit.

5. The electrolysis system according to claim 1, wherein the conversion device is a bidirectional conversion device that is configured to decrease a voltage on its DC-output by transferring an electric power from the DC-output to the grid during a transfer to a fault-operating-mode (FOM) and/or during the fault-operating-mode (FOM).

6. The electrolysis system according to claim 1, further comprising a control device that is configured to control the conversion device during a fault-operating-mode (FOM) or during a transfer to the fault-operating-mode (FOM) to stop a power conversion and/or to reduce a DC-voltage at the DC-output.

7. The electrolysis system according to claim 1, wherein the at least one overcurrent protection circuit comprises two or more overcurrent protection circuits that are each arranged at a different intermediate location within the series connection of electrolysis cells and that are each connected in series with an intermediate power line connecting two adjacent electrolysis cells of the series connection of electrolysis cells.

8. The electrolysis system according to claim 1, wherein in addition to the at least one overcurrent protection circuit in series with an intermediate power line connecting two adjacent electrolysis cells and/or in series with the grounding line between the connection point and ground (PE), the electrolysis system comprises a further overcurrent protection circuit located at a positive DC-line and/or a further overcurrent protection circuit located at a negative DC-line.

9. The electrolysis system according to claim 1, wherein one or more of the at least one overcurrent protection circuit comprises a melt-fuse or an electronic fuse.

10. The electrolysis system according to claim 1, wherein the plurality of electrolysis cells is formed by a plurality of electrolysis stacks connected in series to each other, wherein each electrolysis stack comprises a group of multiple electrolysis cells connected in series to each other, and wherein the at least one overcurrent protection circuit comprises a plurality of overcurrent protection circuits, wherein each overcurrent protection circuit out of the plurality of overcurrent protection circuits is arranged between two adjacent electrolysis stacks.

11. A method of operating an electrolysis system according to claim 1 comprising: operating the electrolysis system in a normal-operating-mode (NOM), wherein a DC-power is supplied to the series connection of electrolysis cells by the conversion device, and in response to a ground fault occurring at the series connection of electrolysis cells, initiating a tripping of one or more of the at least one overcurrent protection circuit and transferring operation of the electrolysis system to a fault-operating-mode (FOM) during which a damaging overcurrent and/or overvoltage applied to one, or more, or each of the plurality of electrolysis cells and/or the conversion device is prevented.

12. The method according to claim 11, wherein in response to a transfer to the fault-operating-mode (FOM) and/or during the fault-operating-mode (FOM) of the electrolysis system, controlling a control circuit of the electrolysis system to control the conversion device to stop its power conversion and/or reduce its DC-output-voltage.

13. The method according to claim 11, wherein during the fault-operating-mode (FOM) of the electrolysis system controlling the control circuit to control the conversion device to at least temporarily continue its power supply to the series connection of the electrolysis cells, if one of the at least one overcurrent protection circuit arranged in series with the grounding line between the connection point and ground (PE) is tripped.

14. The method according to claim 11, wherein in response to the transfer to the fault-operating-mode (FOM) or during the fault-operating-mode (FOM), generating a signal in the electrolysis system indicating its fault-operating-mode (FOM) and/or an information about the one or more of the at least one overcurrent protection circuits that has or have been tripped.

15. The method according to claim 11, wherein during a transfer to the fault-operating-mode (FOM) and/or during the fault-operating-mode (FOM), measuring multiple voltages (U1-U5) each between an intermediate power line connecting two adjacent electrolysis cells and ground (PE), or each between two intermediate power lines for a plurality of different intermediate power lines of the series connection of electrolysis cells in order to localize the ground fault.

16. The method according to claim 12, wherein the controlling of the control circuit of the electrolysis system is performed only when one of the at least one overcurrent protection circuit arranged in series with the intermediate power line connecting adjacent electrolysis cells of the series connection of electrolysis cells is tripped.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the disclosure is further explained and described with respect to example embodiments illustrated in the drawings.

(2) FIG. 1 illustrates a first embodiment of an electrolysis system according to the present disclosure;

(3) FIG. 2 illustrates a second embodiment of an electrolysis system according to the present disclosure.

(4) FIG. 3 illustrates an embodiment for an overcurrent protection that can be used in each of the electrolysis system of FIG. 1 or FIG. 2.

(5) FIG. 4a illustrates a first embodiment of a fault localization means useable for an electrolysis system as shown in FIG. 1 or FIG. 2.

(6) FIG. 4b illustrates a second embodiment of a fault localization means useable for an electrolysis system as shown in FIG. 1 or FIG. 2.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates an electrolysis system 1 according to the present disclosure in a first embodiment. The electrolysis system 1 comprises an electrolyzer 10, a conversion device 20 and a control unit 5 controlling the conversion device 20. The conversion device 20 is formed as an AC/DC-converter 26 that, on its AC-side is connected to an AC-grid 32 as grid 30. A DC output 21 is connected via a positive DC line 2a and a negative DC line 2b to a DC input of the electrolyzer 10. In one embodiment, the electrolyzer 10 comprises a series connection of multiple (here exemplarily: five) electrolysis stacks 12, that are connected to each other by intermediate power lines 2c. Each electrolysis stack 12 itself comprises a plurality of electrolysis cells 11 connected in series to each other. The electrolyzer 10 further comprises multiple (here exemplarily: four) overcurrent protection circuits 50 each arranged between two adjacent electrolysis stacks 12 and connected in series to a respective intermediate power line 2c. In series with the positive DC-line 2a and in series with the negative DC-line 2b the electrolysis system comprises two further overcurrent protection circuits 40, a respective one in each of the DC-lines 2a, 2b.

(8) During a normal-operation-mode (NOM) of the electrolysis system 1 the control unit 5 controls the conversion device 20 to convert an AC power delivered from the AC grid 32 into a DC power that is supplied to the electrolyzer 10 for performing the electrolysis reaction. If a ground fault 60 occurs (here exemplarily sketched at the third electrolysis stack 12) the series connection of electrolysis stacks 12, and thus also the series connection of electrolysis cells 11, is divided by the ground fault 60 into a first sub-string 13a and a second sub-string 13b. The series connection of the electrolysis cells 11 within the first sub-string 13a, and thus each respective electrolysis cell therein, is short-circuited via the ground fault 60 and the conscious ground PE provided at the negative DC line 2b. That short-circuit leads to a discharge of the electrolysis cells 11 within that first sub-string 13a along a current path 61 that has been generated by the ground fault 60. In addition thereto, the series connection of electrolysis cells 11 within the second sub-string 13b, and thus each respective electrolysis cell in the second sub-string 13b, is exposed to an overvoltage. This is due to the fact that the total voltage at the DC output 21 of the conversion device 26, that previously was applied to the DC-input of the electrolyzer (here: applied to 5 electrolysis stacks 12 connected in series) after the ground fault 60 is applied to a smaller number of electrolysis stacks 12 connected in series (here: two electrolysis stacks 12).

(9) The discharge of electrolysis cells 11 in the first sub-string 13a leads to fault current across the current path 61 and the intermediate power lines 2c arranged between two adjacent electrolysis stacks 12 in that first sub-string 13a. That fault current is decoupled from and cannot be controlled by the conversion device 26. In a conventional electrolysis system, that fault-current therefore typically leads to a damage of the respective electrolysis cells 11 in the first sub-string 13a. In the electrolysis system 1 in FIG. 1, however, that fault-current also has to pass the overcurrent protection circuits 50 connected in series with the intermediate power lines 2c in the first sub-string 13a and thus results in a tripping of at least one, optionally also more, thereof. Thus, the fault current is interrupted and a damaging effect to the respective electrolysis cells 11 within the first sub-string 13a is prevented.

(10) The overvoltage applied to the electrolysis cells 11 within the second sub-string 13b leads to an increasing current to the electrolyzer, and consequently also an increasing electrolysis reaction, therein. The increasing current is supplied by the conversion device 20 via the positive DC-line 2a and the intermediate power lines 2c within the second sub-string 13b. Thus, the increasing current also has to pass the overcurrent protection circuits 50 associated with the intermediate power lines 2c within the second sub-string 13b, and if present, also the further overcurrent protection 40 in the positive DC-line 2a. As a result, one or more of these overcurrent protection circuits 50 and the optionally provided further overcurrent protection 40 is tripped and the current in the second sub-string 13b is also interrupted.

(11) The increasing fault current and/or the tripping of the overcurrent protection circuits 50 can be communicated, e.g. via the control lines illustrated in dashed lines, or otherwise signaled to the control circuit 5. Therefore, the control circuit 5 is aware of the fault-operating-mode and/or the transfer to the fault-operating-mode. In addition, the increasing current within the second sub-string 13b is typically also detected by the conversion device 20 or detected by the control circuit 5 controlling that conversion device 20. Thereby in addition, a transfer to the fault-operating-mode (FOM) or an operation of the electrolysis system 1 in the fault-operating-mode FOM can be signaled to the control circuit 5.

(12) In case the conversion device 20 is a bidirectional one, it is also possible, that during the transfer to the fault-operating-mode FOM or in the fault-operating-mode FOM of the electrolysis system 1 the control circuit 5 controls the conversion device to reduce a voltage present at the DC-output 21, e.g. by a reverse power flow from the DC-output 21 to the grid 30, here: the AC-grid 32. In such an embodiment, a damaging effect of the overvoltage and the overcurrent to the electrolysis cells 11 in the second sub-string 13b can be avoided, eventually also without a tripping of the respective overcurrent protection circuits 50, 40.

(13) In FIG. 1 the overcurrent protection circuits 50 are each exemplarily illustrated as a melt fuse. However, it is also possible that one, more or each of the overcurrent protection circuits 50 is/are formed by an electronic fuse. In FIG. 1 the conscious grounding of the electrolysis system 1 is exemplarily provided at a connection point 41 at the negative DC line 2b a grounding line 3 between the connection point 41 and ground PE. However, in one embodiment, another location of the conscious grounding is also possible e.g. at the positive DC-line 2b or at one of the intermediate power lines 2c connecting two adjacent electrolysis cells 11 within the series connection of electrolysis cells 11.

(14) FIG. 2 illustrates a second embodiment of an electrolysis system 1 according to the present disclosure. The second embodiment in many features is similar to the electrolysis system shown in FIG. 1. Therefore, with regard to identical features it is referred to the description of FIG. 1 provided above. In the following, mainly the differences between the second embodiment system 1 and in the first embodiment are described.

(15) In contrast to FIG. 1, the electrolysis system 1 in FIG. 2 is connected via its conversion device 20 to grid 30 that is formed by a DC grid 31. Consequently, the conversion device 20 is formed as a DC/DC converter 25, for example, a bidirectional DC/DC converter 25. The conscious grounding electrolysis system 1 is provided via a grounding line 3 at a connection point 41 at the positive DC-line 2a. One of the at least one overcurrent protections 50 is provided in series to the grounding line 3 between the connection. 41 and ground PE. In addition, a single one of the at least one overcurrent protection circuit 50 is provided in series to each associated intermediate power line 2c connecting two adjacent electrolysis stacks 12, and thus connecting two adjacent electrolysis cells 11 of the series connection of electrolysis cells 11.

(16) During the normal-operating-mode NOM the electrolysis system 1 is supplied by an electric power from the DC grid 31, that is converted by the DC/DC converter 25, wherein the converted DC-power is delivered to the electrolyzer 10. If, in addition to the conscious grounding, a ground fault 60 occurs at this series connection of electrolysis stacks 12 (and thus at this series connection of electrolysis cells 11) the series connection is divided into multiple (here exemplarily two) sub-strings 13a, 13b. In FIG. 2 the short circuited first sub-string 13a is connected to the consciously grounded positive terminal of the DC-output 21 and comprises the two electrolysis stacks 12 shown on the left side of FIG. 2. The respective electrolysis stacks 12 in the first sub-string 13a therefore start to discharge along the current path 61, that emerges due to the ground fault 60. The series connection of the remaining electrolysis stacks 12b form the second sub-string 13b and are connected on one of its sides to the negative DC-line 2b. They are each exposed to an overvoltage, since the total voltage of the DC-output 21, that prior to the ground fault 60 was applied to the series connection of all (here 5) electrolysis stacks, after the ground fault 60 is applied to a reduced number (here 2) of electrolysis stacks 12 connected in series.

(17) The fault current generated by the discharge of the electrolysis stacks 12 in the first sub-string 13a not only flows through the overcurrent protection circuits 50 associated with an intermediate power line 2c in the first sub-string 13a, but also through the particular overcurrent protection circuit 50 arranged in series to the grounding line 3. In one embodiment, that particular overcurrent protection 50 in the grounding line 3 comprises a lower tripping level than each of the other overcurrent protection circuits 50 in the intermediate power lines 2c, such that the overcurrent protection circuit in the grounding line trips prior to a tripping of the other overcurrent protection circuits 50.

(18) After the tripping of the overcurrent protection circuit 50 associated to the grounding line 3, not only the respective fault current in the first sub-string 13a, but also the other fault current associated with the overvoltage of the electrolysis stacks 12 within the second sub-string 13b is interrupted. That is due to the fact that the conscious grounding of the electrolysis system 1 is interrupted by the tripping of the overcurrent protection at the grounding line 3 and the electrolysis system 1 then again is grounded via only one ground connection thatafter interruption of the conscious groundingthen is represented by the ground fault 60. Although, the grounding is at another location than previously (i.e. the conscious grounding), a stop of the electrolysis reaction in the fault-operating mode FOM is not absolutely necessary in this embodiment. Moreover, the electrolysis system 1 may be further operated to perform its electrolysis reaction also during the fault-operating-mode FOM. However, the transfer to the fault-operating-mode FOM and/or the operation within the fault-operating-mode FOM can be forwarded to an operator or a service personal of the electrolysis system 1.

(19) FIG. 3 shows one embodiment of an overcurrent protection circuit 50 that can be used in an electrolysis system 1 as shown in FIG. 1 or FIG. 2. The overcurrent protection circuit 50 is configured as an electronic fuse that is connected in series to an intermediate power line 2c and comprises a current sensor 54, an electromechanical switch 51 and a semiconductor switch 52. The semiconductor switch is connected in parallel to the electromechanical switch 51, wherein the parallel connection of both switches 51, 52 is connected in series to the current sensor 54. The overcurrent protection can comprise a separate control circuit unit (not shown in FIG. 3) for controlling the electrochemical switch 51 and the semiconductor switch. Alternatively, it is also possible that the switches 52, 51 are controlled by the control circuit 5 of the electrolysis system 1.

(20) During the normal-operating-mode NOM of the electrolysis system 1 the electromechanical switch 51 is closed in order to provide a low impedance current path for its associated intermediate power line 2c. The current sensor 54 detects a current I(t) flowing in the intermediate power line 2c and sends that current to the control circuit, i.e. either the separate control circuit or the control circuit 5 of the electrolysis system 1. The detected current I(t) is then compared to a threshold value ITH. If the current is smaller than the threshold value, the electromechanical switch 51 is kept closed. If, however, the detected current I(t) is equal to or exceeds the threshold value the control circuit initiates a tripping of the overcurrent protection circuit 50.

(21) For tripping, in one embodiment, at first the semiconductor switch 52 is closed if it is not already closed. Then the electromechanical switch 51 is opened and the current I(t) commutates to the semiconductor switch 52. Then the semiconductor switch 52 is opened, whereby the current I(t) is interrupted. The control circuit can also be configured to control a closing of a tripped fuse. The tripped fuse comprises an opened semiconductor switch and an opened electromechanical switch. When a closing is desired, the control circuit at first controls the opened semiconductor switch to close in order to provide a low impedance path for the intermediate power line 2c. After closing of the semiconductor switch the control circuit controls the opened electromechanical switch 51 to close. As a result, a current that flows in the intermediate power line 2c across the semiconductor switch 51 commutates to the electromechanical switch 51 due to its lower impedance. When operating in the normal operating mode the semiconductor switch 51 can be controlled to be open. However, that is not necessarily needed and it is also possible for the semiconductor switch to be closed during the normal-operating-mode NOM.

(22) As explained above, the overcurrent protection 50 that is configured as an electronic fuse is controlled based on a signal from the current sensor 54. In an alternative embodiment it is also possible that the overcurrent protection 50 configured as an electronic fuse can be controlled based on a voltage value that is related to its respective intermediate power line 2c. For each of the intermediate power lines 2c these voltage values, e.g. can be detected by a fault localization circuit or device 70 shown in FIG. 4a or FIG. 4b. For example, as explained in combination with FIG. 4a and FIG. 4b, the fault localization circuit 70 is configured to detect an occurrence and also a location of the ground fault 60. In response to a detected ground fault 60, the occurrence and the location of the ground fault 60 are signaled to the control circuit 5 of the electrolysis system 1 which then initiates a tripping of one or more of the overcurrent protections 50 in order to transfer the electrolysis system 1 from its normal-operating-mode NOM to its fault-operating-mode FOM.

(23) In FIG. 4a a first embodiment of a fault localization circuit 70 is illustrated, that can be used in an electrolysis system 1 as shown in FIG. 1 or FIG. 2. The fault localization circuit 70 operates based on voltage measurements conducted at multiple ones of the intermediate power lines 2c associated with the electrolysis system 1 and, therefore, comprises a plurality of input connections 72.1-72.4, each configured to connect to a different one of multiple intermediate power lines 2c of the electrolysis system 1. In addition, the fault localization circuit comprises a ground connection terminal 73 configured to connect to the ground potential PE of the electrolysis system 1.

(24) During operation of the electrolysis system 1, i.e. during its normal-operating-mode NOM and also during its FOM mode, voltages present between each of the intermediate power lines 2c connected to the fault localization circuit and in each case ground potential PE are detected by respective voltage sensors 71.1-71.4. During the normal-operation-mode NOM the voltages are dependent on the number of electrolysis cells between two adjacent intermediate lines 2c that are measured, the total number of electrolysis cells 11 in the series connection of electrolysis cells of the electrolyzer, and the voltage at the DC-output.

(25) If a ground fault 60 occurs at a particular location in the electrolysis system 1, each voltage sensor 71.1-71.4 connected to an intermediate power line 2c that is localized in the short-circuited first sub-string 13a of the series connection of electrolysis cells 11, indicates a voltage value close to 0V or 0V, whereas the other voltage sensors, that are comprised by the second sub-string 13bor, if existing, the third sub-string 13cindicate larger absolute voltage values U1-U4 than they have shown during the normal-operating-mode NOM of the electrolysis system 1, for example, immediately before the occurrence of the ground fault 60.

(26) In FIG. 4b a second embodiment of a fault localization circuit or device 70 is illustrated that also operates by voltage measurements conducted at the intermediate power lines 2c of the series connection of electrolysis cells 11. However, instead of detecting the voltages between each intermediate power line 2c and ground potential PEas shown in FIG. 4ain FIG. 4b voltages that are present between a respective intermediate power line 2c and one of its adjacent intermediate power lines 2c are detected for each intermediate power line 2c, wherein for one outer intermediate power line 2c (here intermediate power line 4) a voltage between that outer intermediate power line 2c and the positive DC-line or the negative DC-line is measured. Therefore, the voltage sensors 71.1-71.3 are connected between adjacent ones of the respective input connections 72.1-72.4 and the voltage sensor 71.4 is connected between the outer input connection 72.4 and the positive DC-line 2a or the negative DC-line 2b. Also, this second embodiment enables one to localize the ground fault 60 by comparing the measured voltages U1-U4 taken during the fault-operating-mode FOM or during the transfer to the fault operating-mode FOM with the respective voltages U1-U4 taken during the normal-operating-mode NOM immediately before the ground fault.

(27) With both embodiments of the fault localization circuit it is not only possible to localize the ground fault 60, but also to indicate the occurrence of the ground fault 60 by respective changes in the detected voltage values U1-U4. Therefore, the fault localization circuit 70 can also be used to signal to the control circuit 5 if the electrolysis system 1 operates in the normal-operating-mode NOM or if a ground fault 60 has occurred in the electrolysis system that requires a transfer to the fault-operating-mode FOM and/or, consequently, an operation in the fault-operating-mode FOM.